@article { author = {Mirzaei Hajibaghloo, Sude and Alimohammadian, Habib and Oveisy Moakhar, Mohsen}, title = {Investigation of replacement and flow direction of granitic body at Golpaygan region using anisotropy of magnetic susceptibility (AMS)}, journal = {Journal of the Earth and Space Physics}, volume = {45}, number = {1}, pages = {1-15}, year = {2019}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2019.249507.1006964}, abstract = {The Golpaygan massive granite in the northern part of Golpaygan city is a part of Sanandaj – Sirjan zone. This granitic body has been intruded in surrounding metamorphosed schists of Paleozoic age. The Paleocene age (58 Ma) with K/Ar method has been assigned for this granite. Basalts, Porphyritic tuffs and Cataclastics volcanic rocks are the main rocks of this formation. The major minerals of the granite are Quartz, acidic to intermediate plagioclase (oligoclase, andesite) and orthoclases which occasionally show pertitic texture. The micaceous minerals include biotite, muscovite and sericite. In order to study AMS of Golpayegan granite, 171 cores with 10 cm length and 2.5 cm diameter were collected with drilling portable machine. The dip and azimuth of the cores were measured with magnetic compass. Each core was cut to 22 mm  length in the paleomagnetic laboratory of geological survey of Iran. Bulk samples were also collected in order to examine rocks petrogically and mineralogically. The polished thin sections show the following metallic minerals: Rutile and Anatase, Oxides and oxyhydroxides, Hematite, Pyrite and Ilmenite. Anisotropy of magnetic susceptibility (AMS) is defined as a second order tensor. Due to symmetry of nondiagonal components, only diagonal ones K33, K22, K11 remain which are named as Kmax, Kmin and Kint. Lineation intensity values show alignment of magnetic dipole moments of the specimens. This parameter is maximum for sites 8, 12 and 17. The dip and direction of lineation parameter of the above sites are 261.5/44, 38.2/79 and 22/17 respectively. The dip value of site 12 , i.e. 79, may indicate place of the source of Golpayegan granite. The direction of lineation in sites 17 and 8 are opposite to each other which may indicate the existence of a fault in this area. The map of foliation parameter shows that in the central part of the study area, the dip of foliation has much more value than the surrounding area. The shape factor values are negative in the north east and center of the granite body which indicate prolate shape of magnetic susceptibility ellipsoid while in the other parts it is positive which means it is oblate. The AMS results also reveal that the study area can be divided in to two parts which have separate convergence directions. The diffusion directions may indicate mushroom type of the granite intrusion at two phases. The main mushroom type granitic body has intruded at the first phase and then in the second phase, another granitic body with the same pattern is injected into the main body. The AMS directions of the granite show northwest- southeast and northeast- southwest trends while at the center, they show on east-west trend. On the basis of the interpretation of total granitic body directions, we propose the existing of a probable fault with north-south trend at the center of the granite. The intensity of anisotropy of magnetic susceptibility at the western side of this fault is high in comparison to that of the eastern side. The occurrence of this fault can also be proved by petrological investigation and other studies. The susceptibility-temperature analysis of the granite rocks shows that magnetite and hematite are the main magnetic carriers which may indicate I or A type origin of this massive granite.}, keywords = {AMS,Granite,Lineation,Fault}, title_fa = {بررسی جای‌گیری و جهت حرکت توده گرانیت گلپایگان با استفاده از روش ناهمسانگردی پذیرفتاری مغناطیسی}, abstract_fa = {توده گرانیت گلپایگان واقع در بخش شمالی شهرگلپایگان متعلق به زون ساختاری سنندج-سیرجان دارای سن مطلق پالئوسن‌ بوده که داخل شیست‌های دگرگون شده منسوب به دوره پالئو‌زوئیک نفوذ کرده است.این توده شامل توده‌های بازالتی، توف‌های پورفیری و سنگ‌های ولکانیکی کاتاکلاستیکی است. در این مقاله نحوه شارش و جای‌گیری توده گلپایگان به‌روش ناهمسانگردی پذیرفتاری مغناطیسی مورد مطالعه قرار گرفته است. بر اساس جهت‌های به‌خط‌شدگی، منطقه به دو قسمت، قابل‌تقسیم می‌باشد که تداعی‌کننده جای‌گیری قارچی شکل توده در دو مرحله می‌باشد. در مرحله اول، توده اصلی به‌صورت قارچی‌شکل به‌سمت بالا صعود کرده و احتمالاً به‌درون آن در مرحله بعدی توده قارچی‌شکل دیگری تزریق شده است. جهت‌های حاشیه‌ای این توده نشان دهنده روند‌های شمال غرب-جنوب شرق و شمال شرق-جنوب غرب بوده و در قسمت مرکزی جهت‌ها دارای روند شرقی-غربی می‌باشند. بنابراین بر اساس تفسیر کل جهت‌های ناهمسانگردی در پذیرفتاری مغناطیسی توده فوق، وجود گسلی با روند تقریبی شمالی- جنوبی در قسمت مرکزی محتمل می‌باشد. نتایج و تفسیر مطالعات سنگ‌شناسی، تأیید دیگری بر وجود گسلی با روند تقریبی شمالی-جنوبی در مرکز توده گلپایگان است. وجود گسل‌ها و نفوذ توده آذرین در تشکیلات قدیمی‌تر در محل مطالعه توسط محققین دیگر هم گزارش شده است. این مطالعه نشان می‌دهد که شدت ناهمسانگردی مغناطیسی در بخش غربی گسل از شدت بیشتری نسبت به شرق آن برخوردار است. دمای ‌کوری نمونه‌ها نشان می‌دهد که مگنتیت و هماتیت کانی‌های اصلی حاملین مغناطیسی توده گلپایگان می‌باشند.}, keywords_fa = {AMS,Granite,Lineation,Fault}, url = {https://jesphys.ut.ac.ir/article_69140.html}, eprint = {https://jesphys.ut.ac.ir/article_69140_acecf0c51eb21a4093cd83dc86404b15.pdf} } @article { author = {Sharifi, Javad and Hafezi Moqaddas, Naser and Lashkaripour, Gholam Reza and Javaherian, Abdolrahim and Mirzakhanian, Marzieh}, title = {Fluid replacement modeling in Ilam Formation in one of the southwest Iranian oil reservoirs}, journal = {Journal of the Earth and Space Physics}, volume = {45}, number = {1}, pages = {17-30}, year = {2019}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2019.259047.1007012}, abstract = {Seismic technologies have been recently evolved into a central position in reservoir characterization and monitoring with the recent improvements and its cost efficiency. In this regards rock physics play an essential role by connecting seismic data to the presence of in-situ hydrocarbons. Modeling the effects of pore fluids on rock velocity and density is an essential part which normally is used to detect the influence of pore fluids on seismic signature. In recent years, one of the most important developments in rock physics has been the fast progress toward quantifying the relations between geologic processes and geophysical signatures. This quantification is normally done through application of different types of rock physics models: theoretical, empirical and hybrid models. However, fluid substitution methods make it possible to predict the elastic response of a rock saturated with one type of fluid from the elastic response of the same rock saturated with another fluid. This infers that seismic wave velocity could be predicted in geological formations for any possible hydrocarbon signature based on the measured velocities in the counterpart water-saturated formations. Therefore, fluid substitution is an important part of any seismic rock physics analysis (e.g., amplitude versus offset and time lapse studies), and can provides an efficient tool for fluid identification and quantification in a given reservoir. Fluid substitution commonly performed by using Gassmann’s equation which has already being discussed frequently. In general, Gassmann applicability is questionable in carbonates as it can under-predict, over- predict or even correctly predict seismic velocity changes by changing pore fluids. This is normally attributed to the violation of some of the Gassmann assumptions like their pore space connectivity in carbonates. The goal of this study is to perform fluid substitution and seismic modelling of one of the Iranian carbonate oil field to investigate validity of Xu and Payne (2009) for the carbonate field. This model generally emphasizes the behavior of rocks related to different pore types. Fluid substitution results are then compared and verified with the laboratory measurements of core sample taken from the same reservoir intervals. The final output of fluid substitution is saturated bulk modulus, shear modulus and density for either of the defined saturation scenarios. Our results show that Xu and Payne (2009) can be used on the studied reservoir. Also, the obtained results were confirmed using other source of information like ultrasonic measurements. Furthermore, this model was used to model frame bulk modulus as an input into the fluid substitution purposes. The results of the fluid substitution confirm the applicability of the introduced approach to discriminate different fluid responses in this field.}, keywords = {Fluid detection,Carbonate reservoir,Rock Physics model,Fluid Replacement Modeling}, title_fa = {مدل‌سازی جانشینی سیال در سازند ایلام یکی از مخازن هیدروکربنی جنوب غرب ایران}, abstract_fa = {با توجه به اینکه اکثر مخازن هیدروکربنی ایران در کربنات‌ها واقع شده است، مطالعه جانشینی سیال و انتخاب یک مدل فیزیک سنگی مناسب جهت این سنگ‌هاضروری به نظر می‌رسد. در این مطالعه، به‌منظور مدل‌سازی جانشینی سیال جهت تشخیص نوع هیدروکربن، یک مخزن کربناته از میادین نفتی جنوب ایران (سازند ایلام) انتخاب و مورد ارزیابی قرار گرفته است. در ادامه پس از بررسی‌های میدانی، اطلاعات زمین‌شناسی و پتروفیزیکی لازم گردآوری شده و جهت مدل کردن پاسخ کشسان مخزن به‌کار رفته است. در این راستا، ابتدا سنگ متخلخل با استفاده از روابط فیزیک سنگی کربناته مدل‌ شده و در مراحل بعد با استفاده از جانشینی سیال، سیال‌های مختلف در مخزن تزریق و پاسخ موج تراکمی و برشی آن به‌دست آمده است. نتایج مدل‌سازی نشان داد که مخزن مورد مطالعه در صورت تغییر سیال دارای حساسیت مناسبی برای نشان دادن تغییرات پارامترهای کشسانی می‌باشد. همچنین نتایج تحقیق نشان داد که مخزن کربناته مورد مطالعه اگر اشباع از گاز، نفت و یا آب باشد به نحوه قابل‌ملاحظه با در نظر گرفتن یک مدل فیزیک سنگی مناسب از هم تفکیک می‌شود. به‌علاوه در این تحقیق یک الگوی مناسب جهت جدا‌سازی سیالات مختلف برای مطالعات ژئوفیزیک مخزن ارائه شده است.}, keywords_fa = {Fluid detection,Carbonate reservoir,Rock Physics model,Fluid Replacement Modeling}, url = {https://jesphys.ut.ac.ir/article_69147.html}, eprint = {https://jesphys.ut.ac.ir/article_69147_8a685e4743c6eeefb7c941e66bb2e7f2.pdf} } @article { author = {Abdollahi, Mohadeseh and Arab Amiri, Ali Reza and Kamkar Rouhani, Abolghasim and Nejati Kalateh, Ali and Akhavan Aghdam, Mohammad Reza}, title = {Determination and depth estimation of lineaments in Northwest of Iranshahr city using airborne magnetic and electromagnetic data}, journal = {Journal of the Earth and Space Physics}, volume = {45}, number = {1}, pages = {31-46}, year = {2019}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2018.259304.1007013}, abstract = {Airborne magnetic and electromagnetic methods are among the most efficient geophysical techniques for the detection of buried anomalies. There are several methods that can be used to estimate the depths of the buried anomalies. In general, modeling methods can be used not only to estimate the depths of the buried anomalies, but also, to determine physical and other geometric factors of the anomalies such as lateral extension, thickness, dip and so on. In this research, magnetic lineaments have been determined using the airborne magnetic data, acquired in a part of Bazman area with an area of 24 square kilometers located in about 125 kilometers northwest of the city of Iranshahr. By applying filters such as reduction to the pole, first horizontal derivatives, analytical signal, tilt angle and upward continuation filters. For processing and interpretation of the airborne magnetic data, the Oasis Montaj module of Geosoft software package has been used. The processing, display and interpretation of the airborne electromagnetic data have been made Conductivity Depth Imaging (CDI) using EM Flow and Profile Analyst software packages of Encom Company. Furthermore, the depths of the lineaments in this area have been estimated using Euler deconvolution method. Then, the obtained results have been compared with the results of airborne electromagnetic investigations for the frequencies of 900, 7200 and 56000 Hz using horizontal and vertical coplanar coils. Also, the obtained findings from the airborne magnetic and electromagnetic methods have been validated by the geological information of the area. The airborne magnetic and electromagnetic data of the area have been acquired using airborne magnetometer and DIGHEM5 electromagnetic instruments, respectively. The airborne magnetic and electromagnetic surveys over the study area have been made by Geological Survey of Iran (GSI) in 2005. As a result of this study, 22 magnetic lineaments in the area have been identified in which 4 lineaments coincide on the main faults of the area as the validation results indicate. In this regard, the main faults can be observed on the obtained magnetic maps in which different filters have been applied, however, the tilt angle magnetic map indicates the main faults of the area more clearly. This implies the better performance of the tilt angle filter over the other filters in displaying magnetic lineaments. Totally, 22 magnetic lineaments have been determined on the magnetic maps. By the results of this study, we can conclude that the main faults of the area have an approximate trend of northeast-southwest. Some of these faults, which have been determined from the airborne magnetic investigations of the area, cannot be determined from geological studies of the area as they have been overlain by the Quaternary sediments. The different performances of these main faults on the lithological variations and tectonic activities of the area have been clearly evident by the result of this study. The main faults of the area have also played a vital role on the formation of folds and fractures, and occurrence of weak earthquakes. The approximate depths of the lineaments, which have been estimated by applying the Euler deconvolution method on the acquired magnetic data are around 100-200 meters.}, keywords = {Euler deconvolution,Airborne magnetic,Airborne electromagnetic,Reduction to the pole,First horizontal derivatives,Analytic signal}, title_fa = {تشخیص و تخمین عمق خطواره‌ها در شمال‌غرب شهرستان ایرانشهر با استفاده از داده‌های مغناطیس و الکترومغناطیس هوابرد}, abstract_fa = {روش‌های مختلفی جهت شناسایی و همچنین تخمین عمق بی‌هنجاری‌های مدفون در روش مغناطیس و الکترومغناطیس هوابرد وجود دارد. در پژوهش حاضر، با استفاده از داده‌های مغناطیس هوابرد برداشت شده در منطقه‌ای حوالی 125 کیلومتری شمال‌غرب شهرستان ایرانشهر، به تشخیص خطواره‌های مغناطیسی با اعمال فیلترهایی نظیر برگردان به قطب، مشتق افقی مرتبه اول، فیلتر زاویه تیلت و سیگنال تحلیلی بر روی این داده‌ها پرداخته شد. همچنین با استفاده از روش واهمامیخت اویلر، تخمین عمق این خطواره‌ها در این منطقه انجام شده است. سپس نتایج به‌دست آمده از روش مغناطیس هوابرد با نتایج حاصل از مطالعات الکترومغناطیس هوابرد مربوط به فرکانس‌های 900، 7200 و 56000 هرتز، مقایسه و همچنین یافته‌های حاصل از این دو روش با اطلاعات زمین‌شناسی منطقه، اعتبار‌سنجی شده است. مطالعات انجام شده منجر به شناسایی حدود 2۲ خطواره مغناطیسی در منطقه شد که براساس نتایج اعتبار‌سنجی، 4 خطواره منطبق بر گسل‌های اصلی منطقه می‌باشند. این گسل‌ها دارای روند تقریبی شمال‌شرق-جنوب‌غرب هستند. میانگین عمق تقریبی گسل‌های تشخیص داده شده به‌وسیله اعمال روش واهمامیخت اویلر بر روی داده‌های مغناطیس‌سنجی در حدود 200-100 متر تخمین زده شده است.}, keywords_fa = {Euler deconvolution,Airborne magnetic,Airborne electromagnetic,Reduction to the pole,First horizontal derivatives,Analytic signal}, url = {https://jesphys.ut.ac.ir/article_67775.html}, eprint = {https://jesphys.ut.ac.ir/article_67775_74c2cff7824b35827365a1a0f53204f1.pdf} } @article { author = {Soodmand niri, Soosan and Ebrahimzadeh Ardestani, Vahid and Vatankhah, Saeed}, title = {Using graph theory in 3D inversion of gravity data to delineate the skeleton of homogeneous subsurface sources}, journal = {Journal of the Earth and Space Physics}, volume = {45}, number = {1}, pages = {47-62}, year = {2019}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2019.260544.1007018}, abstract = {In this paper, three-dimensional (3D) inversion of gravity data using graph theory is used. The methodology was initially introduced by Bijani et al. (2015) and, here, we provide more details for the steps and required parameters of the algorithm. An ensemble of simple point masses are used to model a homogenous subsurface body. Then, in the presented inversion methodology, the model parameters are the Cartesian coordinates of point masses and their total mass. Consequently, the algorithm is able to reconstruct the skeleton of the subsurface body and to yield its total mass. Here, the set of point masses is associated to the vertices of a weighted full graph in which the weights are computed by the Euclidean distances separating vertices in pairs. Then, the Kruskal’s algorithm can be used to solve the Minimum Spanning Tree (MST) problem for the graph. A stabilizer, called equidistance function, is obtained using the MST, which computes the statistical variance of the distances among point masses. The function restricts the spatial distribution of points, and suggests a homogeneous distribution for the point masses in the subsurface. Here, a non-linear global objective function for the model parameters comprising data misfit term and equidistance function with balancing provided by a regularization parameter that should be minimized. A genetic algorithm (GA) is used for the minimization of the objective function. GA consists of a random search algorithm based on the mechanism of natural selection and natural genetics. Then, to solve the optimization problem in our algorithm, there is no need to calculate the derivatives of the objective function with respect to model parameters, or any matrix operation. Simulations for two synthetic examples, including a vertical and a dipping dike, demonstrate the efficiency and effectiveness of the implementation of the present algorithm. The skeleton and total mass of the bodies are estimated very accurately. We also show that although the search limits for the model parameters must be used, they are not very limitative. Even with less realistic bounds, acceptable approximations of the body are still obtained. Unlike Bijani et al. (2015) which used the L-curve method for estimating the regularization parameter, here, we present a new strategy to approximate the parameter. We demonstrate that if: 1. the equidistance function converges almost monotonically to zero with increasing numbers of generation; 2. minimum of the objective function at the final iteration becomes small; and 3. the predicted data by the reconstructed model is approximately close to observed data, then, the selected regularization parameter is nearly optimum and the results are reliable. This provides a suitable and inexpensive methodology for estimating the regularization parameter. The method is tested on gravity data from the Mobrun ore body, north east of Noranda, Quebec, Canada. The anomaly is associated with a massive body of base metal sulfide, mainly pyrite, which has displaced volcanic rocks of middle Precambrian age (Grant and West, 1965). With application of the algorithm, a skeleton of the body is obtained which extends about 350 m in the east direction, and shows a maximum extension of 200 m in depth.}, keywords = {Gravimetry,inversion,Graph,Minimum Spanning tree,Genetic Algorithm,Mobrun}, title_fa = {استفاده از تئوری گراف در وارون‏سازی سه‏بُعدی داده‏های گرانی‏سنجی برای تعیین پیکربندی توده‏های زیرسطحی همگن}, abstract_fa = {در این مقاله وارون‎‏سازی سه‏ بعدی داده‏های گرانی‏ سنجی براساس تئوری گراف مورد استفاده قرار گرفته است. توده همگن زیر‏سطحی با استفاده از مجموعه‏ای از جرم‏های نقطه‏ای یکسان مدل می‏شود. با تطبیق این مجموعه جرم‏های نقطه‏ای با یک گراف کامل و با استفاده از الگوریتم کروسکال، درخت فراگیر کمینه (minimum spanning tree) برای این گراف محاسبه شده و سپس یک تابع پایدار‏کننده تحت عنوان تابع هم‏فاصله به‌دست می‏آید. این تابع علاوه بر پایدارکردن مسأله وارون، سبب می‏شود که در مدل حاصل فواصل میان جرم‏های نقطه‏ای تقریباً یکسان باشد. بنابراین توزیع فضایی مناسب برای جرم‏های نقطه‏ای، الگوریتم را به‌سمت حصول پیکربندی نزدیک به شکل توده اصلی سوق می‏دهد. تابع هدف کلی در این مسأله، ترکیب یافته از تابع هم‏فاصله و عدم انطباق داده، غیرخطی است و کمینه‏سازی آن با استفاده از الگوریتم ژنتیک انجام می‏شود. دو نمونه مدل مصنوعی متفاوت برای بررسی الگوریتم ارائه‏شده مورد استفاده قرار گرفته است. خروجی الگوریتم برای هر دو مدل، پیکربندی صحیح را نشان می‏دهد. برای تخمین و صحت‏سنجی پارامتر منظم‏سازی در این الگوریتم، راه‏کاری مؤثر توسط نویسندگان ارائه شده است. این شیوه وابسته به روند همگرایی تابع هم‏فاصله و برازش داده حاصل از مدل با داده مشاهده‏ای است. کاربر با اجرای الگوریتم برای تعداد کمی پارامتر مختلف و بررسی این شرایط به‌سمت انتخاب پارامتر بهینه هدایت می‏شود. در پایان، داده گرانی توده سولفیدی موبرون در کانادا به‌عنوان یک نمونه داده واقعی مورد استفاده قرار گرفته است. گسترش این توده در راستای شرق 350 متر و در عمق حداکثر 200 متر برآورد می‏شود.}, keywords_fa = {Gravimetry,inversion,Graph,Minimum Spanning tree,Genetic Algorithm,Mobrun}, url = {https://jesphys.ut.ac.ir/article_69149.html}, eprint = {https://jesphys.ut.ac.ir/article_69149_375ef799cf90f66cd7fda76e7b7d7e45.pdf} } @article { author = {Irani Mehr, Mohammad and Riahi, Mohammad Ali and Goudarzi, Ali Reza}, title = {The effects of oscillatory behavior of the mother wavelet in the discrete wavelet transform in order to suppress seismic random noise}, journal = {Journal of the Earth and Space Physics}, volume = {45}, number = {1}, pages = {63-79}, year = {2019}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2019.263998.1007031}, abstract = {  Seismic data have a variable characteristic. Overlooking this important characteristic will reduce the effectiveness of any signal processing tool. Wavelet transform is a useful tool in seismic data processing and in recent years it has been the subject of attention of geophysicists. In this study we investigate the role of the resolution of the wavelet transform and the Q-factor (Q-factor in band-pass filters is the ratio of central frequency to the bandwidth) of the mother-wavelet on the filter performance with the goal of reducing the random noise and examining the effects of the mother wavelet Q-factor and its oscillatory behavior on the filter performance. We use Rational-Dilation Wavelet Transform (RADWT) and Dual-tree RADWT. These methods have the capability to achieve variable frequency resolution that can also provide a variety of Q-factors. To evaluate the effect of Q-factor of mother wavelet on filter function, the DT-RADWT with different Q-factors is applied on a Ricker Wavelet and synthetic shot gathers and the results are discussed in the manuscript. In the following, we investigate the relationship between seismic signal Q-factor and suitable Q-factor for seismic data processing. The method is applied to high-frequency shallow Sub-Bottom Profiler data and land data. In this study, a new wavelet transform called Rational Dilation Wavelet Transform (RADWT) and its Dual Tree analytical version DT-RADWT is used to attenuate random noise in seismic data. These transforms can achieve a limited range of Q-factor by selecting appropriate parameters p, q and s. The advantage of this transform over the common discrete wavelet transforms is that its rational sampling which provides higher time-frequency resolution. We also investigate the effect of Q-factor of mother wavelet on the performance of wavelet transform filters, and the relation between seismic signal Q-factor and Wavelet transform filter Q-factor. Increasing the Q-factor can reduce the bandwidth of wavelet in each scale. We test the effect of random noise on Q-factor of Ricker wavelet, with different noise levels. The results showed that by changing the level of random noise, the range of Q-factor remains constant. Next, we added the constant noise to Ricker wavelet, and we analyzed the noise-infected wavelet by RADWT and DT-RADWT with different Q-factors, here the soft threshold was used. The result of denoising is presented in Table 2. In last part of manuscript high Q-factor Dual Tree Rational wavelet transform was used to attenuate random noise from synthetic shot gather and marine and land seismic data (figures 9 & 11& 14& 15). Suitable parameters for random noise attenuation, p, q, and s was selected respectively 7, 8, 1 that made WT Q-factor 7.48. This research investigated the role of Q-factor value in suppressing random noise from reflection seismic data. Many Q-factors were tested to evaluate the effect of wavelet transform Q-factor on random noise denoising, and it was observed that with an increase in the Q-factor of the wavelet transform, the signal-to-ratio of filtered trace was improved. The data Q-factor was also calculated, but there was no significant correlation between the appropriate Q-factor of WT for noise reduction and the signal Q-factor. DT-RADWT was better than RADWT in distinguish was the random noise from the signal, due to the use of two parallel filter banks. DT-RADWT with high Q-factor was applied to synthetic data with a variable level of random noise and results are summarized in table4. In addition, the method was also applied to real shallow marine data from sub-bottom profiler with a wide frequency content. Results confirm the effectiveness of WT filter which is increased with the increase of wavelet transform Q-factor.}, keywords = {Random Noise,Discrete Wavelet Transform,Time-Frequency Domain,Wavelet Q-factor,Offshore Data,Rational Dilation,Dual-Tree Wavelet Transform}, title_fa = {اثر رفتار نوسانی موجک مادر در تبدیل موجک گسسته به‌منظور تضعیف نوفه لرزه‌ای تصادفی}, abstract_fa = {ابزارهای پردازش داده لرزه‌ای ویژگی‌های متنوعی دارند و چشم‌پوشی از این ویژگی‌ها اثرگذاری ابزارهای پردازش سیگنال را کاهش می‌دهد. در این تحقیق نقش تفکیک‌پذیری در تبدیل موجک و نسبت فرکانس مرکزی به پهنای باند موجک (WQ-factor) موجک مادر بر عملکرد تضعیف نوفه اتفاقی بررسی خواهد شد. در این تحقیق از نسخه دوشاخه تحلیلی تبدیل موجک اتساع گویا (DT-RADWT) به‌منظور بررسی نقش نسبت فرکانس مرکزی به پهنای باند موجک (WQ-factor) در تبدیل موجک استفاده شده است. این تبدیل‌ها می‌تواند بازه متنوعی از WQ-factor ها را فراهم کنند. برای بررسی تأثیر WQ-factor موجک مادر بر روی عملکرد تبدیل موجک DT-RADWT با WQ-factor های مختلف بر روی داده مصنوعی اعمال می‌شود، در ادامه تحقیق ارتباط بین نسبت فرکانس مرکزی به پهنای باند موجک داده و نسبت فرکانس مرکزی به پهنای باند موجک مناسب برای پردازش داده‌های لرزه‌ای بررسی می‌شود، نتایج نشان داد که نسبت فرکانس مرکزی به پهنای باند موجک نگاشت لرزه‌ای ارتباط معناداری با نسبت فرکانس مرکزی به پهنای باند موجک مناسب برای تجزیه سیگنال ندارد و ضمناً با افزایش نسبت فرکانس مرکزی به پهنای باند موجک تبدیل موجک، پردازش سیگنال بهتر صورت می‌گیرد. در قسمت بعد، این روش بر داده‌های Sub-Bottom Profiler و همچنین داده‌های خشکی استفاده شده است. نتایج DT-RADWT نشان داد که انتخاب WQ-factor بالا در تبدیل موجک، موجب کاهش بهتر نوفه تصادفی از داده لرزه‌ای خواهد شد.}, keywords_fa = {Random Noise,Discrete Wavelet Transform,Time-Frequency Domain,Wavelet Q-factor,Offshore Data,Rational Dilation,Dual-Tree Wavelet Transform}, url = {https://jesphys.ut.ac.ir/article_69152.html}, eprint = {https://jesphys.ut.ac.ir/article_69152_6aa620baed70b9c3f08c23f5c8d78745.pdf} } @article { author = {Azizi, Fatemeh and Mirtorabi, Mohammad Taghi}, title = {Calculation of period of δ Scuti stars using generalized Lomb-Scargle periodogram technique}, journal = {Journal of the Earth and Space Physics}, volume = {45}, number = {1}, pages = {81-88}, year = {2019}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2019.249957.1006967}, abstract = {Astronomical observations are usually sparse and non-uniform, sometimes contaminated with random or systematic noises. They always packed in certain time periods (nights) separated by several hours or maybe days. Fourier analysis which regularly used to analyze periodicities in time series could not be implemented in astronomical time series because it generates fake signals in power spectrum. Lomb-Scargle periodogram is a well-known algorithm to detect periodicities in a set of non-uniformly spaced data. This method implements least-squares fitting of sine and cosine waves in form of  and search for best fitted frequencies. It is suitable for time series with zero mean. The significance of the detected periods is inferred by comparing power of the signal with a random estimation of false alarm probability (FAP). In this paper, we manipulate the generalized Lomb-Scargle periodogram (GLS) to calculate periods for a typical δ Scuti star. The GLS is an extension to the Lomb-Scargle periodogram which takes into account the measurement of errors and also is more suitable for time series with non-zero average. GLS tries to fit the equation  to the time series and find the power spectrum for frequencies. We consider a given periodogram peak, derived from GLS, significant when it exceeds the one present “false alarm probability” level (FAP), which means there is 99% confidence that it is real and could not be simulated by Gaussian noise. FAP levels are calculated by performing random permutations of the data with similar times of observations. δ Scuti variable stars lie in the lower part of the instability strip on the main sequence in Hertzprung-Rassell diagram with luminosity classes between III to V. They are belonging to the disc population and usually are not observed in globular clusters. The variability of this type of stars was discovered in 1963 and was assigned to the group of irregular variables. They are obeying a period-luminosity relation like cepheids and can be used as standard candles. Their pulsating period is less than 1 day. Many of these stars show multiple periods with amplitudes less than 0.1 mag. These stars pulsate in radial and non-radial modes and are important as their pulsations can be used as tracer of their internal structures. We implement the generalized Lomb-Scargle periodogram to detect period for high amplitude variable star BS Aqr (HD223338) which is a δ Scuti of A8 III spectral type with very short period (0.01-0.2 days) and low amplitudes (less than 0.9 mag) and almost sinusoidal light curves. Different interpretations are given in the literature about the nature of variability for this star. Its period is continuously decreasing. Most authors have agreed with the monoperiodic nature of this star. Using photometric data taken in La Silla Observatory that covered 30 September to 6 November 1983, we find that BS Aqr is an monoperiodic δ Scuti and detect a period of 0.1977 days for the star pulsation. The result is in good agreement with pervious results from this star which demonstrates the capability of the Generalized Lomb-Scargle method to study brightness variation in variable stars.}, keywords = {Variable star,Period,Periodogram technique,δ Scuti}, title_fa = {محاسبه دوره‌تناوب ستاره‌های متغیر دلتا اسکوتی با استفاده از تکنیک تناوب‌نگار لمب-اسکارگل تعمیم‌یافته}, abstract_fa = {هدف اصلی این مقاله بررسی کارایی تکنیک تناوب‌نگار لمب-اسکارگل تعمیم‌یافته برای تعیین دوره‌تناوب سیستم‌های متغیر از جمله ستاره‌های دلتا اسکوتی می‌باشد. برای این منظور از داده‌های نورسنجی رصد خانه لاسیا در شیلی برای ستاره متغیر از نوع دلتا اسکوتی با نام (HD223338) BS Aqr و نوع طیفی A8III که بازه زمانی۳۰ سپتامبر تا ۶ نوامبر ۱۹۸۳ را پوشش می‌دهد استفاده شده است. در تحقیقات قبلی، دوره‌تناوب تپش‌های این ستاره اکثرا ۱۹۷۸/۰ روز گزارش شده است. در این کار با استفاده از تکنیک لمب-اسکارگل تعمیم‌یافته، دوره‌تناوب تپش این ستاره ۱۹۷۷/۰ روز به‌دست آمده است که در توافق بسیار خوبی با نتایج به‌دست آمده از سایر روش‌ها برای تعیین دوره‌تناوب این ستاره است. در واقع نتایج مان تأیید کننده کارایی تکنیک تناوب‌نگار لمب-اسکارگل تعمیم‌یافته در تعیین دوره‌تناوب ستاره‌های متغیر دلتا اسکوتی می‌باشد.}, keywords_fa = {Variable star,Period,Periodogram technique,δ Scuti}, url = {https://jesphys.ut.ac.ir/article_69141.html}, eprint = {https://jesphys.ut.ac.ir/article_69141_df7bfa7cf4c60b1a0f0194b1b8c5a178.pdf} } @article { author = {Shafiei, Maryam and Bazrafshan, Javad and Irannejad, Parviz}, title = {Comparison of four Sensitivity Analysis Methods of HBV Conceptual Model Parameters in Karkheh Basin and its Sub-basins}, journal = {Journal of the Earth and Space Physics}, volume = {45}, number = {1}, pages = {89-105}, year = {2019}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2019.253304.1006979}, abstract = {The HBV (Hydrologiska Byråns Vattenbalansavedlning) is a conceptual model widely used for hydrological forecasting and water resource studies. In this study, sensitivity analysis of parameters of the HBV model is investigated for Karkhe basin and its sub-basins for four different periods 1, 5, 10 and 25 years with four methods including FAST (Fourier Amplitude Sensitivity Test), RSA (Regional Sensitivity Analysis), Sobol and regression. After determining the most sensitive parameters, the model is calibrated using Nondominated Sorting Genetic Algorithm (NSGA) method. In all statistical periods, one year has been used for warm-up to eliminate the effects of initial conditions. In this study, the MOUSE Toolbox is used to analyze the sensitivity of the HBV model parameters. This software is based on Java programming language. To analyze the sensitivity of the HBV model parameters based on the Monte Carlo sampling method and the Halton sequence method for each of the samples (time periods) in each sub-basin separately, 1000 samples are taken for the set of input parameters with a specified range for each parameter taken. Objective functions for evaluating performance of model are NSE, RMSE, RSR and BIAS. The results of sensitivity analysis of the parameters show that Sobol and RSA are more reliable methods because of variability in time intervals and different sub-basins. Fast and regression methods in the Karkheh basin and its sub-basins for different time periods show similar results that considering the change in hydroclimate conditions in this basin, isn't practical and the results of these methods can not be used for investigating sensitivity of parameters and their identification in the studied basin. The most sensitive parameters of HBV model for Karkheh basin and its sub-basins in soil routine is maximum soil moisture content (Fcap) and in the response routine is the storage of soil surface moisture content (hl1). These parameters have shown the most sensitive factor in minimum fluxes. The snow routine parameters, especially the threshold temperature for ice freezing (ttlim), are sensitive in the sub-basins of Ghare Sou and Kashkan in short periods (1 and 5 years). For a specific sub-basin, the sensitivity of the parameters in different time periods is not completely stable and a little variability has been observed in different periods. But the most sensitive parameters (hl1 and fcap) have maintained their sustainability almost in all periods. Parameters of response and soil routines are more sensitive to the parameters of snow and routing routines. The results of the interaction between the parameters using the Sobol method in different sub-basins indicate that the strongest interactions are between the soil routine parameters, especially Fcap, with the response routine parameters and also the response routine parameters with each other. The time variability of parameters indicates that the soil routine and response parameters in the minimum discharge show the most sensitivity. Other parameters are more sensitive in the dry season of the basin (summer and autumn). The HBV model has the ability to simulate runoff in the Karkhe basin and its sub-basins with high precision. This study shows that selection of shorter period of calibration gives better simulation results. For one year's period the best NSE, RSR and RMSE are in Gamasyab sub-basin respectively 0.95, 0.21 and 1.4 and the best BIAS is in Kashkan sub-basin and Karkhe basin with 0.13.}, keywords = {HBV conceptual model,Sensitivity analysis,calibration,Karkhe basin}, title_fa = {مقایسه چهار روش تحلیل حساسیت پارامترهای مدل مفهومی HBV در حوضه آبریز کرخه و زیرحوضه‌های آن}, abstract_fa = {مدل HBV (Hydrologiska Byråns Vattenbalansavedlning) یک مدل مفهومی است که به‌طور گسترده­ای برای پیش­بینی­های آب‌شناسی و مطالعات منابع آب به‌کار می­رود. در این مطالعه تحلیل حساسیت پارامترهای مدل HBV برای زیرحوضه‌های کرخه و کل حوضه کرخه در چهار بازه زمانی مختلف 1، 5، 10 و 25 سال با چهار روش FAST (Fourier Amplitude Sensitivity Test)، (Regional Sensitivity Analysis) RSA،Sobol  و رگرسیون بررسی شده است. پس از تعیین حساس­ترین پارامترها مدل با روش الگوریتم ژنتیک با مرتب­سازی نامغلوب، NSGA (Nondominated Sorting Genetic Algorithm) واسنجی شده است. توابع هدف برای بررسی عملکرد مدل شامل NSE، RMSE، RSR و BIAS می­باشند. نتایج تحلیل حساسیت پارامترها نشان می­دهد که روش­های Sobol و RSA به‌علت تغییرپذیری در بازه­های زمانی و زیرحوضه­های مختلفروش­های قابل اطمینان­تری هستند. حساس­ترین پارامترهای مدل HBV برای زیرحوضه­ها و حوضه کرخه در روال خاک پارامتر بیشینه ذخیره رطوبت خاک (Fcap) و در روال پاسخ پارامتر بیشینه ذخیره رطوبت لایه سطحی خاک (hl1) هستند، این پارامترها در دبی­های کمینه بیشترین حساسیت را نشان داده­اند. پارامترهای روال برف مخصوصاً پارامتر دمای آستانه برای یخ­زدگی (ttlim) در زیرحوضه­های قره­سو و کشکان و در بازه­های زمانی کوتاه­مدت (1 و 5 سال) حساسیت نشان داده­اند. مدل HBV توانایی شبیه­سازی رواناب در حوضه کرخه و زیرحوضه­های آن با دقت بالا را دارد. این مطالعه نشان می­دهد انتخاب بازه­های زمانی کوتاه­تر واسنجی، نتایج شبیه­سازی بهتری ارائه می­دهد. در بازه زمانی یک سال بهترین ضریب NSE، RSR و RMSE مربوط به زیرحوضه گاماسیاب به‌ترتیب به‌مقدار 95/0، 21/0 و 4/1 و بهترین BIAS مربوط به زیرحوضه کشکان و حوضه کرخه به‌مقدار 13/0 است.}, keywords_fa = {HBV conceptual model,Sensitivity analysis,calibration,Karkhe basin}, url = {https://jesphys.ut.ac.ir/article_69145.html}, eprint = {https://jesphys.ut.ac.ir/article_69145_7e6a3643ad7b73a6486ee948dd29db8a.pdf} } @article { author = {Mohammadi, Ali and Mohebalhojeh, Ali Reza and Mazraeh Farahani, Majid}, title = {Using cubic Hermite polynomials in constructing monotone semi-Lagrangian methods for advection equation}, journal = {Journal of the Earth and Space Physics}, volume = {45}, number = {1}, pages = {107-127}, year = {2019}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2019.253532.1006982}, abstract = {Semi-Lagrangian methods have been widely applied in general circulation models of the atmosphere as they do not suffer from a Courant–Fredericks–Levy (CFL) constraint for computational stability. Ease of application, high accuracy and speed of execution in general circulation models are other reasons for the popularity of semi-Lagrangian methods. Two fundamenta lissues in semi-Lagrangian methods are related to the trajectory computation and interpolation from the regular grid to departure points. If sufficiently accurate schemes are used to solve for trajectories with interpolations, one can expect good performance from the semi-Lagrangian scheme in solving the equations of motion of the atmosphere. Two general methods of solving the trajectory equation are the forward and backward methods. Most semi-Lagrangian methods use backward-trajectory schemes for estimating positions of the air parcels that arrive at the grid points in the future time step. Solving the trajectory equation is carried out by iteration. In the research reported, two iterations are used for trajectory computation. The fundamental difference between the forward and backward trajectory scheme rests in the calculation of advective quantity at the departure and destination points. While in the backward solution procedure, it is necessary to make interpolation from the regular grid to departure points; in the forward scheme, it is necessary to make interpolation from the irregular grid of destination points to the regular grid. The usually used interpolation methods in the semi-Lagrangian method include piecewise cubic Lagrange and Hermite, cascades, and monotone Hermite. Increasing the degree of polynomial interpolation leads to a higher degree of formal accuracy, but it leads to the generation of unwanted oscillation in regions with severe gradients of the transported quantities. Eliminating the unwanted oscillations is done through a variety of methods which generally increase the computational cost and reduce the accuracy of the scheme. To address the issue, in this research, a new selective monotone semi-Lagrangian method is developed and tested along with two standard methods based on the Lagrange and Hermite interpolations. The Lagrange polynomials have been considered by researchers for the high speed of computation in operational models. The fictitious oscillations produced at the edges of sharp gradients of the advected quantities are the main shortcoming of this method. The fictitious oscillations cannot be eliminated by increasing the degree of interpolation polynomials, which can only lead to a reduction in the wavelength of the oscillations. The results presented on increasing the degree of interpolation polynomials clearly show that the removal of the fictitious oscillations requires the use of monotone polynomials for interpolation. It is important to note that the Hermite interpolation polynomials are not inherently monotone. To make them monotone, one needs to manipulate the derivatives at the grid points appropriately. This process, however, may lead to a substantial deteriration of accuracy. For this reason, in this paper, a selective interpolation method is desined to obtain the best accuracy in solution of the advection equation, while preserving monotnonicity and removing the issue with the fictitious oscillations. In the selective method, first the interpolation is done by the non-monotonic cubic Hermite and then a properly designed slope function is calculated at each grid interval. If the slope function takes values outside the range, it indicates that a fictitious oscillation has occurred in the interpolantion. To remove the oscillation, the non-monotone interpolation is abandoned and the monotone interpolation is performed by limiting the derivative to the monotone region. This technique can minimize the error caused by the changes in the derivatives. Results are shown to demonstrate the working and superiority of the seclective montone scheme.}, keywords = {Advection,Semi-Lagrangian,Monotone,Hermite polynomial,Mass,Humidity}, title_fa = {کاربست چندجمله‌ای‌های هرمیت مکعبی در ساخت روش نیمه‌لاگرانژی یکنوا برای معادله فرارفت}, abstract_fa = {از آنجا که روش­های نیمه­لاگرانژی محدودیت پایداری به‌شرط کورانت-فردریکس-لوی (CFL) ندارند، به­صورت وسیعی در مدل­های گردش کلی به­کار برده می­شوند. در غالب صورت­های روش نیمه­لاگرانژی، برای محاسبه کمیت حل­شونده (مانند سرعت باد، رطوبت، دما و جرم) درون‌یابی در فاصله بین نقاط شبکه ای لازم است. از مشکلات مواجه در کاربرد روش نیمه­لاگرانژی تولید نوسان اضافی در مناطق با گرادیان شدید است. دو رویکرد برای حذف نوسان­های اضافی در مناطق با گرادیان شدید به­کار گرفته می­شود: الف) ترکیب یک روش با مرتبه بالا با روش پادجریان­سو، ب) استفاده از روش­های درون‌یابی یکنوا. در این پژوهش از روش درون‌یابی گزینشی با چندجمله­ای­های هرمیت مکعبی نایکنوا و یکنوا با صافی مشتق برای درون‌یابی مقادیر کمیت حل­شونده در فاصله بین نقاط شبکه­ای استفاده شده است. نتایج نشان می­دهد که حل معادله فرارفت با روش مذکور نوسان اضافی در مناطق با گرادیان شدید ایجاد نمی­کند و میزان میرایی آن نیز ناچیز است. عدم تولید مقادیر منفی با استفاده از درون‌یاب یکنوای هرمیت در حل میدان­های ذاتاً نامنفی مانند رطوبت و جرم از دیگر نتایج این پژوهش است.}, keywords_fa = {Advection,Semi-Lagrangian,Monotone,Hermite polynomial,Mass,Humidity}, url = {https://jesphys.ut.ac.ir/article_69144.html}, eprint = {https://jesphys.ut.ac.ir/article_69144_e8fbce9675ca2a1000628bdfdc804bf0.pdf} } @article { author = {Mohammadi, Chenour and Farajzadeh, Manuchehr and Ghavidel Rahimi, Yousef and Aliakbari-Bidokhti, Abbas Ali}, title = {Evaluation of estimator variables in air temperature estimation in January and June based on land cover}, journal = {Journal of the Earth and Space Physics}, volume = {45}, number = {1}, pages = {129-147}, year = {2019}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2018.253769.1006985}, abstract = {The near-surface temperature, Ts measured by ground stations provides limited information on the spatial distribution of Ta pattern. A correct estimation of Ta distribution pattern is necessary for a wide range of applications such as hydrology, ecology, meteorology (Wenbin et al., 2013) and biology of vector-borne diseases. In this study, near-surface air temperatures (Ta) using environmental parameters including land surface temperature (LST), altitude, slope, vegetation, latitude, albedo, and mean sea level pressure (MSLP), were estimated for January and July in the period 2001-2015 for Iran. In this study, due to the use of different data sources with different spatial resolutions, all maps were converted to the same spatial resolution of Era-Interim (0.125˚). Then spatial distributions of Ta and LST were determined. The spatial distribution patterns of these two components were also determined by applying the Moran spatial autocorrelation index. Finally, according to the land cover, multivariate regression models are presented for estimating Ta based on seven parameters, including LST, altitude, slope, vegetation and latitude, albedo and MSLP. In the following, the characteristics of each of these data are also described. Standardized regression coefficients were used to determine the most important estimator in each land cover. The correlation between the parameters involved in the study with the absolute difference between the air and surface temperature are negative in January, which means that by increasing, slope, altitude, NDVI, latitude, albedo and MSLP, the difference is reduced and vice versa. Nonetheless, this kind of relationship is not valid in the whole study area, and there are some exceptions. In July the relationship between this difference and slope and NDVI is positive, which means that with increasing altitude, latitude, albedo and MSLP, the differences also increase. In January, waters (99%), urban areas (95%), and barren or sparsely vegetated (92%) have the highest R2. While, mixed forests had the lowest R2 equal to 27% (Figure 4). The least errors are related to urban areas (0.69 ° C), water (0.75 ° C), and then forest areas (0.9 ° C). The highest errors were observed in cropland and open shrubland equal to 1.35˚C and 1.34˚C. The highest R2 was calculated for water (95%), urban areas (94%), mixed forest and open shrubland (93%). The least error occurred in mixed forest (0.3˚C). The main objective of the present study was to develop a model of air temperature estimation from surface temperature and other auxiliary variables (elevation, slope, vegetation, latitude, land cover, albedo and mean sea level pressure). Regression models were presented for estimating Ta in monthly scale. The results can be summarized as: Between the air and surface temperature, the most variability is related to the Ta which in the region of Iran has an annual variation coefficient of 92% in January and 41% in July. In January, slope and altitude are the most important variables in the estimation model so that up to 16% and 12% can explain LST-Ta differences, respectively, while latitude and MSLP are the most important variables in July so that each one of them explains up to 9.6% of these differences in July. The role of land cover in estimating Ta is very important. In addition, the number of pixels located on each land cover category can also play a decisive role in estimation model. Category of water, urban and barren area in January, exhibited the highest R2 of 99%, 95% and 92%, respectively. The lowest R2 (approximately 27%) is related to grassland and mixed forest. In July, the highest R2 is related to water and urban areas about 95 and 94%. R2 of grassland increases by approaching summer. The lowest error is recorded for urban area, water and mixed forest in January while the lowest error is related to mixed forest, open shrubland and barren areas in July. The accuracy of estimation models varies according to the months and the land cover. Based on standardized regression coefficients, in January altitude (in barren, urban and cropland area) mean sea level pressure (in grassland and shrubland), slope of mixed forest area and latitude in water area were of great importance in air temperature estimation. While, in June, due to presence of low pressure unter in Iran, the role of local climatic factors has been minimized and mean sea level pressures was the most important estimator almost in all landcovers.}, keywords = {Air temperature estimation,Land surface temperature,Regression,Estimator variables}, title_fa = {بررسی نقش متغیرهای پیش‌بین در تخمین دمای هوا در ماه‌های ژانویه و ژوئیه در طبقات پوشش اراضی مختلف}, abstract_fa = {هدف اساسی این مطالعه تخمین دمای هوا با استفاده از متغیرهای پیش‌بین شامل دمای سطح زمین، ارتفاع، شیب، پوشش گیاهی، عرض جغرافیایی، آلبیدو و میانگین فشار سطح دریا طی دو ماه ژانویه و ژوئیه در سال‌های 2001 تا 2015 در طبقات پوشش اراضی مختلف می‌باشد. از 6 مدل رگرسیونی تک‌متغیره تا چندمتغیره به‌تفکیک 7 پوشش اراضی موجود در کشور استفاده شد و 42 مدل برآوردگر برای هر ماه توسعه داده شد. نتایج بیانگر آن بود که بیشترین اختلافات بین دمای هوا و دمای سطح زمین در طبقه با پوشش سطحی بایر یا پوشش گیاهی تنک دیده شد. در ژانویه، ارتفاع (در پوشش‌های زمین‌های بایر، بافت‌های شهری و پهنه‌های کشاورزی) فشار (در پوشش‌های علف‌زارها و بوته‌زارها)، شیب منطقه جنگلی و عرض جغرافیایی در پهنه آب، مهم‌ترین برآورد‌گرهای دمای هوا هستند. در‌حالی‌که در ژوئیه در سطح زمین یک کم‌فشار حرارتی چسبیده به زمین با ارتفاع کم در بخش وسیعی از پهنه کشور تشکیل شده و این عامل اقلیمی ناشی از گرمایش شدید سطح زمین نقش عوامل میکرواقلیمی از قبیل ارتفاع، شیب و پوشش زمین را به‌حداقل رسانده و تأثیر آنها را در تخمین دمای هوا کم‌رنگ می‌کند. لذا می‌توان عامل فشار را در ماه ژوئیه مهم‌ترین برآوردگر تغییرات فضایی دمای هوا در پهنه ایران دانست.}, keywords_fa = {Air temperature estimation,Land surface temperature,Regression,Estimator variables}, url = {https://jesphys.ut.ac.ir/article_67777.html}, eprint = {https://jesphys.ut.ac.ir/article_67777_ccd91184326d16b2d1282593154ef9e3.pdf} } @article { author = {Panjehkoobi, Parviz and Masoodian, Seyed Abolfazl and Ghanghermeh, Abdolazim}, title = {Calibration of Amirabad radar parameters for estimating precipitation in hot weather}, journal = {Journal of the Earth and Space Physics}, volume = {45}, number = {1}, pages = {149-163}, year = {2019}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2018.252269.1006991}, abstract = {Meteorological radar is usually used to estimate rainfall. The relationship between rainfall and the reflectivity of the radar is exponential. Measurement of the intensity and amount of precipitation in the management of water resources, agriculture, and flood alert is widely used. Radar and rain gauges can better estimate the amount and spatial distribution of rainfall. Marshall et al. (1947) proposed based on the relationship between the reflectivity coefficient Z and the precipitation intensity R. Here, a and b are coefficients of the model and may differ in different places and seasons. The factors affecting these variables are: 1- type of rainfall, 2- Season; 3-Geographic and Topographic Surface of the Region. The size of precipitation drops and their distribution varies in different rainfalls. The sources of error in the radar are (1) the difference in radar reflection height, that is related to the height of the ground, while the rain-gauge measures rainfall on the earth's surface. 2) Radar calibration error. 3) Echoes of recurrences from obstacles near the ground. 4) Radar beam attenuation 5) Unrealized echoes of solid phenomena such as hail, snow, melting region. Estimates are more credible near radar. The best way to collect rainbow data is to use both radar and rain gauge simultaneously. Data used in this study include two series of ground station data and radar data. The rain gauge was used between 30 and 100 kilometers from Amirabad radar. The rainfall in July and September 2015 were selected. The severity of the two selected rainfall was appropriate, and their rainfall was remarkable. In this research, radar beam angles were measured at 0.2, 0.3, 0.4, 0.5 and 0.6 degrees as well as radar beam at constant altitudes of 200, 500 and 1000 meters from ground level. At the specified times, the radar reflection value was matched to the amount of precipitation obtained from the rainfalls during the same time interval. In the coordinate system on the vertical axis, the values of log Z (logarithm of reflectivity) were plotted on the horizontal axis and log R (rainfall rainfall intensity logarithm) and correlation between the logarithm of reflection and the logarithm of precipitation were obtained by regression method by which linear equation is extracted where the slope of this line is equal to b and the width of its origin is log a. For all the studied stations and for both selected precipitation and all selected angles, the values of the new radar parameter were obtained separately and the new values of radar precipitation were estimated with the help of new parameters and the relation . Using the obtained coefficients, the intensity and total radar rainfall were estimated. The results were different for each station. Regarding estimated radar rainfall values and station distance from the radar, for each station, the optimal beam angle was chosen to have the best estimate of precipitation. In Gorgan, Sari, and Dash-e-Naz ratio of precipitation estimated by radar to rain gauge measurement is about 90 percent. Meanwhile in Babolsar and Banda-e-Gaz the ratio is only 2 percent. Estimated rainfall was 12 percent higher at Gomishan station. At Amol station, it was 25% less than the rain, measured. Because it was difficult to get radar coefficients for each station as it took a lot of time. So, for the rain event of September 1 and 2, 2015, using the rainfall data of all ground stations and the radar reflection coefficient Z, a general equation was obtained. Comparison of total radar precipitation data before calibration and after calibration, with rainfall values of ground stations, showed that in most stations, the total estimated rainfall data of the radar after calibration, approached the amounts of actual rainfalls. The average rainfall increased from 6.8 mm to 28.5 mm, and just 3 mm lower than the average rain gauges. Estimated rainfall data in two samples of the hot season of the Amir Abad radar showed that the range of radar parameters was high, and their value was very different from the radar default value. The estimated rainfall was much lower than the rainfall before calibration. If a radar is calibrated for each precipitation and location, the estimated radar precipitation value is very close to what is measured by ground stations. The results of this study showed that radar coefficients are different for each rainfall. It is also different for rainfall that occurs in one area at different times, and this depends on the geographic location and distance from the radar. To achieve better results, the number of additional stations and the number of additional rainfalls should be studied.}, keywords = {Radar,Rainfall estimation,calibration,Eastern Caspian}, title_fa = {واسنجی فراسنج‌های رادار امیرآباد برای برآورد بارش فصل گرم}, abstract_fa = {رادار هواشناسی در برآورد مقدار بارش بر روی گستره­های پهناور کاربرد زیادی دارد. پیوند میان بارش و بازگشت­پذیری رادار پیوندی نمایی است . a و b فراسنج­های مدل هستند و چنانچه درست انتخاب نشوند، بارش برآوردی رادار با اشتباه همراه می‌شود. اندازه و توزیع چکه­های بارش اثر زیادی بر فراسنج­های این مدل دارد. دامنه وردشِ این فراسنج­ها بسیار زیاد است. دراین پژوهش بارش­های 28 تا 29 تیر و 10 تا 11 شهریور سال 1394 ایستگاه­های آمل، بابلسر، ساری، دشت ناز، بندر گز، گمیشان و گرگان که در محدوده 30 تا 100 کیلومتری رادار امیرآباد بهشهر (رادار خزر­شرقی) جا گرفته­اند بررسی شد. در بارش اول برای هرایستگاه، زاویه ارتفاع بهینه پرتو انتخاب و فراسنج­ها واسنجی و رابطه مربوط به آن نقطه به‌دست آمد. با استفاده از این رابطه مقدار بارش برآوردی رادار از 22 درصد به 97 درصد افزایش یافت و میانگین مجموع بارش برآوردی رادار از 8/9 به 4/43 میلی­متر رسید که از میانگین واقعی فقط 1 میلی­متر کمتر است. در بارش دوم، با استفاده از داده­های بارش تمام ایستگاه­ها، فقط یک معادله به‌دست آمد و رادار واسنجی شد. نتایج برآورد بارش رادار به این روش نیز با تقریب خوبی مورد قبول بود و میانگین مجموع بارش برآوردی رادار از 6/8 به 5/28 میلی­متر افزایش یافت که 3 میلی­متر از مقدار واقعی کمتر بود.}, keywords_fa = {Radar,Rainfall estimation,calibration,Eastern Caspian}, url = {https://jesphys.ut.ac.ir/article_67785.html}, eprint = {https://jesphys.ut.ac.ir/article_67785_ca6fa98d9d84e684f87f23c7c40989bd.pdf} } @article { author = {Mahmoudian, Ali Reza and Kalaee, Mohammad Javad}, title = {New Approach of Low-Frequency Electromagnetic Wave Generation in the Near-Earth Environment}, journal = {Journal of the Earth and Space Physics}, volume = {45}, number = {1}, pages = {165-176}, year = {2019}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2019.256926.1007002}, abstract = {This work presents the study on the electromagnetic wave penetration into the ionosphere in the frequency range of 10 Hz to 3 kHz and 3 kHz to 30 kHz, corresponding to the Extremely Low Frequency (ELF) and Very Low Frequency (VLF) for telecommunication applications and earthquake prediction. The ELF-VLF waves can also be generated through natural phenomena such as lightning as well as pre-seismic activities. The ELF generation before major earthquakes has been reported in several studies. Therefore, having a complete model capable of simulating the ELF waves generation and propagation in the disturbed ionospheric conditions, associated with pre-earthquake activities can be used to save human lives by predicting the exact location of a major earthquake. This study aims at developing a computational model in order to investigate the ELF –VLF wave generation and propagation in the lower ionosphere that can be used as a precursor for seismic events. Another application of this frequency band is in the radio navigation. The VLF navigation system known as OMEGA was very popular and used for many applications such as navigation of ships, airplanes and also in the land. The system was in use until the late 1990s when it was replaced by Global Positioning Systems (GPS) due to high accuracy and low cost. Very recently, there has been an effort to renew the VLF navigation systems at a low cost. This will require a new approach for VLF wave generation in the ionosphere at a lower cost in comparison with regular transmitters. The efficiency of VLF wave generation in the lower ionosphere using a ground-based dipole antenna in the equatorial region is examined in this study. In this study, we have shown that transmitted signal from the ground into the ionosphere can generate a current in the lower ionosphere, which may expand up to a few kilometers depending on the ionospheric conductivities and the frequency or modulation of the transmitted signal from the ground. This study investigates the generation of secondary currents and the artificial antenna in the ionosphere in order to develop a new technique for generating these signals for navigation applications. The approache for improving the efficiency of this technique including pre-modulation of the ionosphere using high-power high frequency (HF) signal for modifying the conductivities in the ionosphere is discussed. The main idea here is to investigate the efficiency of Whistler wave generation in the E region in different ionospheric conditions. Specifically, the effect of pulse and continuous probing of the lower ionosphere with ELF-VLF signals and the generation of secondary waves and currents due to high conductivities are investigated. We have also proposed the application of this model to study the generation and propagation of ELF-VLF signal associated with the earthquake in the disturbed ionospheric conditions. This includes the variation of background ionospheric plasma and its effect on the penetration of the signal in the ionosphere and length scale of the excitied currents. This study may be critical to determine the exact location of a major earthquake using the pre-seismic activities such as generation and propagation of ELF waves. The variation of background ionospheric parameters such as electron density and ionospheric disturbances due to pre-earthquake conditions on the excitation and penetration of ELF-VLF waves into the E-region will be investigated in future studies.}, keywords = {Radiowave propagation,ELF-VLF wave generation,Ionosphere,radio navigation,earthquake prediction}, title_fa = {بررسی تحریک و انتشار امواج الکترومغناطیس باند فرکانسی بسیار پایین در ناحیه نزدیک به سطح زمین}, abstract_fa = {تحریک و انتشار امواج الکترومغناطیسی در باند‌های فرکانسی بسیار پایین در جو زمین، کاربردهای بسیاری در زمینه‌های مختلف، از جمله فیزیک فضا، ارتباطات رادیویی و پیش‌نشانگری زلزله دارد. لذا این طیف فرکانسی همواره مورد توجه پژوهشگران بوده است. با توجه به پیچیدگی‌های بسیار زیاد، مطالعه و بررسی تحریک این نوع امواج الکترومغناطیسی همواره مشکل بوده است. هدف از این پژوهش بررسی تحریک امواج رادیویی در طیف فرکانسی بی‌نهایت پایین (ULF (Ultra Low Frequency (300 Hz to 3 kHz)) و ELF (Extremely Low Frequency (3 to 30 Hz))) در بازه فرکانسی 3 هرتز تا ۳ کیلوهرتز، و طیف فرکانسی خیلی پایین (VLF (Very Low Frequency (3 to 30 kHz))) در بازه فرکانسی ۳ تا ۳۰ کیلو‌هرتز در لایه E یون‌سپهر، در ارتفاع 8۰ تا ۱۲۰ کیلومتری از سطح زمین می‌باشد. در این تحقیق از روش‎‌های عددی، برای تحریک جریان الکتریکی، و ایجاد آنتن مجازی در لایه پلاسما برای تولید امواج VLF استفاده شده است. همچنین تحریک لایه پلاسما و تغییر میزان ضرایب هدایت با استفاده از امواج الکترومغناطیسی باند فرکانسی بالا HF (High Frequency) مورد بحث قرار گرفته است. مدل عددی مورد استفاده در این تحقیق شامل قوانین ماکسول و ضرایب رسانایی لایه یون‌سپهر می‌باشد که در نوع خود منحصر بفرد است. این مدل تغییرات لایه یون‌سپهر بر روی انتشار امواج ارسالی، و همچنین تحریک امواج ثانویه را از طریق ترکیب ضرایب هدایت با قوانین ماکسول شبیه‌سازی می‌کند، به‌طوری‌که زمان انجام محاسبات تا حد قابل توجهی کاهش می‌یابد. نتایج نشان می‌دهد که آنتن‌های زمین پایه در باند فرکانسی ELF دارای بازدهی بسیار خوبی بوده و می‌توانند جایگزین مناسبی برای ایجاد این امواج توسط فرستنده‌های قوی باند HF که به گرم‌کننده لایه بالای جو معروف هستند، باشند. همچنین نتایج این شبیه‌سازی نشان می‌دهدکه میزان نفوذ موج پالسی در لایه یون‌سپهر کمتر از۱۰ کیلومتر در فرکانس ۱۰۰ هرتز بوده و امواج تحریکی دارای سرعت انتشار در حدود ۱۰۰۰ کیلومتر بر ثانیه می‌باشند. میزان نفوذ امواج الکترومغناطیسی در جو زمین با افزایش فرکانس ارسالی به طیف فرکانسی خیلی پایین VLF به‌میزان بسیار زیادی کاهش می‌یابد.}, keywords_fa = {Radiowave propagation,ELF-VLF wave generation,Ionosphere,radio navigation,earthquake prediction}, url = {https://jesphys.ut.ac.ir/article_69146.html}, eprint = {https://jesphys.ut.ac.ir/article_69146_36965323679273b1cf1e2621f5d7dd4f.pdf} } @article { author = {Ahmadi, Hamzeh and Fallah Ghalhari, Gholam Abbas and Baaghideh, Mohammad}, title = {Projection of Climate Change Impacts on Seasonal Precipitation in Iranian Cold Regions Based on Radiative Forcing Scenarios (RCP)}, journal = {Journal of the Earth and Space Physics}, volume = {45}, number = {1}, pages = {177-196}, year = {2019}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2018.256956.1007003}, abstract = {Climate change and its impacts stand as the most important challenge to the world. One of the fundamental issues that have emerged in recent decades is the limited water resources. Because of the high dependence on precipitation, water resources are heavily susceptible to damage from climate change. Projection the effects associated with climate change is a major part of strategic planning in the current century. Cold climate regions are the main reservoir and feeding source for surface and underground water and a vital supplier of hydroelectric power in Iran. Any change in the seasonal precipitation situation will have severe outcomes for the status of water resources in cold regions. The purpose of this study is to investigate the impacts of climate change on seasonal precipitation in cold regions of Iran based on the outputs of new CMIP5 models and radiative forcing (RCP) scenarios. Alongside this, changes were first observed for the period 1980-2005. Afterwards, the data for the upcoming period up to the 2090 horizon were processed using the models BCC-CSM1.1, HadGEM2-ES, GFDL-CM3, MIROC-ESM and GISS-E2-R from the series of CMIP5 models of the MarksimGCM database based on the radiative forcing scenarios RCP8.5 and RCP4.5. The data were subsequently validated based on weighing method and RMSE, MAE, MBE and R2 evaluation criteria. The results of the processing were drawn on the digital elevation layer (DEM) of cold climate regions of Iran in the form of temporal-spatial seasonal precipitation distribution. Is The results showed that based on the weighing method and applying statistical indices on the output of CMIP5 models, the output of the HadGEM2.ES general circulation model is accompanied by fewer simulation errors in illustrating the climate change of the future period than the observation or baseline period. In fact, based on the evaluation criteria or errors, this model showed a higher compliance with observational data. In the monthly pattern in cold regions of Iran during the cold months, especially in the autumn and winter months, the precipitation parameter indicates a slight increase from 10-20 mm relative to the baseline period. This small increase in precipitation over the coming decades, based on the structure of the models, cannot be stable because of increasing temperature and evapotranspiration. However, in the annual and normal long-term pattern, the precipitation level will be less than the preceding period such that in the 2020-2055 period in the annual pattern, precipitation decreases by 54 mm, equivalent to 20.1% decrease. Seasonal precipitation will decrease in winter, autumn, and summer of the upcoming period up to the 2090 horizon, according to radiative forcing scenarios. Precipitation reduction in the summer will be more severe than in other seasons. Only in spring season will the amount of precipitation in the coming period increase slightly compared to the baseline period. Most of the spatial variations in precipitation distribution will occur in the cold climate regions of Iran in the high-altitude areas of the middle Alborz and especially in high Zagros regions. The center of areas with maximum precipitation in cold regions will mainly move to higher latitudes. In fact, the regions with substantial precipitation will become smaller, whereas areas with low rainfall will be extended. Therefore, climate change will have an impact on the temporal-spatial distribution of precipitation in the cold climate regions of Iran and will face with a future with less and variable precipitations.}, keywords = {climate change,Cold region,CMIP5,RCP,Precipitation}, title_fa = {پیش‌نگری اثرات تغییر اقلیم بر بارش فصلی مناطق سردسیر ایران براساس سناریوهای واداشت تابشی RCP))}, abstract_fa = {پیش‌نگریاثرات تغییر اقلیم یکی از مهم­ترین بخش­ها در برنامه­های راهبردی در قرن حاضر محسوب می­شود. تحقیق حاضر با هدف پیش‌نگریتغییرات بارش فصلی مناطق سردسیر ایران انجام شد. در این راستا ابتدا تغییرات دوره مشاهده‌ای برای دوره آماری 1980-2005 بررسی شد. در ادامه داده دوره آینده تا افق 2090 از میان مدل­های (BCC-CSM1.1، HadGEM2-ES، GFDL-CM3، MIROC-ESM و (GISS-E2-R، از سری مدل­های CMIP5 پایگاه MarksimGCM براساس سناریوهای واداشت تابشی RCP8.5 و RCP4.5، پردازش شد. سپس صحت‌سنجی براساس معیارهای RMSE، MAE، MBE و R2 بر روی داده­ها انجام شد. نتایج نشان داد که مدل HadGEM2-ES از وزن و توانایی بالاتری نسبت به دیگر مدل­ها برخوردار می­باشد و نتایج نشان داد که تغییرات زمانی-مکانی بارش در دوره آینده یکسان نخواهد بود. براساس سناریوهای RCP8.5 و RCP4.5، در الگوی ماهانه در بیشتر مناطق سردسیر ایران در فصول پاییز و زمستان، مقدار بارش افزایش ناچیزی در حدود 20-10 میلی­متر نسبت به دوره پایه خواهد داشت، اما در الگوی سالانه مقدار بارش در دوره آینده کاهش خواهد یافت. منطقه پربارش زاگرس مرتفع در الگوی ماهانه و سالانه، با بیشترین تغییرات کاهش بارش برای آینده مواجه خواهد شد. به‌طوری‌که در دوره (2020-2055) در الگوی سالانه، مقدار بارش تا 54 میلی­متر معادل 1/20 درصد کاهش نشان می­دهد. تغییرات مکانی شدید در مقدار بارش فصلی در مناطق پربارش جنوب غرب ایران بیشتر از دیگر نواحی خواهد بود. از نظر توزیع مکانی، کانون نواحی پربارش در منطقه زاگرس کوچک‌تر شده و به عرض‌های بالاتر جا‌به‌جا خواهد شد و بر گستره مناطق و پهنه­های با بارش کمتر افزوده خواهد شد. بنابراین تغییر اقلیم بر توزیع زمانی – مکانی بارش مناطق سردسیر ایران تأثیر خواهد داشت و آینده­ای با بارش کمتر و متغیر را نشان خواهد داد.}, keywords_fa = {climate change,Cold region,CMIP5,RCP,Precipitation}, url = {https://jesphys.ut.ac.ir/article_67776.html}, eprint = {https://jesphys.ut.ac.ir/article_67776_4956a1954e84c6fbc31ec4a92919093b.pdf} } @article { author = {Ghafarian, Parvin and Pegahfar, Nafiseh and Mohammadpour Penchah, Mohammad Reza}, title = {Simulation of the surface wind field by the WRF model in Oman Sea region with different initial and boundary conditions}, journal = {Journal of the Earth and Space Physics}, volume = {45}, number = {1}, pages = {197-209}, year = {2019}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2018.258409.1007009}, abstract = {Oman Sea and its coastlines have an important role in the international trade, coastal management and marine industries. Large weather instability and intense wind occur in Oman Sea due to tropical cyclones. The wind field simulated by atmospheric models can be used in ocean model for wave prediction. The main purpose of this research is to investigate applicability of WRF mesoscale model version 3-7-1 in surface wind simulation using various boundary and initial conditions over Oman Sea. for this aim, three data sets including Era-Interim reanalysis data, FNL and GFS analysis data have been used. Simulated wind at the coasts of Oman has been evaluated using observational data measured at synoptic stations in Iran and Oman and also data measured by buoy at Gheshm Island. Evaluation of simulated offshore wind has been done using data from National Climatic Data Center Blended Sea Winds with 0.25 degree horizontal resolution and 6-hourly time step. Moreover, SST data from NCEP dataset with 0.083 degree in horizontal resolution have been used as WRF input data. Model outputs have been improved based on nudging technique. In this research, WRF model has been run using three 3-, 9- and 27-km nests, that the smaller one covers Oman Sea and some portions of the Persian Gulf. The model has been run for a time of 60 hour with 12 hour spin-up period for June 2009. Finally, fifteen “2-day re-started” simulations were performed to complete one month simulations. Results show that all three simulations overestimate wind speed at the considered coast area and the largest error belong to simulations that used Era-Interim dataset and the smallest error occurred in simulations that used FNL dataset. Comparison of the three datasets (analysis and reanalysis ones) with observational data indicated that using GFS dataset provided more accurate data due to its higher resolution. Moreover, ECMWF datasets underestimated them, while simulations using ECMWF them data as initialization and boundary conditions overestimated the winds. Bias-averaged values over the offshore areas demonstrated that using GFS and FNL datasets leads to underestimation, while using Era-Interim dataset resulted in overestimation in of predicted winds. Histogram of wind speed reveals that maximum error occurred for low wind speed for all three datasets (wind speed smaller than 3 m/s). In the mid-range (wind speed between 3-12 m/s), the model has an appropriate performance for simulating wind speed. Using GFS and FNL underestimates wind speed larger than 12 m/s, while using Era-Interim data overestimates that. Simulations using GFS and FNL have little discrepancy for various wind speeds, due to same model in producing these datasets. While results obtained from Era-Interim differ significantly with those from GFS and FNL datasets. Using FNL dataset produced the least error in wind direction. Since both GFS and FNL datasets are produced in NCEP with the same data assimilation techniques and forecast systems, the significant difference between these two datasets refers to the number of used observational data in producing analysis dataset (more observational datasets have been used in producing FNL dataset, comparing with those used in producing GFS dataset). Therefore, it can be concluded that dense grid of observational data in producing analysis dataset has an important role in mesoscale simulations. As a conclusion, using FNL dataset an input of WRF model led to the best performance in simulation of wind speed and wind direction for coasts and offshore part of Oman Sea.}, keywords = {Wind field,WRF model,Oman Sea,reanalysis and analysis data,Initial and boundary conditions,Nudging}, title_fa = {شبیه‌سازی میدان باد سطحی در منطقه دریای عمان با مدل WRF با شرایط اولیه و مرزی متفاوت}, abstract_fa = {در این تحقیق کارایی مدل میان­مقیاس WRF برای شبیه­سازی باد سطحی تحت شرایط اولیه و مرزی متفاوت در سواحل و فراساحل دریای عمان ارزیابی شده است. بدین منظور از داده بازتحلیل Era-interim و داده­های تحلیلی NCEP-FNL و NCEP-GFS به‌عنوان شرایط اولیه و مرزی استفاده شده است. خروجی میدان باد حاصل از شبیه­سازی مدل با داده­های ایستگاه­های سینوپتیکی واقع در سواحل دریای عمان در کشورهای ایران و عمان، داده بویه قشم و داده ماهواره ترکیبی مقایسه شده‌اند. از روش کشانش (Nudging) برای بهبود در نتایج خروجی مدل استفاده شده است. نتایج هر سه شبیه­سازی نشان می­دهند که مدل در نقاط ساحلی، مقادیرسرعت باد را پیش برآورد کرده است. به گونه­ای که بیشترین برآورد مربوط به داده Era-Interim و کمترین مربوط به داده FNL بوده است. برای مناطق فراساحلی، میانگین اریبی روی کل دامنه مورد مطالعه نشان داد که شبیه­سازی­هایی که با داده­های GFS و FNL انجام شده بود، تمایل به کم­برآوردی داشته، درحالی­که داده­های Era-Interim سرعت باد را بیش­برآورد کرده­اند. از مقایسه نمودار هیستوگرام سرعت باد مشخص شد که در هر سه شبیه­سازی بیشترین میزان خطا در بازه­های زمانی که سرعت باد کم بوده، رخ داده است. ارزیابی جهت باد نیز نشان داد که داده FNL نسبت به دو داده دیگر عملکرد بهتری را به‌عنوان شرایط اولیه و مرزی برای شبیه­سازی در منطقه مورد مطالعه داشته است. در کل بهترین عملکرد مدل برای شبیه­سازی میدان باد در دوره مورد مطالعه با داده­های FNL در نقاط ساحلی و فراساحلی بوده است.}, keywords_fa = {Wind field,WRF model,Oman Sea,reanalysis and analysis data,Initial and boundary conditions,Nudging}, url = {https://jesphys.ut.ac.ir/article_67772.html}, eprint = {https://jesphys.ut.ac.ir/article_67772_ae08922dabf08b7383288eeeff73ae7d.pdf} } @article { author = {Ahmadi, Mahmoud and Shakiba, Ali Reza and Dadashi Roudbari, Abbas Ali}, title = {Investigating the role of vegetation indices and geographic components on seasonal aerosol optical depth over Iran}, journal = {Journal of the Earth and Space Physics}, volume = {45}, number = {1}, pages = {211-233}, year = {2019}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2018.260582.1007019}, abstract = {Investigation of the role of vegetation indices and geographic components on seasonal aerosol optical depth (AOD) over the Iranian region is carried out. Aerosols are suspended particles in an air that have diameters between 0.001 and 100 micrometers. Aerosols play an important role in the radiation properties of atmosphere and hence affect the earth climate system. Vegetation cover can impede surface erosion by wind and hence, has a close relationship with the emission. Dust emission leading to dust events in urban area can have an adverse effect on human health as well as human activities, for example by reduction in visibility. This research aims to seasonally evaluate the roles of geographical locations and vegetation indices on AOD over Iran, based on satellite data. This includes the evaluations the role of each of these components in AOD550 nm variations. In this study, the daily data of the 6-level 3 products (MYD08_M3_6) including AOD550 nm, Deep Blue Algorithm, MODIS sensor data, Aqua satellite data, are used. Pixel data were downloaded over the Iranian region from 2003 to 2017 with a spatial resolution of 1 × 1 arc. Two indicators, namely the Enhanced Vegetation Index (EVI) and Normalized Difference Vegetation Index (NDVI) of the Aqua Satellite, for the study period with AOD data were used. The optical sensitivity of aerosols data was verified using the Aqua Satellite data from the Aerosol Robotic Network (AERONET). The GWR and OLS methods were used to find the spatial relationships of aerial photo sensor optical depths with geographic location and vegetation indices. The average values of AOD over Iran, based on the data of the Aqua, are between (0.11 for spring) and (0.16 for autumn) respectively. The average AOD value in the spring indicates the enhancement of dust events in the region. In winter, the average AOD value over Iran is 0.12, with the lowest standard deviation. In the summer, according to Aqua satellite data, this value is 0.133, with the maximum scatters and deviation from the largest mean observed value. Based on the EVI and NDVI indexes, the maximum statistical values, including the range of changes, maximum, average, scatter level and deviation from the typical values of both indicators were observed in the warm season of the year. The maximum EVI index peaked in the summer with 0.478 and the lowest of 0.043 in the winter. The maximum NDVI index, like the EVI index, was obtained for the summer with 0.777 and its lowest value is -0.69 for the spring. The maximum correlation between the atmospheric optical depth and geographic components of the area is for the altitude and then the latitude and then the longitude. The correlation between the AOD with the altitude and latitude of location of the area is negative and significant, and the correlation of the AOD with longitude is not significant in any seasons. There is a negative correlation between AOD and NDVI, and also EVI index in all seasons, although it is 0.039 in winter, which is relatively low. The results of the AOD assessment show that the maximum spring and autumn has the lowest average AOD over the Iranian area. This is due to the combination of dry conditions and relatively strong wind speeds in the spring those results in dust storms that increase the amount of AOD. In contrast, the maximum AOD over Iran is for the spring with a value of 0.48 that occurs in southwestern part of Iran. The second largest focal point, highlighted in all AOD seasons, is for the Persian Gulf coast area between Bushehr and Bandar Abbas. AOD over this coastal area can be associated with favorable wind conditions in mineral dust deposition which transported to the area and sea salt. Other areas with high AOD can be found in the Makran coastal area in the southeast of Iran, between the plain of Lut and the Mangrove plain, as pervious AOD study in southeastern Iran indicted. Based on the climate distribution of the EVI and NDVI vegetation indices and the seasonal spatial variation of aerosols, it is shown that vegetation factor in dust emission efficiency varies from one region to another with season. This regional disparity is due to the variation of vegetation-humus-release and the coupling of two or more of these factors; therefore, vegetation can significantly improve the treatment of dusty storm areas with the internal sources in the country. The maximum correlations with the geographic components of the location with the optical depth over the Iranian area are for the elevation and then the latitude and then the longitude. The correlation between the AOD with height and latitude is negative and with 5% level.}, keywords = {Aerosol Optical Depth,Vegetation indices,MODIS Sensor,Iran}, title_fa = {بررسی نقش شاخص‌های پوشش گیاهی و مؤلفه‌های جغرافیایی مکان بر عمق نوری هواویزهای فصلی ایران}, abstract_fa = {عمق نوری هواویزها (AOD) کمیتی بی‌بعد است که میزان عبوردهی پرتو نور در جو را نشان می‌دهد. شناخت AOD برای درک تأثیرات آن بر کیفیت هوا و ارائه راهکاری‌های مقابله با آن ضروری است. هدف از این پژوهش بررسی نقش مؤلفه‌های جغرافیایی مکان و شاخص‌های پوشش گیاهی بر عمق نوری هواویزهای فصلی (AOD550nm) موجود در جو ایران است. در این پژوهش از فرآورده 6 سنجنده MODIS ماهواره Aqua برای ارزیابی مقادیر AOD، NDVI و EVI به‌ شکل فصلی طی دوره آماری 2017-2003 استفاده شد. جنوب غرب، شرق و سواحل خلیج‌فارس بالاترین و شمال غرب کشور و زاگرس کمترین مقدار AOD را به خود اختصاص داده‌اند. دلیل بالا بودن مقدار AOD در ایران بار ورودی گردوغبار، احتراق سوخت‌های فسیلی و کاهش ارتفاع لایه‌مرزی (BLH) در دوره سرد سال است چرا‌که اکثر آلاینده‌های جوی در لایه مرزی منتشر می‌شود و از راه فرآیندهای تلاطمی لایه آمیخته همگن می‌شود. همبستگی AOD با ارتفاع و عرض جغرافیایی منفی و در سطح 5 درصد معنی‌دار می‌باشد. همبستگی منفی معنی‌دار بین شاخص‌های EVI، NDVI و AOD در فصول تابستان و انتقالی سال وجود دارد به‌طوری‌که کاستی پوشش گیاهی با افزایش AOD در هر فصل با یکدیگر متناظرند. رگرسیون وزن‌دار جغرافیایی (GWR) نشان داد که مقدار پوشش گیاهی توانایی بالایی در کنترل هواویزهای وردسپهر پایینی و ارتفاعات نقش سد‌کنندگی مسیر ترابرد ذرات را دارند و در نتیجه بر انتشار گردوغبار در حالت محلی و منطقه‌ای نیز تأثیر خواهند داشت.}, keywords_fa = {Aerosol Optical Depth,Vegetation indices,MODIS Sensor,Iran}, url = {https://jesphys.ut.ac.ir/article_67771.html}, eprint = {https://jesphys.ut.ac.ir/article_67771_09b8da9d41d51522f83986a5c33bcfd1.pdf} } @article { author = {Saberian, Ehsan}, title = {Ion-acoustic Solitons in Solar Winds Plasma Out of Thermal Equilibrium}, journal = {Journal of the Earth and Space Physics}, volume = {45}, number = {1}, pages = {235-246}, year = {2019}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2019.261483.1007024}, abstract = {In this paper, by applying the reductive perturbation method to the plasma fluids equations and by using a non-Maxwellian distribution function which is labeled via an invariant spectralindex  and an independent parameter  as the potential degrees of freedom via perturbation, a generalized Korteweg-de Vries (KdV) equation is derived for the ion-acoustic solitons in Solar winds plasma, which involves near-equilibrium and out of thermal equilibrium states. Here, the spectralindex  describes the deviations from thermal equilibrium of plasma and itself is independent of the number of degrees of freedom of plasma. The near-equilibrium states where the spectral indices are distributed with the values of  are applied for the inner Heliosphere regions, and the far-equilibrium states which are described by the spectral indices as  that belongs to the Heliosheath regions. The analytical solution to the generalized KdV equation is calculated and its solitary wave solution is derived. Then, effects of the spectralindex , the potential degrees of freedom via perturbation , and the speed of pulse on the generalized dispersion coefficient () and generalized nonlinear coefficient () of KdV equation, and also on the structure of the ion-acoustic solitons are studied numerically.   It is found that in the asymptotic limit of , it indicates a plasma in thermal equilibrium and the generalized KdV equation reduces to the standard KdV equation and its solitary wave solution. We show that the generalized dispersion coefficient  tends smoothly to the standard limit of  in the near-equilibrium states as , while it tends to zero in out of thermal equilibrium regions as . Furthermore, the generalized nonlinear coefficient  has negative large values in far-equilibrium states with ,while it tends smoothly to the standard limit of  in the case of an equilibrium plasma with . Moreover, the invariant spectral index has a critical value  in the far-equilibrium states, where for the generalized nonlinear coefficient  has positive values and for the generalized nonlinear coefficient  has negative values. We found that in the vicinity of , corresponds to the escape state (where the transitions between near-equilibrium and far-equilibrium states happens), the variations of the coefficients  and  are considerable. We also found that the generalized dispersion coefficient () and the generalized nonlinear coefficient () depend on the potential degrees of freedom via perturbation, but their dependences are not considerable. Futhermore, depending on the values of the parameters  and , the occurrence of ion-acoustic solitons with both positive and negative potentials is possible. In the near-equilibrium states () only positive polarity solitons are possible, which is in consistence with the standard KdV theory. But, the occurrence of negative polarity solitons is predicted in the far-equilibrium states with . Analyzing of the solitary wave profile shows that the amplitude and steepening of the ion-acoustic solitons grows in far-equilibrium states, labeled via indices . It is because of the existence of more fraction of suprathermal particles, which provide more effective interactions with the soliton and make it more prominent. Furthermore, propagation of a soliton with more speed results in a pulse with larger amplitude and narrower width, in consistence with the standard KdV theory. Moreover, examining the results with the various degrees of freedom, shows that the amplitude and steepening of the ion-acoustic solitons decrease with an increase in the potential degrees of freedom via perturbation. It is to be noted that for a perturbed potential as in KdV theory, the potential degrees of freedom  has small values.  Finally, we have analytically derived the amplitude () and the width () of the ion-acoustic solitons as functions of the spectral index  and the potential degrees of freedom .Then, numerical plotting of  and  with respect to  for various values of  has confirmed the mentioned results.}, keywords = {Non-Maxwellian distribution function,Invariant kappa index,degrees of freedom,Soliton,Korteweg-de Vries equation,Solar wind}, title_fa = {سالیتون‌های یون- صوتی در پلاسمای دور از تعادل بادهای خورشیدی}, abstract_fa = {در این مقاله، با استفاده از روش اختلالی کاهنده و اعمال آن بر روی معادلات دینامیک سیال پلاسمایی و با به‌کار بردن یک تابع توزیع غیر ماکسولی که توسط یک شاخص طیفی ناوردای  و یک پارامتر مستقل  (تعداد درجات آزادی وابسته به پتانسیل اختلالی) برچسب زده می‌شود، یک معادله کورته وگ-دی وری (KdV) تعمیم‌یافته برای سالیتون‌های یون-صوتی در پلاسمای بادهای خورشیدی استخراج شده است، به‌طوری‌که در‌برگیرنده حالت‌های نزدیک تعادل و دور از تعادل گرمایی است. در اینجا شاخص طیفی  میزان انحرافات از حالت تعادل در پلاسمای باد خورشیدی را توصیف می‌کند و خود به تعداد درجات آزادی پلاسما بستگی ندارد. حالت‌های نزدیک به تعادل که در آن شاخص طیفی با مقادیر  توزیع شده است، عمدتاً برای نواحی داخلی هورسپهر (Heliosphere) کاربرد دارد، و حالت‌های دور از تعادل که با مقادیر  توصیف می‌شوند، مربوط به نواحی پوش خورشیدی (Heliosheath) هستند. حل تحلیلی معادله KdV تعمیم‌یافته محاسبه شده است و جواب سالیتونی آن استخراج شده است. سپس اثرات شاخص طیفی ، تعداد درجات آزادی وابسته به پتانسیل اختلالی و سرعت پالس روی ضریب پاشندگی تعمیم‌یافته () و ضریب غیرخطیت تعمیم‌یافته () در معادله KdV و همچنین روی ساختار سالیتون‌ها به‌طور عددی بررسی شده‌اند. ملاحظه می‌شود که جواب سالیتونی به‌دست آمده تابع حساسی وابسته به شاخص طیفی  می‌باشد و علاوه‌بر این به تعداد درجات آزادی وابسته به پتانسیل اختلالی نبز وابستگی دارد. بسته به مقادیر  و  امکان وقوع سالیتون‌های یون- صوتی با پتانسیل مثبت و منفی پیش‌بینی می‌شود.}, keywords_fa = {Non-Maxwellian distribution function,Invariant kappa index,degrees of freedom,Soliton,Korteweg-de Vries equation,Solar wind}, url = {https://jesphys.ut.ac.ir/article_69150.html}, eprint = {https://jesphys.ut.ac.ir/article_69150_5a72e613d0d1aa0172f88a73260370e2.pdf} }