موسسه ژئوفیزیک دانشگاه تهرانفیزیک زمین و فضا2538-371X39320131023Determination of local magnitude scale, ML, for north-west Iran using accelerتعیین رابطه بزرگی محلی برای شمال غرب ایران با استفاده از شتابنگاشتها1143559510.22059/jesphys.2013.35595FAمحبوبهشریفیدانشجوی کارشناسی ارشد، گروه فیزیک زمین، موسسه ژئوفیزیک دانشگاه تهران، ایراناسماعیلبایرامنژاداستادیار، گروه فیزیک زمین، موسسه ژئوفیزیک دانشگاه تهران، ایران0000-0002-9683-459Xظاهرحسینشمالیدانشیار، گروه فیزیک زمین، موسسه ژئوفیزیک دانشگاه تهران، ایرانJournal Article20120527<sup>*</sup>نگارنده رابط: تلفن: 61118230-021 دورنگار: 88630479-021 E-mail:ebayram@ut.ac.ir
According to accelerograms that do not clip in small distances unlike seismograms, results for local magnitude estimation can be more acceptable than that from seismogram data. The dataset used in this study contains 780 two-component horizontal accelerograms from 390 earthquakes with magnitudes range M<sub>n</sub> ≤ 4. To enhance the quality of the data, we employed baseline correction. We processed the uncorrected strong-motion data to make baseline and instrument correction and band-pass filtering. The local magnitude introduced by Richter (1935) is based on the amplitude recorded by the Wood-Anderson torsion seismograph with a natural period of 0.8 sec, a damping constant of h=0.8, and a static magnification, v=2800. Richter chose his reference earthquake with M<sub>L</sub>=3, such that amplitude was 1 mm on a Wood-Anderson seismograph at an epicentral distance of 100 km. He determined –log A<sub>0</sub> attenuation function for southern California region. Log A<sub>0 </sub>depends on the effects of geometrical spreading and an elastic attenuation and also these effects depend on the characteristics of the crustal structure (Bakun and Joyner, 1984). For large variability of velocity and attenuation, structure of the Earth’s crust does not permit to develop a unique calibration function for local events. Therefore, it is necessary to calibrate it for any region. In this article, we calibrate M<sub>L</sub> for northwest Iran using synthetic Wood-Anderson seismograms. The area under study extends from 36 to 40 degrees north latitude and from 44 to 50 degrees east longitude. The local magnitude is determined within the period range of greatest engineering interest. So it is a very useful scale for engineering. Many structures have natural periods close to that of a Wood-Anderson instrument, and the extent of earthquake damage is closely related to M<sub>L</sub>. Nowadays, the lack of W-A Seismograph prevents the calculation of such magnitude in the original form. Kanamori and Jennings (1978) proposed an alternative method of calculation. The accelerograph records are used as acceleration input to an oscillator with characteristics of the Wood-Anderson instrument to produce a synthetic seismogram. Measurements of peak amplitudes on Wood-Anderson instruments were studied to determine a distance correction curve for use in determining the local magnitude M<sub>L</sub>. We also use the approach suggested by Hutton and Boore (1987) to invert for the empirical distance-correction function in the local magnitude scales. The distance – correction function can be expressed as:
-log A<sub>ij</sub> = n log )r<sub>ij</sub> / 100( +K )r<sub>ij</sub> -100+ (3.0 - M<sub>Li</sub> + S<sub>j</sub> ,
where the n and k are parameters related to the geometrical spreading and an elastic attenuation. A<sub>ij</sub> is the horizontal maximum amplitude of the ith event observed at the jth station component, r<sub>ij</sub> is the hypocentral distance from the ith event to the jth station component, M<sub>Li </sub> is the local magnitude of the ith event, and S<sub>j </sub>is the correction factor for the jth station component. The n=1, is appropriate for body-wave propagation in homogeneous media, but the earth is not perfectly elastic and seismic waves attenuate or decrease in amplitude as they propagate. The geometrical spreading and an elastic attenuation can also reduce wave amplitudes. The above Equation can be cast into a standard matrix formation: Gm=d, which represents a typical linear inversion problem in geophysics that can be solved using least-squares or generalized inversion methods. First we used generalized inverse method to calculate the attenuation relationship but we found a negative an elastic attenuation coefficient which is not correct physically. Negative value of k indicates that the assumption of a simple shape for the attenuation curve, with a constant geometrical spreading for different distances is not correct. At the closest ranges, the direct arrival dominates the waveform; but at larger ranges, the rays reflected from boundaries and all of the energy is reflected upward, so postcritical reflections become more important. The range at which the Moho reflection becomes postcritical is indicated by the abrupt increase in amplitude of that ray (Burger et al., 1987). So we performed the trilinear form of attenuation on the data (Atkinson and Mereu, 1992) to avoid the negative values of k. We used Monte Carlo technique to evaluate distance correction curves for north-westIran, and testing all possible combination that minimizes the average residual errors. Results show that we have 3 values for geometrical spreading. Apparent geometric spreading depends on the geometry of spreading in a layered crust, which is a function of distance, but anelasticity is independent of distance. These three values for geometrical spreadings are:
<em>R</em> ≤ 85 km, <em>n</em><sub>1</sub> = 0.73; 85<em> >R</em>≤ 120 km, <em>n</em><sub>2</sub> = -0.46; R>120 km, n<sub>3</sub> = 0.22; <em>k </em>=0.00037
The distances less than 85 km related to direct waves. Note that distance ranges between 85 and 120 km is the distance where the Moho reflection becomes postcritical and is indicated by the abrupt increase in amplitude. The focal depth, crustal thickness, and the crustal velocity gradient have important influences on the range at which the amplitude increases. The result of ground motion in north-west Iran demonstrates that crustal structure can influence the strong motion attenuation relations. The uniform distribution of the residuals about their baselines (Fig. 4) show that the trilinear distance attenuation relation developed in this study provide more reliable estimates of M<sub>L</sub> values than those from linear relation. M<sub>L</sub> values using the linear distance attenuation are overestimated at distance larger than about 85 km (Fig. 3). We used trilinear method to estimate the local magnitude, but distance attenuation is independent from crustal structure. The attenuation along the energy ray path and the site geology conditions play roles of great importance in the recorded amplitudes. In the process of magnitude calculation, such effects are reduced if a proper attenuation function and magnitude station corrections are applied, so we applied the station correction on the amplitudes and performed a linear regression analysis on the data to obtain n and k.The results represent a logical response. No trend is evident on the distribution of residual in the corrected linear method, thus the attenuation function determined in this study does not depend on geology variation or hypocentral distances, as it works well for the north-west Iran region. The distance – correction and local magnitude function can be expressed as:
-Log A<sub>0</sub> = (1.52±0.0057) log(r/100) + (0.00137±3.20E-07) (r-100) + 3,
M<sub>L</sub> = log A + (1.52 ± 0.0057) log(r/100) + (0.0013 ± 3.20E-07) (r-100) +3,
The parameter k can be related to the inelastic attenuation coefficient Q using the Bakun and Joyner (1984) formula γ = ln 10k = πf/QV<sub>S</sub>, where V<sub>S</sub> is the average crustal S-wave velocity. Taking an average S wave of V<sub>S</sub> = 3.4 km /s, the k ≈ 0.00137 value obtained in the present study introduces a value of γ = k ln (10) = 0.00317 and Q(1 Hz) = 280.
Nuttli (1980) found that a γ value of 0.0045 km <sup>-1 </sup>(between 0.003 and 0.006) corresponds to an apparent Q of 200 (between 152 and 303) for S<sub>g</sub>. The γ and Q value agree with the result given by Nuttli. He showed that the attenuation of 1-sec period crustal phases in Iran is relatively high. The high attenuation value is due to the tectonic complexity and the widespread young volcanics in the region. This result should be treated with caution, because the maximum amplitude data do not necessarily correspond to a single seismic phase .با توجه به اینکه دستگاههای شتابنگاری در فاصلههای نزدیک برخلاف دستگاه لرزهنگار در جنبشهای نیرومند زمین کارایی خود را از دست نداده و بریده و ناقص ثبت نمیکنند، نتایج حاصل برای محاسبه بزرگای محلی میتواند قابلقبولتر ازدادههای لرزهنگارها باشد. دادههای مورد استفاده در این تحقیق شامل 781 ثبت دومولفهای افقی شتاب برای 390 زلزله با بزرگای 4 ≤ <sub>n</sub>M ثبت شده در 66 ایستگاه شتابنگاری در منطقه شمال غرب ایران است. ثبتهای شتابنگاشت برای ایجاد لرزهنگاشت مصنوعی ووداندرسن مورد استفاده قرار گرفته است. ابتدا پس از اِعمال تصحیحات لازم روی شتابنگاشتها، لرزهنگاشتهای مصنوعی ووداندرسن بازسازی شد. سپس از روش وارونسازی دادهها برای بهدست آوردن ضرایب میرایی، بزرگیها و تصحیحات ایستگاهی استفاده شد. به علت اینکه مقدار ضریب تضعیف ناکشسان منفی بهدست آمد، روش مونتکارلو اِعمال شد تا منحنی تصحیح فاصله برای شمال غرب ایران بهدست آید. نتایج نشان میدهد که منحنی تصحیح فاصله دارای 3 مقدار برای ضریب گسترش هندسی است.
<em>R</em> ≤ 85 km, <em>n</em><sub>1</sub> = 0.73; 85<em> >R</em>≤ 120 km, <em>n</em><sub>2</sub> = -0.46;R>120 km, n<sub>3</sub> = 0.22; <em>k </em>=0.00037
فاصلههای رومرکزی کمتر از 85 کیلومتر مربوط به تضعیف امواج مستقیم است. فاصلههای بین 85 و120 کیلومتر دربرگیرنده امواج با بازتاب بحرانی از ناپیوستگیها است که باعث افزایش ناگهانی دامنهها میشود . اما پارامترهای منحنی تضعیف مستقل از ساختار پوسته است بنابرین برای بهدست آوردن ضرایب میرایی واحد و قابلقبول برای منطقه تصحیحات ایستگاهی با در نظر گرفتن فاصله روی دامنهها اِعمال شد و مجددا روش وارونسازی تکرار شد که در نتیجه، پارامترهای قابلقبولی برای تضعیف ناکشسان و گسترش هندسی به شرح زیر بهدست آمد:
<em>n</em> = 1.52, <em>k </em>= 0.00137موسسه ژئوفیزیک دانشگاه تهرانفیزیک زمین و فضا2538-371X39320131023Deep alluvial effects on one-dimensional seismic site response in Qom cityبررسی اثر آبرفتهای عمیق بر پاسخ لرزهای یکبُعدی در شهر قم15313559610.22059/jesphys.2013.35596FAعبدالهسهرابیبیداراستادیار، دانشکده زمینشناسی، دانشگاه تهران، ایرانلیلاجاسمپوردانشجوی کارشناسی ارشد، دانشکده زمینشناسی، دانشگاه تهران، ایرانJournal Article20121110<sup>*</sup>نگارنده رابط: تلفن: 61112985-021 دورنگار: 66491623-021 E-mail:sohrabi@khayam.ut.ac.ir
Nowadays in many site response analyses of alluvial, environment with shear wave velocity 600 m/sec < νs < 800 m/sec is considered as the seismic bedrock. Results of these analyses did not confirm those from empirical analyses based on the recording of microtremors or weak earthquake motions. Recently, effects of deep alluviums and contrast between geologic bedrock and alluviums are considered as a possible cause for this inconformity. This study examines the site effects of deep alluviums of Qom city. Qom is located at the northern margin of central Iran zone and on the Quaternary young alluviums. Based on the geoelectrical resistivity surveys, thickness of alluviums in some parts of the city is greater than 250m. Earlier empirical studies based on the recording of microtremors had shown that at the frequencies ranging from 0.6 to 1.2 Hz, a clear amplification can be seen in the studied alluviums. Amplification at these frequencies did not confirm results from one-dimensional numerical analysis of the soft sediments on the conventional seismic bedrock. At the current study, in order to determine the geometrical properties and thickness of deep alluviums, resistivity surveys have been conducted in Qom plain was used and dynamic properties of the soil layers were determined by geological descriptions. Considering the uncertainty resulting from the lack of dynamic properties of soil layers, a parametric study was conducted and three models of low, medium and high velocity were considered for alluvial layers and bedrock. One-dimensional numerical analysis was carried out using the software Deepsoil. As the results will be compared with those from empirical analysis of small strain displacements of microtremors, a linear elastic behaviour was assumed. Amplification curves were measured using different dynamic properties of alluvial layers and the bedrock and the results were compared with those from amplification of microtremors. In all analyses conducted using different dynamical properties (three models of low, medium and high velocity), a specific amplification at the frequencies less than 1 Hz was obtained. Furthermore, amplified frequency resulted from previous empirical studies corresponds with the amplified frequency resulted from numerical analysis with high velocity model. Amplification at this frequency range and its correspondence with results of microtremors studies shows the effects of deep alluviums on the site amplification functions. The importance of deep alluviums insists on attention to the shape of the sedimentary basin and consideration of the effects of deep alluviums on the numerical site effects studies. In the case of inadequate information about the deep alluviums, it is necessary to use empirical analysis recorded motion at the site such as microtremors or weak earthquake motions. At present, consideration of site effects in most of building codes for design earthquake resistant structures are limited to effects of shallow alluviums, however, as discussed in this paper, deep alluviums are effective on site amplification specially in low frequencies and it is necessary to take them into account in the design of tall structures.امروزه در بسیاری از تحلیلهای دینامیکی آبرفت، اثرات لایههای نرم سطحی قرار گرفته روی سنگ بستر لرزهای (سرعت موج بُرشی بین 600 تا 800 متر بر ثانیه) مدنظر قرار میگیرد. نتایج چنین تحلیلهایی بعضاً با نتایج حاصل از بررسیهای تجربی مبتنی بر ثبت خُردلرزه یا جنبشهای ضعیف زمین ناسازگار است. در این پژوهش اثرات ساختگاهی آبرفتهای عمیق شهر قم مورد بررسی قرار گرفته است. بهمنظور تعیین ویژگیهای هندسی و ضخامت لایههای آبرفتهای عمیق از بررسیهای مقاومتسنجی صورت گرفته در دشت قم استفاده شده و مشخصات دینامیکی لایههای خاک براساس توصیف زمینشناسی تعیین شده و سه مدل سرعت کم، متوسط و زیاد برای لایههای آبرفت و سنگ بستر مدنظر قرار گرفته است. منحنیهای بزرگنمایی بهازای ویژگیهای دینامیکی متفاوت لایههای آبرفت و سنگ بستر محاسبه و نتایج با بزرگنمایی حاصل از دادههای خُردلرزه مقایسه شده است. در همة مدلهای گوناگون سرعت کم، متوسط و زیاد، بزرگنمایی مشخصی در محدوده بسامدهای کمتر از 1 هرتز بهدست آمده است. علاوه بر این سازگاری بسیار مناسبی بین بسامد بزرگنمایی حاصل از بررسیهای عددی حاضر در وضعیت مدل سرعت موج بُرشی زیاد و بسامد بزرگنمایی حاصل از بررسیهای تجربی پیشین مشاهده میشود. وجود بزرگنمایی در این محدوده بسامدی و سازگاری نسبی آن با نتایج تحقیقات خُردلرزه حاکی از اثرگذاری آبرفتهای عمیق در تابعهای بزرگنمایی ساختگاه است و این مسئله ضرورت توجه به وضعیت شکل حوضه رسوبی با در نظر گرفتن اثرات آبرفتهای عمیق در بررسی آثار ساختگاهی به روش عددی را نشان میدهد.موسسه ژئوفیزیک دانشگاه تهرانفیزیک زمین و فضا2538-371X39320131023Local gravity field modeling using radial basis functions, case study: coastal area of the Persian Gulfمدلسازی محلی میدان گرانی زمین با استفاده از تابعهای پایه شعاعی، بررسی موردی: مدلسازی میدان گرانی در سواحل خلیج فارس33483559710.22059/jesphys.2013.35597FAعبدالرضاصفریدانشیار، گروه مهندسی نقشهبرداری، پردیس دانشکدههای فنی دانشگاه تهران، ایران0000-0001-5938-5468محمدعلیشریفیاستادیار، گروه مهندسی نقشهبرداری، پردیس دانشکدههای فنی دانشگاه تهران، ایران0000-0003-0745-4147اسماعیلفروغیدانشجوی کارشناسی ارشد ژئودزی، گروه مهندسی نقشهبرداری، پردیس دانشکدههای فنی دانشگاه تهران، ایرانJournal Article20121225<sup>*</sup>نگارنده رابط: تلفن: 66752215-021 دورنگار: 66752214-021 E-mail:e.foroughi@ut.ac.ir
The determination of the earth Gravity field has various applications in geodesy and geophysics. Measuring the earth gravity field can be divided into satellite, airborne and terrestrial methods. Traditional method for gravity field modeling using these data is approximation by spherical harmonics expansion. Although spherical harmonic is one of the most popular methods to approximate gravity filed, based on their global characteristic, a small regional variation make big changes in whole spherical harmonic coefficients:
Where is a point with spherical coordinate, and are normalized Legendre functions up to degree and order and are spherical harmonic coefficients.
To deal with this problem, different groups of regional basis systems were introduced, as in case we can refer to gravity field modeling using radial basis functions:
Where are the expansion coefficients (scale coefficients) and Bjerhammar is a sphere with radius which is entirely inside the topographic masses of the earth, are the set of radial basis functions with following representation:
Where are points inside and outside of the Bjerhammar sphere respectively, is the Legendre polynomial of degree and are the Legendre coefficients, the point <em>y </em>is called the centre of the RBF. If locations and depths and coefficients as Radial basis function’s parameters are chosen properly we will have a good representation of potential anomaly and related earth functions. In this paper we used Levenberg Marquardt algorithm (LM) to find optimal RBF parameters, LM is a iterative regularization method, can find the best answer with following equation:
Where is the Hessian matrix evaluated at , this update rule is used as follows, if the error goes down following an update, it implies that our quadratic assumption on is working well and we reduce (usually by a factor of 10) and vice versa.
In this paper, we used combination of gravity data (gravity anomaly) and gravity potential data (gravity potential anomaly) derived from satellite altimetry. Significant points in this algorithm are: removing global effect of gravity anomaly by spherical harmonic up to degree and order 360 (EGM2008) and centrifugal force from gravity anomaly data, using potential anomaly in test area those are calculated on Bruns formula from satellite altimetry data, removing global effect of potential anomaly by spherical harmonic up to degree and order 360 (EGM2008) and centrifugal force from the previous step data, forming the observation equations with radial multipole of order 1 by residual gravity anomaly and residual potential anomaly data. Levenberg Marquardt algorithm is then used to choose optimal number and, location and depth of the radial basis functions. We also used some of potential anomaly observations as control point s in the region of coastal Persian Gulf for appraisal this algorithm and then present the gravity field in this area.یکی از هدفهای مهم ژئودزی، مدلسازی محلی میدان گرانی زمین است. یکی از روشها برای مدلسازی محلی میدان گرانی زمین استفاده از تابعهای پایۀ شعاعی کروی است. در این تحقیق از تابعهای پایه شعاعی برای مدلسازی محلی میدان گرانی با استفاده از دادههای بیهنجاری جاذبه و بیهنجاری پتانسیل حاصل از ارتفاعسنجی ماهوارهای در مناطق ساحلی استفاده شده است. برای این منظور بیهنجاری پتانسیل بهصورت ترکیبی از این تابعها در نظر گرفته میشود. در این تحقیق برای مدلسازی از هسته دوقطبی شعاعی مرتبۀ اول استفاده شده است. برای تعیین پارامترهای مدلسازی با استفاده از این تابعهای شعاعی، الگوریتم لونبرگ-مارکواردت به کار رفته است. برای تعیین بهینه<sup>ء</sup> تعداد، مکان، عمق و ضرایب مقیاس تابعهای پایه، بیهنجاری پتانسیل، برآورد، و سپس نتیجه با بیهنجاری پتانسیل مشاهده شده در نقاط آزمون مقایسه میشود. از نکات برجسته در این تحقیق تعداد کم تابعهای پایه شعاعی کروی برای مدلسازی میدان گرانی در مقایسه با الگوریتمهای مشابه است. برای ارزیابی روش عرضه شده، میدان گرانی با استفاده از بیهنجاری جاذبۀ مشاهده شده در منطقه فارس ساحلی و همچنین بیهنجاری پتانسیل حاصل از ارتفاعسنجی ماهوارهای در خلیج فارس، مدلسازی شده است.موسسه ژئوفیزیک دانشگاه تهرانفیزیک زمین و فضا2538-371X39320131023Forward modeling of magnetic resonance sounding (MRS) for karsts and the effect of depth increase and saturation and half-saturation on inversionمدلسازی پیشرو در روش سونداژ هستهای مغناطیسی (MRS) پدیده کارست و تأثیر افزایش عمق کارستی در دو حالت اشباع و نیمهاشباع بر وارونسازی دادهها49663559810.22059/jesphys.2013.35598FAامینابراهیمیبردردانشجوی دکتری، گروه فیزیک زمین، موسسه ژئوفیزیک دانشگاه تهران، ایرانمحمدکاظمحفیظیاستاد، گروه فیزیک زمین، موسسه ژئوفیزیک دانشگاه تهران، ایرانJournal Article20100629<sup>*</sup>نگارنده رابط: تلفن: 88630477-021 دورنگار: 88630479-021 aebrahimib@ut.ac.ir E-mail:
Forward modeling is regarded as the backbone of inversion methods in geophysics. Magnetic Resonance Sounding (MRS) is a rather new method in the exploration of groundwater water resources. In this method, when an E.M. field induced by Larmor frequency of water hydrogen protons the underground by a transmitter on the surface. Part of its energy is absorbed exclusively by the water molecules. When the excitation field is removed, the absorbed energy acts as a new source and it is released in the form of a new electromagnetic field which can be detected by a receiver at the surface. The response of this method is due to the presence of water in the underground layers and the basic parameters of the aquifer could also be calculated by this method. Karsts are considered as one of the most important water sources in many parts of the world. It is significant to investigate them especially in hydrology. However, the imaging of such targets is generally a difficult task for most geophysical methods. In this study, karsts are considered as complicated phenomena. Depth of karst conduit is the first important parameter and saturation of karst is the second one. They are modeled in different levels of depth in two cases of saturated and half saturated conditions.
Whilst natural noise within the Larmor frequency range is generally not very large (excepting magnetic storms or other temporary disturbances). But the level of civil noise (electrical power-lines, generators, etc.) may be very high, which depends on region. The depth of investigation and resolution of the MRS method are dependent on signal to noise ratio. If the measured data are ruined by noise, it will have an adverse effect on the precision and validity of MRS results. As a result, the MRS signal has to be measured with an acceptable signal to noise ratio. We can apply different filtering methods to fulfill the best signal to noise ratio. Selection of the filtering plan depends on the noise origin. In any case study, application of the stacking is necessary. The inversion is shown in the main terms as usual, for the geophysical data, with reliance on the main issues of the plan. Data inversion is then performed and finally the effects of depth and saturation on both qualitative and quantitative data interpretation are examined. It was shown that the inversion part has a very important role and recognition of model parameters, and geology is the critical part of inversion. In this way it was shown that the interpretation of MRS Data qualitative methods for karsts appropriate response can be obtained. In addition, proficiency of filtering techniques, inversion tactics and effect of noise on MRS results are discussed.مدلسازی پیشرو پایه و اساس روشهای وارون در ژئوفیزیک به شمار میآید. روش سونداژ تشدید هستهای مغناطیسی (MRS) یک روش نسبتاً جدید در اکتشاف منابع آبهای زیرزمینی است. پاسخ این روش نسبت به وجود آب در لایههای زیرزمینی وابسته بوده و پارامترهای اساسی آبخوان نیز میتواند توسط این روش بدست آیند. کارستها از مهمترین منابع آب به شمار میآیند و بررسی آنها در هیدرولوژی از اهمیت خاصی برخوردار است. در این مطالعه مجرای کارستی به عنوان یک پدیده پیچیده بررسی میگردد و این مجرا در اعماق مختلف و در دو حالت اشباع و نیمهاشباع مدل میشود. سپس دادهها وارونسازی شده و تاثیر افزایش عمق بر تفسیر کیفی و کمی بررسی شد. در این روش مشخص شد که از تفسیر کیفی روش SNMR برای کارست پاسخ مناسب بدست میآمد.موسسه ژئوفیزیک دانشگاه تهرانفیزیک زمین و فضا2538-371X39320131023Investigation of North American sector Sq-field in year 1997 using spherical harmonic analysisبررسی تغییرات میدان Sq سال1997 در قطاع امریکای شمالی با استفاده از تحلیل هماهنگهای کروی67823559910.22059/jesphys.2013.35599FAاسدالهجوععطا بیرمیاستادیار، گروه ژئوفیزیک، دانشگاه تحصیلات تکمیلی صنعتی و فناوری پیشرفته، کرمان، ایرانJournal Article20120501The daily record of geomagnetic variations at any world location typically shows a multitude of irregular changes in the field that represent the superposition of many spectral components whose amplitudes generally increase with increasing period. It has been a long established fact that variations in ground magnetic records are caused by the dynamo action in the upper atmosphere. These daily variations in the geomagnetic fields at the earth's surface during geomagnetically quiet conditions are known to be associated with the dynamo currents which are driven by winds and thermal tidal motions in the E-region of the ionosphere.
Unique current sources in the upper atmosphere and magnetosphere have been identified as origins of many of these spectral field variations. On occasion there are days when the magnetic records smoothly change with primarily 24-, 12-, 8-, and 6-hour period spectral components dominating the field composition and few of the irregularly appearing, shorter or longer period changes are present. On these days, the oscillations of three orthogonal field components produce records that are predictably similar to others recorded many days earlier or later and follow a pattern of gradual change through the seasons of the year. Such records describe the quiet daily geomagnetic variations. When the small but persistent effects ascribed to the lunar- tidal current system have been removed, the changes are called Sq for solar quiet fields, referring to their local-time changes when solar-terrestrial disturbances are absent.
Solar activity, identified with the sunspot number, controls the percentage of magnetically quiet days in a year as an inverse relationship. The quietest geomagnetic levels usually occur on, or a year after, the minimum in sunspot number. Because of the 10.6-year cycle in solar activity, a similar cycle of geomagnetically quiet years occurs.
The quasilogarithmic <em>Kp</em> is a convenient three-hour index for selecting the quiet conditions; its linear counterpart is the <em>Ap </em>index. Some authors prefer to select quiet days by a limiting value of the day's <em>Ap</em> (e.g., <em>Ap</em> = 10). Others take a fixed number (e.g., five) of the quietest days (judged by the day's <em>Ap</em>) for a given month, whatever the values may be.
The 19 North American observatories are selected in this study. There are 60 days in 1997 in which the global geomagnetic disturbance index, <em>Kp</em>, have all 8 daily values less than 2<sub>+</sub>. These days are taken as preliminary “quiet day” recordings. All observatories have 60-min sample records. The original recordings of field are in Universal Time (UT) as orthogonal north, east, and into-the-earth components of field as <em>X</em>, <em>Y</em>, and <em>Z</em>. The data for each component are Fourier analyzed for each quiet day.
A systematic change in pattern of the daily variation with change in latitude is clearly evident. The large amplitude of X occurs at all observatories near the geomagnetic dip equator because of existence of the equatorial electrojet. The relation between the Chapman factor (cosχ)<sup>0.5</sup> and<em> Sq (Z)</em> is investigated and concluded that the <em>Sq (Z),</em> corresponds in onset and subsidence with Chapman-factor change.
It has been concluded that the maximum amplitudes of magnetic potentialoccur near the midlatitudes which are the locations of the external current foci. The internal <em>Z</em> is in the opposite direction to that of the external <em>Z</em>. The external and internal currents must be oppositely directed to obtain the similar pattern of <em>X</em> and <em>Y</em> but opposite pattern of <em>Z</em>. It seems that all three internal variation amplitudes are less than the corresponding external amplitudes.در این تحقیق تغییرات روزهای آرام خورشیدی امریکای شمالی در سال 1997 در حکم سال آرام مغناطیسی با استفاده از تحلیل هماهنگهای کروی بررسی شده است. پنج روز از آرامترین روزهای هر ماه با شاخص مغناطیسی و به منزلة روزهای آرام هر ماه انتخاب شدهاند. تغییر منظمی در طرح تغییرات روزانه با عرض ژئومغناطیسی دیده میشود. تغییرات در عرضهای بالا تا عرضهای میانه، طرح مشابهی دارد و از عرضهای میانه بهسمت عرضهای پایینتر تغییر فاز میدهد. ولی مؤلفههای طرح یکسانی را در عرضهای مختلف نشان میدهند. نقش مولفه تغییرات آرام، زاویه سمترأسی خورشیدی و فاکتور چپمن بهدست آمده است. تحلیل فوریه موید غالب بودن مؤلفههای طیفی 24، 12، 8 و 6 ساعته است. مؤلفههای داخلی و خارجی در جهت مخالف یکدیگر هستند که علت آن در جهت مخالف بودن جریانهای داخلی و خارجی است ولی مؤلفههای داخلی و خارجی و تغییرات مشابهی را نشان میدهند. دامنه تغییرات مؤلفههای داخلی از مؤلفههای خارجی نیز کمتر بهدست آمده است.موسسه ژئوفیزیک دانشگاه تهرانفیزیک زمین و فضا2538-371X39320131023Identifying and monitoring dust storm in the western part of Iran using remote sensing techniquesتشخیص و پایش توفان گرد و غبار غرب ایران با استفاده از روشهای سنجش از دور83963560010.22059/jesphys.2013.35600FAفرحنازتقویاستادیار، گروه فیزیک فضا، موسسه ژئوفیزیک دانشگاه تهران، ایران0000-0003-4399-882Xالههاولاددانشجوی کارشناسی ارشد هواشناسی، گروه فیزیک فضا، موسسه ژئوفیزیک دانشگاه تهران، ایرانطاهرصفرراددانشجوی دکتری اقلیمشناسی، دانشکده جغرافیا دانشگاه تهران، ایرانپرویزایراننژاددانشیار، گروه فیزیک فضا، موسسه ژئوفیزیک دانشگاه تهران، ایرانJournal Article20120303Mineral dust can directly affect the solar and terrestrial radiation in both visible and infrared (IR) spectral regions through scattering and absorption processes. Due to specific optical properties of dust particles, satellite observed radiances carry the spectral signatures of dust particles that are different from molecular, cloud, and underlying surface. Based on these differences, various detection schemes have been developed to distinguish dust. In practice, the detection is based on the analysis of reflectance (or radiance) in visible bands or brightness temperature (BT) in IR bands. The magnitude of the difference in BT in selected bands (or channels) can be used to infer the signature of dust. This is the essence of aerosol imagery detection algorithms (Zhao et al, 2010).
Iran is located in a region that is strongly affected by dust storms. The frequency and intensity of these storms have increased in recent years. Recent studies have shown that numerical weather models alone are not able to track and detect dust storms and in many cases have significant errors (Taghavi, 2010). Remote sensing provides a valuable tool for detecting this phenomenon.
In west of Iran some areas are much more prone to dust storms than others due to differing soils and climates. Even in bare deserts, the sandy areas, such as those found on the Arabian Peninsula, generally do not generate dust storms. Generally, areas with silt- and clay-rich soils are responsible for most dust storms. These storms occur when the sub-tropical jet stream migrates northward from south of the Arabian Peninsula and the polar front jet stream moves southward from the European continent (Taghavi, 2008). In this study, we enhance and survey two dust events that occurred in the west of Iran on March the 4<sup>th</sup> and April the 13<sup>th</sup>, 2011, using two different algorithms. The first algorithm uses MNDVI index and threshold temperature of 290 K in MODIS band-32 to differentiate dust from semi-arid areas with low vegetation cover and clouds, respectively. Surveys show that MNDVI index cannot clearly detect dust over water surfaces. Therefore, we use the algorithm of combining brightness temperature difference of dust between the wavelengths of 8.5μm (MODIS band-29) and 11μm (MODIS band-31) with negative values of bands-31 and 32 brightness temperature differences. For defining dust areas we use (BT8.5-BT11) – (BT11-BT12) values larger than the obtained threshold and (BT11-BT12) smaller than zero. To study the dust loading, we also use the Dust Regional Atmospheric Model (DREAM-8b). The Earth Sciences Department of Barcelona Supercomputing Center (BSC) uses the DREAM-8b model (Nickovic et al. 2001; Perez et al. 2006a, Perez et al. 2006b) to conduct modelling research and development for short-term prediction of dust. The model predicts the atmospheric life cycle of the eroded desert dust and was developed as a pluggable component of the Eta/NCEP (National Centers for Environmental Prediction) model.
The recent method (using thermal infrared spectrum) detects dust well, especially over water. Comparison with quantitative aerosol optical thickness (AOT) retrieval is performed to validate the enhancement algorithms. At the end with comparing the enhanced images using IR technique with synoptic maps, MODIS AOT values, DREAM 8b model outputs and synoptic stations data, it is found that the applied enhancement algorithms provide a more reliable approach for monitoring dust storms compared to MODIS AOT retrievals or model outputs. For both dust storm cases, a low pressure was the main cause of the dust storms. Using trajectory maps, we can track the transport of dust from the main sources. Results show that for the dust storm occurred on the 4<sup>th</sup> March dust originated from the border of Iran and Iraq, then moved southward towards the Persian Gulf coasts, while that occurred on the case 13<sup>th</sup> April moved northward and approached Caspian Sea.ایران در منطقهای قرار گرفته که بهشدت تحتتاثیر توفانهای گرد وغبار است. تحقیقات نشان میدهد که بسامد و شدت این توفانها در سالهای اخیر افزایش یافته است. علاوهبر این، مدلهای عددی هواشناسی نیز بهتنهایی قادر به ردیابی و آشکارسازی توفانهای غبار نیستند و این امر ضرورت استفاده از روشهای بارزسازی گرد و غبار براساس داده سنجش از دور را نمایان میسازد. در این تحقیق دو رویداد گرد و غبار غرب ایران (١٤ اسفند ١٣٨٩ و ٢٤ فروردین ١٣٩٠) با استفاده از دو الگوریتم متفاوت، بارزسازی و بررسی میشود. الگوریتم اولیه به کار رفته، برای جداسازی اراضی نیمهبیابانی با پوشش کم گیاهی و ابر از پدیده گرد و غبار، بهترتیب از شاخص MNDVI و آستانه دمایی ٢٩٠ درجه کلوین در باند ٣٢ حسگر مادیس استفاده کرده است. بررسیهای صورت گرفته نشان داد که شاخص MNDVI روی آب بارزسازی را بهطور کامل عملی نمیسازد. بنابراین، از الگوریتم ترکیب تفاوت دمای درخشندگی BTD گرد و غبار در طول موجهای ٥/٨ میکرومتر (باند ٢٩ حسگر مادیس (و ١١ میکرومتر (باند ٣١ حسگر مادیس) با مقادیر منفی اختلاف دمای درخشندگی باندهای ٣١ و ٣٢ بهره گرفتیم. در روش دوم مقادیر (BT8.5-BT11) – (BT11-BT12) بزرگتر از آستانه بهدست آمده و (BT11-BT12) کوچکتر از صفر برای استخراج مناطق دارای گرد و غبار اِعمال شد. روش اخیر، یعنی استفاده از محدودة فروسرخ گرمایی، گرد و غبار را بهخوبی آشکار میکند. در نهایت با مقایسه تصاویر بارزسازی شده با استفاده از طول موجهای فروسرخ و مرئی با نقشههای همدیدی، مقادیر ضخامت نوری هواویز (AOT)، خروجی مدل DREAM 8b و همچنین گزارشهای ایستگاه میتوان دریافت که استفاده از الگوریتمهای بارزسازی گرد و غبار در مقایسه با روشهای دیگر (بازیابی هواویز یا خروجی مدل)، راه مطمئنتری برای پایش گرد و غبار است. در هر دو رویداد بررسی شده استقرار کمفشار در سطح زمین، دلیل اصلی وقوع گرد و غبار است. با توجه به نقشههای مسیر گرد و غبار، امکان بررسی دقیقتر منشا دو رویداد توفان و مناطق برداشت ذرات گرد و غبار نیز فراهم میشود. موسسه ژئوفیزیک دانشگاه تهرانفیزیک زمین و فضا2538-371X39320131023Effect of Mediterranean systems on drought in west of Iranاثر سامانههای مدیترانهای بر خشکسالی غرب ایران971103560110.22059/jesphys.2013.35601FAعلیرضامحمدنژاداستادیار، گروه فیزیک، دانشکده علوم دانشگاه بیرجند، ایرانفرهنگاحمدی گیویدانشیار، گروه فیزیک فضا، موسسه ژئوفیزیک دانشکاه تهران، ایران0000-0002-9487-4862پرویزایراننژاددانشیار، گروه فیزیک فضا، موسسه ژئوفیزیک دانشکاه تهران، ایرانJournal Article20120428The areas of the world that have Mediterranean style climate are found at about 35 degrees north and south of the equator, on the western sides of continents. The distinctive feature of this climate is the small amount of rain in the summer. Overall, the climate has a moderate amount of rainfall and warm winters and hot summers and. The climate of the Mediterranean region is conditioned by its position in the transition area between the subtropical high pressure belt and the midlatitude westerlies. In addition, the cyclones have been recognized since long as, a major meteorological feature influencing weather and climate in the Mediterranean region, often producing severe weather events. Mediterranean cyclones have also an influence on areas outside the Mediterranean region. Cyclones generated in the Mediterranean influence the weather and climate further east in Asian areaof the region to the east, including Syria, Iraq, Iran and Afghanistan. Important cyclogenesis centers of the Mediterranean consist of East and West Mediterranean, Gulf of Geneva (in North Italy), South Italy and Cyprus.
In this research, effects of the Mediterranean conditions and some other large scale atmospheric factors on precipitation of Iran during 1960 to 2005 are studied. For this purpose, effect of mean sea level pressure of Mediterranean cyclogenesis centers and the positions of subtropical high pressure belt (STPB) and the Siberian high pressure on both Mediterranean cyclogenesis and precipitation in Iran are investigated. To dynamically and synoptically study the effects of these factors on precipitation in the west of Iran, sea level pressure, cyclones frequency in the cyclogenesis centers, horizontal and vertical wind, temperature and moisture fields, and temperature and moisture fluxes are analyzed.
Results show that precipitation in the west of Iran depends on the mean annual surface pressure, the annual number of cyclones generated in Mediterranean centers and the position of the subtropical high pressure. In dry years, positive mean sea level pressure anomaly and negative cyclone frequency anomaly are observed in all cyclogenesise centers of Mediterranean Sea. Positive anomaly of monthly sea level pressure in cyclogenesis centers over the Mediterranean is greatest in January and gradually decreases in later months. In winter during which the west of Iran is dry, the Siberian and Azores high pressures join, and hence the cyclogenesis centers of the Mediterranean are dominated by a high pressure system. In such conditions, the Siberian high pressure is weaker and the Azores high pressure is stronger than in normal winters. In dry winters, a negative anomaly of relative and specific humidity over the Mediterranean Sea and a negative anomaly in the meridional and zonal wind in the Mediterranean Sea and over the northwest of Iran develop. This leads to a decrease flux of moisture to the west and northwest of Iran. This is consistent with what expected from dominance of Azores high pressure over the Mediterranean region in dry winters. In this situation, moisture flux from Red Sea to the south and southeast of Iran remains unaffected. در این پژوهش تاثیر دریای مدیترانه و برخی عوامل جوّی بزرگمقیاس منطقهای در دوره 1960 تا 2005 بر خشکسالی غرب ایران بررسی شده است. در سالهای خشک غرب ایران، افزایش در میانگین سالانه فشار و کاهش در فراوانی چرخندهای اکثر مراکز چرخندزا مشاهده میشود. بهعلاوه، بیهنجاریهای فشار ماهانه نیز در شروع سالهای خشک وجود دارد ولی بهتدریج با دور شدن از ژانویه کاهش مییابد. الگوهای بیهنجاری فشار نشاندهنده تضعیف پُرفشار سیبری و تقویت پرفشار آزورز در زمستانهای خشک هستند. کاهش فشار یا بیهنجاری منفی میانگین فشار سطح دریا روی مدیترانه، موجب تقویت چرخندزایی و افزایش فراوانی چرخندهای مدیترانه میشود که حاصل آن ایجاد زمستانهای مرطوب در غرب ایران است
در زمستانهای خشک، بیهنجاری جهت بُردار باد در غرب ایران، به سمت مدیترانه و به معنی کاهش تندی باد از مدیترانه به سمت این ناحیه از ایران است. بهعلاوه مولفههای مداری و نصفالنهاری باد در شمال غرب کشور و سطح مدیترانه دارای بیهنجاری منفی هستند. این بیهنجاری، موجب بیهنجاری منفی رطوبت نسبی روی مدیترانه و در نتیجه کاهش شار رطوبت از مدیترانه به غرب کشور میشود. از طرفی دیگر، شار رطوبت از دریای سرخ به جنوب و جنوبشرق کشور کاهش محسوسی ندارد. توزیع جغرافیایی بیهنجاری سرعت قائم در زمستانهای خشک غرب ایران، در سرتاسر مدیترانه و غرب ایران منفی است که معنی آن نزول هوا در این زمستانهای خشک است. موسسه ژئوفیزیک دانشگاه تهرانفیزیک زمین و فضا2538-371X39320131023Detection of temperature and precipitation trends and their attribution it to the greenhouse gases (Case study: West Azerbaijan Province)آشکارسازی روند تغییرات دما و بارش در دورههای گذشته و نسبتدهی آن به افزایش گازهای گلخانهای (بررسی موردی: استان آذربایجان غربی)1111283560210.22059/jesphys.2013.35602FAعلیرضامساح بوانیدانشیار، گروه منابع آب، پردیس ابوریحان، دانشگاه تهران، پاکدشت، ایرانالههگودرزیدانش آموخته آبخیزداری، دانشکده منابع طبیعی و کویرشناسی، دانشگاه یزد، ایراننرگسظهرابیاستادیار، گروه آبیاری، دانشگاه آزاد اسلامی واحد علوم و تحقیقات خوزستان، ایرانسعیدلطفیکارشناس، گروه سیاستگذاری و تخصیص منابع آب، دفتر برنامه ریزی کلان آب و آبفا، وزارت نیرو، تهران، ایرانJournal Article20120506Detection of changes in climate variables during the past periods and attributing them to the identified factors plays a major role in climate studies and projection of the future. Different factors can unbalance the stationary time series of a region’s climatic variables. Part of these factors are related to the interactions between the components of the Earth’s climate system which can cause internal variability in time series of climatic variables. Two important natural factors that influence climate are the Sun’s energy and volcanic eruptions. Overall changes due to natural external factors and internal climate variability in earth climate system are called natural climate variability. The increase in the carbon dioxide concentration due to human activities has been the principle factor causing warming over the past 50 years. It should be noted that the existence of a trend in the climate data of a region can not necessarily be attributed to the increase in greenhouse gases. In other words, after proving the existence of a trend in the past climate data of a region, the relationship between the trend and the increase in greenhouse gases should be proved.
This study was carried out to detect the trend of temperature and precipitation of West Azerbaijan Province, Iran for the period of 1968-2008 and attributing them to the greenhouse gases. The Basin located at longitude 44º 00' to 47º 31.7' north and latitude 35º 55.2' to 39º 42' east in northwest of Iran. The Basin area is 37411/1 km<sup>2</sup> that the thirteenth largest Province in Iran.
Two approaches were used to evaluate the changes in annual series of temperature and precipitation during the period 1968-2008. The first one is based on analysis of standardized departures and the second approach is based on a multiple trend tests (Mann, 1945; Kendall, 1975). This test identifies gradual monotone rising and falling trends in a time series. On the other hand distinction between gradual trend and a rapid change is important, particularly for climate- change impacts studies. Therefore to identify temporal changes in annual precipitation and temperature series of main stations in the West Azerbaijan, we conducted multiple trends tests as suggested by McCab and Wolock (2002) by varying the beginning and ending date of the time series in 5 years steps for the period of 1968-2008. Afterward, in order to separate climate changes caused by greenhouse gases from natural variability, long-term statistics (1000 years) of temperature and precipitation, resulting from control run (fix greenhouse gases) of CGCM3 model, were used for West Azerbaijan Province. To analyze the natural variability range of two “temperature” and “precipitation” variables of the study area, first, their annual anomaly time series with respect to the average base period is calculated [By definition, temperature anomaly is the temperature difference from a base temperature, while precipitation anomaly is the precipitation ratio difference from a base precipitation, (Base period, 1971-2000)].The range of natural climate variables is determined by providing two-dimensional graphs of temperature and precipitation based on two-variant normal distribution (Von Storch and Zwiers, 2002). Finally, anomaly values of the observation stations in different regions of the case study were compared with the natural climate variability range of the region.
The results show that the increase in temperature and decrease in precipitation trends are due to the climate change in 1968-2008 periods. Additionally in different parts of the studied area, the range of natural climate variables for temperature and precipitation changes is between 1.8 to -1.8°C and +40 to -40 percent, respectively. However, in the most of the regions of the West Azerbaijan Province, the last ten years of the period (1998 to 2008) have almost been located outside the range of natural climate variables. The result indicates the effect of climate changes on the climatic variables of the case study in recent years.این تحقیق با هدف بررسی روند تغییرات متغیرهای دما و بارش در دوره 1968 - 2008 و نسبتدهی احتمالی این تغییرات به افزایش گازهای گلخانهای در استان آذربایجان غربی صورت گرفته است. در این راستا ابتدا دو رویکرد تحلیل انحراف معیار و آزمونهای روند چندگانه من کندال بهمنظور ارزیابی روند تغییرات سریهای زمانی متغیرهای دما و بارش مورد بررسی قرار گرفت. نتایج، افزایشروند دما و کاهش روند بارش را در دوره تحقیقاتی نشان داد. بهمنظور نسبتدهی احتمالی این تغییرات به افزایش گازهای گلخانهای، در ابتدا محدوده نوسانهای درونی اقلیمی منطقه با استفاده از آمار بلندمدت (1000 ساله) دما و بارش حاصل از اجرای کنترل (ثابت ماندن گازهای گلخانهای) مدل CGCM3 بهصورت گرافهای دوبُعدی دما و بارش بر مبنای توزیع نرمال دومتغیره تعیین شد. در ادامه روند تغییرات آشکار شده در دورههای گذشته با محدوده نوسانهای درونی اقلیم منطقه مقایسه شد. نتایج نشان داد که در قسمتهای گوناگون منطقه تحقیقاتی، محدوده نوسانهای درونی اقلیم برای متغیر دما و بارش بهترتیب بین 8/1 تا 8/1- درجه سلسیوس و 40 تا 40- درصد بوده و تقریبا سالهای انتهایی دوره مورد بررسی تحتتأثیر پدیده تغییر اقلیم، خارج از محدوده نوسانهای درونی اقلیم واقع میشود و نشاندهنده اثرات تغییر اقلیم بر متغیرهای اقلیمی در سالهای اخیر است.موسسه ژئوفیزیک دانشگاه تهرانفیزیک زمین و فضا2538-371X39320131023Investigation of the effect of outflow intrusion on acoustical signal
fluctuations in laboratoryبررسی اثر جریان نفوذی روی افتوخیزهای سیگنال آکوستیکی در آزمایشگاه1291433560310.22059/jesphys.2013.35603FAمحمداکبرینسبدانشجوی دکتری، گروه فیزیک دریا، دانشگاه علوم و فنون دریایی خرمشهر، ایرانعباسعلیعلیاکبری بیدختیاستاد، گروه فیزیک فضا، موسسه ژئوفیزیک دانشگاه تهران، ایرانمسعودصدرینسبدانشیار، گروه فیزیک دریا، دانشگاه علوم و فنون دریایی خرمشهر، ایرانوحیدچگینیاستادیار، موسسه ملی اقیانوسشناسی، تهران، ایرانمحمدمهدیمهدیزادهاستادیار، گروه فیزیک دریا، دانشگاه هرمزگان، ایرانJournal Article20120501From the acoustical oceanography point of view the ocean is a sophisticated environment. Existence of outflow intrusion (for instance, outflow of the Persian Gulf), internal waves, and small-scale turbulence perturb the horizontally stratified character of the sound velocity and cause spatial and temporal fluctuations of the sound propagation. In this experimental study, we have investigated signals fluctuations over time (was powered by a 20 MHz/Arbitrary Waveform Generator Model DG 1022 set to generate a 10 cycle sinusoid burst at frequency of 120 kHz with amplitude of 20 volts peak-to-peak) in a pre-stratification environment outside of the intrusion of turbulent plume. All experiments were carried out in a glass tank 2.19 m long, 1.27 m wide and 0.8 m deep. Before the experiments, four transducers (of which three of them are transmitters and the rest of them as receiver) are mounted opposite to each other with a separation of 1.65 m on two iron bars inside the tank. The distance between each transducer is 0.14 m. These holders are facing each other at a distance 0.3m from the tank wall. Prior to the beginning of the experiments with stratification, the acoustic measurements were executed in fresh water. All received signals were sampled at 5 MHz in all experiments. A fourth-order Butterworth band-pass filter was applied to the received voltage time series, with cutoff frequencies at 110 and 130 kHz for the 120-kHz data. In case where a “filling box" stratification (Baines and Turner, 1969) is used, the tank was initially filled with fresh water to a depth of 0.48 m. The water was then stratified using a plume of dense salt solution falling from the end of small tube (a nozzle of 3 mm diameter) placed at 0.47 m from the base with a buoyancy flux of F=g<em><sup>'</sup></em>×V<sub>o</sub>=. After the set-up of the “filling box" stratification in the tank (Fig 1), acoustic signals and hydrophysical data were measured simultaneously. Then to produce the outflow intrusions, a source of dyed salt solution with a density less than the previous case (“filling box") with volume flux of was entered into stratified environment. At the start of the experiment with plume intrusion the speed of the nose of the outflow increased with time. The intrusion is also thickened, and eventually split to generate a new tongue of dyed plume water growing beneath the first layer. The dye tracer in the outflow water was slowly adverted upward to replace water entrained into the plume at shallower depths, and eventually reached to the source level. The outflow intrusion is produced at the start of the experiment at the location of the transmitter in the middle of the tank (at the depth of 0.22 m). The dyed outflow water is wedged-shaped with a sloping interface beneath. In different time intervals the acoustic and hydrophysics data are measured simultaneously, and then these signals in different times, based on the place of the plume outflow, are processed. After investigating the output signals, these results are found: when the transmitter and receiver is positioned into the outflow intrusion (dyed outflow) location, the signal amplitude is decreased at different moments of plume intrusion, but if the transmitter is positioned in the upper and lower part of the outflow intrusion, it causes the signal amplitude to increase (Snell’s law). By applying trace envelope techniques on the received signals, shape of signal change was found with time. Thereby, results indicate that outflow intrusion could be important on acoustical signal fluctuations. Results indicate that outflow intrusion could be important in shapes of the received signals. Also we have observed the occurrence of major signal fluctuations over time is accordance with the sound speed vertical structure changes. It is noticed that this phenomenon is also taken place at the outflow of the Persian of Gulf to the Oman sea. The result of such simulation could be used with attention to the acoustic scale rule, (<em>k </em>is the wave number.) where a lab by thickness of this current at outflow of the Persian Gulf which is about <10 km.از دیدگاه آکوستیکی، اقیانوس بهطور گسترده متغیر است. وجود جریان نفوذی (برای مثال، خروجی خلیج فارس)، امواج داخلی و تلاطم ریزمقیاس، مشخصه افقی لایهبندی سرعت صوت آشفته میکند و باعث افتوخیزهای زمانی و مکانی انتشار صوت میشود. در این تحقیق علاوه بر شبیهسازی جریان نفوذی شوری در آزمایشگاه، نحوه افتوخیزهای سیگنال آکوستیکی که با 10 عدد بسته موج سینوسی در بسامد 120 کیلوهرتز ایجاد شده را با جابهجایی منبع در بالا، پایین و داخل جریان نفوذی، مورد اندازهگیری و تجزیه و تحلیل قرار گرفته شده است. نتایج حاصل نشان میدهد که چنانچه منبع و گیرنده در داخل لایه جریان نفوذی نصب شود، دامنه سیگنال در لحظات گوناگون ورود پلوم آب نمک، کاهش مییابد ولی چنانچه منبع در بالا و پایین این لایه جریان نفوذی نصب شده باشد، دامنه سیگنال افزایش مییابد (قانون اسنل). با اِعمال فناوریtrace envelop روی سیگنالهای آکوستیکی ضبط شده، مشخص شد که شکل و فاز سیگنال با گذشت زمان تغییر میکند. این تحقیق نشان داد که جریان نفوذی، پدیده مهمی است که روی افتوخیزهای سیگنالهای آکوستیکی تاثیر میگذارد. براساس محاسبات باور و همکاران، پهنای جریان خروجی (نفوذی) تنگه هرمز کمتر از 10 کیلومتر است، در نتیجه میتوان نتایج این شبیهسازی آزمایشگاهی را بر طبق رابطه مقیاسسازی آکوستیکی (a ضخامت پدیده و k عدد موج ) با آزمون میدانی در محدوده جریان نفوذی تنگه هرمز در بسامد 5ر1 هرتز متناسب در نظر گرفت.موسسه ژئوفیزیک دانشگاه تهرانفیزیک زمین و فضا2538-371X39320131023Numerical simulation of the North Atlantic Oscillation and its impact on the South West Asiaشبیهسازی عددی نوسان اطلس شمالی (NAO) و آثار آن در جنوب غرب آسیا1451583560410.22059/jesphys.2013.35604FAمحمدعلینصراصفهانیاستادیار، دانشکده کشاورزی دانشگاه شهرکرد، ایران0000-0001-6249-3355فرهنگاحمدی گیویدانشیار، گروه فیزیک فضا، مؤسسه ژئوفیزیک دانشگاه تهران، ایران0000-0002-9487-4862علیرضامحبالحجه2 دانشیار، گروه فیزیک فضا، مؤسسه ژئوفیزیک دانشگاه تهران، ایرانJournal Article20120806The impact of the North Atlantic Oscillation (NAO) on meteorological parameters in the South West Asia (SWA), especially on temperature and precipitation, is certain according to recent studies. Due to differences in methods for analyzing the effects of the two phases of NAO, however, there are differences among researchers on the details of the impact. Perhaps one reason for this inconsistency is the weakness of the impact due to the fact that the NAO occurs far upstream of the SWA. So the interaction with other stronger forcings makes it almost impossible to extract the net effects of NAO. Hence some of the previously published results are in doubt. More certain results can be obtained using numerical models when we are able to do control experiments by fixing certain desirable parameters of the atmosphere and changing the forcings of interest at the same time.
In this article the general climate model ECHAM5 is employed to simulate the NAO and its impact in the SWA. Two experiments named "control experiment" (COEX) and "climatological experiment" (CLEX) are designed to verify the results previously reported by the authors in 2008. In the COES, the actual sea surface temperature (SST) and in the CLEX, the long-term mean of SST is used as an input of the model. Artificially changing the NAO index is the aim of CLEX which is done by changing the lower boundary condition of the model. For both experiments, the NAO index is computed on the basis of the method suggested by Hurrell in 1995 using sea level pressure values in the northern and subtropical regions of the North Atlantic Ocean. Then on the basis of the COEX NAO index, the critical positive and negative months of NAO are determined and the ensemble mean of some important meteorological parameters in these two groups of months are computed and analyzed.
The simulation of the NAO index shows that the ECHAM5 is unable to simulate the real atmospheric values of the monthly NAO index. In particular, the positive trend of the NAO index from 1970 onwards is not predicted by ECHAM5. However this model is successful in simulation of the low-frequency variability of the NAO index. The latter findings show that the high-frequency variability of the NAO index is effectively controlled by forcings other than the SST. However it seems that the SST acts as a main forcing for low-frequency variability of the NAO index.
Analysis of the ensemble mean of meteorological parameters in the critical positive and negative months shows that the patterns obtained for COEX are similar to those reported by the authors in 2008. Some small differences observed in location and magnitude of centers could be due to the differences in the type and resolution of the data. As mentioned above, the critical months are selected here on the basis of the NAO index computed for COEX. So the selected months are not critical in the CLEX. If we examine the NAO index for CLEX in the same critical months, the result is like a random distribution. Hence, no significant difference is observed between the ensemble mean of meteorological parameters in CLEX in the critical positive and negative months. Therefore, it can be concluded that the results reported by the authors in 2008 are related to the real impact of NAO in the selected months. Finally, since in the experiments carried out here only the boundary conditions and forcing functions related to the numerical representation of the atmosphere are present, it should be possible to explain the observed impact of NAO in the SWA by means of the dynamics represented by ECHAM5.در این تحقیق با استفاده از مدل اقلیمی-جهانی ECHAM5، آثار نوسان اطلس شمالی در جنوبغرب آسیا از راه دو آزمایش کنترل و اقلیمی شبیهسازی شده است. در آزمایش کنترل، از دمای سطح دریای واقعی و در آزمایش اقلیمی، میانگین بلندمدت دمای سطح دریا در حکم ورودی مدل به کار رفته است. براساس شاخص نوسان اطلس شمالی که از خروجی آزمایش کنترل بهدست آمده است، دو دسته ماه بحرانی مثبت و منفی شناسایی و میانگین همادی برخی کمیتهای هواشناختی برای این دو آزمایش محاسبه شده است. نتایج حاکی از اثر قابلملاحظه دمای سطح دریا بر وردایی کمبسامد شاخص نوسان اطلس شمالی است، در حالیکه این کمیت بر میانگین ماهانة شاخص چندان مؤثر نیست. نتایج میانگین همادی بیانگر همخوانی کامل اختلاف مشاهده شده بین فازهای مثبت و منفی نوسان اطلس شمالی در آزمایش کنترل با نتایج تحقیقات قبلی است. همچنین میانگین کمیتها در آزمایش اقلیمی تفاوت قابلملاحظهای را بین ماههای مثبت و منفی نشان نمیدهد. بر این اساس میتوان گفت که تفاوت کمیتهای هواشناختی در جنوبغرب آسیا بین فازهای مثبت و منفی نوسان اطلس شمالی یک برهمکنش جوّی و براساس دینامیک مدل ECHAM5 کاملاً قابل توضیح است و چنین تفاوتهایی نمیتواند تصادفی باشد.موسسه ژئوفیزیک دانشگاه تهرانفیزیک زمین و فضا2538-371X39320131023Preparation of atmospheric temperature and humidity isopleths maps using thermal bands of MODIS satellite imagesتهیه نقشههای همدما و همرطوبت جوّ با استفاده از باندهای گرمایی تصاویر ماهوارهای مادیس1591763560510.22059/jesphys.2013.35605FAمجیدرحیمزادگاندانشجوی دکتری سنجش از دور، دانشکده مهندسی نقشه¬برداری، دانشگاه صنعتی خواجه نصیرالدین طوسی، تهران، ایرانمحمدرضامباشریدانشیار، دانشکده مهندسی نقشه¬برداری، دانشگاه صنعتی خواجه نصیرالدین طوسی، تهران، ایرانJournal Article20120916In recent years, extraction of atmospheric temperature and humidity profiles from thermal bands of satellite images is a common practice. The most deployed images for this task have been acquired by Moderate Resolution Imaging Spectroradiometer (MODIS). This sensor which is onboard of Terra and Aqua platforms consists of a spectroradiometer with 36 bands in visible (VIS), near infra-red (NIR) up to thermal infra-red (TIR) region (0.405 – 14.385 ( )). The combination of sixteen infrared spectral channels is suitable for sounding temperature and humidity profiles in the atmosphere with a relatively acceptable precision. Different daily atmospheric products of MODIS images are in access on MODIS site. Atmospheric temperature and humidity profiles are two of these products that were used in this work. These products are named MOD07 and MYD07 for Terra and Aqua platforms respectively. Other MODIS products used in this work were MOD35 and MYD35. These products are mainly used for detection of pixel cloud contamination as well as for detection of aerosol concentration in pixel.
Presently, maps of temperature and humidity isopleths from MODIS images are being extracted by applying some global algorithms. In these algorithms, global profiles of temperature, moisture, and ozone are being used in the calculations, where it is believed that these algorithms are not usually valid in regional scales. It is believed that the regional algorithms can boost the precision of aforementioned maps. In this work, 5 MODIS images of 8 and 11, June 2004 and 8, 15 and 22 June 2007 and their corresponding temperature and moisture profiles were used for modeling and 4 MODIS images of June 2, 6, 7 and 21 of 2007 were used for evaluation. In order to prepare a temperature and moisture profile as an initial guess in model, a 5 year (2004–2008) radiosonde data set consisting of 240 temperature profiles all interpolated for the times of satellite overpass in June were averaged. The aforementioned radiosonde measurements were acquired from the vicinity of synoptic station. This station is located at 51<sup>o</sup>, 21’E and 35<sup>o</sup>, 41’N in the south of Tehran at an altitude of 1191 (m) from mean sea level. Also some data from other synoptic stations including Kermanshah, Tabriz, Shiraz, Ahwaz, Bandarabbass, Zahedan and Mashhad stations were used for model evaluation.
A practical method for extraction of temperature from MODIS measurements is to use the predefined statistical relationship between measured or modeled radiance flux densities and the corresponding temperature and moisture profile in the atmosphere. In statistical extraction method, the regression between flux density radiated from CO<sub>2</sub> and water vapor in corresponding absorbing bands are modeled. This method is usually used in producing the first guess profile to be used in physical models later on. A method named Localized Statistical Regression Profile Retrieval (LSRPR) for extraction of temperature profiles from MODIS images based on statistical regressions is introduced in this work. In this method an approach for improving the clear sky temperature profile calculation is presented, where using local atmospheric profiles collected by Radiosondes and corresponding MODIS images, some regression coefficient matrix is calculated locally. Then by applying this matrix to other MODIS images, one can calculate temperature profiles with a precision better than what is achieved by MODIS research team i.e. MOD07/MYD07.
Here radiosonde data along with concurrent MODIS images were used and the relevant regression coefficients were calculated. The average RMSE between temperature profile calculated from LSRPR and the one measured by radiosonde in the selected stations around the country was about 3.43K. This for MODIS products was 4.66K. The average RMSE between humidity profiles calculated from LSRPR and the one measured by Radiosonde in the selected stations was 1.27 g/kg and this value for MODIS products was 1.41 g/kg. As can be seen LSRPR model shows improvement in the isopleths of temperature compared to MODIS products. This improvement for humidity isopleths was not as good as for temperature. This could be due to the low amount in humidity in June. On the other hand considerable improvements in the precision of temperature isopleths extraction can be due to the use of local temperature profiles as the first guess in extraction algorithm.
Moreover the results show that in the stations other than Mehrabad airport, the RMSE between temperature and humidity profiles extracted from LSRPR algorithm and those calculated from radiosonde measurements is increased.
Based on the achievements in this research, it seems that LSRPR algorithm can enhance the precision compared to MODIS and the values calculated by this method are well comparable with the radiosonde collected data. So this algorithm can be used as an efficient method in regions such as Iran with relatively low number of radiosonde stations and irregular radiosonde measurements for producing temperature and humidity isopleths maps at different pressure levels in the atmosphere. It is hoped that by using these maps the accuracy of weather and climate prediction in the regional scale can be increased.در سالهای اخیر استفاده از باندهای گرمایی تصاویر ماهوارهای به روشی رایج در ایجاد نیمرخهای دما و رطوبت جوّ تبدیل شده است. تصاویر طیفسنج پرتویی تصویربردار با قدرت تفکیک متوسط (MODIS) با دارا بودن قدرت تفکیک مکانی مناسب یکی از تصاویر پُرکاربرد در زمینه تهیه نقشههای منحنیهای همدما و همرطوبت با دقت نسبتاً مناسب است. در روشهای رایج تهیه نقشههای همدما و همرطوبت از تصاویر مادیس از الگوریتمهای جهانی استفاده میشود که در مقیاس محلی دقت مناسبی ندارند و استفاده از الگوریتمهای محلی میتواند موجب بهبود دقت تهیه این نقشهها شود. در این پژوهش از دادههای رادیوسوند و تصاویر مادیس مربوط به 5 سال در ماه ژوئن و دادههای ایستگاه سینوپتیک فرودگاه مهرآباد برای مدلسازی استفاده شده و از دادههای کل ایستگاههای سینوپتیک موجود در ایران در ارزیابی کارایی مدل، استفاده شد. استخراج نیمرخ از روش رگرسیونهای محلی آماری (LSRPR) روش منتخب این پژوهش بود که در آن برای استخراج نیمرخهای جوّی از روش رگرسیونهای آماری از تصاویر مادیس، با استفاده از نیمرخهای جوّی حاصل از دادههای رادیوسوند محلی و تصاویر متناظر با آنها، ضرایب رگرسیون بهصورت محلی استخراج میشود. مقادیر متوسط RMSE بین نیمرخهای دمای حاصل از الگوریتم LSRPR و اندازهگیریهای رادیوسوند برای همة ایستگاههای کشور 43ر3 و برای نیمرخ دمای حاصل از الگوریتم مادیس و داده رادیوسوند 66ر4 درجه کلوین بهدست آمد. همچنین مقادیر پیشگفته برای نیمرخهای رطوبت بهترتیب 27ر1 و 41ر1 گرم بر کیلوگرم بهدست آمد. نتایج بهدست آمده نشان داد که منحنیهای همدما و همرطوبت استخراج شده از LSRPR همخوانی مناسبی با اندازهگیریهای رادیوسوند دارند.موسسه ژئوفیزیک دانشگاه تهرانفیزیک زمین و فضا2538-371X39320131023Application of ordinary and complex methods for filling random gaps in total ozone dataکاربست روشهای درونیابی معمول و پیچیده برای پرکردن خلأهای تصادفی ایجاد شده در دادههای اُزن کلی1771893560610.22059/jesphys.2013.35606FAمریمقرایلواستادیار، گروه فیزیک فضا، موسسه ژئوفیزیک دانشگاه تهران، ایراننفیسهپگاهفراستادیار، پژوهشگاه ملی اقیانوس شناسی و علوم جوی، تهران، ایرانمجیدمزرعه فراهانیاستادیار، گروه فیزیک فضا، موسسه ژئوفیزیک دانشگاه تهران، ایرانJournal Article20121110Ozone gas has a major controlling factor for solar radiation of the shortest wavelength that reaches the earth surface. This gas is formed by chemical reaction and its formation process has been considered in various researches. Ozone is closely related to sun radiation time, relative air humidity and temperature. So ozone gas has been investigated from various interests. But one of remarkable problems challenge scientists is missing data or even unmeasured data in some periods. Hence suggesting a technique to solve this problem has a high degree of importance. Therefore, the main aim of this paper was formed.
In this study, six years observed data (2005-2010) of total ozone measured both by Dobson and TOMS satellite were used. Dobson spectrophotometer (D109) has been installed at the Institute of Geophysics of University of Tehran. This institute situated in the north of Tehran with geographical characteristics of 35.44 <sup>o</sup>N and 51.23 <sup>o</sup>E and elevation of 1418.6 m above sea level. The correlation coefficient between the observational Dobson and measured satellite data has been calculated. The results show that the maximum value of the determination coefficient occurred in spring, winter, autumn and summer, respectively. Also the minimum value of the determination coefficient (R<sup>2</sup>=0.0596) happened in autumn of the year of 2005, while the maximum value of this coefficient (R<sup>2</sup>=0.9623) computed in autumn of the year of 2010. Following to investigate the accuracy of each ordinary interpolation methods to fill total ozone data gaps, some interpolation methods were selected. These methods includes Nearest, Linear, Spline and Pchip.
Data investigation showed that frequent gaps last 1, 2, 3, 4 and 5 days. To clarify the accuracy of each method, first randomly missing periods were produced with the same length. Then to evaluate the performance of the four interpolation methods, Index of Agreement (IOA) was computed. In this evaluation method, the predicted values are compared with the measured values. Values of IOA greater than 0.5 indicate that the applied method for predicting performs well (Willmott 1981). In this paper, values of IOA were calculated using the results of interpolation methods and the original observed data for each period.
The present paper indicates that the Spline method produces the more acceptable IOA, but this method creates least accuracy in estimating missed data, compare with other methods. It is also worthwhile to note that other interpolation methods produced similar IOA.
In second step, the operation of a complex method, namely wavelet transform, for filling real gaps was studied. It should be noted that the wavelet transform has also been used in other meteorological fields such as the time series analysis of soil changes, the relationship between rainfall and runoff, simulations of photochemical reactions, mountain waves, ENSO and predicting floods and droughts.
For this aim, missed data in signal of total ozone data for 2009 were constructed using wavelet theory. The outcomes of applying this theory to the observed data were compared with satellite data at the same time. The results showed that the reconstructed signal and the signal measured by satellite were consistent.
در این تحقیق دادههای مشاهداتی اُزن کلی اندازهگیری شده با دستگاه دابسون و ماهواره TOMS در بازه زمانی 2005-2010 بهکار گرفته شد تا ابتدا ضریب همبستگی بین دادههای مشاهداتی دابسون و ماهواره محاسبه شود. در ادامه بهمنظور بررسی دادههای ازدسترفته با حداکثر فراوانی بازههای کوتاهتر از 5 روز، 4 روش درونیابی بهکار گرفته میشود تا دقت هر روش در پرکردن خلأ دادههای ازدسترفته اُزن ارزیابی شود. برای ازریابی هرکدام از این روشها شاخص سازگاری محاسبه میشود. این شاخص در سالهایی که طول بازه دادههای از دسترفته آنها بیش از 30 روز است نتیجه مطلوبی بهدست نمیدهد. از اینرو بهمنظور روشن شدن سهم طول بازه داده از دسترفته در دقت روش درونیابی اتخاذ شده، مجموعهای از دادههای از دسترفته بهطور تصادفی از مجموعه دادههای مشاهداتی دابسون و با بازه های1، 2، 3، 4 و 5 روزه تولید شد. سپس کارایی هر 4 روش درونیابی با استفاده از شاخص سازگاری (IOA) ارزیابی و با دادههای واقعی مقایسه شد. با بررسی روشن شد که روش اسپیلاین علیرغم تولید شاخص سازگاری مطلوب، کمترین دقت را نسبت به سایر روشها در برآورد مقدار دادههای از دسترفته دارد.
در ادامه با استفاده از اطلاعات اُزن کلی شهر تهران در سال 2009، بازسازی دادههای از دسترفته اُزن با استفاده از روش تبدیل موجک صورت گرفت. سپس نتایج حاصل از کاربست این نظریه با دادههای مشاهداتی ماهواره در همین بازه زمانی مقایسه شد. نتایج نشان داد که شاخص سازگاری بین سیگنال بازسازی شده و سیگنال اندازهگیری شده با ماهواره برابر 7996/0 بهدست آمد که با نتایج حاصل از روشهای معمول درونیابی قابل مقایسه است. موسسه ژئوفیزیک دانشگاه تهرانفیزیک زمین و فضا2538-371X39320131023Investigation of surface ozone over Tehran for 2008-2011بررسی آلاینده اُزن سطحی در شهر تهران طی دوره سالهای (2008-2011)1912063560710.22059/jesphys.2013.35607FAزهراشرعیپورکارشناس ارشد هواشناسی، گروه فیزیک فضا، مؤسسه ژئوفیزیک، دانشگاه تهران، ایرانعباسعلیعلیاکبری بیدختیاستاد گروه فیزیک فضا، مؤسسه ژئوفیزیک دانشگاه تهران، ایرانJournal Article20130218Near surface ozone in urban areas can be potentially hazardous for the city dwellers. As a secondary pollutant it can also be an indicator for other air pollutants as nitrogen oxides, NOx and phenol acetate nitrate (PAN). In this paper time and spatial variations of near surface ozone and the effective meteorological parameters influencing it concentrations, have been investigated for Tehran for the period 2008-2011. The hourly ozone data of four stations namely Aghdasieh (north east), Geophysics (central), Poonak (north west) and Ray (south) for this period were acquired from the Air Quality Control company of Tehran, and the hourly temperature difference between the near surface and 8 m height were also from the Resalat Mast west of the city. The meteorological data were acquired from the Geophysics station and the data of the vertical distributions of humidity were from Wyoming University data base that provides Skew-T data of the troposphere. The synoptic maps were also acquired from NOAA.
Ozone air pollution index for some air pollution stations as Aghdasieh (north east of the city) show that the period with highest concentration during the year are warm summer months in which 93% of the days were unhealthy. The daily peak of ozone concentration is found at 15-17 hours local time, depending on various meteorological parameters especially air temperature and solar radiation. There is also a strong correlation between the ozone concentration at 11AM local time and its daily mean. Usually the mean daily ozone concentration is about 66% of that of the values at 11AM local time.
The annual peak of the ozone concentration is also in summer as expected. It is also found that as the nocturnal temperature inversion in the surface layer is reduced or the overall stability of the atmosphere is reduced the near surface concentration of ozone increased. This is attributed to the easier down mixing of the ozone in the residual layer (formed previous day) towards the surface. Tehran is surrounded by high mountains in the north and to some extent in the east affecting local near surface circulation. Such flows may advect air with different air pollutants especially from the emission areas (mainly center and south of the city) towards north or east, as towards Agdasieh, the station with an ozone monitoring facility.
Spring time surface ozone variations also show that some mid-latitude low pressure weather system can cause strong tropospheric mixing, including tropopause folding, hence down transport of stratospheric ozone rich air towards the surface. While meteorological conditions associated with maxima of near surface ozone in summers are those with anticyclonic systems in the mid-troposphere of this area. Such conditions are associated with clear skies and strong solar radiations leading to strong photochemical activities that are essential for ozone formation in the atmosphere.
It is also found that precipitation strongly reduces the air pollutants including ozone. It is interesting that following such perceptive events as the sky clears, ozone rate of concentration increase is faster than those of other pollutants. More clear sky following such events leads to stronger solar radiation near the earth surface, leading to stronger built up of ozone near surface.در این تحقیق، تغییرات زمانی مکانی آلاینده اُزن سطح زمین و عوامل هواشناسی مؤثر بر آن در شهر تهران طی سالهای 2008 تا 2011 بررسی شده است. بررسی مقادیر روزانه شاخص کیفیت هوا نسبت به آلاینده اُزن سطحی در ایستگاه اقدسیه نشان داده است که بیشترین درصد روزهای ناسالم در ماههای تیر و مرداد (93%) قرار دارد. اوج روزانه اُزن در ساعتهای 15-17 رخ داده و متأثر از عوامل گوناگونی، بهویژه دمای هوا و تابش خورشیدی است. غلظت اُزن در ساعت 11 قبلازظهر، همبستگی مثبت زیادی با غلظت میانگین روزانه آن دارد. یکی از جالبترین نتایج این است اغلب کاهش وارونگیهای دمایی شبانه و کاهش پایداری جوّی میتواند باعث افزایش غلظت اُزن سطحی شبانه شود.
بررسی بیشینههای آلاینده اُزن سطحی بهاری روشن ساخته است که برخی سامانههای کم ارتفاع وَردسپهر میانی همراه با پدیدههای وَردْایست تاشونده که منطقه ایران را در عرضهای شمالی دریای خزر تحتتأثیر قرار میدهند، میتوانند از راه نزول هوای خشک سرشار از اُزن پوشنسپهری به وَردسپهر، باعث افزایش مقدار آلاینده اُزن سطح زمین شوند. بررسی بیشینههای اُزن سطحی تابستانی و مقایسه آن با شرایط هواشناسی جوّ بالا نشان داده است که اغلب این بیشینهها در اثر حضور واچرخندها در وَردسپهر میانی منطقه ایران ایجاد میشوند. شرایط هواشناسی آفتابی، خشک و آرام در طی روز ناشی از این سامانهها باعث افزایش تولید اُزن طی واکنشهای فوتوشیمیایی میشود. بررسی تأثیر بارش بر مقدار آلاینده اُزن سطحی روشن ساخته است که در روز بارشی غلظت همه آلایندهها ازجمله اُزن کاهش مییابد ولی در یک تا دو روز پس از بارش درحالیکه هنوز اکثر آلایندها غلظت بهنسبت کمی دارند، غلظت اُزن افزایش مییابد؛ که این نشانه شفافتر بودن جوّ برای تابش خورشیدی و ترغیب بیشتر فرایند فوتوشیمیایی تشکیل اُزن است. موسسه ژئوفیزیک دانشگاه تهرانفیزیک زمین و فضا2538-371X39320131023Application of improved local phase filter for edge detection of magnetic anomalies, A case study: Tighe Now Ab iron deposit (Byrjand)کاربرد فیلتر فازی محلی تعمیمیافته در برآورد مرز بیهنجاریهای مغناطیسی، بررسی موردی:کانسار آهن تیغه نوآب (بیرجند)2072193560810.22059/jesphys.2013.35608FAمسلمفاتحیدانشجوی دکترای مهندسی معدن - اکتشاف، دانشگاه صنعتی اصفهان، ایرانغلامحسیننوروزیدانشیار، دانشکده مهندسی معدن، پردیس دانشکدههای فنی، دانشگاه تهران، ایرانمیثمعابدیدانشجوی دکترای مهندسی معدن – اکتشاف، دانشکده مهندسی معدن، پردیس دانشکدههای فنی، دانشگاه تهران، ایرانJournal Article20110706Magnetic survey is nowadays the most efficient non-destructive geophysical method. This technique puts emphasis on the measurement of anomalies of the Earth’s magnetic field, caused by the presence of archaeological remains in the ground. Magnetic survey is one of the oldest geophysical methods for airborne and land use. That is why there is a large volume of data that could be used for geological studies and deposits exploration.
In this method, the intensity of earth's magnetic field is measured. The method is used for metal objects exploration in archeology, engineering investigations, metal mineral exploration, oil and gas exploration, as well as the regional geological studies for the study of igneous basement. The magnetic techniques in mineral exploration are used for both of the magnetic minerals and non-magnetic minerals exploration associated with magnetic ones.
Magnetic and gravity surveys are usually based on potential field methods. In potential field data processing the edge enhancement is an important issue. Edge enhancement of potential field data has been widely used as a tool in mineral exploration prospects. Vertical derivatives of potential field data are in current approach to enhance observed probable anomalies. A well-known method of enhancing boundaries of underground structures corresponds to the zero contour of the second vertical derivative of gravity or reduced-to-the-pole of magnetic fields. However, as is well known, the estimated boundaries acquired by such technique are systematically shifted from the true position even for vertical-sided sources, and application of this method produces fairly complicated results in multi-source cases (Fedi and Florio, 2001). Cordell and Grauch (1985) also showed that the maximum of horizontal derivative is applied to the gravity or pseudo gravity anomalies localized above abrupt changes of density or magnetization.
Potential field data often contains anomalies with a wide range of amplitude, and while the weak anomalies may be considered as useful geological phenomenas, they can be difficult to recognize among the strong anomalies in the total horizontal derivative (THD) method (Ma, 2013). The other complexity in potential field data is the effect of adjacent anomalies. The THD method is not successful to enhance the boundary of these models. Analytic signal (Nabighian, 1972, 1974) is another method for processing and interpretation of magnetic field data. Analytical signal is combination of vertical and horizontal derivatives of magnetic field that can also be used to determine the location of the masses. The high values in this map indicate the location of the masses.
Recently, numerous edge-detection filters have been used which are based on the horizontal and vertical derivatives of potential field data and they display a balanced result. Miller and Singh (1994) proposed using the tilt angle to enhance the edges of the sources. Tilt angle is an effective method in balancing the amplitude of strong and weak anomalies, but it is not exactly an edge detection filter.
Wijns et al. (2005) introduced the theta map as an edge detection method that uses the amplitude of analytic signal relative to the total horizontal derivative. The maximum of the theta map are located over the edges of causative sources. The theta map displays the edges of the shallow and deep bodies simultaneously, but the edges of the sources are diffused.
In order to increase the resolution of theta map filter, Ma (2013) proposed second order of the theta map (STM). He also suggested a high resolution filter to enhance the edges of potential field data (improved local phase (ILP)), which consists of first order and second order horizontal derivatives.
In this paper we use and compare phase based methods (such as tilt angle and theta map) and improved local phase filters in magnetic data interpretation. To evaluate the capability of the methods, magnetic anomalies caused by synthetic bodies are examined. After acquiring satisfactory results, these techniques are applied on real data. Ultimately, magnetic anomaly of iron ore body belonged to Tighe Now Ab iron deposit located in the north-east of Iran is used. As a consequence, drilling borehole results are incorporated to validate the outcomes.
برجستهسازی مرز یکی از مهمترین مراحل و اهداف در تفسیر دادههای مغناطیسی است. دو مورد از پیچیدگیهای دادههای مغناطیسی، ادغام اثر بیهنجاریهای مجاور و قرار گرفتن دو توده با عمقها یا خواص مغناطیسی متفاوت که ایجاد یک بیهنجاری ضعیف و یک بیهنجاری قوی در کنار یکدیگر میکنند، است. بسیاری از روشهایی که برای برآورد و برجستهسازی مرز از آنها استفاده میشود در موارد پیشگفته با مشکل مواجه هستند و نمیتوانند بهخوبی مرز تودهها را برجسته کنند (ازجمله مشتق افقی، سیگنال تحلیلی و مانند آن). برای برجستهسازی همزمان مرز بیهنجاریهای ضعیف و قوی، در سالهای اخیر از فیلترهای کسری که حاصل از نسبت بین مشتقهای افقی و قائم هستند، استفاده شده است. در این مقاله این روشها که با عنوان روشهای فازی شناخته میشوند (مانند زاویه تیلت، تتا و سایر موارد) مورد بررسی قرار گرفته است و با اِعمال روی دادههای مصنوعی محدودیتهای آنها بررسی میشود. علاوه بر آن فیلترهای فاز محلی تعمیمیافته که نتایج بهتری نسبت به روشهای فازی دارند معرفی شدهاند. فیلترهای فاز محلی تعمیمیافته عملکرد قابلقبولی در تفکیک و برآورد مرز تودههای مجاور هم دارند. در نهایت این روشها روی دادههای مغناطیسی کانسار تیغه نوآب اِعمال و از گمانههای اکتشافی حفاری شده در منطقه برای اعتبارسنجی نتایج استفاده شده است.موسسه ژئوفیزیک دانشگاه تهرانفیزیک زمین و فضا2538-371X39320131023The improvement of reduced-dynamic orbit of LEO satellites using best-fitting reference orbitبهبود مدار دینامیکی تبدیل یافته ماهوارههای ارتفاع کم به کمک مدار مبنای بهینه2212323560910.22059/jesphys.2013.35609FAمحمدرضاسیفدانشجوی دکتری ژئودزی، گروه مهندسی نقشه¬برداری، پردیس دانشکده¬های فنی، دانشگاه تهران، ایرانمحمدعلیشریفیاستادیار، گروه مهندسی نقشه¬برداری، پردیس دانشکده¬های فنی، دانشگاه تهران، ایران0000-0003-0745-4147مسعودعباس هادیدانشآموخته کارشناسی ارشد ژئودزی، گروه مهندسی نقشه¬برداری، پردیس دانشکده¬های فنی، دانشگاه تهران، ایرانJournal Article20110907Satellite orbit determination is a method of determining the state vector, i.e., position and velocity, of a Low Earth Orbiting (LEO) satellite or interplanetary spacecraft. During the past two decades, many satellites with various applications including geodetic applications have been launched at low altitudes. For instance, TOPEX / POSEIDON, CHAMP, GRACE and GOCE are the examples of the geodetic LEO satellites. They are dominantly affected by the disturbances forces, i.e., the Earth’s gravity field anomalies and the atmospheric drag. Therefore, the LEO satellites orbit determination has special complexity and challenges which needs particular consideration.
In many researches, three techniques namely dynamic, kinematic and reduced dynamics approaches are implemented for LEO satellite orbit determination. In the dynamic approach, the satellite’s motion is modeled by the equation of motion which is expressed in the Earth Centered Inertial (ECI) frame. In this method, all forces acting on a satellite are computed using the dynamical model and numerically integrated to propagate the state vector to the subsequent epochs from an initial state vector. The dynamic model describing the satellite motion with time is constructed using the forces acting on the satellite. The gravitational forces such as the Earth and the Sun and Moon and any other third body gravitational attraction and their indirect effect and non-gravitational forces such as atmospheric drag and solar radiation pressure have been modeled for orbit determination procedure.
Kinematic orbit determination is a purely geometrical approach based on the observations that requires neither dynamic force models nor the physical information. The kinematic orbit is derived from observations. In the classical implementation of this approach, the orbital elements are derived from angular observations, e.g., azimuth and elevation of satellite.
Nowadays, Global Navigation Satellite Systems (GNSS) especially Global Positioning System (GPS) could represent independent continuous kinematic orbit. The kinematic orbit derived from GPS observations is a dense and accurate orbit. It provides necessary information for many applications in satellite geodesy. However, the accuracy of kinematic orbit is limited to noise, systematic and gross errors of observations.
The mismodeling of dynamic orbit and GPS measurement errors of kinematic orbit are both reduced when dynamic and geometrical information is combined in the reduced-dynamic orbit. The reduced dynamic orbit is generated by incorporating dynamic models as the dynamic model of the dynamic system of the orbital motion with the kinematic orbit in dynamic filtering process. Using the dynamic model, the effects of observation errors, noise, systematic and gross errors, will be reduced.
Kalman filtering is the most widely used method in satellite reduced-dynamic orbit determination process. It is useable for linear dynamic system with linear observation equations. However, the Extended Kalman Filter (EKF) or the linearized form the system equations should be used. In the case of linear form application, the initial value of unknowns is required.
The problem of orbit determination is one the highly nonlinear problem in engineering applications. For the implementation of the standard form of the Kalman filter for orbit determination, the initial orbit has to be computed. Different orbit determination methods are introduced for this purpose. In this article the idea of reference orbit determination based on the numerical integration is introduced.
The reference orbit is an initial approximation of the observed satellite orbit that can be used for linearizing purposes. The reference orbit is determined using numerical integration methods. It deviates from the real orbit because of using erroneous initial values and difference in the Earth’s real and reference gravitational field. Consequently, the reference positions of satellites, derived from the reference orbit, are different from the actual positions. The differences in positions are called the location errors. In order to minimize the location errors, the reference orbit should be computed as close as possible to the real orbit.
In this paper, the least squares approach is proposed for selecting the initial conditions in a way that the total misfit of the reference orbit and to the observed orbit is minimized. When integrating a reference orbit in a time interval, the location error is zero at the initial time and it increases linearly to a maximum at the end of time interval or the so-called the v-shaped pattern of the error. It may be better to uniformly distribute the differences over the interval. In other words, the v-shaped pattern of the differences is changed in such a way that the deviation of two orbits remains constant. This orbit is called the best-fitting reference orbit.
The more accurate reference orbit the less linearization error occurs. By using the best-fitting reference orbit instead of initial one in Kalman filter algorithm, 3D RMS of reduced-dynamic orbit is reduced to 1 meter over a full day. روش فیلتر کالمن یکی از الگوریتمهای متداول و پُرکاربرد در تعیین مدار ماهوارهها است. این روش یک برآوردگر خطی است و بهمنظور بهکارگیری آن برای مدلهای دینامیکی و مشاهدات غیرخطی، باید از مدلها خطیشده آنها استفاده کرد. در حل همة مسئلههای غیرخطی به روش خطیسازی ( روشهای گرادیان-مبنا ) به مقدار اولیه مجهولها نیاز است که این مقدار اولیه در مسئله تعیین مدار، همان مدار مبنا است. هرچه مقادیر اولیه (مدار مبنا) به جواب نهایی نزدیکتر باشد، خطای خطیسازی در فرایند تعیین مدار کاهش مییابد. هدف اصلی این تحقیق بهبود مقادیر اولیه موردنیاز برای خطیسازی مدلهای دینامیکی و مشاهداتی روش فیلتر کالمن و رسیدن به یک مدار مبنای بهینه است که کمترین اختلاف را با مدار مشاهده شده داشته باشد. این مدار به کمک الگوریتم بهینهسازی کمترین مربعات تعیین شد. استفاده از مدار مبنای بهینه در تعیین مدار، منجر به بهبود مجذور متوسط مربعات سهبُعدی (دستگاه مختصات دکارتی) جواب نهایی تعیین مدار دینامیکی تبدیل یافته تا حد یک متر میشود.