موسسه ژئوفیزیک دانشگاه تهرانفیزیک زمین و فضا2538-371X39420131222The effect of radiactive dose and infrared laser on adjacent aliquots while dating Golbaf samples based on [POST-IR] OSL methodاثر دُز پرتوزا و لیزر فروسرخ بر الیکوتهای کناری در هنگام اندازهگیری سن نمونههای گلباف به روش رخشانی پس از فروسرخ1163597610.22059/jesphys.2013.35976FAمرتضیفتاحیاستادیار، گروه فیزیک زمین، موسسه ژئوفیزیک دانشگاه تهران، ایراننیناعطاییدانشجوی کارشناسی ارشد ژئوفیزیک، گروه فیزیک زمین، موسسه ژئوفیزیک دانشگاه تهران، ایراننسرینکریمی مویددانشجوی کارشناسی ارشد ژئوفیزیک، گروه فیزیک زمین، موسسه ژئوفیزیک دانشگاه تهران، ایرانJournal Article20121212<sup>*</sup>نگارنده رابط: تلفن: 61118253-021 دورنگار: 88630479-021 E-mail: mfattahi@ut.ac.ir
Gowk fault which is located west of the Lut-block east of Iran is one of the main and active structures in the region. To estimate the activity of this fault, we need to calculate its’ slip rate. The South part of the Gowk fault passes through the Golbaf Lake and has displaced the rivers which have cut the lake. The displacement is around 30 meters and if we can find the time of displacement we can then calculate the slip rate. One of the most useful methods to date the Quaternary sediments directly, is Luminescence dating. This method has been widely used and the range of materials that can be dated, using different procedures of luminescence dating, is being developed. In this paper, we are presenting part of the research which was done to sort out the problems that we had for dating the samples that were collected from the Golbaf lake. To measure the age of the samples, two parameters are needed; the equivalent dose and the dose rate. To determine the equivalent dose, the single aliquot regenerative dose (SAR) protocol was used. In this method, after measuring the natural signal, the sample is exposed to different known doses in the laboratory and the related luminescence signal is measured. Then, a standard growthcurve is built, which the equivalent dose can be calculated from.
To examine the suitability of the SAR protocol in dating the collected samples, the capability of this method in order to recover a known laboratory dose was investigated. We confronted some unexpected results while recovering the dose because the determined dose overestimated the certain given dose in the laboratory by around20 percent. Three possible reasons were considered: methodological factors which can influence the determination of the equivalent dose, physical processes affecting the luminescence signal and technological factors(the measurement device).The first two reasons were assessed experimentally (according to tables 1 and 2). Thirty aliquots were built from the GB3 feldspar sample and the Risoe automated TL/OSL DA-15 reader was employed for all experiments. The first 15 aliquots were used for determinations according to the left column in table1 (the cut heat is fixed). The natural signal was depleted and after 10 hours gap, the signal was measured again (Figure1). Then, all samples were exposed to 26 Gy dose (assuming as the natural dose), the procedure in the left hand side of table1 was followed to test the capability of SAR in recovering this dose. In table1, Lx shows Ln (natural luminescence signal) and LR (regenerative luminescence signal) and Tx shows Tn (natural test dose signal) and TR(regenerative test dose signal).The results in figure2 demonstrate that, the recovered dose is more than the given dose by approximately 20% (about 30 Gy).After that, the same procedure was followed for the next 15 aliquots according to the right column of table1, but with equal preheat and cutheat. The results are shown in figure3 which is the same as figure2.We then repeated one stage of the SAR protocol five times for each aliquot using a fixed dose and expected that the results for all to be similar. This stage was completed according to table2 for four aliquots. The results are shown in figures 4, 5 and 6. As is shown in figure 4, the first signal consists of more photons in comparison with the other signals. Figure 5 shows the regenerative dose and the test dose curves for the four aliquots in five cycles. As is clear in the diagram, the first point of the regenerative dose curve for all the four aliquots are more than the other points in the curve, for both IR and Post-IR methods. Figure 6 shows the Lx/Tx ratio. It can be explicitly seen that the first stage is 40% more than other stages. As all the luminescence signals following the test doses (Tx) are almost similar, this 40% difference cannot be due to sensitivity change.
The above experiments show that electron exchange from heat-sensitive traps to light-sensitive ones because of the preheat effect cannot be the reason for the dose recovery overestimate, since both IRSL and OSL signals measured 10 hours after natural measurements, are negligible in compare to natural signals. Electron exchange from the light-sensitive traps to the heat-sensitive ones due to laser light and subsequently in the opposite pattern cannot be a possible reason since all the standard growth curves pass through the origin (figure 7).Incomplete evacuation of the electrons because of inadequate intensity and time of the laser beamis not responsible for the dose recovery overestimate because laser beam has been similar for all the stages through the experiments. Inability of the SAR protocol to correct the sensitivity according to heat, dose and light is not the case since the SAR method has provided almost similar result for the last four stage of figure 6.
As the methodological and physical factors could not be the reason for overestimating the recovered dose in the laboratory, we focused on the third factor, technology. Although the device (TL/OSL DA-15 reader) is claimed to be complete and without any defect, some reports of its failure has been presented. The effect of the dose and light on adjacent aliquots as reported by Bray et. al (2002), was found to be responsible for dose overestimation. This is because of the packed arrangement of aliquots on a disk. Since we wanted to investigate and eliminate the possible effect of the radioactive dose and the laser beam on adjacent aliquots, we decided to rearrange the aliquots. So the same procedure presented in tables 1 and 2 was followed for aliquots 1, 4, 7, 10 and 13. The results have been shown in figures 10 and 11. Figure 10 shows the result of repeating a cycle for these aliquots. This figure demonstrates that there was not much sensitivity change for the sample in this case. Figure 11 shows that the SAR method was capable of recovering the dose properly at different temperatures, but 2400 and 2800 are the most suitable temperatures in this case.
So the problem was solved by putting the aliquots in every two other positions, and the SAR protocol could recover the given dose properly. We repeated this procedure by setting the aliquots in every other position too and the results were the same. Based on above result we put the natural aliquots in every other position and determined the age of the GB3 sample. This procedure provided an age of 4100 years for this sample. Similar approach was considered for calculating the age of other samples from the same site. Detailed information about the process of dating and the slip rate of Gowk fault could be found in the paper ‘Determination of the slip rate on the Gowk fault’ by Fattahi et al. (submitted).
مقاله پیش رو عرضه کننده قسمتی از تحقیقاتی است که بهمنظور اندازهگیری سن نمونههای برداشت شده از دریاچه قدیم گلباف صورت گرفته است و میتوان به کمک آنها سن فعال بودن آن دریاچه و فعالیت گسل گوک را برآورد کرد. بهمنظور اندازهگیری سن نمونهها به روش رخشانی (لومینسانس) تحریک شده با نور، به دو پارامتر دُز معادل دُز طبیعی و دُز سالانه نیاز است. برای اندازهگیری دُز معادل از روش سار استفاده شد. در ابتدا توانایی این روش در بازیابی دُز مشخصی که در آزمایشگاه به نمونه داده شد بررسی شد. در هنگام بازیابی دُز مشخص آزمایشگاهی، میزان بهدست آمده حدود 20% بیش از دُز اِعمال شده در آزمایشگاه بود. موضوع تحت تحقیق قرار گرفت. عوامل روششناختی برای تعیین دُز معادل، فرایندهای فیزیکی موثر بر سیگنال رخشانی و موارد فنی مورد بررسی دقیق قرار گرفت. توانایی روش سار در اندازهگیری و تصحیح تغییر حساسیت در اثر دُز و گرما و نور بررسی شد. میزان سیگنال رخشانی در نخستین اندازهگیری، حدود 40% بیش از سیگنال سایر اندازهگیریهای بررسی تغییر حساسیت بود. این پدیده غیرقابل انتظار و نامانوس بود. لذا آزمایشهایی طراحی و مواردپیشگفته مورد تفحص قرار گرفت. این مقاله به توضیح کامل این تحقیق میپردازد و نشان میدهد پس از بررسیهای گوناگون متوجه شدیم که موارد پیشگفته چگونه در اثراِعمال دُز پرتوزا و لیزرفروسرخ بر الیکوتهای کناری اثر گذاشته است؛ یعنی الیکوت موردنظر، ناخواسته تحتتاثیر دُز و نور قرار گرفته است. با قرار دادن دو در میان الیکوتها این پدیده غیر متعارف حذف شد و روش سار با موفقیت توانست دُز مشخص آزمایشگاهی را بازیابی کند.
https://jesphys.ut.ac.ir/article_35976_117abc510773a7373923d24650d57b0e.pdfموسسه ژئوفیزیک دانشگاه تهرانفیزیک زمین و فضا2538-371X39420131222Earthquake swarms, introduction to the records in Iranهنگلرزهها، آغاز بررسی پیشینه در ایران17293597710.22059/jesphys.2013.35977FAمحمدرضاقاسمیاستادیار، پژوهشکده علوم زمین، سازمان زمینشناسی و اکتشافات معدنی کشور، تهران، ایرانJournal Article20130507<sup>*</sup>نگارنده رابط: تلفن: 64592476-021 دورنگار: 66070511-021 E-mail:m.r.ghassemi@gsi.ir
Earthquakes usually occur not as separate individual events, but they usually constitute parts of an earthquake sequence with different but defined characteristics. Earthquake swarms include earthquake sequences, which start gradually and end gradually with no dominant earthquake in the sequence in terms of magnitude. Study of earthquake swarms of the world has started from about half a century ago. The first stages of these studies suggested that earthquake swarms are closely related to volcanic regions, and upwelling of pore fluids. It was also suggested that this kind of sequences occur in regions with strong strength gradients. Non-double-couple focal mechanisms are reported to be associated with earthquakes in geothermal regions and with earthquakes related to tensile faulting resulted from pore pressure in geothermal or volcanic areas. Some other various subordinate settings are also suggested for earthquake swarms. They include settings related to geothermal regions, thrusting, releasing stopovers, pull-apart basins and mud volcanoes. Some earthquake swarms are suggested to be triggered by a distant major earthquake in distant regions. Most of earthquake swarms are not accompanied by surface ruptures; however some exceptions have been reported from California in United States.
Due to their relatively small magnitudes, the earthquake swarms have been less considered by researchers in Iran, although some of them have caused damages and destructions. This research studies 24 events of earthquake swarms that have occurred during the historical and instrumental periods of seismic activity in Iran, and tries to investigate their general characteristics and geological settings. The earliest accounts of a historical earthquake swarm in Iran probably dates back to 1482 A.D., when a sequence of foreshocks jolted the western Makran region in southeastern Iran for about 3 months; the earthquakes culminated in a destructive earthquake of 1483 A.D. in Hormuz Straight. Two sequences of earthquakes in 1819 and 1856 A.D. caused destruction in the Tabriz region of northwestern Iran. One of the deadliest earthquakes in Zagros region (Qir-Karzin earthquake of 1972, Ms=6.9) was preceded by a sequence of small and moderate earthquakes which had started about one month earlier. Results of this research indicate that most of the earthquake swarms in Iran occur in Zagros (54%), then in southern central Alborz (17%) and Azarbayjan (17%) areas. The rest are observed within Central Iran, Makran and Eastern Iran. It is interesting that despite their seismotectonic activity, the Eastern Iran and Kopeh-Dagh regions are not associated with important earthquake swarms. This may be related to a rather continuous seismogenic layer as compared to other parts of the Iranian Plateau. Earthquake swarms in Iran are observed both independent and related to the larger main shocks. Duration of occurrence of the earthquakes depends on to the general size of their magnitudes, and varies between 2 days for earthquakes smaller than 2.3 to more than a year. The longest sequence in Iran occurred after the Western Marivan earthquake of 1946, which lasted for 398 days. Number of reported events within an earthquake swarm sequence varies between 6 and 236, and even reportedly 1200. Size (diameter) of the epicentral region in which earthquake swarms occur varies between 12 and 146 km. None of the studied events in Iran, even those close to the volcanic regions, show any clear relationships to volcanic activities or upwelling of pore fluids. The only exception may be the Arak earthquake swarm of 2012, where thermal spring in the region may suggest some relationships with upwelling of pore fluids. The <em>b</em> value for the events in the Arak area does not deviate very much from 1, despite the early suggestions by some researchers of values greater than one for earthquake swarms. Spatial distribution of the Arak sequence does not conform to any planar (tectonic) structure at depth. Depth distribution of the earthquake swarms in Iran indicates that all of them have occurred within the crust. We suggest detailed study of focal mechanisms for the events in earthquake swarms of Iran to discriminate events related to earthquake faults from those which may be related to fluid injection at depth. In some regions, such as Zagros, earthquake swarms may be related to the mechanical discontinuities within the crust. Statistical analysis of earthquake swarms in Iran indicates that the cumulative magnitude of earthquakes within a sequence does not exceed more than 0.5 unit over the largest event of the same sequence. Statistics on magnitude, number of events, spatial and temporal distribution characteristics of the earthquake swarms in this study provide a ground on which seismologists may investigate this type of seismic activity in more details, and discriminate between the earthquake swarms and mainshocks or foreshokes.پژوهش روی هنگلرزهها در دنیا از حدود نیم سده پیش آغاز شده است. گامهای آغازین این پژوهشها بر پیوند بین هنگلرزهها و گسترههای آتشفشانی تاکید دارد. برخی جایگاههای فرعی گوناگون دیگر نیز برای این گونه زمینلرزهها پیشنهاد شده است. رشته هنگلرزهها به واسطه بزرگای بهنسبت کمی که در آنها مشاهده میشود، کمتر در ایران مورد توجه قرار گرفتهاند، اگرچه برخی از آنها سبب آسیب و ویرانی نیز شدهاند. این پژوهش با بررسی 24 رویداد از اینگونه زمینلرزهها که در طی دوره تاریخی و دستگاهی در ایران روی دادهاند، تلاش دارد تا ویژگیهای عمومی و جایگاه آنها را مورد شناسایی آغازین قرار دهد. نتیجه این پژوهش آشکار میسازد که هنگلرزههای ایران بیش از همه در زاگرس و سپس جنوب البرز مرکزی و آذربایجان روی میدهند و هیچگونه پیوند آشکاری بین آنها با جنبشهای آتشفشانی وجود ندارد. این زمینلرزهها همگی در پوسته روی دادهاند. در برخی گسترهها مانند زاگرس، شاید بتوان اینگونهزمینلرزهها را به ناپیوستگیهای مکانیکی درون پوسته نسبت داد. بررسی آماری هنگلرزههای ایران آشکار میسازد که بزرگای تجمعی زمینلرزههای روی داده در هر دسته رویداد، از بزرگای بزرگترین رویداد آن دسته بیش از 5/0 واحد بزرگا بیشتر نیست. آمار ویژگیهای بزرگا، تعداد رویداد، پهنه رویداد و بازه زمانی رویداد این زمینلرزهها زمینهای را فراهم میسازد تا لرزهشناسان این دسته از جنبشهای لرزهزمینساختی را با دقت بیشتر مورد کنکاش قرار دهند و آنها را از لرزههای اصلی و یا پیشلرزهها بازشناسند.موسسه ژئوفیزیک دانشگاه تهرانفیزیک زمین و فضا2538-371X39420131222Fault detection in reflection seismic data by common diffraction surface stack, a case study in Rheine Graben, Germanyشناسایی گسلها در دادههای لرزهنگاری بازتابی به روش سطح پراش مشترک بررسی موردی، منطقه گرابن راین، آلمان31443597810.22059/jesphys.2013.35978FAمهردادسلیمانی منفرداستادیار، دانشکده معدن، نفت و ژئوفیزیک، دانشگاه صنعتی شاهرود، ایرانهاشمشاهسونیاستادیار، دانشکده معدن، دانشگاه سنندج، کردستان، ایرانیورگنماناستادیار، موسسه ژئوفیزیک، دانشگاه کارلسروهه، آلمانJournal Article20120623<sup>*</sup>نگارنده رابط: تلفن: 09133070411 دورنگار: 3395509-0273 E-mail:msoleimani@shahroodut.ac.ir
A seismic survey in a geothermal site near the Karlsruhe city in Rheine river graben in Germany was performed to provide a detail map of structures for geothermal usage of that area. The geothermal site uses the enhanced geothermal system (EGS) for power generation. The EGS system needs a hot dry rock (HDR) in depths with a spread system of faults and cracks. An injection well, injects the surface water to the fractured hot rock and water pass through the fractures and faults and becomes hot. Then two pumping wells will pumps up the hot water to the surface. One of the pumping well in that site did not perform with efficiency that was planned for. The problem might be due to the impermeable rock between injection well and pumping well in that part of the hot rock. Therefore mapping the faults, major or minor ones, and the boundary of the layers is an important task in that project. It should be mentioned that before the surface seismic project, a vertical seismic profiling (VSP) was performed in that well that due to the high temperature in well, the receiver sounding devise was failed and no data was gathered. The second VSP project even with thermal resistant devise was also failed. Therefore obtaining a reasonable seismic image of that part was so critical for stopping or continuing the geothermal activities there. Then a surface seismic project was planned with two 2D seismic lines. However, seismic imaging in such faulted regions is among the crucial task by conventional methods. The CMP stack followed by DMO and post stack migration and prestack depth migration (PSDM) were both performed on the data. Result of the conventional post stack time and depth migration was not so ideal that interpreter could trace the minor faults on the final section. PSDM method also needs an accurate velocity model that would be obtained by so much effort. However, the prestack depth migration was carried out and faults could be traced in that section. However, the seismic image has some ambiguities in interpretation and the velocity model was not fully trustable. Therefore it was needed to use new imaging method for seismic imaging in such media. The common reflection surface (CRS) stack is among the new methods for seismic imaging. It has some advantages that make it usable for imaging in such regions. It is also independent from macro velocity model. Therefore, accuracy of the velocity model is not a big concern here. The CRS stack method also gives three kinematic wavefield attributes that could be used for further interpretation. These attributes relates to the dip, curvature and depth of the reflector. The best advantage of the method is that it gives an enhanced section for migration correction. The CRS stack method use a higher order of traveltime equation rather than the CMP stack method. Therefore the CRS stack operator works on a surface in time domain rather than on a trend. These properties make the CMP stack method a special case of the CRS stack method. Moving to a higher order traveltime equation will dramatically increase the signal to noise ratio in the final section. Höcht (1998) derived equations that give the traveltime of ray by kinematic wavefield attributes, known as CRS equation. In his calculation, the second order of travel time for t<sup>2</sup>, is known as CRS stacking operator:
(1)
where R<sub>NIP</sub>, R<sub>N</sub> and α are CRS attributes, V<sub>0</sub> is the near surface velocity and X<sub>0</sub> is the point of the emergence of the central ray. As it could be seen from the equation, this equation does not need any information about the velocity model of the subsurface, and only knowing the near surface velocity would be enough. Then the CRS stack method was performed on the data. The result of the CRS stack method was comparable to the result of PSDM. It should be noted that in the CRS stack method, an accurate velocity model is not necessary and the final section has better quality. However, in the CRS stack processing chain, mapping the position of faults was difficult due to the problem of conflicting dips that exists at the end points of faults. Therefore a new method was developed here designed especially for imaging the faults or any type of discontinuity in the reflectors, while preserves advantages of the CRS stack method. To achieve this goal, the idea of diffraction stack migration in Kirchhoff migration was used to modify the CRS stack operator. To have an idea about how the CDS operator works, consider a segment of a reflector in a predefined position in zero offset (ZO) section. This segment would be defined by its related wavefield attributes on that point. Now consider a hypothetic diffraction point exactly at the same point (in the middle of the segment). The ray path for diffraction and reflection in that point would be the same for both situation and the traveltime and emergence angle are the same, too. In the literature of the CRS stack method; we can see that the parameter R<sub>NIP</sub> is independent from the curvature of the reflector in the point of imaging. Soleimani and Mann (2008) proved that the Kirchhoff migration operator is a special case of the CRS operator with R<sub>NIP</sub>=R<sub>N</sub>. In other words, if the CRS stack operator for an arbitrary reflector segment is known, an approximation of the associated Kirchhoff migration operator is readily available by substituting R<sub>NIP</sub> for R<sub>N</sub> in equation. To perform diffraction stack migration on the CRS stack method, the operator should switch from reflection response to diffraction ones. Therefore the method could be called common diffraction surface (CDS) stack method. The new introduced CDS operator will gather all of the diffracted energy in the data. The CRS stack method gives the priority to the most coherent event for producing the operator in (<em>x<sub>m</sub>,t,h</em>) space and will have only one stacking surface, while the CDS stack, does not put any criteria for selecting the surfaces. Otherwise there is a risk to lose a relatively weak diffraction that is masked by strong reflection. Thus, there would be no image of the geological phenomena that was responsible for that lost diffraction in final migrated section. It is the reason of not imaging faults or discontinuity in the layers in most of the seismic imaging method. To preserve all diffraction shown in (<em>x<sub>m</sub>,t,h</em>) space, there would be as many as operators according to the number of diffraction in that space. To switch CRS stack traveltime to the diffraction CDS stack, the following combination between two kinematic wavefield attributes was considered and the new attribute (R<sub>CDS</sub>) was derived:
(2)
where . The new introduced method was applied on the data. Like as the conventional method, the first section obtained in the processing chain was the stacked section by CDS method. In the CDS stacked section, the quality of the section was not improved well. However, as it was mentioned, the advantage of this method would be clearer in the migrated section. In the next step, all the stacked sections obtained by the CMP, CRS and the CDS methods have been migrated by the Kirchhoff post stack depth migration. In the migration section that was obtained by migration correction on the CDS stacked section, more reflection events and more faults were imaged with better quality. In comparison to the post stack time migration on conventional method and CRS stack method, the CDS stack operator even with a smooth velocity model could gather more diffracted energy for imaging than the other migration operators. The final CDS migrated section is of a better quality and contains more detail about the location of the minor faults. The result of this migration is also comparable with the PSDM result. In some cases, the new method could image faults better than the PSDM result. It should be mentioned that the post stack depth migration applied on the CDS stacked section, needs only a smooth velocity model that would be easily obtained. With detail geological interpretation on this section, the results show that the region contains many small faults that transfer the pumped water from injection well through the hot rock to the steam extraction well. شرایط زمینشناسی در منطقه گرابن بزرگ راین در منطقه مرزی بین فرانسه و آلمان به گونهایی است که برای بهرهبرداریهای زمینگرمایی مناسب به نظر میرسد. در این تحقیق، دادههای لرزهنگاری بازتابی برداشت شده، به روشهای نوین مورد پردازش قرار گرفت. در این تحقیق، علاوه بر چندین مقطع زمانی برانبارش که به روشهای مرسوم، روش سطح بازتاب مشترک و روش سطح پراش مشترک تهیه شد، مدل سرعت منطقه نیز به روش توموگرافی موج عمود در نقطه ورود بهدست آمد. سپس دادههای برانبارش شده تحت کوچ عمقی پیش و پس از برانبارش قرار گرفتند. در مقطع کوچ عمقی پس از برانبارش که روی مقطع بر انبارش شده به روش سطح پراش مشترک صورت گرفت، روش پیشگفته توانست همة ساختارها و گسلهای ریز را به خوبی آشکار کند. مقایسه این مقطع با مقطع کوچ عمقی پیش از برانبارش و مقطع بهدست آمده به روش سطح بازتاب مشترک نشان داد که در این روش، در عین سادگی مدل سرعت، به علت کسب همه انرژیهای پراشیده شده در اثر برخورد با گسل ها، نتیجه کوچ بسیار خوب و قابل مقایسه با نتیجه مقطع حاصل از کوچ عمقی پیش از برانبارش است. در نهایت نتایج تفسیر این مقاطع نشان میدهد که بخش انتخاب شده بهمنظور کاربرد زمینگرمایی، دارای گسلهای متعددی است که باعث انتقال آب از چاه تزریقی به سازند موردنظر میشود. https://jesphys.ut.ac.ir/article_35978_0cc1587d4bc9b1697b87d2cf3efd0dce.pdfموسسه ژئوفیزیک دانشگاه تهرانفیزیک زمین و فضا2538-371X39420131222Anti-leakage Fourier transform (ALFT) and its application for seismic data reconstructionتبدیل فوریة ضد نشت (ALFT) و کاربرد آن برای بازسازی دادههای لرزهای45603597910.22059/jesphys.2013.35979FAصابرجهانجویدانشجوی کارشناسی ارشد ژئوفیزیک، گروه زمینشناسی، دانشکده علوم، دانشگاه ارومیه، ایرانحمیدرضاسیاهکوهیاستاد، گروه فیزیک زمین، موسسه ژئوفیزیک دانشگاه تهران، ایرانرامیننیکروزاستادیار، گروه زمینشناسی، دانشکده علوم، دانشگاه ارومیه، ایرانJournal Article20130109<sup>*</sup>نگارنده رابط: تلفن: 61118277-021 دورنگار: 88630479-021 E-mail: hamid@ut.ac.ir
Discrete Fourier Transform (DFT) is the basic part of various algorithms of signal processing in many fields of science and technology. For analysis of signals with DFT, the length of discrete signal must be finite so signal to be analyzed must be divided to some windows. Consequently, spectrum leakage appears in frequency domain. Energy leakage of DFT spectrum can also occur due to non-uniform sampling in time or spatial domain and usually is more serious. The leakage can hide smaller spikes among actual spectrum and is an important factor that affects spectrum estimation. In practice, we should try to reduce the energy leakage of DFT spectrum to improve the resolution of frequency spectrum. For evenly sampled signals, suppressing approaches of spectrum leakage are diverse; most common method among them is windowing method. Study on how to suppress spectrum leakage of non-uniform Fourier transform is important both in theory and practice. Here we introduce and apply an anti leakage Fourier transform (ALFT) algorithms for suppressing spectrum leakage of non-uniform Fourier transform, improving the resolution of temporal frequency spectrum or spatial wave number spectrum.
One of the areas of study that has the same problem is seismic exploration technology. Seismic data sets are generally irregularly sampled in inline midpoints, cross-line midpoints, offset and azimuth. This irregular sampling can limit the effectiveness of high end 3D de-multiple and imaging algorithms such as 3D surface related multiple elimination, wave equation pre-stack depth migration and many other processes. To overcome this issue, it is common in seismic data processing to use regularization and interpolation. Interpolation processes fill the missing traces and regularization transfer traces from their irregular recorded location to locations on a regular grid. We apply ALFT for seismic data interpolation and regularization that leads to reconstruction of seismic data on a regular grid.
ALFT is an iterative algorithm that acts on frequency slices and reconstruct each temporal frequency spectrum along spatial dimensions. For an input data with N_p known samples, the original algorithm of ALFT can be performed as follow:
1- Computing Fourier components of the data using equation 1.
(1)
2- Selecting the largest coefficient and adding it to the precomputed coefficients.
3- Updating data by subtracting the contribution of selected coefficient (equation 2) from input data (equation 3).
(2)
(3)
4- Iterating steps 2 and 3 until reaching the threshold.
The idea of ALFT is simple and intuitive: first seismic data will be transformed to f -x domain, by applying DFT the f -k spectrum of data will be estimated. The largest Fourier coefficient is selected and subtracted from the input data. In the subsequent iterations, successive maximum components are subtracted until the norm of the residual is negligible. This iterative processes is able to recover a sparse spectrum that, when evaluated at sampling points, approximates regularly sampled data. This method relies on the common assumption that sparsely sampled data can be represented by a few Fourier components. ALFT can handle pure non-uniform seismic data and uniform seismic data with gap and missing traces. For regular data sets, by applying an anti-alias mask ALFT can handle steep dips. Generalization of ALFT to higher dimensions is simple and straightforward and for high dimension data ALFT can reconstruct very sparse data sets. Performance of the method was tested on both synthetic and real seismic data.
We applied ALFT algorithm to reconstruction of synthetic and real seismic data sets. The results show the effectiveness of ALFT in interpolation and regularization of input data on any desired regular sampling grid. Compared to those interpolation methods that use FFT, ALFT has a slow procedure. However, computing the DFT’s in small windows of data sets, greatly reduces the computational cost of the algorithm. On the other hand, when the input data sets are sampled on a regular grid which has missing traces or gaps, one can use FFT instead of DFT to compute Fourier transform. ALFT reconstruction method suffers much less from edge effects and gibs phenomenon.
The sequence of computing Fourier coefficients from maximum energy to minimum energy, and subtraction of contribution of them from remained data, plays a key rule in ALFT algorithm.معمولاً در مراحل گوناگون پردازش دادههای لرزهای، فرض بر آن است که این دادهها بهصورت منظم در راستای مکان و زمان نمونهبرداری شدهاند. اما اغلب در عمل به علت محدودیتهای دسترسی در منطقه مورد بررسی و نقص دستگاهی، این فرض صادق نیست. از اینرو محاسبه طیف بسامدی سیگنالهایی با نمونهبرداری نامنظم و بازسازی آن روی یک شبکه با نمونهبرداری منظم، یکی از مهمترین بحثهای رایج در پردازش سیگنال بشمار میرود. در متن حاضر ضمن معرفی الگوریتم تبدیل فوریه ضد نشت، از آن برای حذف نشت بسامدی ناشی از پنجره کردن دادهها و نمونهبرداری نامنظم، استفاده و طیف بسامدی سیگنال را با دقت زیادی محاسبه میکنیم. با استفاده از طیف بسامدی بهدست آمده میتوان سیگنال را روی هر شبکة منظم دلخواهی بازسازی کرد.
تبدیل فوریة ضد نشت الگوریتمی تکراری است که در هر تکرار تبدیل فوریة گسستة سیگنال را محاسبه میکند. در هر تکرار، بزرگترین ضریب فوریه انتخاب و روی شبکة نمونهبرداری شده در حوزه t-x برگردانده و از سیگنال ورودی کسر میشود. این عمل تا زمانی که انرژی سیگنال باقیمانده به مقدار آستانة از قبل تعیین شده برسد، روی سیگنال باقیمانده تکرار میشود.
در این مقاله الگوریتم تبدیل فوریه ضد نشت در حوزه F-X بر برشهای بسامد زمانی دادههای لرزهای اِعمال شده و هر بسامد روی شبکة دلخواه، بازسازی میشود. روش معرفی شده، دادههای لرزهای کاملاً نامنظم و دادههای لرزهای منظم با ردلرزة گم شده را با دقت زیادی بازسازی میکند. در مورد دادههای لرزهای با نمونهبرداری نزدیک به منظم نیز با اِعمال یک ماسک ضد دگرنامی میتوان رویدادهای با شیب بسیار تند را بازسازی کرد. کارایی روش روی دادههای لرزهای مصنوعی و واقعی ارزیابی، و نتایج آن عرضه شده است.https://jesphys.ut.ac.ir/article_35979_17fbd54a6555585a890dc28992c21623.pdfموسسه ژئوفیزیک دانشگاه تهرانفیزیک زمین و فضا2538-371X39420131222Using the factorial Kriging analysis to filter spatial structures in gravity data acquired from Faryab chromite mine areaبهکارگیری روش آنالیز کریجینگ فاکتوری در فیلتر کردن ساختارهای دادههای گرانیسنجی منطقه معدنی کرومیت فاریاب61723598010.22059/jesphys.2013.35980FAمحمدرضاآزادفارغ التحصیل کارشناسی ارشد اکتشاف معدن، دانشگاه صنعتی شاهرود، ایرانمحمدکنشلواستادیار، دانشکده مهندسی معدن، نفت و ژئوفیزیک، دانشگاه صنعتی شاهرود، ایرانابوالقاسمکامکار روحانیدانشیار، دانشکده مهندسی معدن، نفت و ژئوفیزیک، دانشگاه صنعتی شاهرود، ایرانJournal Article20121212<sup>*</sup>نگارنده رابط: تلفن: 3392205 -0273 دورنگار: 3395509 -0273 E-mail: web2-koneshloo@shahroodut.ac.ir
Considering this fact that chromite masses possess high density, the gravity method is the most common geophysical method suggested for prospecting of chromite deposits. Usually, the result of superposition of several factors is observed in the acquired datum, which includes different spatial scales. The observed potential field could be assumed as the sum of the regional field, the residual field, and noise. Despite filtering out several factors to obtain a bouguer anomaly map from gravity survey data, the obtained values are still the result of superposition of several components; these components are different from the view points of scale and importance. Definition and recognition of these components are essential in interpretation of geophysical surveys. There are various methods for processing and interpretation of bouguer gravity anomaly maps. These methods, e.g. potential field filters, are mostly based on mathematical analyses using trial and error technique. There are many different methods concerned with separation of the regional and residual components from the gravity map. Upward continuation technique is frequently used to identify regional anomalies and gravity variations of deeper recourses. The upward continuation is a general filter in processing geophysical data that can remove or considerably lessen the contribution of high-frequency, near-surface, shallow causative bodies from the gravity field, resulting in a smooth field reflecting the deeper causative bodies and/or density structures. This method is applied to separate a regional anomaly from the observed gravity. This filter is a low pass filter since the residual component, which is concerned with local anomalies, can be assumed as high frequency part of the signal. The main weakness of usual potential field filters comes from the fact that they cannot take into account spatial structure of components while filtering them.
Spatial structure of a variable is an indicator of the amount of data correlation with respect to the distances between the data. Factorial Kriging analysis (FKA) is principally a geostatistical filtering method that includes classic factorial analysis and geostatistics. The FKA method consists of three basic steps: variogram, factorial analysis and Kriging/co-Kriging. This method
computes of the experimental variograms to choose the number of spatial scales to be considered and fit by theoretical models, (generally linear model of regionalization/coregionalization),
applies the decomposition method on variance-covariance/variogram matrix of spatial components (generally principle component analysis/spectral decomposition),
estimats the regionalized factors in order to determine the relative contribution of each factor for the estimation of a particular location and mapping.
Factorial Kriging decomposes the raw variable into as many components as the identified structures in the variogram. The basic step in FKA is experimental variogram calculation and fitting a valid model to this variogram. If the variogram is nested, it can be represented as a combination of several individual components variograms.
The FKA method includes two types of univariate and multivariate. In the case of a geophysical variable, the univariate type is applied. Therefore, the variogram in this case can be written as a linear combination of its components.
In this research, the gravity data, acquired from Faryab chromite mine area, are processed and interpreted using the FKA method. Based on this study, three components, which may represent regional, local, and noise components are defined and filtered based on spatial structure study. Moreover, two locations are proposed for further detailed exploration considering the extracted local component map. Also, the gravity data are processed using potential field filters. In this regard, different heights are considered in the upward continuation filter method applying on the gravity data, and then, the results are shown in the relevant maps. Low value gravity anomalies can be interpreted as the geological structures having low density or special geometric shapes such as a geo-anticline. High value gravity anomalies can be considered as densie masses like chromite lenses.
Finally, in this research work, the obtained results from applying the FKA method on the gravity data are compared with the potential field filtering results using the upward continuation filter method. The basic difference between the upward continuation and the FKA methods is that the latter method takes into account the spatial structure of the data while the former does not. This study clearly indicates the capability of the FKA method in filtering gravity data. با توجه به این واقعیت که تودههای کرومیت وزن مخصوص زیادی دارند، در اکتشافات معدنی معمولترین روش ژئوفیزیکی که برای اکتشاف ذخایر کرومیت پیشنهاد میشود، روش گرانیسنجی است. در نقشههای بیهنجاری بوگه حاصل از برداشتهای گرانیسنجی گرچه تاثیر بسیاری از عوامل فیلتر و حذف میشود، لیکن بازهم مقادیر بازماند بهدست آمده نتیجه برهمنهی چند مولفة متفاوت از حیث ابعاد تاثیر و درجه اهمیت هستند. برای پردازش و تفسیر نقشههای بیهنجاری گرانی اصولاً از روشهای متعددی استفاده میشود. نقطه ضعف فیلترهای ژئوفیزیکی معمول در نظرنگرفتن ساختار فضایی دادهها حین تفکیک آنها است. ساختار فضایی در واقع بیانگر میزان همبستگی دادهها نسبت به فاصله بینشان است. آنالیز کریجینگ فاکتوری (FKA) اساساً یک نوع فیلترینگ زمینآماری است که قادر است با توجه به تشخیص ساختارهای فضایی از روی واریوگرام تودرتوی دادهها و تفکیک ساختارها، به تجزیه متغیر اولیه به مولفههای اصلی آن و یا در واقع عوامل اصلی تغییرپذیری بپردازد. در این تحقیق، دادههای گرانی منطقه معدنی کرومیت فاریاب با استفاده از روش FKA پردازش و تفسیر شده است. براساس بررسیهای ساختاری سه ساختار متناسب با فاکتورهای ناحیهای، محلی و نوفه تشخیص داده و دو محدوده برای ادامه عملیات اکتشافی براساس مولفه ناحیهای فیلتر شده پیشنهاد شده است. نتایج حاصل از این روش با نتایج حاصل از فیلترهای ژئوفیزیکی مقایسه شده است. این تحقیق بهخوبی قابلیت کاربرد این روش را در فیلتر کردن دادههای گرانیسنجی نشان میدهد. https://jesphys.ut.ac.ir/article_35980_9407eec59ce1603ddafc6d40eac73afa.pdfموسسه ژئوفیزیک دانشگاه تهرانفیزیک زمین و فضا2538-371X39420131222Gravity data interpretation using the algorithm fourth horizontal derivatives and s- curves methodتفسیر دادههای گرانی با استفاده از الگوریتم مشتق چهارم افقی و منحنی–s73823598110.22059/jesphys.2013.35981FAفائزهبهرامیدانشجوی کارشناسی ارشد، دانشگاه آزاد اسلامی واحد همدان، ایرانوحیدابراهیمزاده اردستانیاستاد، گروه فیزیک زمین، موسسه ژئوفیزیک دانشگاه تهران، ایرانJournal Article20130113The gravity method is one of the first geophysical techniques used in oil and gas exploration. An algorithm is developed for a fast quantitative interpretation of gravity data generated by geometrically simple but also the estimated depths and other model parameters of a buried structure.
Following Abdelrahman et al (1989). The general gravity anomaly expression produced by a sphere, an infinite long horizontal cylinder and a semi- infinite vertical cylinder can be represented by the following equation
(1)
where
and z is the depth of the body, x<sub>i</sub> is the horizontal position coordinate, σ is the density contrast, G is the universal gravitational constant and R is the radius and q is factor related to the shape of the buried structure and is equal to 0.5,1.0,and 1.5 for the semi- infinite vertical cylinder, horizontal cylinder and the sphere respectively.
Consider nine observation point (x<sub>i </sub>-4s),<sub> </sub>(x<sub>i </sub>-3s),<sub> </sub>(x<sub>i </sub>-2s),<sub> </sub>(x<sub>i </sub>-s),<sub> </sub>(x<sub>i </sub>),<sub> </sub>(x<sub>i </sub>+s),<sub> </sub>(x<sub>i </sub>+2s),<sub> </sub>(x<sub>i </sub>+3s), (xi + 4s), along the anomaly profile where s=1,2,3,M spacing units and is called the window length.
Using equation (1) the simplest first numerical horizontal gravity gradient (dg/dx<sub>)</sub>
(2)
the second horizontal derivative gravity anomaly is obtainedfrom equation (2) as
(3)
the third horizontal gradient is(3)
(4)
Similarly, the fourth horizontal gradient is (4)
5)
Which yields;
Where
(7)
Equation (5) can also be solved using a simple iteration method.
Equations (5) can be used to determine the depth and the shape of a buried structure using the window curves method. The validity of the method is tested on synthetic data white and without random errors.
The method was applied to a gravity anomaly from the Abade of Iran .The results shows that the s-curves intersect each other in a narrow region where 7.220 <z<7995 m and 1.40<q<1.51 ;
The central point of this region occurs at the location z= 7.6900 m and q= 1.43.
The aim of the present study is to develop a simple method (s-curves method) for analysis of gravity anomalies due to derivative calculations that can be used to estimate the depth and the shape of the causative bodies. In all cases examined, the estimated depths are found to be in good agreement with the actual values.در این تحقیق، یک الگوریتم برای تفسیر کمّی سریع دادههای گرانی تولید شده از شکل اجسام هندسی ساده و برآورد عمق و دیگر پارامترهای یک ساختار مدفون، توسعه داده شده است. این الگوریتم مشتق عددی افق چهارم محاسبه شده از بیهنجاری گرانی مشاهده شده را با استفاده از صافیهای متوالی طول پنجره برای برآورد عمق و شکل ساختار مدفون مورد استفاده قرار میدهد. برای یک طول پنجره ثابت شده، عمق با استفاده از یک فرمول ساده برای هر نوع شکل برآورد، و تغییر در عمقهای محاسبه شده نسبت به انواع شکل روی یک نمودار رسم میشود. همه نقاط برای یک طول پنجره ثابت با یک منحنی پیوسته (منحنی-s) به هم وصل میشوند و برای تعیین عمق و شکل ساختار مدفون، محل تلاقی مشترک از منحنی-s خوانده میشود. این روش برای دادههای مصنوعی با و بدون خطاهای تصادفی در یک میدان نمونه در ایران بهکار برده شد. در موارد مربوط به آزمایش، عمقهای بهدست آمده تطابق خوبی با مقادیر واقعی دارند.https://jesphys.ut.ac.ir/article_35981_c595d64db6a0f65fb4000957675a405b.pdfموسسه ژئوفیزیک دانشگاه تهرانفیزیک زمین و فضا2538-371X39420131222Processing and interpretation of ground magnetic data corresponding to geothermal resources using Euler and AN-EUL method, north-east of Mahallatپردازش و تفسیر دادههای مغناطیس زمینی مرتبط با منابع زمینگرمایی با استفاده از دو روش اویلر و AN-EUL، شمال شرق محلات83963598210.22059/jesphys.2013.35982FAمحمودمیرزائیدانشیار، گروه فیزیک، دانشکده علوم پایه، دانشگاه صنعتی اراک، ایرانمحمدمحمدزاده مقدمدانشآموخته کارشناسی ارشد، گروه فیزیک زمین، مؤسسه ژئوفیزیک دانشگاه تهران، ایرانبهروزاسکوییاستادیار، گروه فیزیک زمین، مؤسسه ژئوفیزیک دانشگاه تهران، ایرانفریدونقدیمی عروسمحلهاستادیار، دانشکده معدن، دانشگاه صنعتی اراک، ایرانسید سجادجزائریدانشآموخته کارشناسی ارشد، گروه فیزیک زمین، مؤسسه ژئوفیزیک دانشگاه تهران، ایرانJournal Article20120616<sup>*</sup>نگارنده رابط: تلفن: 61118238-021 دورنگار: 88630479-021 E-mail: sjazayeri@ut.ac.ir
Ground magnetic survey was carried out in Mahallat region, Iran, as the first part of exploration and development of geothermal energy program conducted by Arak and Tehran universities. The magnetic method is useful in mapping near-surface volcanic rocks that are often of interest in geothermal exploration. The magnetic method has come into use for identifying and locating masses of igneous rocks that have relatively high concentrations of magnetite. Strongly magnetic rocks include basalt and gabbro, while rocks such as granite, granodiorite and rhyolite have only moderately high magnetic susceptibilities. The surface manifestations of thermal activity in the area are in the form of hot springs, hydrothermal deposits, thermal alteration, vast travertine outcrops and young volcanic rocks.
In the geological dividing of Iran, Mahallat area is located in the volcanic zone of Central Iran. This zone has been one of active zones during the different geological periods that is located in Central Iran with triangle form. This area, from permeability aspect and by regarding to expansion of calcareous and dolomite units and also presence of cracks and joints, has a good condition. Also, with regard to presence of hot water springs and regard to geologic settings in the area, we can define it as one of important and suitable geothermal potential in Iran.
Existence of many hot springs in Mahallat and also its special geology show a big probable deep geothermal system in the area. During activities performed since 1996 in Iran, few encouraging area with geothermal potential have been introduced by the Renewable Energy Organization of Iran and one of the corresponding areas is Mahallat. In order to delineate susceptible area with geothermal potentials accurately, ground magnetic survey was performed around hot springs of Mahallat. Total magnetic field data was collected along 10 profiles, with station distance of 40 m and profile distance of 1.5 km. During this survey, measurements were performed at over 4000 stations.
In this research, magnetic data of magnetometry operations are interpreted by two practical methods: standard Euler deconvolution and AN-EUL. The standard Euler method is based on the Euler equation, and using this method in the depth estimation of magnetic anomalies inserts the geology of the region into the calculations. AN-EUL is a new automatic method for the simultaneous approximation of depth, geometry and location of magnetic sources. The principle advantage of this method is its combining both the analytic signal and the Euler Deconvolution methods. In this method, the determination of the source location is based on the position of the maximum value of the analytic signal amplitude.
Results of depth estimation of the main source of the anomaly, from these two methods, have estimated existence of geothermal resource, with probable depth of more than 1000 m and structural index of 1.8. Estimated structural index from these two methods shows that source of anomaly has a conical cylinder shape. Absence of negative magnetic pole in the area imply of extension of anomaly in depth. Results of this research also show that Euler method in addition to estimation of anomalous depth is also able to investigate trend of depth variations in different position of the anomaly, while AN-EUL can only estimate depth in special position.
Gravity, resistivity and MT surveys and also exploratory drillings over the interpreted geothermal anomalies in the area are suggested for the future assessment of geothermal energy in the region on an industrial and scientific scale.چشمههای آبگرم متعدد در منطقه محلات و همچنین نوع زمینشناسی منطقه، نشاندهنده وجود یک سامانة زمینگرمایی بزرگ در اعماق منطقه است. طی فعالیتهای صورت گرفته از 1374 در ایران، چندین ناحیه امیدبخش از لحاظ پتانسیل زمینگرمایی از سوی مرکز انرژیهای نو وزارت نیرو معرفی شده که محلات یکی از مناطق مهم در این زمینه است. بهمنظور شناسایی دقیق نواحی مستعد زمینگرمایی، عملیات مغناطیسسنجی زمینی در طول 10 نیمرخ بهنسبت بلند، جمعا به طول حدود 160 کیلومتر با فاصله ایستگاهی 40 متر و فاصله نیمرخی 5/1 کیلومتر، در محدوده اطراف چشمههای آبگرم محلات صورت گرفت. در مجموع بیش از 4000 ایستگاه مغناطیسسنجی برداشت شد. در این پژوهش دادههای حاصل از عملیات مغناطیسسنجی زمینی با استفاده از دو روش بسیار کاربردی اویلر و روش تلفیقی سیگنال تحلیلی و اویلر (AN-EUL) مورد تفسیر قرار گرفته است. نتایج برآورد عمق منبع اصلی بیهنجاری بهدست آمده با این دو روش، وجود یک منبع زمینگرمایی با عمق حداقل یک کیلومتر در منطقه را برآورد میکند. مقدار شاخص ساختاری بهدست آمده از این دو روش پردازشی، مؤید این است که منبع بیهنجاری احتمالا داری شکلی شبیه به یک استوانه قائم است. نبود قطب منفی مغناطیسی بارز در منطقه احتمالا حاکی از گسترش این توده در عمق است. همچنین نتایج این پژوهش نشان میدهد که روش اویلر علاوه بر برآورد عمق بیهنجاری، به بررسی روند تغییر عمق در نقاط متفاوت بیهنجاری هم میپردازد ولی روش AN-EUL فقط در نقاط خاصی میتواند برآورد عمق را عملی سازد.https://jesphys.ut.ac.ir/article_35982_a138b56f360415807ffd1e6866f25dd2.pdfموسسه ژئوفیزیک دانشگاه تهرانفیزیک زمین و فضا2538-371X39420131222The determination of boundaries of layers and geothermal bodies using 2D inversion of magnetotelluric (MT) data, in Sabalan areaبررسی مرز لایهها و تودههای زمینگرمایی منطقۀ سبلان با استفاده از برگردان دوبُعدی دادههای مگنتوتلوریک971083598310.22059/jesphys.2013.35983FAمیلادتکلوکارشناسی ارشد ژئوفیزیک، ژئوالکتریک، گروه فیزیک زمین، موسسۀ ژئوفیزیک دانشگاه تهران، ایرانبهروزاسکوییاستادیار، گروه فیزیک زمین، موسسۀ ژئوفیزیک دانشگاه تهران، ایرانسهیلپرخیالاستادیار، دانشگاه آزاد کرج، ایرانJournal Article20130428<sup>*</sup>نگارنده رابط: تلفن: 61118238-021 دورنگار: 88630479-021 E-mail: boskooi@ut.ac.ir
Geophysical methods play a key role in geothermal exploration since many objectives of geothermal exploration can be achieved by these methods. The geophysical surveys are directed at obtaining indirectly, from the surface or from shallow depth, the physical parameters of the geothermal systems. The other geophysical techniques like gravity, magnetic, self-potential studies, and shallow seismic refraction also provided valuable information about the shallow geothermal zone. The earlier magnetotelluric (MT) that was survey carried out (Singh and Drolia, 1983), provided qualitative information with limited narrow band data and limited quantitative result due to noisy electric field data. Due to both limitations in interpretation methods and the cost of data acquisition, magnetotelluric (MT) data have been traditionally obtained in profiles targeted to the geology, and then interpreted with two-dimensional inversion. In such an interpretation, one fits the off-diagonal impedances (Zxy and Zyx), generally after rotating the coordinate system so that the main diagonal components (Zxx and Zyy) are minimum, or at least small. It is seldom possible to find a single strike angle that is optimal for the full frequency range and for all sites, and possible impacts of off-profile structure must always be considered.
MT is an appropriate tool for identification of the deep subsurface structures. In this method, recording the erpendicular to horizontal components the fluctuations of the magnetic and electrical fields are measured at the earth surface. Using these measurements, the electrical conductivity distribution can be determined.
Geothermal resources are ideal targets for EM methods since they produce strong variations in underground electrical resistivity. Geothermal waters have high concentrations of dissolved salts that result in conducting electrolytes within a rock matrix. The resistivities of both the electrolytes and the rock matrix (to a lesser extent) are temperature dependent in such a way that there is a large reduction in the bulk resistivity with increasing temperature. The resulting resistivity is also related to the presence of clay minerals, and can be reduced considerably when clay minerals and clay-sized particles are broadly distributed. On the other hand, resistivity should be always considered with care. Experience has shown that the correlation between low resistivity and fluid concentration is not always correct since alteration minerals produce comparable, and often a greater reduction in resistivity. Moreover, although water-dominated geothermal systems have an associated low resistivity signature, the opposite is not true, and the analysis requires the inclusion of geological and, possibly, other geophysical data, in order to limit the uncertainties (Spichak, and Manzella, 2009). Geothermal energy has been harnessed by using the steam or hot water stored underground at high temperatures and pressures for the generation of electric power in conventional steam turbines, and by the direct use of the heat content of the resources in heat exchangers in industrial or domestic utilizations. Temperature and the circulation of subsurface hydrothermal fluids, both of which are characteristic features of geothermal systems, are capable of generating a surface electrical potential field. Such electric fields are the result of streaming potential, caused by the movement of hydrothermal fluids around the subsurface heat source (Fitterman and Corwin, 1982). Based on hydrodynamic geothermal sources, the flow can play the role of on initial parameter in the resistivity contrast of the geothermal source and its surrounding. using this feature, MT is capable of determining the boundary between geothermal system and the neighboring medium.
In order to investigate more closely Sabalan geothermal reservoirs and determine the injection and exploration wells, the magnetotelluric data was scheduled in two phases. The first phase was carried out at 28 MT stations in 2007. The second phase 50 magnetotelluric stations were taken in 2009. MT measurements, in Sabalan area, could clearly highlight the geothermal reservoir. The results of the MT survey are presented through isoresistivity maps sliced at different elevations to show the resistivity changes with depth, and through cross sections to show the resistivity structures that were modeled. The changes in resistivity with elevation and observed resistivity layers are discussed in detail. Interpretation of these results will help in delineating the arbitrary boundaries geothermal resource at Mt. Sabalan and pinpoint the best drilling targets in the area.
After dimensional analysis using skew parameters (for skew below 0.2) study area shows a two-dimensional behavior. After removing data outside of category that caused by environmental noise, magnetotelluric inversion was performed. The aim designing of the two profiles S01 and S02 including some part of reservoir and we also wanted to S01 profile to pass the exploration wells. Profiles S01 and S02 cover the Moil Valley and the present development block of the Mt. Sabalan Geothermal Project.
Along the profile S01, resistivity of the top layer varies from 50 to >250 Ω-m. An anomalous conductive layer extending from Moil Valley to wells NWS-7D and NWS-8D was observed to about 1000 m above sea level (a.s.l.) This conductive layer has a thickness of about 500-1000 m and is underlain by a moderate to highly resistive layer with resistivity values >50 to 250 Ω-m.
Along the profile S02 two conductive zones (<30 Ω-m) are detected, one within the well NWS-7D, in the western portion, beneath MT stations 249 and 24, and another one beneath station 216, on the eastern portion. The conductive anomaly on the west is part of the conductive layer observed in P01. A high resistivity block (>100 Ω- m) is modeled separating the conductive zones, its boundaries marked by steep resistivity gradients. The shallowest portion of this resistive body is found beneath stations 109, 219 and 218, at elevations of about 1500 m a.s.l.
The resistivity sections derived from 2D inversion in conjunction with exploration wells and geology surveys showed that Sabalan geothermal system is in agreement with Johnston’s studies (1992) in which the thicker conductive layers are found in the outer areas.بهمنظور بررسی مخزن زمینگرمایی سبلان و هدفگذاری چاههای جدید اکتشافی و تزریقی، دادههای مگنتوتلوریک در دو فاز طی سالهای 2007 و 2009 برداشت شد. پس از بررسی ابعادی محیط و تصحیح دادههای خارج از رده که ناشی از نوفههای محیطی بودند، معکوسسازی دادههای مگنتوتلوریک صورت گرفت. نتایج بهدست آمده در محدودۀ سبلان، مخزن زمینگرمایی را به شکل مناسبی آشکار کرد. بررسی مقاطع مقاومت ویژه حاصل از برگردان 2D در کنار دادههای چاههای اکتشافی و برداشتهای زمینشناسی نشان داد که سامانه زمینگرمایی سبلان با مدل مطالعاتی که جانستون (1992) عرضه کرده است و در آن لایههای رسانای ضخیمتر معمولا در نواحی خروجی جریان زمینگرمایی یافت میشوند، مطابقت دارد.https://jesphys.ut.ac.ir/article_35983_fa3ff702b167b53c629ecdb9445d9158.pdfموسسه ژئوفیزیک دانشگاه تهرانفیزیک زمین و فضا2538-371X39420131222The impact of urban air pollutants on atmospheric visibility in Tehran, 2008ارتباط آلایندههای شهری با دید افقی منطقه تهران در سال 20081091223598410.22059/jesphys.2013.35984FAسمانهثابتقدمدانشجوی دکتری هواشناسی، گروه فیزیک فضا، مؤسسة ژئوفیزیک دانشگاه تهران، ایرانفرهنگاحمدی گیویدانشیار، گروه فیزیک فضا، مؤسسة ژئوفیزیک دانشگاه تهران، ایران0000-0002-9487-4862یحییگلستانیاستادیار، گروه فیزیک فضا، مؤسسة ژئوفیزیک دانشگاه تهران، ایرانعباسعلیعلیاکبری بیدختیاستاد، گروه فیزیک فضا، مؤسسة ژئوفیزیک دانشگاه تهران، ایرانJournal Article20120624Atmospheric visibility has been defined as the greatest distance at which an observer can see a black object viewed against the horizon sky, which in quantitative terminology is known as visual range. Visibility, in the absence of special meteorological events (e.g. rain and fog), is an excellent indicator of air quality. Visibility impairment results from light scattering and absorption by atmospheric particles and gases that can originate from natural or anthropogenic sources. It is an important factor in everyday life mainly in aviation industry and surface traffic. Air pollution in big cities, which is a serious environmental problem, especially in developing countries, may cause remarkable visibility reduction.
Much of emphasis in the recent atmospheric visibility studies has been to establish the factors contributing to visibility reduction. Since the factors used to determine visibility impairment, including absorption and scattering of incoming light, depend on time and location, then it should be studied on local scale.
In this paper, the effect of different air pollutants on horizontal visibility is presented in the south-west of Tehran for 2008. Tehran is a highly industrializes and densely populated city in our region that is well-known for its air pollution problem. The data used in this study are based on midday measurements of meteorological quantities such as horizontal visibility distance, relative humidity, wind speed, present weather code, dew point and wet bulb temperature performed at Mehrabad synoptic station. Moreover, intensive measurements of particulate matter (PM<sub>10</sub>) and gaseous materials (e.g., CO, NO<sub>2</sub>, SO<sub>2</sub>, and O<sub>3</sub>), carried out in Tehran-Azadi-Square station, were used for further analysis.
The monthly and annual changes in atmospheric visibility and air pollutant concentrations including SO<sub>2</sub>, NO<sub>2</sub>, and PM<sub>10</sub>, as well as their relationships with each other are studied. In order to focus mainly on the changes in visual air quality, the cases of visibility impairment that were concurrent with reports of fog, mist, precipitation or relative humidity of %90 or above were filtered from the visibility data using the present weather code that is a part of WMO synoptic coding system. Then both the yearly and monthly correlations between visibility and air pollutant concentrations were examined.
The results from regular measurements of air pollutant concentrations indicate that air pollution in Tehran is severe in comparison with other cities around the world. The results of regression analysis also show that the most correlated pollutants with visibility are CO and NO<sub>2</sub> followed by PM<sub>10</sub>. The fairly significant correlation between reduced visibility and NO<sub>2</sub> concentration implies that the impact of primary emissions of NO<sub>2</sub> and enhanced secondary pollutants, formed via photochemical processes in the atmosphere, that could not be ignored.
The monthly analysis of visibility shows that the cold season is the most affected one by air pollutants and the significant anti-correlation is found between visibility and SO<sub>2</sub> in this season. More detailed analysis presents the significant role of relative humidity on the correlation of visibility and pollutants, especially on SO<sub>2</sub>.میدان دید در جوّ، علاوه بر عوامل طبیعی، متاثر از پراکنش و خاموشی نور در ذرات و مولکولهای موجود در آن است. از اینرو دید افقی و تغییرات آن یک نشانگر مشاهداتی ساده و خوب برای کیفیت هوا به شمار میرود. در مقاله حاضر، اثر غلظت آلایندههای جوّ شهری بر دید افقی منطقه جنوب غرب تهران در سال 2008 بررسی شده است. دادههای استفاده شده در این مقاله، شامل دیدبانیهای روزانه ایستگاه هواشناسی مهرآباد و غلظت آلایندههای جوّی در ایستگاه میدان آزادی در شهر تهران است. نتایج نشان میدهد که میزان غلظت آلایندههای جوّی در منطقه شهری تهران در مقایسه با دیگر شهرهای آلوده و پُرجمعیت دنیا بسیار بالاتراست. آلایندههای اصلی و مهم تاثیرگذار بر کاهش دید بهترتیب کربن مونوکسید، نیتروژن دیاکسید و سپس ذرات معلق با قطر کمتر از 10 میکرون هستند. نتایج بررسی ماهانه حاکی از آن است که در ماههای سرد سال، آلایندههای شهری نقش بارزتری در کاهش دید افقی دارند. بیشترین همبستگی منفی میان گوگرد دیاکسید و محدوده دیداری در فصل زمستان مشاهده شده است و بررسی دقیقتر نشان میدهد که میزان رطوبت نسبی جوّ، اثر تعیینکنندهای در چگونگی ارتباط انواع آلایندهها، بهجز کربن مونوکسید، با دید افقی دارد.https://jesphys.ut.ac.ir/article_35984_1ff3477537cc1c0aa2e22bd00bad43a8.pdfموسسه ژئوفیزیک دانشگاه تهرانفیزیک زمین و فضا2538-371X39420131222A laboratory study of the role of ions in warm cloud formationبررسی آزمایشگاهی نقش یونها در تشکیل ابر گرم1231343598510.22059/jesphys.2013.35985FAمحمد حسینشوشتریکارشناس ارشد هواشناسی، گروه فیزیک فضا، مؤسسه ژئوفیزیک دانشگاه تهران، ایرانفائزهناجیکارشناس ارشد هواشناسی، گروه فیزیک فضا، مؤسسه ژئوفیزیک دانشگاه تهران، ایرانعباسعلیعلیاکبری بیدختیاستاد، گروه فیزیک فضا، مؤسسه ژئوفیزیک دانشگاه تهران، ایرانJournal Article20120924Aerosol formation due to ions in the atmosphere is not well understood, although it seems to play an important role in cloud formation. The ions in the atmosphere can enhance cloud formation and can increase nucleation as well as impeding the evaporation from the surfaces of the droplets. Recently there has been some experimental work to find the relation between ions concentrations and cloud initiation. Experimental and field studies show that the classical nucleation theory cannot explain the formation of the aerosols at their early stages formation. Although some ideas have been given concerning this problem, e.g. ion-induced nucleation (Arnold 1980; Raes et al. 1986; Turco et al. 1998) and ternary nucleation (Kulmala et al. 2000). The experimental considerations of the role of aerosol formation by ions are also not wide spread, particularly those that can be applicable to the lower atmosphere. Along this line, we have studied this problem in the warm cloud in the laboratory. By warm cloud we mean that the experiments were carried out at room temperature.
In these experiments the role of ions in warm cloud formations is studied in a cloud chamber of 20 liters in the laboratory. Ions were produced by a strong electric field in the chamber. The ion concentration is controlled by the time of ionization of air between two electrodes. The cloud concentration was also measured by the attenuation of a laser beam going through the cloud chamber. With cloud formation the opacity of the chamber was changed, so that with the increase of cloud concentration due the scattering of laser light by cloud droplets less light reached the detector, resulting in smaller laser signal. The laboratory facility for this study includes a cloud chamber, a laser beam (red with 598 nm) with a detector, signal amplifier, pressure gauge (water column manometer), temperature and humidity sensors of which their signals are digitized using a computer with an Analogue to Digital convertor, with typical sampling time of 0.5 of second. Cloud concentration is determined by fluctuations in the laser signal. Some 25 experiments were carried out with different ions concentrations. The warm cloud in the chamber was produced by an adiabatic the expansion of nearly saturated moist air. As soon as the expansion starts the cloud forms, although it takes a few 10s of seconds to clear off. The clearing times also seems to be dependent on the size of the cloud droplets, as they precipitate differently due to gravity.
In this paper we report the results of experiments concerning ions with different concentration in the cloud chamber. Preliminary results show that as the ion concentration increases to some level the cloud formation is enhanced. But as the ion concentration increases more than a certain (optimum) value the cloud formation is hampered and we acquire less cloud with perceptible droplet sizes. We found that the over seeding process occurs as a result of increasing ion concentration more than the optimum value leading to less perceptible cloud. This leads to an increase of cloud clearing time after an optimum point.در این مقاله اثر یونها در تشکیل ابر گرم در محیط آزمایشگاه بررسی شده است. همانطور که وجود یونها در جوّ در تشکیل ابرها موثر است این تاثیر در آزمایشگاه بررسی شده است. در آزمایشهای صورت گرفته، از دو الکترود که به ولتاژ بالا متصل شدند برای یونیده کردن هوای داخل محفظه شیشهای استفاده شده است، بهطوریکه ولتاژ زیاد با اِعمال یک میدان الکتریکی قوی سبب یونیده شدن هوای داخل محفظه شده است. تشکیل ابر گرم مصنوعی با استفاده از انبساط بیدررو در حالتهای بدون یون و با حضور یون و با غلظتهای متفاوت بررسی شده است. سامانة اندازهگیری غلظت ابر گرم مصنوعی متشکل از یک لیزر (با طول موج 598 نانومتر)، آشکارساز، آمپلیفایر و یک رایانه مجهز به مبدل (A/D) است، بهطوریکه پرتو لیزر از میان ابر گرم مصنوعی عبور میکند و به آشکارساز میرسد و بسته به غلظت ابر تشکیل شده، سیگنال لیزر تغییر میکند. این سیگنال و شرایط دیگر آزمایش از قبیل دما و میزان رطوبت داخل محفظه ابر و بیرون از آن با رایانه بهصورت مستقیم و پیوسته ثبت میشود. همچنین فشار هوای داخل محفظه با یک دستگاه شامل یک پمپ الکتریکی، شیلنگهای رابط و یک شیر تخلیه تغییر مییابد و با استفاده از یک مانومتر آبی اندازهگیری میشود. نتایج نشان میدهد که حضور یون بهطور چشمگیری در تشکیل ابر در شرایط آزمایشگاهی مؤثر است. بهصورت کیفی با افزایش غلظت یون، ابر غلیظتری تشکیل میشود ولی افزایش بیش از حد غلظت یون به علت اثر فراباروری، نقش کاهنده در باروری ابر تشکیل شده دارد و ریزش ابر در غلظتهای بیش از حد بهینه، کاهش پیدا میکند.
https://jesphys.ut.ac.ir/article_35985_584c53c01df8e81f81c9b814c328c615.pdfموسسه ژئوفیزیک دانشگاه تهرانفیزیک زمین و فضا2538-371X39420131222Relationships between Arab sea and Indian Ocean surface temperature anomalies with precipitation over southern of Iranارتباط بیهنجاریهای دمای آب سطح اقیانوس هند و دریای عرب با بیهنجاریهای بارش نیمه جنوبی ایران1351573598610.22059/jesphys.2013.35986FAعباسرنجبرسعادتآبادیاستادیار، پژوهشکده هواشناسی و پژوهشکده هواشناسی و علوم جو، تهران، ایرانپریساایزدیکارشناس ارشد، سازمان هواشناسی کشور، تهران، ایرانJournal Article20121003Iran is located in arid and semiarid areas based on continental divisions; any change in precipitation would have potential effects on agriculture, economic and other related issues in general. Therefore, it is of high importance to know and identify the moisture-related sources needed to study the country’s precipitation data. For this purpose, it is important to correlate monthly precipitation with Sea Surface Temperature (SST) anomalies. The SST variations are responsible for a large portion of the atmospheric circulation and precipitation variability. Many studies have been done for empirical evidence of relationships between SST anomalies (deviation from the long-term mean) and rainfall anomalies (e.g., Tae-Suk and Moon, 2010; Uvo et al., 1998; Mechoso et al., 1990; Moron and Navarra, 2001; Shabbar and Skinner, 2004). This paper is mainly concerned with indentifying the relationships between the abnormalities seen in the Indian Ocean’s water surface temperatures and the ones seen in Arab sea.
As apparently seen, it has not only some potential effects on moisture-based feeding but also on the ways, the climate scales and flows are being formed. To verify the relationship between Sea Surface Temperature Anomalies (SSTA) and rainfall over southern of Iran, by using ARPEG model output and divergence of specific humidity flux in the low levels of troposphere including 1000, 925, 850, 800 and 700 hPa, moisture resources and how the moisture is transfered to the southern parts of iran, were studied. The second step will be concerned with the study of the relationship between SST anomalies and precipitation. The basic data used in this study consists of, 1) mean monthly values of SST from Octebr to March for the years 1956- 2005 over the Arabian Sea and Indian Ocean; 2) mean monthly rainfall for 9 synoptic stations over southern of Iran. Because precipitation and SSTs exhibit strong seasonality, it is of interest to correlate monthly precipitation anomalies with the SST anomalies. To do this, correlation coefficients, between the SST anomaly of the three parts (Arabian sea, western and eastern Indian Ocean) and the precipitation anomaly for each month, were calculated.
The results of case studies, based on wind and streamlines, vector and divergence of specific humidity flux show that the Arabian Sea, the Red Sea and Persian Gulf have to important role in feeding moisture to the southern Iran, and the maximum flux divergence were occurred in the lower troposphere (1000 and 925hPa) over these area. In addition, the maximum convergences were observed in the southern of Iran and the south east of Saudi Arabia.
Monthly correlation coefficients between Arab sea SST anomalies and precipitation anomalies are summarized in Table 1. Correlation coefficients that exceed the weak threshold of relationship (above 0.30 or below -0.30) are highlighted in bold. No strong relationships (coefficients above 0.60 or below -0.60) were found, however some values do approach more than 0.40. The positive relationships have been found in October, November, January, and February at these stations. No stations exhibits significant (either weak, or strong) relationships in December and March (Table 1).
Monthly correlation coefficients between the eastern Indian Ocean SST anomaly and precipitation anomaly are summarized in Table 2. Most of the stations have very little correlation between monthly rainfall and SST anomalies, as evidenced by correlation coefficient between 0.20 and -0.20. However, the coefficients do reveal a few interesting relationships. The positive coefficients (more than 0.30) are found in October at stations Abadan, Boushar, Shiraz and Yazd. There are not any significant relationships for December and March (Table 2). The correlation coefficients for the western Indian Ocean are found positive, in October in Yazd, in November in Ahvaz and in January in Ahvaz, Boushar and Bandar Abbas stations. No stations exhibits significant (either weak, or strong) relationships in December, February and March (Table 3).
The data presented above reveal that precipitation anomalies over southern Iran are related to SST anomalies in both the Arab sea and Indian Ocean. However, this study found indications that positive relationship may exist for southern Iran in some months. The correlation coefficients were not randomly dispersed throughout the seasonal (October-March) precipitation. The most positive coefficients were found in the autumn months of October and November, especially for Arab Sea and eastern Indian Ocean in the winter months of January and February for Arab Sea and western Indian, implying that warmer than normal SSTs, are connected with increased precipitation. Only a few stations have positive coefficients in November and February. Also in December and March not any significant correlation werefound.
Several possible reasons exist to explain these relationships. For the majority of sites in the southern Iran, precipitation has no strong relationship with SST anomalies of Arab and Indian Ocean in the all months (October-March). Precipitation is, in a basic sense, a function of local vertical motion and water vapor quantity. These two variables are influenced by a variety of global-, synoptic-, and meso-scale features, including planetary waves, mid-latitude cyclones, upper-tropospheric subsidence, mid-tropospheric humidity, local topography and other humidity sources. It is interesting to examine these for more sites and months that do exhibit positive correlations. The stations that reported positive correlations are mostly located in the south of Iran. So, positive SST anomalies can be considered as one of the forcing for increasing precipitation over the southern Iran. بیهنجاریهای دمای سطح آب اقیانوس هند و دریای عرب میتواند در تغذیه رطوبتی و شکل گیری سامانههای جوّی نقش مؤثری داشته باشد در این تحقیق، بهمنظور شناسایی ارتباط بیهنجاریهای دمای سطح آب و بیهنجاریهای بارش در نیمه جنوبی ایران، ابتدا بهصورت موردی منابع رطوبتی و نحوه انتقال رطوبت با استفاده از برونداد مدل ARPEG و محاسبه بردار شار رطوبت ویژه، همگرایی و واگرایی آن در ترازهای پایین جوّ بررسی شد. سپس همبستگی بین بیهنجاریهای دمای سطح آب با بارش نیمه جنوبی کشور بهصورت ماهانه بررسی شده است. برای این منظور طی دوره آماری 50 ساله (1956-2005) برای ماههای اکتبر تا مارس دادههای بیهنجاری دمای سطح آب دریای عرب و اقیانوس هند و دادههای 9 ایستگاه سینوپتیک برای بیهنجاریهای بارش نیمه جنوبی ایران مورد بررسی قرار گرفت. ضریب همبستگی بین بیهنجاریهای بارش و بیهنجاریهای دمای سطح آب دریای عرب، شرق و غرب اقیانوس هند محاسبه شد. نتایج حاصل نشان داد که بردار شار رطوبت ویژه، همگرایی و واگرایی آن و خطوط جریان در ترازهای پایین جوّ به گونهای است که در زمان فعالیت سامانههای کمفشار دینامیکی، شرایط مناسبی برای تغذیه رطوبت از روی دریای عرب، دریای سرخ و خلیج فارس فراهم میشود. بیشترین ضریب همبستگی مربوط به دریای عرب در ماههای اکتبر، نوامبر، ژانویه و فوریه بوده است. همچنین همبستگی معنیداری بین بیهنجاری بارش و بیهنجاری دمای سطح آب نواحی غربی اقیانوس هند در ماههای اکتبر، نوامبر و ژانویه و برای نواحی شرقی آن در ماههای اکتبر و نوامبر بهدست آمد. برای ماههای دسامبر و مارس همبستگی معنیداری حاصل نشد.https://jesphys.ut.ac.ir/article_35986_7d6713af8da130d8365c262de9c0b66e.pdfموسسه ژئوفیزیک دانشگاه تهرانفیزیک زمین و فضا2538-371X39420131222Examining the energetics of secondary downstream development for two cyclone cases over western Iranدو بررسی موردی برای تحقیق گسترش جریانسوی ثانویه در تقویت چرخندهای غرب ایران ازدیدگاه انرژی1591753598710.22059/jesphys.2013.35987FAمجیدآزادیدانشیار، پژوهشکده هواشناسی، تهران، ایرانمحمدمهدیخدادیکارشناس مرکز پیشبینی سازمان هواشناسی کشور، تهران، ایرانJournal Article20130218In this research energetics of the barotropic and baroclinic development for two planetary waves over eastern Mediterranean, Syria and west of Iran and their interaction with surface cyclones were investigated.
Ahmadi-Givi et al. (1384) calculated and examined several selected important terms in the eddy kinetic energy (EKE) tendency equation during life cycle of six troughs that were developed with downstream development over Europe. They showed that almost for all cases the ageostrophic flux convergence (AFC) was the main factor in development of the systems. AFC causes radiative energy transport from upstream of the wave to the downstream of the trough. For mature baroclinic waves, this radiative energy transport causes dispersion of the upstream wave and forming a new wave downstream. Orlanski and Gross (1993) simulated the effect of topography on cyclone development over the Mediterranean using primitive equations. They showed that when mature troughs cross east-west Mountains, strong cyclones form over the south of the mountain and if the isotherms are also oriented in the east-west direction, baroclinic development is intensified. Northward advection of warm and moist air to higher latitudes accounts for baroclinic development and secondary development. In some cases baroclinic energy conversion between separated cyclones is responsible for the cyclone development (Chang, 2000). Decker and Martin (2005) examined the life cycle of two cyclones that had similar track over North America. They showed that the first cyclone intensified and damped much faster than the second cyclone. The reason for this is that the development and damping of the first and second cyclones occurred upstream and downstream of the trough respectively. Nasre-Esfahani et al. (1389) examined the effects of several important forcing terms in the EKE tendency equation for critical positive months (CPM) and critical negative months (CNM) of the North Atlantic Oscillation (NAO) over the Mediterranean and Middle East. Their results indicated that there is no considerable difference in the amount of EKE between CPM and CNM in the Mediterranean region. However, moving eastward, the values of EKE become greater in the CPM than in the CNM in such a way that the difference between the two reaches its maximum over the south west of Iran. Also, in the CPM, all of the computed forcing terms are larger than in the CNM.
In this research, National Center for Environmental Prediction (NCEP) Climate Forecast System Reanalysis (CFSR, Saha et al., 2010) data with 0.5 degree horizontal resolution, described by Saha et al., 2010 are used to extract several fields including geopotential height, horizontal wind vector, relative vorticity and temperature at several vertical levels. Thickness fields and several important EKE tendency forcing terms for 00, 06, 12 and 18 UTC for two case studies, that cover the period 14-18 January 2004 and 27-29 January 2000 are then calculated. Following Orlanski and Katzfy (1991), different forcing terms in the EKE tendency equation including baroclinic and barotropic conversions, zonal and eddy advections and AFC are derived. Time mean stress term is also calculated according to Decker and Martin (2005).
Results showed that the first cyclone on January 2004 was formed over western Mediterranean. It was then weakened over the eastern Mediterranean and subsequently intensified in two other regions as it moved to the west of Iran. At the beginning, there was a strong energy center over Mediterranean associated with the polar jet at the upstream of the trough. Ageostrophic energy flux from this center to the downstream of the trough causes downstream intensification of the energy center east of the Mediterranean and west of Iran. It is shown that baroclinic energy conversion and ageostrophic flux convergence are the most important factors in the secondary development of the energy center over north of Saudi Arabia and east of the Mediterranean and subsequently over west of Iran. Increase of the energy tendency terms over eastern Mediterranean and Syria is due to the warm and moist air advection over the Red Sea and combination of the thermal Sudanic low and the low pressure situated at higher latitudes. Forced vertical motion over the mountain ranges located west of Iran accounts for the increase of the energy tendency terms.
For the second cyclone on January 2000, similar to the first case, there is a strong energy center over the Mediterranean at the upstream of the associated trough. The subtropical jet causes a strong ageostrophic energy flux from the upstream energy center to the downstream of the trough and developing a downstream energy center over northern Saudi Arabia and west of Iran. Moreover, similar to the first case, warm and moist air advection over northern Saudi Arabia and eastern Mediterranean and subsequently forced vertical motion over the west of Iran are responsible for intensification of the baroclinic factor and downstream development of the energy center. But for this case, barotropic factor (such as Reynolds stress) is important for the intensification of the energy enter. Stated differently, the role of the subtropical jet in intensification of the cyclone over south of Iran is clearly seen.در این تحقیق رشد و گسترش فشاروردی و کژفشاری دو موج سیارهای در ناحیه شرق دریای مدیترانه، سوریه و غرب ایران واندرکنش آنها با چرخندهای سطح زمین از دیدگاه انرژی بررسی شده است. با استفاده از دادههایCFSR با تفکیک افقی 5/. درجه مقدار انرژی و مولفههای گوناگون گرایش انرژی برای این چرخندها محاسبه شده است. چرخند اول مربوط به ژانویه 2004 روی غرب مدیترانه شکل میگیرد و روی شرق مدیترانه تضعیف اما در طی مسیر خود تا نواحی غرب ایران در دو ناحیه دیگر تقویت میشود. نتایج نشان میدهد که مهمترین عامل رشد ثانویه مرکز انرژی درجریانسوی ناوه روی شمال عربستان و شرق مدیترانه و سپس غرب ایران تبدیل کژفشاری انرژی و همگرایی شار آزمینگرد انرژی است.
برای چرخند دوم مربوط به ژانویه سال 2000، مشابه مورد اول ابتدا یک مرکز انرژی قوی روی دریای مدیترانه در پادجریانسوی ناوه وجود دارد. در این مورد حضور جت جنبحاره موجب شار آزمینگرد قوی انرژی از این مرکز به جریانسوی ناوه و در نتیجه موجب گسترش جریانسوی مرکز انرژی روی شمال عربستان و غرب ایران میشود. همچنین نقش فرارفت هوای گرم در شمال عربستان و شرق مدیترانه و سپس صعود اجباری هوا در غرب ایران در تقویت عامل کژفشاری و گسترش جریانسوی انرژی برای این مورد، مشابه مورد پیشین است. اما در این مورد نقش عامل فشاروردی (تنشهای رینولدز) نیز در تقویت این مرکز انرژی قابلتوجه است. بهبیاندیگر تاثیر جت جنبحارهای در تقویت چرخند در جنوب غرب ایران دیده میشود.https://jesphys.ut.ac.ir/article_35987_15f25cc33aedb6a409096b2de823d73f.pdfموسسه ژئوفیزیک دانشگاه تهرانفیزیک زمین و فضا2538-371X39420131222Study of climate indices of Tamar River basin Golestan Province in terms of climate change using by LARS-WG modelبررسی شاخصهای اقلیمی حوضه آبخیز تمر، استان گلستان در شرایط تغییر اقلیم با کاربرد مدل LARS-WG1771893598810.22059/jesphys.2013.35988FAمریمدوستیدانشآموخته کارشناسی ارشد آبخیزداری، دانشکده منابع طبیعی، دانشگاه علوم کشاورزی و منابع طبیعی ساری، ایرانمحمودحبیبنژاد روشندانشیار، دانشکده منابع طبیعی، دانشگاه علوم کشاورزی و منابع طبیعی ساری، ایرانکاکاشاهدیاستادیار، دانشکده منابع طبیعی، دانشگاه علوم کشاورزی و منابع طبیعی ساری، ایرانمیرحسنمیریعقوبزادهدانشجوی دکتری علوم و مهندسی آبخیزداری، دانشگاه مازندران، ایرانJournal Article20130415Global warming caused by human activity and climate change is one of the issues attracted that has attention of many climate scientists. The relationship between climate parameters should be used in climate change studies to understand the complex nature of the environment and predict changes in the future. The reliable tool to investigate climate change effects on different systems is using the climate simulations by coupled general circulation of atmosphere and ocean. These models are capable to model the oceanic and atmospheric parameters for a long time period using IPCC scenarios. Due to the low spatial resolution of down scaled phenomena, in general circulation climate models, these models cannot provide accurately approximation of climate conditions of study areas. Therefore, outputs of these models should be down scale to weather station.
The use of statistical methods especially when lower cost and faster assessment of climatic factors is required, have more advantages and capabilities. These models downscale the large scale circulation data by using outputs of GSM models and applying specific scenarios that produce climate data. In this study a type of GCM model as HADCM3 for the period 2046-2065 was used. To simulate climatic parameters in Tamar Basin, the HADCM3 data downscaled using LARS-WG mode under A2 and A1B scenarios. Tamar river basin is located in Golestan Province north-east of Iran that have 1525.3 km<sup>2</sup> area. There are a few climatology and rain gauges in Tamar river basin. Most of these gauges except Tamar station that have more than 40 years precipitation and temperature data have short inventory period data (15 years rainfall data and 8 temperature data). According to the International organization WMO standards which at least thirty years considered as reference period, therefore, in this study the Tamar climatology data that were recorded for 30 years were used. For this purpose the temperature and rainfall data of Tamar station In a 30-year period (1981-2011) Was extracted. Due to the lack of sunshine data in stations, the Maravehtappe synoptic data, located at 30 km from the centre of the basin, was used. According to the Tamar basin area and variation in hypsometry of basin and also Tamar station located at outlet of basin, the rainfall and temperature data collected in this station cannot present the whole of basin changes. To solve the mentioned problem the temperature data was generalized for the whole of basin using a gradient equation with the differences between altitude of the station and the average altitude of the basin. The rainfall data also after the hydrologic processing, was transfered to the average altitude of basin using gradient equation. So the 30 day data in the month was randomly selected and the minimum and the maximum temperature data based on Tamar, Rebat-e-Ghrabil and Cheshmekhan station that located at the outside of the basin was extracted. Also the rainfall data of Tamar station with Tangrah, Rebat-e-Gharabil and cheshmekhan that are located at the outside of the basin were used. Then according to the obtained data, the gradient related to 30 days for each year was plotted, and a relationship was obtained. Totally, 2700 gradient relationship for 30 year also for maximum and minimum temperature and rainfall data were generated. Then, 30 gradient relationships for the maximum temperature and the minimum temperature and the rainfall data were selected with the gradient relationship of each year with higher correlation coefficient. Then the gradient relationship for each year and according to the highest percentage of watershed area that was located in the same altitude of centroid of the basin was acquired. Maximum and minimum temperature data for each year were moved to the center of the basin and data corresponding to the height of centroid the basin for log to climate models were obtained. In this study, in order to down scale of the atmospheric general circulation model data HADCM3, the LARS-WG model which is one of the weather generator models was used. To run this model in this research, calibration period was selected between 1981-2011, years then the model was run after preprocessing the input data.In the next step the model was assessed with NSE and RMSE and MAE indices.
Results show that the simulation data for this period are in good agreement with observation data. To evaluate climate fluctuations in the Tamar basin, general circulation model data were down scaled using LARS-WG model according to both A1B and A2 scenarios and thus the daily values of the parameters were generated. The results showed that the average temperature will increase under A2 scenario about 2.48 ° C and under A1B scenario about 2.43 ° C. Meanwhile the maximum temperature change will be higher than the minimum temperature change. From this subject we can conclude that the changes (increases) in the average air temperature in the future will be most affected by the minimum temperature. The results show that 16% increase in precipitation under A2 scenario and 2% rainfall under A1B scenario during 2046-2065 periods. Also, sunshine hours in the study period will be reduced under both scenarios. The results indicate that for the A2 scenario has the highest emissions of carbon dioxide, methane and nitrous oxide, higher temperatures and more rain are expected.گرمایش جهانی و تغییرات اقلیم، از جمله مسائلی هستند که امروزه توجه بسیاری از دانشمندان را به خود جلب کردهاند. یکی از روشهای معتبر برای بررسی پدیده تغییر اقلیم، استفاده از مدلهای گردش عمومی جوّ (GCM) است. به علت تفکیک فضایی کم برخی پدیدههای ریزمقیاس در مدلهای گردش عمومی جوّ، این مدلها نمیتوانند تقریب درستی از شرایط آبوهوایی منطقه مورد بررسی بهدست دهند؛ لذا باید خروجی آنها تا حد ایستگاه هواشناسی، ریزمقیاس شود. در این تحقیق یک نوع از مدلهای (GCM) تحت عنوان HADCM3 در دوره سالهای 2046-2065 بهکار گرفته شد. برای شبیهسازی پارامترهای اقلیمی در حوضه تمر استان گلستان دادههای مدل HADCM3 با استفاده از مدل LARS-WG تحت دو سناریوی A2 و A1B ریزمقیاس شدند. نتایج نشان داد که میانگین دما با در نظر گرفتن سناریوی A2، 48/2 درجه سلسیوس و با در نظر گرفتن سناریوی A1B، 43/2 درجه افزایش خواهد یافت. همچنین نتایج نشان از افزایش 16% بارش در سناریوی A2 و 2% بارش در سناریوی A1B، در دوره 2046-2065 دارد. همینطور میزان ساعتهای آفتابی در دوره بررسی و با در نظر گرفتن هر دو سناریو کاهش خواهد یافت.https://jesphys.ut.ac.ir/article_35988_200a1d61ee61cba2b1e3c75fd64f0521.pdfموسسه ژئوفیزیک دانشگاه تهرانفیزیک زمین و فضا2538-371X39420131222Risk analysis and assessment of impacts of climate change on temperature and precipitation of East Azerbaijan in 2013-2022تحلیل مخاطره و ارزیابی اثر تغییر اقلیم بر دما و بارش استان آذربایجان شرقی دوره 2013-20221912083598910.22059/jesphys.2013.35989FAسیده شیماپورعلی حسیندانشجوی کارشناسی ارشد رشته مهندسی کشاورزی – منابع آب، دانشگاه تهران، ایرانعلیرضامساح بوانیدانشیار، گروه مهندسی آبیاری و زهکشی پردیس ابوریحان، دانشگاه تهران، ایرانJournal Article20130428One of the most important impact of climate change is reduction of precipitation in some areas including Iran. Hence, climate change studies are essential in these areas. Besides, according to IPCC, some meteorological stations of Iran, such as Tabriz (capital of East Azerbaijan Province) have showed a downward trend in precipitation. Therefore, East Azerbaijan Province was selected as the study area in this survey. It is one of the north-western provinces with cold dry climate. Firstly, monthly temperature and precipitation observed data over 1981-2012 were gathered from 15 meteorological stations of the region, and they were produced for 0.5-degree cells by interpolation methods and selecting the most appropriate one based on the amount of corresponding errors (RMSE and ME). Thereafter, monthly precipitation and temperature data for 2013-2022 were projected using 16 Atmosphere-Ocean General Circulation Models (AOGCMs) under A2B, A2 and B1 SRES scenarios, and downscaled by Bias Correction/Spatial Downscaling technique at 0.5-degree cells. After applying pattern scaling method on monthly temperature and precipitation data, in order to produce future data under more scenarios, monthly climatic variables were calculated for 10, 25 and 50 percent risk, and risk analysis was done based on the computed parameters. The pattern scaling technique used in this study calculates the variable under a desired scenario, from the base scenario (A2 in this study) with a linear equation in which the global temperature rise was calculated by a model named MAGICC.
Assessing observed climatic variables showed that western parts of the province had lower precipitation and higher temperature, while eastern parts had higher precipitation. However, south-western cells also experienced a better situation. Mean annual temperature over 1981-2012 was between 7.5-13.5 degrees Centigrade, and annual precipitation was 260 to more than 310 millimeters. Moreover, despite precipitation fluctuations over 1981-2012, annual precipitation of the first years is higher than the last years.
After applying pattern scaling method and accessing future monthly precipitation and temperature data under 49 scenarios for 16 AOGCMs, temperature and precipitation boxplots of each month were produced for each month. Results showed that precipitation is right-skewed in all months and all cells. The outliers of March and April are less than others, while August outliers are numerous. Comparing boxplots of temperature and precipitation indicated that outliers of temperature data are much less than precipitation, i.e. uncertainties of AOGCMs and downscaling to project temperature are less than precipitation.
The monthly precipitation and temperature data were calculated for 10, 25 and 50 percent risk and the monthly temperature-risk and precipitation-risk line charts were produced for each cell. The amount of monthly temperature and precipitation with higher and lower risk showed a significant difference. Furthermore, projections with lower risk have less difference and they indicate almost one prediction.
According to the areal interpolated maps of the future mean annual precipitation and temperature, the least temperature will be around Sarab station, and the highest temperature will be near Malekan and Bonab stations. Furthermore, maps showed that the amount of temperature will increase by moving west. Moreover, by moving from high risk to lower risks, the amount of temperature increases about one degree Centigrade. Western regions will experience lower precipitation with all levels of risk, and the maximum annual precipitation will be seen in north-eastern spots.
The difference between the predicted and observed temperature and precipitation with 10, 25 and 50 percent risk for each cell was calculated and their spatial distribution maps were produced by applying different interpolation methods and selecting the best method. It is predicted that temperature will increase 2.9-3.15 degrees Centigrade with 10 percent risk, and the rise amount is bigger in the western areas. Precipitation will decrease about 75 to 150 millimeters. Temperature will increase 2.1-2.25 degree Centigrade with 25 percent risk, and the amount of precipitation in some areas will be lower and in some others will rise even up to 50 millimeters. The temperature with 50 percent risk is projected to increase about 1.2 degree Centigrade, and precipitation will also aggrandize.
In conclusion, the temperature increase in the next decade will be bigger in the southern areas of the province, and precipitation amount of north-western and western areas will experience higher precipitation. The results of this study confirm other research done by others before, indicating the least amount of observed precipitation was in Sarab station. By having these results for future periods the decision makers of this field will have a better vision, ad so they will be able to sufficiently plan for the future.
In addition to this research, some suggestions are proposed as follows to improve and strengthen the results: (i) past and future drought assessment in the area with different drought indexes, (ii) presenting a more logic relationship between temperature and precipitation because of relatively low correlation between temperature and precipitation and so not being linear, or applying models ensemble and comparing the results with this survey, (iii) using daily temperature and precipitation instead of monthly data to improve the results.از جمله آثار پدیده تغییر اقلیم، افزایش دما، و نیز کاهش مقدار بارش در برخی مناطق جهان از جمله ایران است و لذا بررسی اثرات این پدیده ضروری مینماید. در این تحقیق، پس از برداشت دادههای مشاهداتی ماهانه دما و بارش 15 ایستگاه هواشناسی در دوره 1981-2012، دادهها با کمک روشهای گوناگون درونیابی و انتخاب بهترین روش، برای سلولهای 5/0 در 5/0 درجه تولید شد. پس از پیشبینی متغیرهای اقلیمی برای دوره 2013 تا 2022 بهصورت ماهانه با شانزده مدل جفت شده ،گردش عمومی جوّ-اقیانوس (AOGCM) تحت سناریوهای A1B، A2 و B1، و ریزمقیاسنمایی مکانی دادهها در مقیاس 5/0 در 5/0 درجه با کمک روش Bias Correction/Spatial Downscaling، بهمنظور بررسی عدم قطعیت و تحلیل مخاطره پیشبینیها، دادهها با استفاده از روش مقیاس الگو، برای 46 سناریوی دیگر نیز تولید شدند. با محاسبه دما و بارش برای سطوح متفاوت مخاطره مشخص شد که در سطح مخاطره 10 درصد دما 9/2-15/3 درجه افزایش، و مقدار بارش 75-150 میلیمتر کاهش خواهد داشت. در سطح 25 درصد دما 1/2-25/2 درجه افزایش، مقدار بارش در برخی نقاط کاهش و در برخی دیگر تا 50 میلیمتر افزایش را نشان میدهد. در سطح 50 درصد، دما تقریبا 2/1 درجه افزایش خواهد داشت، و در مورد بارش نیز افزایش مقدار پیشبینی میشود؛ بهطوریکه مقدار بارندگی سالانه در منطقه با مخاطره 50 درصد، تقریبا بین 525 تا 350 میلیمتر پیشبینی میشود. https://jesphys.ut.ac.ir/article_35989_012181555f24e2da389701d4df629a75.pdfموسسه ژئوفیزیک دانشگاه تهرانفیزیک زمین و فضا2538-371X39420131222Development of a potential vorticity based dynamical core for general circulation models using the diabatic contour-advective semi-Lagrangian algorithmتوسعه هسته دینامیکی یک مدل گردش کلی جوّ بر مبنای تاوایی پتانسیلی با الگوریتم فرابرد پربندی نیمهلاگرانژی دررو2092213599010.22059/jesphys.2013.35990FAمحمدجغتاییدانشجوی دکتری هواشناسی، گروه فیزیک فضا، موسسه ژئوفیزیک دانشگاه تهران، ایرانعلیرضامحبالحجهدانشیار، گروه فیزیک فضا، موسسه ژئوفیزیک دانشگاه تهران، ایرانJournal Article20130504The development of the dynamical core of a potential-vorticity-based atmospheric general circulation model is explored. There are some advantages of using potential vorticity (PV) as a prognostic variable in that the resulting model can give more accurate simulation of the evolution of PV, as arguably the most fundamental dynamical quantity. Further, there is possibility of explicit representation of unbalanced part of the flow during time integration, though in an approximate manner, by making proper choice of the prognostic variables used alongside PV. In this way, the model is equipped with some built-in form of the balance relation for PV inversion, which helps to maintain the underlying balance. A closed set of equations is constructed using the variables , a PV-like variable described below, and which are, respectively, the horizontal velocity divergence and an approximate form of horizontal acceleration divergence. For the primitive equations linearized around a rest state, it can be shown that there is a direct correspondence between the Rossby modes and the Q variable, on the one hand, and between the inertia-gravity modes and the and variables, on the other hand. Linearizing the primitive equations in the generalized vertical coordinate around a resting basic state, the symmetric matrix relating the column vector of the time tendency of modified pressure to the column vector of horizontal divergence is found. Here, the modified pressure is defined by with and respectively, the perturbation geopotential, temperature and potential temperature, specific heat capacity at constant pressure and the basic state Exner function. The eigenvectors of are used to define the vertical modes and the projection of any given column vector from the physical space to vertical mode space and vice versa. This facilitates to generalize the Boussinesq PV-based multi-layer primitive-equation models to the corresponding non-Boussinesq set of equations. A PV-like quantity is defined by in which is the Coriolis parameter, the relative vertical vorticity, and the normalized perturbation pressure thickness. Here and are, respectively, the perturbation and the basic state pressure. The variable becomes the same as Rossby–Ertel PV whenever coincides with. Further, with the definition of modified pressure given above, the variable becomes equal to with the northward gradient of When coincides withbecomes equal to acceleration divergence. To use the variables and as the prognostic variables, one has to implement an inversion procedure to obtain the velocity field and the thermodynamic variables at each time step. Making use of the definition of and and projecting onto the vertical-mode space results in a modified Helmholtz equation for which is solved by spectral transform in longitude and fourth-order compact in latitude following the procedure introduced by Mohebalhojeh and Dritschel in 2007. Solving for the modified pressure can then be obtained either directly through the matrix relation or through projection onto vertical-mode space. The task is then to find the thermodynamic variables using the information available for at each column of fluid.
The PV as a determining variable for vortical flows is given the highest priority in terms of accuracy. For this purpose, the Contour-Advective Semi-Lagrangian (CASL) algorithm, previously implemented for various settings and models including the many-layer Boussinesq primitive equation models on the sphere, provides the natural choice. An extension of CASL called DCASL has already been applied to the thermally-forced shallow water equations (SWEs) on the sphere. In generalized vertical coordinate, the evolution equation of is similar to that of PV in the thermally-forced SWEs. Therefore, the available DCASL can be generalized for the non-Boussinesq equations with little effort.
The generalized vertical coordinate is set as with defined in such a way as to increase monotonically with geometrical height from zero at the surface to one at the top level. The functions and g are determined in such a way that (i) tends to and when pressure tends to its value at the surface and the top of the model, respectively, and (ii) the condition is satisfied to ensure monotonicity whenever and where and are prescribed values of the lowest value of potential temperature and the vertical gradient of potential temperature with respect to sigma, respectively.
The time evolution of a two-layer baroclinically unstable midlatitude jet over a 30-day period is investigated as a test case to examine the performance of the algorithm developed. It should be mentioned that various experiments using different basic-state structures have been carried out. The experiment reported is however for the one with a uniform stratification obtained by setting a constant lapse rate of from to This choice of the basic-state structure leads to a flow regime with order one Rossby and Froude numbers. Results show the formation and development of an intense baroclinic wave with zonal wave number 3. Further, embedded in the baroclinic wave there are inertia-gravity waves generated by vortical flow in a manner resembling what has previously observed for the Boussinesq primitive-equation model. The successful integration of model in extreme flows gives us confidence to further develop the algorithm to a dynamical code for atmospheric general circulation models.
توسعه هسته دینامیکی هیدروستاتیک برای مدل گردش کلی جوّ بر مبنای تاوایی پتانسیلی با الگوریتم فرابرد پربندی نیمهلاگرانژی دررو مورد بررسی قرار میگیرد. خطیسازی معادلات بسیط با مختصه قائم تعمیمیافته حول حالت پایه ساکن امکان استخراج مُدهای قائم و استفاده از آنها برای طراحی و پیادهسازی طرحواره گامبرداری زمانی نیمهضمنی را فراهم میکند. استفاده از متغیرهای پیشیابی تاوایی پتانسیلی، واگرایی سرعت و تقریبی از واگرایی شتاب در توسعه هسته دینامیکی، مستلزم حل معادلهای بیضوی از نوع هلمهولتز پیراسته در محاسبه ضخامت فشاری لایههای ایجاد شده میان ترازهای متوالی است. استفاده از تصویر به فضای مُدهای قائم حل این معادله بیضوی را هم تسهیل میکند. در حل عددی، طرحوارههای طیفی در راستای مداری، مرتبه چهارم فشرده در راستای نصفالنهاری و نیمهضمنی با سه تراز زمانی به کار میرود.
در این پژوهش، مدل ساخته شده بر مبنای تاوایی پتانسیلی در مختصه قائم تعمیمیافته و استخراج مُدهای قائم در مدل با موفقیت از عهده آزمون ناپایداری کژفشار برمیآید. در آزمون صورت گرفته با دو لایه، حالت اولیه جت متوازنی است که ناپایداری آن با یک پریشیدگی کوچک به راه میافتد. نتایج حاکی از شکلگیری و توسعه امواج کژفشار در طی 30 روز انتگرالگیری عددی برای شارش حدی با عدد فرود نزدیک یک است. آزمون موفق صورت گرفته، زمینه را برای آزمایش کامل مدل درحکم یک هسته دینامیکی در آرایشی نزدیکتر به واقعیت با تعداد زیادی لایه و برهمکُنش با سطح زیرین فراهم میکند. https://jesphys.ut.ac.ir/article_35990_eb43acc7a49dca4e22bf3bfcf2257b85.pdf