@article { author = {Farzaneh, saeed and Sharifi, Mohammad Ali and Kosary, mona and Modiri, mahdi}, title = {Automatic optical observation extraction for the initial satellite orbit determination}, journal = {Journal of the Earth and Space Physics}, volume = {44}, number = {2}, pages = {265-280}, year = {2018}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2018.237290.1006915}, abstract = {In recent years, the development in the space industry and the ability of building, launching and infusion of satellites in the lower orbit has put the limited number of countries with such technology. In order to complete the entire cycle of the space industry, the satellite navigation and control, which have been neglected since the beginning of the movement of space science, has to be considered specially. The orbit determination in one sentence is the application of a variety of techniques for estimating the orbits of objects such as the moon, planets, and spacecraft. In dynamic astronomy, the orbit determination is the process of determining orbital parameters with observations. In particular, orbit determination of planets of solar system is adjustment of noisy orbital observation that consist of random and systematic error for force models and estimation of model parameters by observation (In order to access a mathematical model that illustrates the path of the celestial object in the path before and after the observation time). To simplify, this process is divided into two parts. First, the initial orbit is estimated and then make corrections to the determined orbit. The purpose of initial orbit determination of object that is moving around earth, is calculation of object orbital parameters by a few observations; furthermore initial orbit determination is used for detecting missing object in space. To determine the precise orbit, it is necessary to determine the initial orbit with good accuracy, which indicates the importance of the initial orbit determination. Different type of observations is used to make an initial orbit determination in which observations can be collected by ground stations that contain angular angles, elevations, distance, and distance rate. These observations are made by the radar and the telescope, because the collection of observations without instrument and naked eye does not have enough precision and sensitivity for determination of the space object orbit, but since the extraction of distance observation is expensive and sometimes impossible, angular observation is used. In this paper, a new method has been presented for extracting angular viewing through an optical imaging system. This method is an automatic and efficient method with the ability of real-time data analysis and the base of that is astronomical imaging by CCDs (charge-coupled device). The images captured by this method have a lot of information about stars, galaxy, satellites’ streak, etc. In this paper, automatic method is presented for streak detection which consist of 5 steps: 1) image denoising, 2) extracting of star centers, 3) extracting astronomical coordinates of stars (declination and right ascension), 4) matching between astronomical and pixel coordinate of stars, 5) calculation of satellite streak model. Then, with using the extracted model, the coordinates of beginning and end points are detected. With the celestial coordinates of beginning and end point of streak Azimuth and elevation of satellite on both sides are determined. On the other hand, to evaluate the proposed method and the validity of the input parameters for initial orbit determination, the azimuth and elevation values of the beginning and end points of streak can be calculated by precise orbit file and then these results compare with results of purposed method. Comparing results indicate a difference of about milliseconds.}, keywords = {satellite tracking,satellite streak detection,MSAC,DBSCAN clustering}, title_fa = {استخراج خودکار مشاهدات اپتیکی جهت تعیین مدار اولیه ماهواره‌ها}, abstract_fa = {تعیین مدار در یک جمله، کاربرد انواع تکنیک­ها جهت برآورد مدار اجرام فضایی نظیر ماه، سیارات و فضاپیماها می­باشد. تعیین موقعیت مداری امکان شناسایی اجرام موجود در فضا را فراهم می­آورد. به این معنی که می­توان جرم مورد نظر را در کاتالوگ آرشیوی تعیین مدار موجود جستجو کرد و در صورت عدم وجود در آرشیو به ‌عنوان جرم جدید، کاتالوگ کرد. به‌منظور تعیین موقعیت مداری، مشاهدات به‌صورت اطلاعات خام در فرآیند تعیین مدار مورد استفاده قرار خواهند گرفت. مشاهدات مختلفی ممکن است جهت تعیین مدار اولیه مورد استفاده قرار گیرند، ولی از آنجا که استخراج مشاهدات طولانی، مشکل، گران و گاهی اوقات غیرممکن است، از مشاهدات زاویه­ای استفاده می­شود. در این مقاله روشی جدید برای استخراج مشاهدات زاویه­ای از طریق سیستم تصویربرداری اپتیکی ارائه شده است. در این روش با استفاده از یک CCD و تلسکوپ مناسب، تصویری از آسمان که دارای اطلاعاتی مربوط به ستاره­ها و رد پای ماهواره است، ثبت می‌شود. از آنجا که برای انجام تعیین مدار اولیه باید مقدار آزیموت و زاویه ارتفاعی حداقل دو نقطه از مدار ماهواره در یک فاصله زمانی در اختیار باشد، در این تحقیق روشی خودکار جهت استخراج مدل اثر رد ماهواره ارائه شده است تا با استفاده از مدل استخراج شده مختصات نقاط ابتدا و انتها تشخیص داده شوند. جهت ارزیابی روش پیشنهادی سمت ‌و سوی استخراج شده از رد ثبت شده ماهواره مدار ارتفاع بالا MUOS (Mobile User Objective System) با مقادیر نظیر آن مستخرج از مدار دقیق مقایسه شده‌اند. نتایج حاصل بیانگر اختلافی در حد میلی‌ثانیه می­باشد.}, keywords_fa = {ردیابی ماهواره,استخراج رد پای ماهواره,الگوریتم MSAC,الگوریتم خوشه‌بندی DBSCAN}, url = {https://jesphys.ut.ac.ir/article_64866.html}, eprint = {https://jesphys.ut.ac.ir/article_64866_596b55b6c50eee7f15955d6406abf1be.pdf} } @article { author = {Movaghari, Ramin and Javan Doloei, Gholam}, title = {Upper Crustal Structure of South West of Tehran Using Borehole Ambient Noise Tomography}, journal = {Journal of the Earth and Space Physics}, volume = {44}, number = {2}, pages = {281-295}, year = {2018}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2018.237090.1006914}, abstract = {The crustal structure study based on ambient noise measurements has become a popular, fast and reliable method in earthquake seismology in recent years around the world. Generally, not only in seismology but also in other applications which deal with signals, accept noise as an undesired component of the signal. It is believed that noise obscures data and does not contain useful information. Ambient noise measurements promise significant improvements in the resolution and accuracy of crustal and upper mantle images. Traditional dispersion analysis, however, does not yield reliable estimates of the structure in the shallow crust because of strong scattering at short-periods (T<30). Recent advances in surface-wave ambient noise tomography (e.g., Shapiro et al., 2005; Sabra et al., 2005; Yao et al., 2006; Yang et al., 2007; Lin et al., 2007) greatly enhance our ability to resolve the shallow crustal structure. In this study, we apply ambient noise tomography to image and investigate the shallow shear velocity structure of the upper crust beneath south west of Tehran area. Data from seven stations of Iranian Long Period Array (ILPA) are acquired from IRIS free data center. These data were recorded during 1975 to 1977 in corporation of the FDSN with the Institute of Geophysics at University of Tehran. At the moment, all continuous seismic waveforms are available for researchers. After obtaining the continuous waveforms, we preprocessed and segmented the data into one hour time windows. Hourly cross correlation of ambient noise between all station pairs were calculated and group velocity of Rayleigh waves dispersion curve in periods between 3 to 10 seconds are measured from the Green’s function resulting cross correlations. To determine dispersion curves of surface waves we have used the Frequency-Time Analysis technique (FTAN). Because of using borehole seismometer in ILPA array and our new Gaussian noise selection proposed method; all Green functions had acceptable SNR ratio and greater than 10. Therefore, we predict the suitable and reliable result of Green’s functions in comparison with ambient noise of free surface seismometers. Then using dispersion map in each period, we extracted a local dispersion curve for each grid point. Finally, the quasi-3D shear wave velocity model in the study area provided using nonlinear inversion procedure for each grid point of local dispersion curves by means of Shapiro et al., (2005) technique. By preparing different shear wave velocity profiles in the direction of NE-SW, of the studied area, we try to image the changing velocity variations and trends along the profiles, which can indicate the existence of one of the branches of the IPAK fault, or the existence of an anticline with the axis in this direction and the slope to mards the northeast direction. The results indicate a reliable image from upper crust of south east of Tehran region in consistent with the results of Doloei and Roberts (2003) from teleseismic P-waveform time domain receiver function (RF) method. Moreover, the upper crustal structural model proposed for this area is in agreement with surface geological setting. Therefore, we suggest that for isolating the ambient noise from temporary and very local conditions, the digging and covering the seismic stations prepares a suitable noise level for the crustal structure studies.}, keywords = {ambient noise,cross correlation,Dispersion curves,Tomography,borehole seismometer,TEHRAN}, title_fa = {تعیین ساختار سرعتی پوسته بالایی جنوب غرب تهران با استفاده از توموگرافی نوفه لرزه‌ای درون‌چاهی}, abstract_fa = {روش توموگرافی نوفه محیطی در سال‌های اخیر به‌منظور مطالعه ساختارهای سرعتی در عمق‌های مختلف و در مناطقی با لرزه‌خیزی پایین به‌طور گسترده استفاده شده است. در مطالعه حاضر، نوفه لرزه‌ای ثبت شده در آرایه بلند دوره ایران (ILPA) واقع در ناحیه جنوب غرب استان تهران با به‌کارگیری روش توموگرافی نوفه لرزه‌ای مورد مطالعه قرار گرفته است. با استفاده از تکنیک همبستگی متقابل، توابع گرینتجربی در دوره تناوب بین 3 تا 10 ثانیه با فواصل بین ایستگاهی حداقل 24 کیلومتر محاسبه و سپس منحنی‌های پاشندگی سرعت گروه این توابع برای انجام فرآیند توموگرافی لرزه‌ای محاسبه شده‌اند. به دلیل استفاده از حس‌گرهای درون‌چاهی در عمق 100 متری در شبکه ایلپا (ILPA) و همچنین استفاده از روش انتخاب نوفه گوسی، توابع گرین به‌دست‌آمده بین همه جفت ایستگاه‌های ممکن دارای نسبت سیگنال به نوفه قابل قبول بودند. در ادامه با استفاده از نقشه‌های سرعت گروه برای هر دوره معین، منحنی پاشندگی محلی در هر سلول جغرافیایی تعیین و با انجام فرآیند وارون سازی غیر خطی، مدل عمقی سرعت موج برشی محاسبه و ارائه شد. این روش امکان برآورد مدل شبه سه‌بعدی موج برشی تا عمق 15 کیلومتر را برای پوسته فوقانی ناحیه جنوب غرب استان تهران فراهم نموده است. با بررسی پروفیل‌های سرعت موج برشی در راستای شمال شرق- جنوب غرب، یک تغییر روند سرعت در راستای پروفیل‌ها دیده می‌شود که می‌تواند نشانگر وجود یکی از شاخه‌های گسل ایپک و یا وجود تاقدیسی با سطح محور در این راستا و شیب به سمت شمال شرق در پوسته بالایی منطقه مورد مطالعه باشد.}, keywords_fa = {نوفه,همبستگی متقابل,منحنی پاشندگی,موج برشی,توموگرافی لرزه‌ای,لرزه‌نگار درون‌چاهی}, url = {https://jesphys.ut.ac.ir/article_64854.html}, eprint = {https://jesphys.ut.ac.ir/article_64854_46139aa6b2030ae366f259c39425a85b.pdf} } @article { author = {Reyhani, Sara and Gholamzadeh, Abbas}, title = {Estimation of compressional waves Frequency Dependence of Quality factor in the Faryab region (SE of Sanandaj-Sirjan zone) using aftershocks of Tiab earthquake of 28 Feb 2006}, journal = {Journal of the Earth and Space Physics}, volume = {44}, number = {2}, pages = {297-306}, year = {2018}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2018.239278.1006924}, abstract = {Seismology has an important role in identifying earth structure using seismic waves. The amplitude and frequency of these waves change when they pass into the earth due to anisotropy and heterogeneity. Seismic waves decay as they radiate away from their sources, partly for geometric reasons because their energy is distributed on an expanding wave front, and partly because their energy is absorbed by the material they travel through. The energy absorption depends on the material properties. The amplitude of seismic waves decreases with increasing distance from earthquake, explosion, and impact sources. How this amplitude decrease, occurs, how rapidly it occurs, and how it depends on the frequency of the seismic waves is fundamentally important to the efforts to describe Earth structure and seismic sources. Attenuation of seismic waves is expressed with inverse quality factor (Q-1) and helps us to understand the physical laws governing the propagation of seismic waves in the lithosphere. The observed seismic-wave amplitudes usually decay exponentially with increasing travel distance after the correction for geometrical spreading. These decay rates are proportional to the Q−1 values which characterize the spatial attenuation of seismic waves. The study area is located in Fariab region, south-east of Sanandaj-Sirjan metamorphic zone and adjacent to the Main Zagros Reverse Fault (MZRF). This rejoin is among the rare regions located in Sanandaj-Sirjan area which has high seismic activity. Seismicity in this area has a north east- south west trend. Depths of events are relatively low, in the range of less than 40 km. The 28 Feb. 2006 earthquake with a magnitude of Mw=6.0 has taken place in this region. Despite the remarkable magnitude of this earthquake, no significant damage was reported, even for low strength buildings such as clay buildings. This phenomenon may indicate a significant attenuation of the elastic wave in the area. Aftershocks of this event have been recorded by a temporary network. The well-located aftershocks, with hypocentral distances less than 100 km, have been used for estimation of the P-wave quality factor. The attenuation of P-waves has been estimated using waveforms of 431 well-located aftershocks. The attenuation of P-wave (QP-1) has been estimated at 5 frequency bands (1.5, 3, 6,12,24 Hz) using extended coda normalization method. The estimated QP values show highly frequency dependency. The frequency dependent relation for longitudinal waves in the study area has been derived as Qp=23f-0.78. The QP values have been estimated by using waveforms with two major directions to investigate the probably existed attenuation anisotropy. The frequency dependent relation in two directions of north west-south east and north east-south west were calculated as Qp=10f-0.94 and Qp=25f-0.75, respectively. It has been observed that the quality factor value at the reference frequency of 1 Hz is smaller than 200, which is reported for seismically active regions. Therefore it could be concluded that this region is active in terms of seismicity and tectonics. The small values of the quality factor which demonstrates the relatively high attenuation indicate high seismic activity of this region. This is not so compatible with what we expect for the earth’s crust structure in this area with the metamorphic zone. This high attenuation is probably due to the crushed zone affected by various earthquakes in this region.}, keywords = {Attenuation,compressional wave,Coda normalized method,Sanandaj- Sirjan zone,Faryab}, title_fa = {برآورد ضریب کیفیت امواج تراکمی وابسته به فرکانس در ناحیه فاریاب (جنوب شرق زون سنندج-سیرجان) با استفاده از پس‌لرزه‌های زلزله 9 اسفند 1384 تیاب}, abstract_fa = {گستره مورد مطالعه ناحیه فاریاب، در جنوب شرق زون دگرگونی سنندج- سیرجان و در مجاورت گسل معکوس اصلی زاگرس MZRF قرار دارد. این ناحیه جزو معدود نواحی در گستره سنندج- سیرجان است که فعالیت لرزه­ای بالایی از خود نشان می­دهد. زمین‌لرزه 9 اسفند 1384 با بزرگای 0/6 Mw= در این ناحیه رخ داده است. به‌رغم بزرگی قابل‌توجه، آسیب قابل‌ملاحظه‌ای حتی به ساختمان‌های ضعیف خشت و گلی روستایی وارد نشد که می‌تواند نشانگر توان محیط در جذب بالای انرژی امواج باشد‍. پس­لرزه­های این رویداد جهت محاسبه کاهندگی امواج تراکمی مورد استفاده قرار گرفته است. جهت برآورد رابطه وابستگی فرکانسی ضریب کیفیت امواج P به روش نرمال‌سازی کدا، از 431 پس­‏لرزه به‌دقت تعیین محل شده، استفاده شده است. در این روش ضریب کیفیت امواج تراکمی در 5 بازه فرکانسی در منطقه فاریاب تعیین شده است. رابطه وابستگی فرکانسی برای امواج طولی در منطقه مورد مطالعه به‌صورت Qp=23 f 0.78 به دست آمده است. رابطه وابستگی فرکانس برای پرتو­های منتشر شده در دو امتداد شمال غرب- جنوب شرق و شمال شرق- جنوب غرب به‌ترتیب به‌صورت Qp=10 f 0.94 و Qp=25 f 0.75است که مقدار ضریب کیفیت در بسامد مرجع 0/1 هرتز کمتر از 200 می­‏باشد. بنابراین می­‏توان نتیجه گرفت که این منطقه از لحاظ لرزه‌خیزی و زمین­‏ساختی فعال می­‏باشد. کم بودن فاکتور کیفیت که دلالت بر کاهندگی نسبتاً زیاد دارد نشانگر فعالیت لرزه­ای زیاد این ناحیه است و با انتظار ما از ساختار پوسته این ناحیه که زون دگرگونی است چندان انطباق ندارد. این کاهندگی زیاد احتمالاً ناشی از زون خورد شده در اثر زلزله­های متعدد این ناحیه است.}, keywords_fa = {کاهندگی,امواج تراکمی,روش نرمال‌سازی کدا,سنندج- سیرجان,فاریاب}, url = {https://jesphys.ut.ac.ir/article_64858.html}, eprint = {https://jesphys.ut.ac.ir/article_64858_db86531c9b348bd6cd0b32bf4201b419.pdf} } @article { author = {Fattahi, morteza and Mehrshahi, Dariush}, title = {OSL Dating of Maibod Loess deposits and their formation interpretation}, journal = {Journal of the Earth and Space Physics}, volume = {44}, number = {2}, pages = {307-319}, year = {2018}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2018.253856.1006986}, abstract = {Loess deposits mainly of silt particles with different mineralogical sources have covered about 10 percent of the Earth land area. World-wide studies on loess deposits show that most of the loess deposits accumulated during the Glacial ages while during the inter-glacial phases their accumulation has stopped or dramatically lessened. Loess deposits have recorded the past climatological history within their grains which can be used to distinguish possible climate changes during the Quaternary period. Dating of paleo-proxy records such as loess sediments also have the potential for understanding the chronology of paleo environmental events including tectonic activities. Loess deposits around the world were among the first sediments to be used for luminescence dating particularly within the arid and semi-arid areas. The development of luminescence dating techniques and our understanding of loess palaeosol sequences have progressed over the past 35 years with both fields of study supporting the development and understanding of the other. Luminescence dating dosimeters are grains of feldspar and quartz, which are both typically abundant in loess, and, because loess is a fine-grained aeolian deposit and its nature implies medium-to-long transport distances, any previous luminescence signal should be reset (or ‘removed’) prior to deposition. Luminescence dating is also an important tool for developing numerical chronologies for loess deposits, providing comparison of different records and the study of correlations between records.  Furthermore, the event being dated is the last exposure of the sediments to daylight, which directly relates the luminescence age to the time of deposition of the sediment. Study and dating of loess deposits from different parts of Iran can help to test this hypothesis. Several investigations on loess deposits from North and North-eastern Iran (including North of Alborz Mountains, Gorgan and Gonbad Kavous) led to limited chronological results. On the other hand, although loess sediments have been distinguished in different parts of central Iran (i.e. Kerman and Yazd provinces) there was not a single study of loess deposits in this area so far. As a result, we decided to attempt a research on loess deposits of central Iran. One of important areas of loess remains in central Iran is Maibod area located in central part of Yazd Province. Maibod is located in the main high-way towards the Persian Gulf region.  Loess deposits formed as local ridges accumulated on an extended fault-erosional terrace in southern side of Maibod. Since study and dating of such deposits can clarify parts of tectonic history of Maibod area the outcome from such research is correct can be crucial.  Furthermore, investigation on loess deposits of such dating-free location can significantly add to its Quaternary Paleoenvironmental/Paleoclimatological knowledge. Consequently, we extracted a sample from parts of loess deposits over the Maibod terrace. The extraction point is located on the western side of Maibod City where the loess sediments becoming very hard and they formed wide varieties of yardang to interfluve ridges with a few meters height. Contaminated Quartz grains of 90–180 μm and the post IR single-aliquot regenerative-dose protocol were employed for De determination. Experiments were carried out in Oxford University using a Riso TA-15a automated TL/OSL system (Botter-Jensen, 1997) incorporating an IR laser diode (400mW, 830±5 nm), and a Strontium-90 beta source. After laboratory works and dating of the sample (at 30000 to 39000 years ago) the accumulation period has been distinguished at around the middle of the last glacial age (Wurm). Considering the major water erosion over both top loess (late Quaternary) and its green marl basement (Neogene) and due to the distinct slope escarpment (terrace-like feature) we can conclude that the accumulation phase was after the last fault activity. In other words, most active seismic event has happened earlier than loess deposition before 3000 to 39000 years ago. Due to the relatively intact feature of nearby ancient Narin castle (3000 years old) we can conclude that the most sever tectonic activities in the area occurred between 3000 to 40000 years ago approximately. Such single conclusion needs to be evaluated with more studies and many OSL dating on loess deposits of central Iran.}, keywords = {Dating,OSL,loess,quaternary paleoclimate,meibod}, title_fa = {استفاده از روش لومینسانس نوری جهت تعیین سن رسوبات لسی اطراف شهر میبد و تفسیر شرایط تشکیل آنها}, abstract_fa = {نهشته‌های لسی تاریخچه آب‌و‌هوایی و وضعیت جریان گردوغبار جوی دوران گذشته را در خود ضبط کرده‌اند و وجود آنها در یک منطقه، مراحل مختلفی از تغییر اقلیم در دوره زمین‌شناسی «کواترنر» را نشان می‌دهد؛ اما جهت استفاده مناسب از این منبع اطلاعات، نیاز به تعیین سن این نهشته‌ها و میان لایه‌های کهن خاک بین آنها داریم. جهت سن­یابی رسوبات لس توسط لومینسانس برانگیخته نوری (OSL) به دو پارامتر دز معادل دز طبیعی محیط و دز سالانه نیاز است. به‌منظور اندازه­گیری دز معادل معمولاً از روش SAR استفاده می‌شود. اما در این مطالعه به دلیل خالص نبودن کوارتز پس از دو مرحله شستشو با اسید فلوریدریک به دلیل تولید سیگنال مادون قرمز، از روش نور آبی پس از مادون ­قرمز ([Post IR] OSL) استفاده شد. در این بررسی دز معادل دز طبیعی نمونه­های برداشت شده با تحلیل داده­ها در برنامه آنالیست به روش هیستوگرام محاسبه شد. دز سالانه محیط توسط روش ICP و سن نمونه یا آخرین زمان رسوبگذاری آن 3900 ± 34600 سال پیش به دست آمد. با توجه به این سن، زمان رسوب‌گذاری ذرات سیلت معادل اواسط دوره وورم بوده است که به آخرین عصر یخچالی مربوط می‌شود. به این دلیل رسوب‌گذاری این لس‌ها در ایران مرکزی در شرایط سرد و خشک بوده و با وزش بادهای شدیدی که منجر به ایجاد کوهریگ‌هایی نیز در مناطق اطراف دشت یزد شده بودند مطابقت دارد.}, keywords_fa = {سن‌یابی,لومینسانس برانگیخته نوری,لس,دیرینه اقلیم کواترنر,میبد}, url = {https://jesphys.ut.ac.ir/article_65879.html}, eprint = {https://jesphys.ut.ac.ir/article_65879_f711e3eb9fc2baedba254cdce1d6a5d0.pdf} } @article { author = {Zare, Meysam and Mohebalhojeh, Ali Reza and Mirzaei, Mohammad}, title = {Identification of inertia–gravity waves ducts over Iran during January to March 2016}, journal = {Journal of the Earth and Space Physics}, volume = {44}, number = {2}, pages = {321-332}, year = {2018}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2017.230635.1006889}, abstract = {When a fluid is forced by buoyancy and Coriolis forces, it undergoes oscillations. The frequency of ageostrophic oscillations resulting from these two forces is between buoyancy and inertial frequencies; they are thus called inertia–gravity waves (IGWs). These waves play important roles in propagation of energy and momentum in the atmosphere and exert influence on many atmospheric phenomena. The necessary condition for horizontal propagation of IGWs over a large horizontal distance in the atmosphere is the existence of a statically stable layer in the lower troposphere, which is called a wave duct. Actually a wave duct acts as a waveguide and traps wave energy. The underlying mechanism for the formation of a wave duct is provided by reflection of waves propagating from a layer near the surface of the earth and the constructive interference of the reflected waves with the primary propagating waves. The wave duct provides suitable environment for the maintenance of waves through over-reflection and amplification mechanisms. There are two types of wave duct in atmosphere: thermal wave duct and wind wave duct. Considering that in Iran only a few studies have been carried out on IGWs and their ducts, this study is devoted to the detection and study of the wave ducts happened over Iran in the three-month period from January to March 2016. For this purpose, the data from the Global Forecast System (GFS) with 0.25° × 0.25° resolution are used to identify the spatio–temporal characteristics of the ducts. To identify the wave duct, two conditions are considered that permit wave propagation in the duct: duct should be statically stable and have a minimum thickness of a quarter of the vertical wavelength of the waves observed. By applying these conditions to the data in the domain of study, the number of candidate cases for wave ducts is reduced. Most cases occurred in the Caspian Sea, the Persian Gulf, the north and northeast of Iran. So 10 cases of wave duct were identified; in this research, results for two cases are presented. Also by considering the condition of the existence of an unstable or the reflective layer on top of the wave duct for the two cases, the wave ducts obtained using the first two conditions were further screened. Considering only the points obeying the foregoing three conditions, the wave duct characteristics were then estimated. Given that the lifetime of IGWs propagation in the atmosphere is short, the GFS data used to detect wave ducts are not suitable for identification of IGWs and determination of their propagation mechanisms. In order to detect IGWs propagating in the wave duct, we simulated one of the cases with the WRF mesoscale model. Then, for estimating IGWs properties, the horizontal velocity divergence in different pressure levels was used in the internal domain. The results of led to the identification of two wave packets at different times. Also the cross section of horizontal velocity divergence was used to estimate the properties of the two wave packets. Results showed that for both wave packets, a quarter of the dominant wavelength was less than the average thickness of the ducting layer, so they were consistent with the thickness criterion required for the wave duct formation.}, keywords = {wave duct,inertia–gravity waves,The WRF model,horizontal velocity divergence}, title_fa = {شناسایی مجرای امواج گرانی-لختی بر روی ایران در دورۀ ژانویه تا مارس 2016}, abstract_fa = {یکی از پدیده‌های مهم جوی امواج گرانی‌–لختی هستند که در انتقال انرژی وتکانه نقش بسیار مهی ایفا می‌کنند. شرط لازم برای ماندگاری و انتشار افقی این امواج در جو، وجود مجرای موج یا موجبر است. در این پژوهش، از داده‌های با تفکیک بالای سامانۀ پیش‌بینی جهانی (GFS) برای تعیین مکان و زمان رخداد مجراهای امواج گرانی-لختی در دورۀ سه‌ماهۀ ژانویه تا مارس 2016 بر روی ایران استفاده شد. برای شناسایی مجرای موج، دو شرط برای امکان انتشار امواج در مجرا وجود دارد که مطابق آن مجرا باید از نظر ایستایی پایدار بوده و دارای ضخامت حداقل یک‌چهارم طول موج قائم مشاهداتی باشد. با کاربست این دو شرط در این بازۀ مطالعاتی، ضمن شناسایی 10 مورد رخداد مجرای موج بر روی ایران، دو مورد از آن‌ها انتخاب شد. سپس با کاربست شرط وجود لایه‌ای ناپایدار یا بازتابنده در بالای مجرای موج، به‌عنوان شرط سوم برای این دو مورد مجرا و حذف  نقاطی که این شرط را نداشتند، ویژگی‌های مجرای موج برای سایر نقاط برآورد شد. در ادامه، برای شناسایی امواج گرانی-لختی منتشرشده در مجرای موج، یک مورد انتخابی مجرا با مدل میان‌مقیاس WRF شبیه‌سازی شد. بررسی نتایج این شبیه‌سازی به شناسایی دو بسته‌موج گرانی-لختی منتشرشده در مجرای موج منجر گردید که ویژگی‌های این امواج به کمک ترسیم میدان واگرایی افقی سرعت تعیین شد. نتایج نشان داد که یک چهارم طول موج قائم به‌دست آمده برای دو بسته‌موج فوق کمتر از ضخامت لایة مجراست؛ این امر با شرط ضخامت برای تشکیل مجرای موج مطابقت خوبی دارد.}, keywords_fa = {امواج گرانی-لختی,مجرای موج,مدل WRF,واگرایی سرعت افقی}, url = {https://jesphys.ut.ac.ir/article_63595.html}, eprint = {https://jesphys.ut.ac.ir/article_63595_e96575666022245f9f65eab4ab522081.pdf} } @article { author = {Gerkaninezhad Moshozi, Zahar and Bazrafshan, ommolbanin}, title = {Impact of climatic signals on the wet and dry season precipitation (case study: Persian Gulf and Oman Sea watersheds)}, journal = {Journal of the Earth and Space Physics}, volume = {44}, number = {2}, pages = {333-349}, year = {2018}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2018.231949.1006893}, abstract = {Recently, the occurrences of extreme events such as droughts have been on the rise almost worldwide. Several researchers speculated the chance of an increase in meteorological extreme conditions in relation to local climate change. Rainfall is the final response to complex global atmospheric phenomena and long-term prediction of rainfall remains a challenge for years to come. An accurate long-term rainfall prediction is necessary for water resources management, food production and maintaining flood risks. Several large-scale climate phenomena affect the occurrence of rainfall around the world; of these large - scale climate modes El Nino Southern Oscillation (ENSO) and Multivariate ENSO Index (MEI) are well known. Many studies have tried to establish the relationship between these climate modes for daily, monthly and seasonal rainfall occurrence around the world but the majority of these studies have not considered the effect of lagged climate modes on future monthly rainfall predictions. Interannual to multidecadal natural local climate variability is afflicted by the El Niño/Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO) and Atlantic Multidecadal Oscillation (AMO). ENSO phenomenon on the tropical Pacific and also PDO are quite important because of their enormous impacts on hydro-meteorological disasters like droughts and floods. The El Niño-Southern Oscillation (ENSO) is strongly linked to the inter-annual to inter-seasonal modifications of Sea Surface Temperature (SST) over the Pacific Ocean equators. On the other hand, the Decadal Pacific Oscillation (PDO) is related to near decadal fluctuations of the Pacific SSTs in the northeastern parts of the ocean. The influence of these oscillations on the global climate is generally more obvious when the ENSO or PDO is in its extreme condition. For such circumstances, the SST deviance over a per-defined ocean waters are highly positive or negative (positive or negative period, respectively). Identifying factors impacting the fluctuations in rainfall and forecasting seasonal trends over several months before any significant role in the planning and development of water resources, are among the significant factors impacting different areas of climate signals. Principal component analysis (PCA) was used in this study to explore the impact of climatic indices on the amount of wet and dry season’s precipitation variability in the Persian Gulf and Oman Sea watershed. PCA is used to reduce the dimensionality of spatially distributed time series of precipitation and to interpret spatial patterns, from a statistical viewpoint, through the distribution of significant eigenvectors that explain an important portion of the series variability. PCA can summarize the prevailing variability in a number of dependent factors into fewer principal components. Wet and dry season data were explored from 22 rain gauge stations in the Persian Gulf and Oman Sea watershed in which 40 climatic indices are analyzed in the period of 1970-2014.  PCA analysis is performed using PAST software for the area with 40 synoptic stations. Result showed that there are three variables that determine more than 96.6% of variance consists of NAO, AO and AMO in the dry season, while AO, Nino1+2 and SOI determine more than 97.8% of variance in the wet season. These climate indices can be attributed to precipitation changes over the Persian Gulf and Oman Sea in the dry and wet season, respectively. The study also shows correlation between SPI of 23 rainfall gauges of the Persian Gulf and Oman Sea watershed and climatic signals. These are significant in large number of weather stations. Numbers of stations with significant correlations are 100% and 95% with NAO and AO in the dry season, whereas 85% and 65% have significant correlations with AO and Nino1+2 in wet season. The linkage between climatic signals and precipitation presented in this paper can be used as one of the important components for wet and dry season precipitation prediction over Iran southern stations.}, keywords = {climatic signals,Principal component analysis,correlation,Persian Gulf and Oman Sea}, title_fa = {واکاوی اثر سیگنال‌های اقلیمی بر بارش دوره‌های خشک و تر (مطالعه موردی: بخشی از حوزه آبخیز خلیج‌فارس و دریای عمان)}, abstract_fa = {در این مقاله به بررسی تأثیر شاخص­های اقلیمی بر میزان بارش دو دوره خشک و تر در حوزه آبخیز خلیج‌فارس و دریای عمان با استفاده از تجزیه‌وتحلیل عاملی پرداخته شده است. لذا داده­های دو دوره یادشده در 22 ایستگاه باران‌سنجی در حوزه آبخیز خلیج‌فارس و دریای عمان و 13 سیگنال اقلیمی در طی دوره آماری 2014-1970 مورد بررسی قرار گرفت. با توجه به نتایج تحلیل عاملی داده­ها با استفاده از نرم‌افزار PAST از بین 40 سیگنال اقلیمی، مشخص شد در دوره خشک در حوزه آبخیز خلیج‌فارس و دریای عمان، سه مؤلفه اصلی در مجموع 6/96 درصد از واریانس داده‌های اولیه را تبیین می‌کنند که برای مؤلفه اول، دوم و سوم به‌ترتیب، 1/83، 1/9 و 6/2 درصد می‌باشند و در دوره تر، سه مؤلفه 8/97 درصد از واریانس داده‌های اولیه را تبیین میکنند که مؤلفه اول، دوم و سوم، به‌ترتیب 1/91، 3/4 و 4/2 درصد از واریانس داده‌های اولیه را تبیین میکنند. مشخص شد که مهم‌ترین عوامل مؤثر بر تغییرات بارش در دوره خشک بر روی اقیانوس اطلس و پس از آن قطب (با واریانس 2/92 درصد) واقع شده است و بخش کمی از تغییرپذیری بارش (با واریانس 6/2 درصد) در دوره خشک مربوط به نوسانات چند دهه‌ای اقیانوس اطلس شمالی است؛ به‌طوری‌که در این دوره بالاترین همبستگی بین شاخص NAO و AO (به‌ترتیب 100 و 95 درصد) با ایستگاه‌های مورد مطالعه وجود دارد. در دوره تر مهم‌ترین کانون تغییرات از سوی قطب شمال و تغییرات دمای اقیانوس آرام جنوبی (با واریانس 4/95 درصد) واقع شده و پدیده نوسانات جنوبی تنها تغییرات کمی (4/2 درصد از واریانس) را بر عهده دارد. به‌طوری‌که در دوره تر، 85 و 65 درصد ایستگاه‌ها به‌ترتیب بالاترین همبستگی معنی‌‌دار را با شاخص AO و Nino1+2 دارند.}, keywords_fa = {سیگنال‌های اقلیمی,تحلیل مؤلفه‌های اصلی,خلیج‌فارس و دریای عمان}, url = {https://jesphys.ut.ac.ir/article_65885.html}, eprint = {https://jesphys.ut.ac.ir/article_65885_84c0e0389f50c93ae1d18df006345c9c.pdf} } @article { author = {Salmanpoor, Hosein and Sharifian, Mehdi}, title = {Solitary waves in interstellar plasma with Cairns distributed electrons in the presence of negative ions}, journal = {Journal of the Earth and Space Physics}, volume = {44}, number = {2}, pages = {351-361}, year = {2018}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2017.234404.1006902}, abstract = {Plasma with both negative and positive ion species and electrons is called negative ion plasma. This type of plasma has a great importance in various fields of plasma science and technology. Among the nonlinear structures, ion-acoustic solitons present the most important aspect of nonlinear phenomena in modern plasma research. When the velocity of the ions and the electrons is much smaller than that of the light, an ion-acoustic soliton exhibits the non-relativistic behavior in the plasmas. But, when the electron and the ion velocities approach the velocity of light in the plasma, relativistic effects dominantly change the soliton behavior. Relativistic plasmas can be found in many situations. Nonlinear structures are usually investigated by using some form of perturbation method. In small amplitude approximation, we usually derive nonlinear partial differential equation like Korteweg–de Vries (KdV) or modified KdV and etc. A great numbers of authors used the reductive perturbation technique, Bharuthramand and Shukla (1986); Yadav and Sharma (1991) studied ion-acoustic solitons. Rizzato (1988) showed that plasmas with components such as positrons in addition to electron and positive ions behave differently. The positrons can be used to probe particle transport in tokamaks and since they have sufficient lifetime, the two-component (e-i) plasma becomes a three-component (e-i-p) one (Surko and Murphy 1990). We know that when the ion velocity approaches the velocity of light, relativistic effects may significantly modify the behavior of the solitary waves. Relativistic plasmas occur in a variety of situations, such as, space plasma phenomena (Grabbe 1989), laser–plasma interaction (Arons 1979), plasma sheet boundary layer of earth’s magnetosphere (Vette 1970) and describing the Van Allen radiation belts (Ikezi 1973). The weakly relativistic effects on ion-acoustic wave propagation in one dimension using the KdV equation for cold plasma without electron inertia have been investigated (Das and Paul 1985). Nejoh (1987) has investigated the same results in the warm plasmas. Kalita et al. (1996) have investigated the existence of solitons considering the complete fluid equation of electrons. EL-Labany (1995) investigated the contribution of higher-order nonlinearity to nonlinear ion-acoustic waves in a weakly relativistic plasma consisting of a warm ion fluid and hot non-isothermal electrons by using reductive perturbation theory. EL-Labany et al. (1996) have investigated ion-acoustic solitary waves in weakly relativistic warm plasma at the critical phase velocity by reductive perturbation theory. Large amplitude Langmuir and ion-acoustic waves in relativistic two fluid plasmas deriving the pseudo potential has been considered by Nejoh (1987). The oblique propagation of nonlinear ion acoustic solitary waves (solitons) in magnetized collision less and weakly relativistic space plasma with positive and negative ions and non-thermal (Cairns distributed) electrons is examined by using reduced perturbation method to obtain the Korteweg-de Vries (KdV) equation that admits an obliquely propagating soliton solution. We investigated the effect of ions velocity and non-thermal electrons on amplitude and width of solitary waves and also other effective parameters on them. We find out that four modes exist in our plasma model but the numerical analysis showed that only two types of ion acoustic modes (fast and slow) exist in the plasma. The fast mode corresponds to the propagation of compressive solitons, whereas the rarefactive solitons exist for the slow mode. We also calculated the energy of soliton and discussed the effect of plasma parameters on it. The amplitude of both types of solitons increases with the angle between the wave vector and magnetic field, the relativistic ion drift velocity, negative ion density and also with non-thermal parameter. The strength of the magnetic field doesn’t change the amplitude of soliton (for both types) but makes its width smaller. With increasing relativistic ions drift velocity the amplitudes of solitons become larger but their widths become smaller.}, keywords = {Interstellar Plasma,Ion acoustic waves and KdV equation}, title_fa = {امواج سالیتونی در پلاسمای میان‌ستاره‌ای با الکترون‌های دارای توزیع کرنز در حضور یون‌های منفی}, abstract_fa = {در این مقاله انتشار مایل امواج سالیتونی غیر‌خطی یونی صوتی در پلاسمای میان‌ستاره‌ای نسبیتی ضعیف و غیر‌برخوردی در حضور یون‌های مثبت و منفی و الکترون‌های غیر‌گرمایی (با توزیع کرنز) بوسیلۀ روش اختلال کاهش‌یافته مطالعه شده است. در این مقاله رابطۀ کورتوک-دی وریز یا KdV (Korteweg-de Vries) که دارای جواب انتشار مایل امواج سالیتونی است، به دست آمده است. اثر سرعت یون‌ها و الکترون‌های غیر‌گرمایی را روی دامنه و پهنای امواج سالیتونی بررسی و همچنین اثر پارامترهایی مثل میدان مغناطیسی و چگالی یون‌ها را مطالعه کرده‌ایم. ما به این نتیجه رسیدیم که معادلۀ پراکندگی (که یک معادلۀ درجۀ چهار است) دارای چهار ریشه است ولی چهار ریشۀ آن به معنای وجود چهار موج سالیتونی نخواهد بود و محاسبات عددی نشان می‌دهد که فقط به‌ازای دو ریشۀ آن دو نوع مد یونی صوتی ( مد تند و کند) در پلاسمای درنظر گرفته‌شده در این مقاله وجود دارد. مد تند وابسته به انتشار سالیتون‌های متراکم است، در حالی که مد کند وابسته به انتشار مد رقیق‌شونده است. همچنین انرژی سالیتون‌ها را محاسبه و اثر پارامترهای پلاسما بر آن را بررسی کرده‌ایم. دامنۀ هر دو نوع سالیتون با افزایش زاویۀ بین بردار موج و میدان مغناطیسی، سرعت سوق نسبیتی یون، چگالی یون منفی و پارامتر غیرگرمایی افزایش می‌یابد. قدرت میدان مغناطیسی، دامنۀ هیچکدام از دو نوع سالیتون را تغییر نمی‌دهد اما پهنای آن‌ها را کاهش می‌دهد. با افزایش سرعت سوق نسبیتی یون، دامنۀ سالیتون‌ها افزایش یافته ولی پهنای آن‌ها کاهش می‌یابد.}, keywords_fa = {امواج یونی صوتی,پلاسمای میان ستاره ای,معادله KdV}, url = {https://jesphys.ut.ac.ir/article_63600.html}, eprint = {https://jesphys.ut.ac.ir/article_63600_1541f130d7aa826cf6833713c902721f.pdf} } @article { author = {Nikbakht Shahbazi, Ali Reza}, title = {Climate change impact assessment on agricultural crop virtual water under RCPs Scenarios in Khouzestan province}, journal = {Journal of the Earth and Space Physics}, volume = {44}, number = {2}, pages = {363-378}, year = {2018}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2018.234830.1006907}, abstract = {Agricultural sector has a vital role in the national economy and food production in Iran, so that about 27 percent of the country's gross domestic product and 22 percent of the workforce are related to this sector. Due to special climatic condition of Iran and poor temporal and spatial distribution of rainfall, irrigated farming is the main form in food production. Despite, somehow, the same dry and irrigated cultivation in the country, the highest production is obtained through irrigation, so that during the last 5 years almost always close to 90 percent of total Iran agricultural production has been by irrigated cultivation. In order to meet the food needs until the year 1410, based on approximate 2600 kcal/day, more than 150 billion cubic meters of annual water will be required that is not available in water cart of Iran. In a globalizing world, where problems increase with the effect of warming and climate changes, it is thought that a decrease in usable freshwater bodies will pose a serious problem. Allan presented the term virtual water for the first time. In the last decade, this concept was paid attention by most researchers of water industry. The term virtual water content (VWC) connects water, food, and trade together and is the opposite of water efficiency. This study intends to investigate climate change impacts on the virtual water content of agricultural crop in Khouzestan province in future periods. The strategic products and production whose data is available such as wheat, barley, rice, corn and sugar cane were selected for this study. Potential evapotranspiration of these products were used during the cultivation periods. The average crop production of each city was taken from ministry of Agricultural affairs and each crop virtual water content was calculated. Wheat and barley are planted both in irrigated and rainfed lands in Khouzestan. The cultivation of rice, maize, and sugar cane are just in irrigated form. The virtual water for each crop was calculated separately. In order to investigate climate change impact on VWC, the CanESM2 atmospheric general circulation model (GCM) data under two RCP scenarios (IPCC-AR5) were used. In order to downscale CanESM2 model data, SDSM analysis software was used. The data used in this study include precipitation, minimum and maximum temperature, daily average temperature, and daily evaporation. To determine the feasibility of future periods meteorological data production of SDSM model, calibration and verification were performed for the base periods. Minimum and maximum temperature and precipitation estimated by SDSM method using CanESM2 data in three future periods: 2030s, 2060s and 2090s and compared with historical data. Results showed that temperature on average increased in all selected scenarios, this increase is higher in the case of RCP8.5 compared to RCP4.5, as precipitation will reduce in 2060s and 2090s. Highest increase of average temperature in Khouzestan is about 4.6° C in 2090s under RCP8.5 and decrease in temperature in 2030s is about 1° C under RCP4.5. The maximum and minimum temperature variation compared to the monitoring period under two RCP scenarios from June to November have increasing trends in 2060s. Precipitation under RCP8.5 for most months on average is declining and the sharpest decline occurs in November, while most months are associated with increased precipitation under RCP4.5. The minimum and maximum temperatures will decrease and increase, respectively, in most months of the year in 2090s, and precipitation has a sharp decrease compared to the observed period under RCP8.5, and a decrease will occur in January, February, and December, although precipitation will increase from August to October. Crop virtual water under RCP4.5 compared to baseline is always less than that of RCP8.5 scenario. Wheat, barley and sugar cane VWC increase compared to RCP4.5. There is 22.5% difference for wheat VWC between two RCP scenarios in 2030s compared to baseline period. For barley, there is 17.5% difference between the two RCP scenarios in 2090s compared to baseline period. For rice, there is 18.2% difference between the two RCP scenarios in 2090s compared to baseline period.}, keywords = {climate change,Agricultural crop,Virtual water,Khouzestan province,RCP scenario}, title_fa = {ارزیابی اثرات نوسانات اقلیم بر میزان آب مجازی محصولات کشاورزی استان خوزستان تحت سناریوهای واداشت تابشی}, abstract_fa = {در این تحقیق تأثیر تغییر اقلیم بر میزان آب مجازی محصولات کشاورزی در دوره­های آتی مورد بررسی قرار گرفت. برای این کار از داده­های اقلیمی مدل گردش کلی CanESM2 تحت دو سناریوی واداشت تابشی در استان خوزستان استفاده شد. جهت بررسی امکان تولید و شبیه‌سازی داده‌های هواشناسی در دوره‌های آتی با استفاده از مدل ریزمقیاس‌نمایی آماری SDSM برای دوره پایه (1990-2011) کالیبراسیون و صحت‌سنجی مدل انجام گرفت. از طریق داده‌های CanESM2 میزان بارش و دمای بیشینه و کمینه ایستگاه‌های منتخب برای سه دوره 2020-2040 (متوسط 2030)، 2070-2050 (متوسط 2060) و 2080-2100 (متوسط 2090) میلادی پیش­نگری و با دوره پایه مقایسه گردید. میزان آب مجازی محصولات کشاورزی برای محصولات منتخب شامل گندم، جو، برنج، ذرت دانه‌ای و نیشکر محاسبه شد. با استفاده از مدل CanESM2 و سناریوهای واداشت تابشی هیئت بین‌الدول تغییر اقلیم (IPCC) شبیه‌سازی و تولید داده‌های هواشناسی در دوره‌هایدوره‌های آتی صورت گرفت و میزان تبخیر و تعرق پتانسیل و میزان آب مجازی متوسط دوره‌ها با اطلاعات تولید شده در دوره‌های آتی به دست آمد. نتایج نشان داد میزان دما به‌طور میانگین در همه ایستگاه­های منتخب و در همه سناریوها افزایش می­یابد و این افزایش در مورد سناریوی RCP8.5 از سناریوی RCP4.5 بیشتر است. میزان میانگین بارش نیز در دوره­های 2060 و 2090 کاهش می­یابد. میزان آب مجازی به‌دست‌آمده برای تمامی محصولات کشاورزی مورد مطالعه روند افزایشی دارد اما این افزایش برای محصول برنج و ذرت دانه‌ای به‌طور متوسط در دوره 2060 و 2090 افزایش بیشتری از خود نشان می­دهد.}, keywords_fa = {تغییر اقلیم,محصولات کشاورزی,آب مجازی,استان خوزستان,واداشت تابشی}, url = {https://jesphys.ut.ac.ir/article_64864.html}, eprint = {https://jesphys.ut.ac.ir/article_64864_687ad38694100fda5f87e282063ff323.pdf} } @article { author = {Tajbakhsh, Sahar and Moradi, Mohammad and Rashidzad, Mehdi and Mohammadpur Panja, mohammadreza}, title = {Forecasting fog using some experimental methods (Tehran and Mashhad airports)}, journal = {Journal of the Earth and Space Physics}, volume = {44}, number = {2}, pages = {379-395}, year = {2018}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2017.234790.1006906}, abstract = {Fog is among the most important weather hazards from the aviation perspective. This phenomenon can substantially lead to horizontal visibility reduction. Therefore, accurate prediction is essential for flight safety and easing air traffic. Fog consists of a weather condition in which water drops and ice crystals reduce the horizontal visibility to less than 1000 meters. Various methods are suggested for fog forecasting. Numerical and statistical methods, experimental approaches, and very short range fog forecasting are some of the most common methods. Experimental methods are commonly used for first guess in forecasting centers. Saunders technique is one of the forecasting methods for radiation fogs using radio sounds data. Although this technique goes back to many years ago, it is being used in many parts of the world, including UK Met Office, and is recommended by World Meteorological Organization. Present study tries to evaluate the performance of two experimental methods using real data after studying synoptic condition of fog occurrence in two selected airports. The validity of them is then measured with the real occurrence in a number of case studies of fog occurrence for the selected airports using the bias technique in order to choose the more appropriate method. In the next step, the more appropriate method is administered using the numerical prediction model output and is again evaluated with the bias technique. In both these methods, an index called fog point temperature has been used, and the fog occurrence has been determined by calculating this temperature and comparing it with the minimum temperature. The selected airports are Mehrabad Airport, Tehran and Shahid Hasheminezhad Airport, Mashhad, which have been chosen because of high flight traffic (in Tehran) and high fog occurrence (in Mashhad). Experimental methods examined in this study are Saunders and Prichars-Crodack techniques, which 25 case studies in selected Airports tried to offer the best results for first guess of fog occurrence. The accuracy of these relations was evaluated comparing real conditions using Bias technique. After choosing the more appropriate method, a similar process has been carried out using numerical prediction model of WRF for the next 12 hours. Results of synoptic evaluations show that high-pressure systems are a major factor in creating coldness in lower levels of the atmosphere. Evaluation of pressure field in this study doesn't show figures below 1020 hPa. Specific humidity values were 6-8 g/kg and 4-6 g/kg for 1000 and 925 hPa levels respectively. Winds are frequently northern or eastern and cold weather advection is seen in selected stations.  In Saunders technique, using radio sound data of 1200 UTC in 25 case studies for mentioned airports, the fog point is calculated. This temperature is then compared with next day's minimum temperature and if the difference is less than -2°C, fog occurrence would be ruled out. Saunders considers this method mostly useful for radiation fog. In Crodack-Prichars technique, which is performed by creating a regression association between temperature and dew point temperature, the fog point temperature is determined. Here again, fog is not formed If the temperature difference is less than -2°C. After calculating fog point temperature using Saunders technique and comparing it with actual observation, it was found that among 25 cases, 15 fog observations were consistent with Saunders technique calculations. In the five cases of fog nonoccurrence, the results of this method were consistent with reality. So, Bias evaluation technique shows 75% for probability of detection. The same process has been carried out for Crodack-Prichars technique. In this method, a linear relationship exists between temperature, due point temperature, and fog point temperature. Wind condition and cloudiness are also presented experimentally in the form of a table. For different amounts of these two factors, a numerical amount of 1.5 to -1.5 is added to the fog point temperature. Fog occurrence is determined by calculating fog point temperature using Crodack-Prichars technique and comparing it with the minimum temperature according to table 2. This evaluation showed that in 13 of 20 fog occurrence cases, the right answer were obtained, and 5 cases of fog nonoccurrence, were consistent with reality. Therefore, POD index was reduced to 65%. Based on the results, Saunders technique has been considered as the more appropriate method for initial guessing in fog forecasting in the airports under study. Now, the values of temperature and due point temperature were determined for the next 12 hours using WRF numerical prediction model, and Saunders technique was used again for predicting fog (using predicted data). The results of this evaluation were also investigated using Bias evaluation technique, which were not so agreeable, so that it was consistent with reality in 50% of cases. Hence, it seems that careful consideration of numerical prediction models output is needed.}, keywords = {fog,Sanders Method,fog point,WRF numerical weather prediction}, title_fa = {پیش‌بینی رخداد مه به کمک برخی روش‌های تجربی (فرودگاه‌های تهران و مشهد)}, abstract_fa = {مه یکی از پدیده‌های وضع هواست که در نشست و برخاست هواپیماها، به سبب کاهش دید، نقش مهمی دارد. در این مطالعه سعی شده است در دو فرودگاه مهرآباد تهران و شهید هاشمی‌نژاد مشهد، ضمن ارائۀ الگوهای همدیدی شرایط مه‌آلود، روشی به منظور بهبود حدس اولیه برای پیش‌بینی مه ارائه شود. با در نظر گرفتن داده‌های موجود، 25 مطالعۀ موردی برای رخداد مه به کمک دو روش تجربی متداول (سندرس و کروداک-پریچارز) در فرودگاه‌های یادشده بررسی و دمای نقطۀ مه با داده‌های واقعی و پیش‌بینی تعیین شد. الگوهای همدیدی در حالت‌های موردی معرف حضور پرفشار قوی با مقادیر حداقل 1020 هکتوپاسکال در نوار شمالی ایران است که با فرارفت هوای سرد تراز 850 هکتوپاسکال، باد‌های شمالی و نم ویژۀ 6 تا 8 گرم بر کیلوگرم همراه است. ارزیابی به روش بایاس نشان داد که روش سندرس در 75% حالات با رخداد مه در فرودگاه‌های یادشده هم‌خوانی دارد. این ارزیابی برای روش کروداک-پریچارز به 65% کاهش یافت. با هدف استفاده از این روش‌ها برای پیش‌بینی رخداد مه، روش‌های یادشده به کمک خروجی‌های مدل پیش‌بینی عددی WRF نیز مطالعه شد و ارزیابی نتایج صحت کمتری (50%) را نشان داد. از این رو به نظر می‌رسد روش تجربی سندرس برای حدس اولیۀ رخداد مه روش مناسبی باشد و در صورت افزایش صحت و دقت خروجی‌‌های مدل پیش‌بینی عددی برای 12 ساعت آینده قابل استفاده است.}, keywords_fa = {حداقل دید فرودگاه,دمای نقطۀ مه,روش سندرس,مه,مدل پیش‌بینی عددی WRF}, url = {https://jesphys.ut.ac.ir/article_63601.html}, eprint = {https://jesphys.ut.ac.ir/article_63601_33f76cf2907adcda412a8fae288ed3db.pdf} } @article { author = {Oji, Ruhollah}, title = {Comparison of Multi-site and Single-site Daily Precipitation and Temperature Extremes Downscaling (Case Study: Southern Coast of the Caspian Sea)}, journal = {Journal of the Earth and Space Physics}, volume = {44}, number = {2}, pages = {397-410}, year = {2018}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2017.234927.1006908}, abstract = {To characterize the linkage between large-scale climate conditions and local climate variability, statistical downscaling techniques have been frequently used in climate-related studies. Different single-site and multi-site approaches to downscaling methods are applied in this regard. Most of the studies, however, have been mainly dealing with downscaling of climatic processes for a specific site or watershed average, but few studies are concerned with the multi-sites downscaling techniques because of the complexity in accurately describing both observed at-site temporal persistence and spatial dependence between different variables and locations (Khalili et al. 2013; Chen et al., 2017). In this study, in order to comparison of multi-site and single-site daily precipitation and temperature extremes downscaling, two methods of Single-site Quintile Mapping (SSQ) and multi-site Modular Expanded Downscaling (ModExDs) (Cannon, 2013) were applied to a set of 5 synoptic stations located within Southern Coast of the Caspian Sea, Iran. The SSQ downscaling technique is based on application of the quantile mapping bias correction step from the Bias Correction Spatial Disaggregation (BCSD; Wood et al. 2002) downscaling algorithm directly to daily GCM data, i.e., without spatial and temporal disaggregation (Bürger et al. 2013). In this study, quantile mapping algorithm with delta method extrapolation for nonlinear bias correction is applied. Expanded Downscaling (XDS) is a perfect prognosis technique which maps large-scale atmospheric fields to local station data. The XDS method is based on defining a multivariate linear regression between predictors and predictands, extended by the side condition that the local co-variability between the variables and stations is preserved (Sunyer et al.). The ModExDs, as a modular of XDS which is implemented in R by Cannon (2013), is performed here. The predictands include daily time series of precipitation and temperature extremes for the 1961-2013 period that leads to create a training set consisting of the first 30 years data, and a test set consisting of the remaining observations. Same variables of the NCEP/NCAR (National Centers for Environmental Prediction/National Centre for Atmospheric Research) reanalysis dataset were considered as climate predictors. Missing values of observed data are filled in by using the sequential k-nearest neighbor imputation method (Kim and Yi 2008) and homogeneity tests, of the R packages RHtestsV3 (Wang and Feng 2010) and RHtests_dlyPrcp (Wang et al. 2010), based on penalized maximal t and F tests (Wang et al. 2007; Wang 2008b), are applied both before and after infilling to assess infilling performance. The methods sensitivity to large-scale anomalies and their skill in replication of the observation data distribution during the validation period (1991-2013) are tested, according to the 27 Climate Extremes Indices (CLIMDEX), using Pearson correlation and Kolmogorov–Smirnov (KS) tests, respectively. Combined tests are used to assess overall model performances. The results showed that the multi-site method of ModExDs was able to pass 66.7, 48.9 and 33.3 percent and the single-site method of SSQ, passed 63, 48 and 29.6 percent of the Kolmogorov–Smirnov (KS), the Pearson correlation and the combined tests respectively. Therefore, both methods performed well in terms of temperature and precipitation downscaling. However, multi-site method performed better than single-site overlay. Correlation tests were passed less frequently than KS tests. Both methods downscaled temperature indices better than precipitation indices. According to the Tables 3, 4 and 5, some indices, notably FD, GSL, TN10p, TN90p, TR and DTR, were passed correlation test successfully. Most of the indices related to the precipitation, especially, Rx5day and R10 were not successfully simulated by any of the methods in the region. Model performance varied widely across the study region. Methods performance, however, were better in the Anzali station regarding to the test 1 (corr). More indices were able to pass the test 2 (KS) throughout the region. However, indices such as DTR, FD, TN10p, TN90p, TNN, were not successfully downscaled or appeared to be fairly weak in all stations except for Gorgan in this regard. The indices of GSL and TX90p could pass the combined test throughout the study area. As mentioned before, methods performance varied across the region. So that the methods performed well in Gorgan station, while both performed worse in Rasht station.}, keywords = {Statistical Downscaling,comparison,extreme temperature and precipitation,the south coast of the Caspian}, title_fa = {مقایسۀ ریزگردانی تک‌ایستگاهی و چندایستگاهی فرین‎های دما و بارش (مطالعۀ موردی: سواحل جنوبی دریای خزر)}, abstract_fa = {به منظور مقایسۀ ریزگردانی تک‌ایستگاهی و چندایستگاهی فرین‎های دما و بارش، عملکرد روش‌های تک‌ایستگاهی نگاشت چندکی (SSQ) و ماژول چندایستگاهی بسط‌یافته (ModExDs)، در شبیه‎سازی اقلیمی 5 ایستگاه سینوپتیک سواحل جنوبی دریای خزر مورد آزمون قرار گرفت. پیش‎بینی‌شونده‎های این پژوهش، سری زمانی فرین‎های دما و بارش روزانه طی دورۀ آماری (2013-1961) است که 30 سال به‌منظور آموزش و 23 سال جهت اعتبارسنجی مدل، در نظر گرفته شد. از متغیرهای بزرگ‌مقیاس جوی آرشیو داده‎های واکاوی (NCEP) نیز به‌عنوان پیش‎بینی‌کننده استفاده شد. با به‌کارگیری 27 شاخص فرین اقلیمی، عملکرد این روش‎ها در حساسیت به ناهنجاری‌های بزرگ‌مقیاس جوی و نیز توانمندی آن در بازنمونه‌برداری توزیع داده‌های مشاهداتی در دورۀ اعتبارسنجی، به ترتیب با استفاده از آزمون‌های همبستگی پیرسون و کولموگروف-اسمیرنوف، مورد آزمون قرار گرفت. به‌منظور ارزیابی کلی مدل، از روش ترکیبی استفاده شد. نتایج نشان داد که رویکرد ریزگردانی تک‌ایستگاهی با گذراندن به‌ترتیب 63، 48 و 6/29 درصد و رویکرد چندایستگاهی نیز با موفقیت در 7/66، 9/48 و 3/33 درصد از آزمون‌های کولموگروف-اسمیرنوف و همبستگی پیرسون و نیز آزمون ترکیبی، در ریزگردانی داده‎های واکاوی، نتایج نسبتاً قابل قبولی را ارائه دادند. روش‎های مورد بررسی، شاخص‌های دما را بهتر از شاخص‌های بارش، ریزگردانی کردند. در مجموع، عملکرد روش ریزگردانی چندایستگاهی، به‌ویژه در ریزگردانی شاخص‎های دما، بهتر از روش تک‌ایستگاهی بود. در حالت کلی، هر دو روش نتایج بهتری در گرگان و عملکرد ضعیف‏تری در رشت نشان دادند.}, keywords_fa = {ریزگردانی آماری,سواحل جنوبی خزر,فرین‎های دما و بارش,مقایسۀ عملکرد}, url = {https://jesphys.ut.ac.ir/article_63603.html}, eprint = {https://jesphys.ut.ac.ir/article_63603_8ccd9c95aae9c5dd23ac8f4dccca451e.pdf} } @article { author = {Faghei, Kazem}, title = {The mass ratio of dwarf nova OT J002656.6+284933}, journal = {Journal of the Earth and Space Physics}, volume = {44}, number = {2}, pages = {411-421}, year = {2018}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2018.238948.1006923}, abstract = {Dwarf novae are a class of cataclysmic variables that consist of a white dwarf star (as primary star) and a low-mass donor star (as secondary star).  The white dwarf and the secondary star orbit each other once every few hours. When the low-mass secondary star fills its Roche-lobe, it becomes tidally distorted due to its vicinity to the white dwarf. Thus, the secondary star matter is transferred into the white dwarf Roche-lobe. The matter being transferred has high angular momentum in respect to the white dwarf and it forms an accretion disk around the white dwarf. The angular momentum of the accretion disk is transferred by viscous torques from the inner regions of the disk to the outer regions. The viscosity is also responsible for heat generation in the accretion disk. The energy generated by viscous dissipation inside the disk is radiated away from the surface of it. That is why the accretion disk has been found to be the source of the luminosity in the dwarf novae. The light curve of a dwarf nova shows the suddenly increase of brightness which is known as outburst. The SU UMa stars, which are a subclass of dwarf novae, exhibit two distinct modes of outburst, normal outburst and superoutburst.  The normal outbursts have amplitude of approximately equal to three magnitude and last typically from one to four days. However, the superoutbursts are approximately one magnitude brighter than normal outbursts and last as long as a couple of few weeks rather than just a few days. During superoutburst, the periodic humps with the name of superhump appear in the light curve of SU UMa stars. The superhump is an additional variation of the brightness which has a period that is a few percent longer than the orbital period of binary star system.  The superhumps are seen in systems with the mass ratio smaller than 0.3, with being the mass ratio as the ratio of masses of secondary star to primary star. In such systems, the disk grows to a size a where and a tidal instability that induces the accretion disc to become eccentric and starts to process in the corotating frame. The superhumps are appeared in the light curve, because of the tidal effects of donor star on the disk and also the viscous dissipation is large when the bulk of the eccentric disc passes the donor star. The observations of OT J002656.6+284933 have confirmed that this object should be a dwarf nova of SU UMa type which the superhumps appear in its light curve in during superoutburst. The recent observations imply that dwarf nova OT J002656.6+284933 has the orbital period 0.13d, the secondary star with massand the superhump period 0.13225d. The analysis of observational data has not been successful to calculate an exact value for the mass ratio (which is the ratio of masses of secondary star to primary star); their estimation for the mass ratio has the uncertainty between 0.1 and 0.15. To solve the problem regarding mass ratio estimation and to simulate this object, we have simulated this dwarf nova in a two dimensional approach using the smoothed particle hydrodynamics method. As mentioned before, the superhumps are the distinctive humps on the light curve and its period can be estimated accurately. Thus, we applied the different values of the mass ratio in the simulations that for which one of them, we could reach to the observational superhump period value.  In the simulations, we assumed that the observational orbital period is 0.13d and applied the mass ratio between 0.14 and 0.18. The simulations imply that the superhump period 0.13225d can be obtained approximately for the mass ratio 0.145.}, keywords = {accretion,accretion disks,stars: cataclysmic variables,nova,dwarf nova}, title_fa = {نسبت جرم در نواختر کوتوله‌ی OT J002656.6+284933}, abstract_fa = {OT J002656.6+284933 یک سیستم ستاره­ای دوتایی است که متشکل از یک ستاره کوتوله سفید (ستاره اولیه) و یک ستاره کم جرم (ستاره ثانویه) می­باشد. مشاهدات تأیید کرده­اند که این جسم می‌بایست یک نواختر کوتوله باشد که در دوره ابرفوران، برآمدگی­های متناوب به نام سوپرهامپ را در منحنی نوری‌اش نشان می­دهد. مشاهدات اخیر بر روی نواختر کوتوله­ی OT J002656.6+284933 دلالت بر دوره تناوب مداری 0.13d، مقدار جرم ستاره ثانویه  و سوپرهامپ با دوره تناوب 0.13225d دارد. متأسفانه تحلیل داده­های مشاهداتی موفق در محاسبه دقیق نسبت جرم سیستم (که حاصل تقسیم جرم ستاره ثانویه به جرم کوتوله ­سفید می­باشد) نبوده و عدم قطعیت قابل‌ملاحظه‌ای برابر با 0.1-0.15 را برای نسبت جرم این سیستم ستاره­ای تخمین زده­اند. به جهت رفع مشکل تخمین نسبت جرم و همچنین به جهت مدل‌سازی این سیستم ستاره­ای، در این مقاله با استفاده از روش هیدرودینامیک ذرات همواره شده، این نواختر کوتوله را با توجه به دوره تناوب مداری مشاهداتی 0.13d و نسبت جرمی­ بین 0.14 تا 0.18 شبیه­سازی نموده­ایم. نتایج شبیه­سازی­ها حاکی از آن است که به‌ازای نسبت جرمی تقریباً 0.145 میتوان به دوره تناوب سوپرهامپ مشاهداتی 0.13225d دست یافت.}, keywords_fa = {برافزایش,قرص‌های برافزایشی,ستارگان,متغیرهای کاتالیسمیک,نواختر کوتوله}, url = {https://jesphys.ut.ac.ir/article_64865.html}, eprint = {https://jesphys.ut.ac.ir/article_64865_fc90b509df10d7164c1691d07f8d94d0.pdf} } @article { author = {Hosseini, Morteza and Gharaylou, Maryam and M. Farahani, Majid}, title = {Case study of the impact of some of dynamical and microphysical properties of cloud on the intra-cloud lightning using WRF model}, journal = {Journal of the Earth and Space Physics}, volume = {44}, number = {2}, pages = {423-437}, year = {2018}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2018.239373.1006926}, abstract = {Lightning is one of the distinct characteristics of thunderstorms. This phenomenon is the most important natural hazards for the power stations, the airline industry, wind farms, forestry management and public due to the high current and temperature at lightning channels. Lightning activity usually occurs 10 to 20 minutes earlier than precipitation and so is needed for the skill of short-term forecasts. In this research, to study some of dynamical and microphysical properties of intra-cloud electric field and lightning, the Mesoscale WRF model was used for simulation of two thunderstorm events (on 15 and 17 April 2012) with different CAPE in Tehran area. It is noteworthy that these case studies have been chosen according to data taken from the Iranian Meteorological Organization (IRIMO) and Lightning Imaging Sensor (LIS). Simulations were conducted using the WRF model initiated by FNL data and are provided in 1 degree space and 6-hour time resolution. Each of the simulations was performed for 36 hours and the first 12 hours of simulation were considered as the spin-up time. It uses one-way nesting for 3 meshes of 27-, 9- and 3-km horizontal grid spacings. Thirty-five vertical levels with a maximum height of 50 hPa were used for all domains. Then, the charge separation scheme was coded based on Saunders et al. (1991) relations. Then, the intensity of the intra-cloud electric field was calculated using outputs of the WRF model simulations and Saunders‘s scheme for two selected case studies. Comparison of the intensity of the intra-cloud electric field and threshold electric field, resulted the time of occurrence of intro-cloud lightning. Also, the effect of maximum values of graupel and ice mixing ratios and maximum values of vertical velocity on charge separation was investigated. To verify the results, output of LPI index was compared to LIS data. Vertical profiles of graupel and ice mixing ratios showed the presence of graupels in the lower levels compared to ice crystals. Also, vertical profile of the charge transferred per collision showed that the maximum values of that is consistent with the presence level of graupels. Moreover, time series of above mentioned parameters showed that the increase of vertical velocity lead to not only the increase of the graupel mixing ratio but also the increase of charge transferred per collision. The results also showed that the time of lightning occurrence well matched with the occurrence time of maximum values of the above mentioned parameters. The LPI index well predicted the time evolution of lightning activity in the study area despite of a relative inability to predict the likely area of lightning activity. Comparison between two case studies showed that the presence of updraft core between the core of graupels and ice crystals had more influence on charge transferred and intro-cloud lightning activity. Analysis of charge polarization also showed that the co-existence of graupel and ice crystal was necessary for charge separation. It also showed that the dominant structure of the electric charges were mainly bipolar, and this kind of polarization resulted in the occurrence of intro-cloud lightning based on previous researches.}, keywords = {Lightning,Graupel,Ice crystal,vertical velocity,WRF model,LPI}, title_fa = {مطالعه موردی تأثیر برخی خصوصیات دینامیکی و خردفیزیکی ابر بر آذرخش درون‌ابری با استفاده از مدل WRF}, abstract_fa = {از مشخصه­های بارز توفان­های تندری، آذرخش است. فعالیت آذرخش معمولاً 10 تا 20 دقیقه زودتر از بارش صورت می­گیرد و همچنین آذرخش­های درون­ابری زودتر از آذرخش­های ابر به زمین رخ می­دهند. در این پژوهش به‌منظور مطالعه اثر برخی خصوصیات دینامیکی و خردفیزیکی ابر بر میدان الکتریکی و آذرخش درون­ابری از مدل WRF برای شبیه­سازی دو رخداد توفان تندری با مقادیر CAPE متفاوت در منطقه تهران استفاده شد. در این راستا، طرح‌واره تفکیک بار بر اساس نظریه غیر القایی پیشنهادی توسط ساندرز و همکاران (1991) تهیه و در مدل جایگذاری شد و شدّت میدان الکتریکی درون­ابری محاسبه شد. نتایج حاصل از شبیه‌سازی‌ها و بررسی نیمرخ قائم نسبت­های آمیختگی گویچه برف و بلور یخ نشان­دهنده‌ی حضور گویچه­های برف در ترازهایی پایین­تر از تراز تجمع بلورهای یخ بود. همچنین، نیمرخ قائم بار کل انتقال­یافته به گویچه برف نشان داد که بیشینه بار منتقل­شده به گویچه برف با تراز تجمع گویچه­های برف هم­خوانی دارد. بررسی سری زمانی پارامترهای ذکر شده نیز نشان داد زمان­هایی که سرعت قائم بالارو افزایش پیدا می­کند، نسبت آمیختگی گویچه برف و همچنین بار انتقال­یافته به آن افزایش پیدا کرده است. مقایسه دو مطالعه موردی نشان داد که قرارگیری بیشینه مقادیر سرعت قائم بالارو مابین ارتفاع بیشینه تجمع گویچه­های برف و بلورهای یخ تأثیر بیشتر و بارزتری بر بار انتقال­یافته و میزان فعالیت آذرخش درون­ابری دارد. بررسی و تحلیل قطبش بارها نیز نشان داد که ساختار غالب بارهای الکتریکی عمدتاً به‌صورت دو قطبی بوده و این نوع قطبش بیان می­کند که در موردهای بررسی شده، عمدتاً آذرخش­های درون­ابری رخ داده است.}, keywords_fa = {آذرخش,گویچه برف,بلور یخ,سرعت قائم,مدل WRF,LPI}, url = {https://jesphys.ut.ac.ir/article_64867.html}, eprint = {https://jesphys.ut.ac.ir/article_64867_3759dfb8518713a41876a7ef3e1074d2.pdf} } @article { author = {Saberi, Aref and Soltani-Gerdefaramarzi, Somayeh and Miryaghoubzadeh, Mirhasan}, title = {Study of drought using meteorological and remote sensing data (Azarbaijan province)}, journal = {Journal of the Earth and Space Physics}, volume = {44}, number = {2}, pages = {439-461}, year = {2018}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2018.239626.1006927}, abstract = {In recent years, drought has created a destructive impact on the ecology, water resources management, and ecological processes. In this context, appropriate and appropriate method for predicting and monitoring the drought could have a significant impact in neutralizing the effect of this natural phenomenon. In this research, drought monitoring and evaluation of data from MODIS images were used in the extraction of NDVI and DVI indices. The study area of West Azarbaijan province is one of the northwest provinces of the country. In this study, images of meteorological index of drought or wet year have been used. ArcGIS 9.3 has been used to prepare and perform the necessary corrections on the images, as well as to prepare the vegetation cover index (NDVI) and vegetation difference index (DVI) using ENVI 4.5 software, to classify the results and output in the formg images. The aim of this study was to evaluate meteorological droughts using SPI and ZSI as monthly intervals and also determine the correlation between vegetation and meteorological droughts that happened in this area. The results of SPI and ZSI indices indicate that in the first three months of the year, the vegetation is moderate in the prevailing region, and in the second quarter of the year, the maps indicate weak and uncoated vegetation, because the rainfall is very limited in this time. On the other hand, in these months of the year, overgrazing has caused plant degradation. Vegetation in the first three months of the year seems to have had more favorable conditions due to the melting of snow and winter and autumn rainfall of the previous year. Percentage of vegetation coverage in the study area for the wet years 1383, 1385, 1390 and 1393, was respectively reported as 19.85%, 19.5%, 19.6% and 19.5% and also in the drought years 1384, 1387, and 1389 it was calculated as 18.71%, 18.7% and 19% respectively. The results of SPI and ZSI indices indicate that in the first three months of the year, the vegetation is moderate in the prevailing region, and in the second quarter of the year, the maps indicate weak and uncoated vegetation because the rainfall is very limited at this time. On the other hand, in these months of the year, overgrazing has caused plant degradation. Should be cautious about further action beacause One NDVI index is correlated with meteorological drought indices SPI and ZSI which is varied with respect to the short-term and long-term interval respectively. The result confirmed that NDVI and SPI indices were appropriate for monitoring and assessment of drought. The highest correlation values between NDVI and DVI was observed for short term intervals of SPI and ZSI (1, 2 and 3 months). Generally the highest correlation values during the statistical period between NDVI and SPI was obtained as well as in the year when normal drought conditions were reported. In addition, the determination of trends of the indices using the Man Kendall test indicated that there exist a downward trend in all indices and there was an increase in drought and vegetation decline during the statistical period.}, keywords = {Meteorological drought,index,remote sensing,correlation,MODIS}, title_fa = {مطالعه خشک‌سالی با استفاده از شاخص‌های هواشناسی و داده‌های سنجش‌ازدور (استان آذربایجان غربی)}, abstract_fa = {در سال­های اخیر خشک­سالی تأثیر مخربی در بیشتر بخش­های اکولوژی، مدیریت منابع آب، و فرآیند­های زیست­محیطی برجا گذاشته است. در این تحقیق جهت ارزیابی خشک­سالی از اطلاعات حاصله از تصاویر سنجندهMODIS  در استخراج شاخص NDVI و DVI استفاده شده ­است. هدف از این تحقیق بررسی خشک­سالی­های هواشناسی در منطقه با استفاده از دو شاخص هواشناسی SPI و ZSI به‌صورت دوره­های ماهانه و همچنین بررسی رابطه بین شاخص پوشش گیاهی با خشک­سالی­های هواشناسی می­باشد. درصد کل پوشش در منطقه مورد مطالعه برای سال­های ترسالی 1383، 1385،1390 و 1393 به‌ترتیب 85/19، 5/19، 6/19 و 5/19 درصد بوده و در سال­های خشک‌سالی 1384، 1387، 1389 به‌ترتیب 71/18، 7/18 و 19 درصد محاسبه شد. بیشترین همبستگی بین شاخص NDVI و  DVIبا دوره­های کوتاه‌مدت (1، 2 و 3 ماهه) شاخص­های SPI و ZSI وجود دارد. همچنین همبستگی معنی‌دار بین شاخص­های پوشش گیاهی و دوره‌های بلندمدت شاخص­های هواشناسی مشاهده نشد. به‌طورکلی بیشترین میزان همبستگی در طول دوره آماری بین شاخص­های SPI و NDVI و همچنین در سالی که شرایط خشک‌سالی نرمال گزارش شد، به دست آمد. علاوه بر این تعیین روند شاخص­های مورد مطالعه با استفاده از روش من-کندال نشان از وجود روند نزولی در همه شاخص­ها و افزایش خشک‌سالی و کاهش پوشش گیاهی در طول دوره آماری می­باشد.}, keywords_fa = {خشک‌سالی هواشناسی,شاخص,سنجش‌ازدور,همبستگی,مودیس}, url = {https://jesphys.ut.ac.ir/article_64869.html}, eprint = {https://jesphys.ut.ac.ir/article_64869_2b75f4fec49d6bb754c5f790d9f54a7d.pdf} } @article { author = {Cheraghalizadeh, Majid and Nazi Ghameshloo, Arezoo and Bazrafshan, Javad}, title = {Integrated Monitoring of Hydro–Meteorological Droughts in Kasilian's Basin (Mazandaran Province)}, journal = {Journal of the Earth and Space Physics}, volume = {44}, number = {2}, pages = {463-477}, year = {2018}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2018.244236.1006933}, abstract = {Drought is a temporary status of water deficit with respect to its long term average condition. Combined Drought Indices (CDIs) are new tools to evaluate general status of drought in a region. In this study, we focus on the integrated monitoring of meteorological droughts (based on temperature and precipitation data) and hydrological droughts (only based on streamflow data) in the Kasilian's basin. The main goal of the investigation is to present a combined drought index called Hydro–Meteorological Drought Index (HMDI) using Principal Component Analysis (PCA) in the basin. PCA is a multivariate technique to reduce dimensionality of data in a number of principal components. The Standardized Precipitation Index (SPI) and the Standardized Precipitation–Evapotranspiration Index (SPEI) were applied to monitor meteorological droughts and the Streamflow Drought Index (SDI) for monitoring hydrological droughts. The data were gathered from the meteorological and hydrometric stations located in Kasilian's basin for the period 1349–50 to 1391–92 as the water year. The station Derzikola (in the upstream) was selected for meteorological analysis and two stations Valikbon and Shirgah were employed to analyze hydrologic drought conditions in the upstream and downstream of the basin, respectively. The preliminary controls on the quality of available data were accomplished using some statistical tests for randomness, normality, adequacy of record length, outliers and temporal trend. Employing 49 probability distributions showed that Wakeby is the best fit distribution for precipitation and streamflow data and General Extreme Value for the difference series of precipitation minus evapotranspiration. The meteorological (SPI and SPEI) and hydrological (SDI) drought indices were calculated at four time windows including 3, 6, 9 and 12 months (each of which starts from the month Octobr). In the next stage, for calculation of hydro–meteorological droughts, using PCA technique, two combined drought indices including SPI–SDI and SPEI–SDI were built. The combined indices, which are the standardized form of the first principal component (PC1), was individually calculated at upstream (for hydrometric station of Valikbon) and downstream (for hydrometric station of Shirgah) of the basin. PC1s were able to explain 74.3–87.9% of variabilities in data. The PC1 of the combination SPEI–SDI explained more variability than the SPI–SDI, both in upstream and in downstream of the basin. This may be related to the high correlation of SPEI and SDI series. The results showed that, for identification of dry years, SPEI–SDI is more successful than SPI–SDI at the upstream station. Therefore, combination of two indices with high correlation made satisfactory results in detecting overall status of droughts in the basin of interest. On the other hand, both combined drought indices have no differences in monitoring droughts at the downstream station. Also, during continuing dry periods, combined indices indicated drought status one month earlier in comparison with single indices. Accordance of the classified series of SPI and SPEI with combined drought indices was higher at larger time scales than smaller ones. This may be due to smoother series of single drought indices at larger time scales as well as high correlation level between indices employed in constructing HMDI.}, keywords = {precipitation,Streamflow,Combined Indices,Multivariate Methods,evapotranspiration}, title_fa = {پایش یکپارچه خشک‌سالی‌های هوا-آبشناسی در حوزه آبریز کسیلیان (استان مازندران)}, abstract_fa = {در مطالعه حاضر، پایش یکپارچه وضعیت خشک‌سالی‌ هواشناسی (بر مبنای متغیر‌های دما و بارش) و خشک‌سالی آب‌شناسی (بر مبنای جریان رودخانه) در حوضه کسیلیان مازندران مورد توجه قرار گرفت. هدف اصلی تحقیق حاضر، ارائه یک شاخص خشک‌سالی ترکیبی با استفاده از روش‌ چند متغیره تحلیل مؤلفه اصلی (PCA) در حوضه مورد بررسی است. برای پایش خشک‌سالی هواشناسی از شاخص‌های بارش استاندارد (SPI) و شاخص بارش- تبخیر و تعرق پتانسیل استاندارد (SPEI) و برای پایش خشک‌سالی آب‌شناسی از شاخص خشک‌سالی جریان رودخانه (SDI) استفاده شد. داده­های مورد نیاز این مطالعه از ایستگاه­های هواشناسی و آب‌شناسی مستقر در حوضه کسیلیان برای یک دوره آماری 43 سال آبی (50-1349 تا 92-1391) گردآوری شد. پس از انجام کنترل‌های مقدماتی روی کیفیت داده­ها، شاخص‌های خشک‌سالی هواشناسی و آب‌شناسی در چهار پنجره زمانی 3، 6، 9 و 12 از ابتدای سال آبی محاسبه شد. در مرحله بعد، دو شاخص ترکیبی برای ارزیابی خشک‌سالی‌های هوا-آب‌شناسی، یکی SPI-SDI و دیگری SPEI-SDI با استفاده از روش PCA ساخته شد. شاخص ترکیبی که فرم استاندارد شده نخستین مؤلفه اصلی شاخص‌های مورد استفاده در ترکیب است، به‌طور جداگانه برای ایستگاه‏های آب‌شناسی ولکبن و شیرگاه واقع در بالادست و پایین‌دست حوضه محاسبه گردید. نتایج نشان داد که در شناسایی سال‌های خشک، در بالادست حوضه، ترکیب‏ SPEI-SDI به دلیل ساختار همبستگی قوی‌تر و توجیه درصد تغییرپذیری بیشتر توسط اولین مؤلفه اصلی آنها (5/75 تا 9/87 درصد) موفقیت بیشتری نسبت به ترکیب SPI-SDI دارد. این در حالی است که بین دو ترکیب در پایش خشک‌سالی‌ها در پایین‌دست تفاوت چندانی وجود ندارد. همچنین، در دوره‌های خشک ممتد، شاخص ترکیبی یک ماه زودتر از شاخص‌های منفرد وضعیت خشک‌سالی را اعلام می‌کند.}, keywords_fa = {بارش,جریان رودخانه,شاخص‌های ترکیبی,روش چند متغیره؛ تبخیر و تعرق}, url = {https://jesphys.ut.ac.ir/article_64856.html}, eprint = {https://jesphys.ut.ac.ir/article_64856_ef3befd53e92be1e55a44555e4669d7b.pdf} } @article { author = {Mojarrad, Firouz and Naseriyeh, Mahtab and Hashemi, Sirous}, title = {Investigation of Periodic and Seasonal Variations of Urban Heat Island (UHI) at Night and Day Using Satellite Imagery in Kermanshah City}, journal = {Journal of the Earth and Space Physics}, volume = {44}, number = {2}, pages = {479-494}, year = {2018}, publisher = {Institute of Geophysics, University of Tehran}, issn = {2538-371X}, eissn = {2538-3906}, doi = {10.22059/jesphys.2018.247773.1006952}, abstract = {Urban Heat Island (UHI) as one of the factors influencing human activity within the cities that has become very important simultaneously with the physical development of cities in recent decades. With the advance of thermal satellite imagery in the last few decades and the possibility of retrieve of Land Surface Temperature (LST), these data have been used to assess the Surface Urban Heat Island (SUHI), which is directly linked to the UHI. The purpose of this study is to investigate periodic and seasonal variations of UHI in Kermanshah city using satellite imagery. Kermanshah is the most important city in the central region of western Iran and the capital of Kermanshah Province. The elevation of the city from the sea level is about 1322 meters and its area is approximately 96 square kilometers. Based on the results of the general census of population and housing, the population of this city in 2006, 2011 and 2016 were 784602, 851405 and 946651 respectively. The population of the city during the 60-year period from 1956 to 2016 has increased sevenfold. To study the SUHI in this city, the MODIS product images were used with a 1 km spatial resolution at 10:30 and 22:30 in the two 1-year periods: old period (2000-2001) and the new period (2015-2016), as well as Landsat images at three different times (May 9, 1987, May 4, 2000, and May 15, 2015) to retrieve land surface albedo and vegetation cover. In this way, the diurnal, seasonal and annual variations of the UHI were studied using the Surface Urban Heat Island (SUHI) index, which is difference between the surface temperature of urban and non-urban areas. This difference was studied in two ways: 1- Between the average temperature of all pixels inside and outside the city 2- Between the representative pixel temperature inside the city (near Azadi Square in the city center), and the representative pixel temperature outside the city (a point near the south of Shahid Ashrafi airport). The results of the study showed that the urban areas during the day, especially in the warm period of the year, have a lower surface temperature than non-urban areas due to the role of the reflective roofs in increasing the surface albedo; hence, the Surface Urban Cool Island (SUCI) is formed and the value of the SUHI index is negative. In the new period (2015-2016), due to the further development of the city, the effect of reflective roofs on the city temperature reduction is intensified, and along with the deterioration of the vegetation cover outside the city and the rise of temperature, the SUCI is strengthened so that the average temperature in the city is 1.5 degrees lower than outside the city. In extreme cases, the value of the SUHI index reaches +2.65 and -3.44. At night, the situation is reversed and the temperature inside the city is about 1 to 2 degrees higher than the outside of the city mainly due to the anthropogenic heat. Therefore, the value of the SUHI index is positive and the UHI is formed. In the case of point comparison (the difference between the temperature of two representative pixels inside and outside the city), the differences inside and outside the city increase by about two-fold, i.e, 3 to 4 degrees. In extreme cases, the value of the night time SUHI index reaches +7.4 and -9.9}, keywords = {Urban Heat Island (UHI),Land Surface Temperature (LST),Urban Cool Island (UCI),Satellite images,Kermanshah}, title_fa = {بررسی تغییرات دوره‌ای و فصلی جزیره گرمایی شهر کرمانشاه در شب و روز با استفاده از تصاویر ماهواره‌ای}, abstract_fa = {جزایر گرمایی شهری (UHI) به­عنوان یکی از عواملی که فعالیت انسان را در داخل شهر­ها تحت تأثیر قرار می­دهد، هم‌زمان با توسعه فیزیکی شهرها در دهه­های اخیر، اهمیت زیادی پیدا کرده است. با ظهور تصاویر ماهواره‌ای گرمایی در چند دهه اخیر و امکان بازیابی دمای سطح زمین (LST)، این داده­ها برای ارزیابی جزیره گرمایی سطحی شهری (SUHI) که با UHI ارتباط مستقیم دارد، مورد استفاده بوده است. هدف از این تحقیق بررسی تغییرات دوره­ای و فصلی جزیره گرمایی شهر کرمانشاه با استفاده از تصاویر ماهواره­ای است. بدین­منظور از محصولات دمای سطح زمین سنجنده MODIS در دو دوره یک­ساله (2001-2000 و 2016-2015) برای بررسی تغییرات جزیره گرمایی سطحی شهری و همچنین تصاویر سنجنده­های لندست (TM, ETM+, OLI/TIRS) در سه دوره (2015-2000-1987) برای بررسی تغییرات پوشش گیاهی و بازتاب سطح زمین استفاده شد. نتایج نشان داد مناطق شهری در طول روز به­خصوص در دوره گرم سال، نسبت به مناطق غیرشهری دمای سطح کمتری دارند و در آنها جزیره سرمایی سطحی شهری (SUCI) تشکیل می­شود. در شب، به­ویژه در بهار وضعیت فوق معکوس و دمای مناطق شهری به­دلیل انتقال گرمای محسوس در حدود 1 تا 2 درجه بیشتر از بیرون شهر می­شود و از این‌رو جزیره گرمایی سطحی شهری تشکیل میشود. در حالت مقایسه نقطه­ای، اختلافات دمای سطح داخل و بیرون شهر به حدود دو برابر، یعنی 3 الی 4 درجه افزایش می‌یابد. بررسی تغییرات دوره­ای جزیره گرمایی نشان داد که مقدار SUCI در دوره (2015-2016) نسبت به دوره (2000-2001) در طول روز افزایش و مقدار SUHI در طول شب کاهش یافته است. دلیل این تغییرات، افزایش بازتاب مناطق شهری ناشی از استفاده از بام­های با بازتاب بالا به­جای آسفالت که موجب جذب کمتر انرژی خورشید و ذخیره­سازی کمتر گرما می­شود و کاهش پوشش گیاهی در مناطق غیرشهری به دلایل مختلف از جمله تسطیح اراضی به­منظور گسترش شهر است.}, keywords_fa = {جزیره گرمایی شهری,دمای سطح زمین,جزیره سرمایی شهری,تصاویر ماهواره‌ای,کرمانشاه}, url = {https://jesphys.ut.ac.ir/article_65886.html}, eprint = {https://jesphys.ut.ac.ir/article_65886_9351c70320f7861f3432492f900db4c4.pdf} }