@article { author = {Bahrami, Faranak and Ranjbar SaadatAbadi, Abbas and Meshkatee, Amir Hussain and Kamali, Gholamali}, title = {Autumn Rainfall Anomalies and Regional Atmospheric Circulation along Establishment of Weak La Nina after Strong El Nino in Iran}, journal = {Iranian Journal of Geophysics}, volume = {13}, number = {4}, pages = {1-15}, year = {2020}, publisher = {Iranian Geophysical Society}, issn = {2008-0336}, eissn = {2783-168X}, doi = {10.30499/ijg.2020.104779}, abstract = {To study the Iran precipitation anomaly in September to November of 2016 and its probable connection with ENSO (El Nino-Southern Oscillation). This period with similar cases in the previous 55 years (1964, 1983, and 1995 according to forecasting center of NOAA) was investigated. In all cases, ENSO changed from strong El-Nino to weak La-Nina after a very brief neutral period. In the following, observational data from 44 synoptic stations of Iran, which have long term statistics about 30 years duration, have been used; and also NCEP-NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research) reanalysis data, which include mean sea level pressure, geopotential height at 850, 500 and 300 hPa, wind and humidity at 850 hPa and also 300 hPa zonal and meridional wind have been used. Results show that, along the establishment of weak La Nina after strong El Nino, autumn rainfall decreases strongly so that severe negative precipitation anomaly (up to 100%) happens in more than 70% of synoptic stations. Also, atmospheric anomaly patterns in these conditions suggest the development and establishment of a high-pressure system over Iran so that when Siberian high pressure system strengthens, it blocks the passage of precipitation systems reaching Iran and causes cold and dry air mass establishment in the country. Besides, during these period, extensions of subtropical high over Saudi Arabian, North African high and eastward expansion of Azores high as well as weakening of Iceland low pressure, stop the activity of Mediterranean low-pressure and Sudanese systems. At this time, the transport of moisture has also decreased relative to long term mean.}, keywords = {weak La Nina,strong El Nino,Precipitation anomaly,Atmospheric circulation,Iran}, title_fa = {Autumn Rainfall Anomalies and Regional Atmospheric Circulation along Establishment of Weak La Nina after Strong El Nino in Iran}, abstract_fa = {To study the Iran precipitation anomaly in September to November of 2016 and its probable connection with ENSO (El Nino-Southern Oscillation). This period with similar cases in the previous 55 years (1964, 1983, and 1995 according to forecasting center of NOAA) was investigated. In all cases, ENSO changed from strong El-Nino to weak La-Nina after a very brief neutral period. In the following, observational data from 44 synoptic stations of Iran, which have long term statistics about 30 years duration, have been used; and also NCEP-NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research) reanalysis data, which include mean sea level pressure, geopotential height at 850, 500 and 300 hPa, wind and humidity at 850 hPa and also 300 hPa zonal and meridional wind have been used. Results show that, along the establishment of weak La Nina after strong El Nino, autumn rainfall decreases strongly so that severe negative precipitation anomaly (up to 100%) happens in more than 70% of synoptic stations. Also, atmospheric anomaly patterns in these conditions suggest the development and establishment of a high-pressure system over Iran so that when Siberian high pressure system strengthens, it blocks the passage of precipitation systems reaching Iran and causes cold and dry air mass establishment in the country. Besides, during these period, extensions of subtropical high over Saudi Arabian, North African high and eastward expansion of Azores high as well as weakening of Iceland low pressure, stop the activity of Mediterranean low-pressure and Sudanese systems. At this time, the transport of moisture has also decreased relative to long term mean.}, keywords_fa = {weak La Nina,strong El Nino,Precipitation anomaly,Atmospheric circulation,Iran}, url = {https://www.ijgeophysics.ir/article_104779.html}, eprint = {https://www.ijgeophysics.ir/article_104779_0dea80040a0ec874232f5214dfb723ab.pdf} } @article { author = {Shahsavani, Hashem and Pourkamar, Fatemeh}, title = {Velocity Inversion with an Iterative Normal Incidence Point (NIP) Wave Tomography with Model-Based Common Diffraction Surface (CDS) Stack}, journal = {Iranian Journal of Geophysics}, volume = {13}, number = {4}, pages = {16-25}, year = {2020}, publisher = {Iranian Geophysical Society}, issn = {2008-0336}, eissn = {2783-168X}, doi = {10.30499/ijg.2020.105742}, abstract = {Normal Incidence Point (NIP) wave tomography inversion has been recently developed to generate a velocity model using Common Reflection Surface (CRS) attributes, which is called the kinematic wavefield attribute. In this paper, we propose to use the model based Common Diffraction Surface (CDS) stack method attributes instead of data driven Common Reflection Surface attributes as an input data parameter. In this way, the effects of Normal wave on Normal Incidence Point wave calculation are removed. In the proposed method, the velocity model is updated iteratively by an interactive between Common Diffraction Surface attributes and the velocity model produced by Normal Incidence Point wave tomography inversion. We applied the proposed method on a 2D complex land data set in the northeast of Iran. The events in the Common Image Gathers (CIGs) become flat after migrating the pre stack data by using the obtained velocity. This is while the events on the same Common Image Gathers that are processed by the data driven Common Reflection Surface stake method are not well flatted. These results show a great capability of the proposed method to obtain the velocity model compared to the single step Normal Incidence Point wave tomography inversion with Common Reflection Surface attributes.}, keywords = {Inversion,Tomography,CRS,CDS}, title_fa = {Velocity Inversion with an Iterative Normal Incidence Point (NIP) Wave Tomography with Model-Based Common Diffraction Surface (CDS) Stack}, abstract_fa = {Normal Incidence Point (NIP) wave tomography inversion has been recently developed to generate a velocity model using Common Reflection Surface (CRS) attributes, which is called the kinematic wavefield attribute. In this paper, we propose to use the model based Common Diffraction Surface (CDS) stack method attributes instead of data driven Common Reflection Surface attributes as an input data parameter. In this way, the effects of Normal wave on Normal Incidence Point wave calculation are removed. In the proposed method, the velocity model is updated iteratively by an interactive between Common Diffraction Surface attributes and the velocity model produced by Normal Incidence Point wave tomography inversion. We applied the proposed method on a 2D complex land data set in the northeast of Iran. The events in the Common Image Gathers (CIGs) become flat after migrating the pre stack data by using the obtained velocity. This is while the events on the same Common Image Gathers that are processed by the data driven Common Reflection Surface stake method are not well flatted. These results show a great capability of the proposed method to obtain the velocity model compared to the single step Normal Incidence Point wave tomography inversion with Common Reflection Surface attributes.}, keywords_fa = {Inversion,Tomography,CRS,CDS}, url = {https://www.ijgeophysics.ir/article_105742.html}, eprint = {https://www.ijgeophysics.ir/article_105742_e916d4a55f7312bff4fefab92e0b3476.pdf} } @article { author = {Mahjoobeh, Meskaranian and Pour Moghaddam, Peyman}, title = {Discretized Adjoint State Time and Frequency Domain Full Waveform Inversion: A Comparative Study}, journal = {Iranian Journal of Geophysics}, volume = {13}, number = {4}, pages = {26-42}, year = {2020}, publisher = {Iranian Geophysical Society}, issn = {2008-0336}, eissn = {2783-168X}, doi = {10.30499/ijg.2020.104782}, abstract = {This study derives the discretized adjoint states full waveform inversion (FWI) in both time and frequency domains based on the Lagrange multiplier method. To achieve this, we applied adjoint state inversion on the discretized wave equation in both time domain and frequency domain. Besides, in this article, we introduce reliability tests to show that the inversion is performing as it should be expected. Reliability tests comprise of objective function descent test and Jacobian test. The influence of data imperfections is also being studied. We define data imperfection as any factor that causes deterioration in FWI results. Some of these factors are coherent and incoherent noises in data, source wavelet inaccuracy in phase and amplitude, and the existence of gaps in the seismic survey. We compare time and frequency domain inversion methods sensitivity to data imperfection. In all cases, we found that time domain full waveform inversion is more sensitive to imperfections in the data. In general, we find that time domain FWI result shows more deterioration than frequency domain FWI. All tests have been done using 2D full waveform inversion codes. We employ the multi-scale inversion and finite difference scheme (FDM) for discretization, and the misfit function is minimized via limited-memory Broyden-Fletcher-Goldfarb-Shanno (LBFGS) method.}, keywords = {FWI,Sensitivity analysis,Discretized Adjoint State Method}, title_fa = {Discretized Adjoint State Time and Frequency Domain Full Waveform Inversion: A Comparative Study}, abstract_fa = {This study derives the discretized adjoint states full waveform inversion (FWI) in both time and frequency domains based on the Lagrange multiplier method. To achieve this, we applied adjoint state inversion on the discretized wave equation in both time domain and frequency domain. Besides, in this article, we introduce reliability tests to show that the inversion is performing as it should be expected. Reliability tests comprise of objective function descent test and Jacobian test. The influence of data imperfections is also being studied. We define data imperfection as any factor that causes deterioration in FWI results. Some of these factors are coherent and incoherent noises in data, source wavelet inaccuracy in phase and amplitude, and the existence of gaps in the seismic survey. We compare time and frequency domain inversion methods sensitivity to data imperfection. In all cases, we found that time domain full waveform inversion is more sensitive to imperfections in the data. In general, we find that time domain FWI result shows more deterioration than frequency domain FWI. All tests have been done using 2D full waveform inversion codes. We employ the multi-scale inversion and finite difference scheme (FDM) for discretization, and the misfit function is minimized via limited-memory Broyden-Fletcher-Goldfarb-Shanno (LBFGS) method.}, keywords_fa = {FWI,Sensitivity analysis,Discretized Adjoint State Method}, url = {https://www.ijgeophysics.ir/article_104782.html}, eprint = {https://www.ijgeophysics.ir/article_104782_de2a53de78bd3063c3c83da35acd6aa1.pdf} } @article { author = {Dadashi-Roudbari, Abbasali and Ahmadi, Mahmoud and Shakiba, Alireza}, title = {Seasonal Study of Dust Deposition and Fine Particles (PM 2.5) in Iran Using MERRA-2 Data}, journal = {Iranian Journal of Geophysics}, volume = {13}, number = {4}, pages = {43-59}, year = {2020}, publisher = {Iranian Geophysical Society}, issn = {2008-0336}, eissn = {2783-168X}, doi = {10.30499/ijg.2020.104783}, abstract = {The research results indicated that wet and dry dust deposition is a function of geographical characteristics. The seasonal wet and dry dust deposition and Fine Particles (PM 2.5) correlation in Iran with elevation, latitude and longitude results that the maximum correlation belongs to height, followed by latitude and longitude; meanwhile height and latitude are strongly and reversely correlated with each other. The Regional ratio of dry to wet deposition indicated that the share of dry deposition was high in south-eastern and western regions of Iran indicating the distance from dust sources. Wet and dry deposition fluxes of mineral dusts were both high in spring and summer low in clod season, showing similar seasonal variations to frequency of Aeolian dust events in Iran. The high amount of wet deposition in summer and autumn in northern regions (Mazandaran and Gilan Provinces) is due to the sea salt and anthropogenic factor dust that is washed out by local precipitation. Relatively high concentration of Fine Particles (PM 2.5) with different compounds in Iran is due to two factors: natural particles (mineral dust and sea salt) and anthropogenic activities (fossil fuel and biofuel). The maximum value of PM 2.5 can be seen in the south and southwestern regions of Iran due to local and trans-regional sources of sand and dust storms (SDS).}, keywords = {Atmospheric Pollution,Dust Deposition,Fine Particles (PM 2.5),MERRA-2,Iran}, title_fa = {Seasonal Study of Dust Deposition and Fine Particles (PM 2.5) in Iran Using MERRA-2 Data}, abstract_fa = {The research results indicated that wet and dry dust deposition is a function of geographical characteristics. The seasonal wet and dry dust deposition and Fine Particles (PM 2.5) correlation in Iran with elevation, latitude and longitude results that the maximum correlation belongs to height, followed by latitude and longitude; meanwhile height and latitude are strongly and reversely correlated with each other. The Regional ratio of dry to wet deposition indicated that the share of dry deposition was high in south-eastern and western regions of Iran indicating the distance from dust sources. Wet and dry deposition fluxes of mineral dusts were both high in spring and summer low in clod season, showing similar seasonal variations to frequency of Aeolian dust events in Iran. The high amount of wet deposition in summer and autumn in northern regions (Mazandaran and Gilan Provinces) is due to the sea salt and anthropogenic factor dust that is washed out by local precipitation. Relatively high concentration of Fine Particles (PM 2.5) with different compounds in Iran is due to two factors: natural particles (mineral dust and sea salt) and anthropogenic activities (fossil fuel and biofuel). The maximum value of PM 2.5 can be seen in the south and southwestern regions of Iran due to local and trans-regional sources of sand and dust storms (SDS).}, keywords_fa = {Atmospheric Pollution,Dust Deposition,Fine Particles (PM 2.5),MERRA-2,Iran}, url = {https://www.ijgeophysics.ir/article_104783.html}, eprint = {https://www.ijgeophysics.ir/article_104783_e48408eb54207cadd4bc940adce977ce.pdf} } @article { author = {Ghanati, Reza and Azadi, Yosra and Fakhimi, Razieh}, title = {RESIP2DMODE: A MATLAB-Based 2D Resistivity and Induced Polarization Forward Modeling Software}, journal = {Iranian Journal of Geophysics}, volume = {13}, number = {4}, pages = {60-78}, year = {2020}, publisher = {Iranian Geophysical Society}, issn = {2008-0336}, eissn = {2783-168X}, doi = {10.30499/ijg.2020.104784}, abstract = {Forward modeling is an integral part of every geophysical modeling resulting in the numerical simulation of responses for a given physical property model. This Forward procedure is helpful in geophysics both as a means to interpret data in a research setting and as a means to enhance physical understanding in an educational setting. Calculation of resistivity and induced polarization forward responses is carried out using simulation of the current flow into the earth’s surface through solving the Poisson’s equation. In this contribution, a finite-difference algorithm is applied to discretize the simulated models restricted by a mixed boundary condition. To account for the 3D source characteristic, a spatial Fourier transform of the partial differential equations with respect to a range of wave numbers is performed along the strike direction. Then, an inverse Fourier transformation is conducted to obtain the potential solutions in the spatial domain. The present package provides a user-friendly interface designed to understand and handle for various conventional electrical configurations in the frame of the MATLAB programming language. To verify the program, initial responses of some simple models are compared with those of analytic solutions, which proved satisfactory in terms of accuracy. For further evaluation, the code is also examined on some complicated models.  }, keywords = {RESIP2DMODE,Resistivity,Chargeability,Forward modeling,MATLAB,finite-difference}, title_fa = {RESIP2DMODE: A MATLAB-Based 2D Resistivity and Induced Polarization Forward Modeling Software}, abstract_fa = {Forward modeling is an integral part of every geophysical modeling resulting in the numerical simulation of responses for a given physical property model. This Forward procedure is helpful in geophysics both as a means to interpret data in a research setting and as a means to enhance physical understanding in an educational setting. Calculation of resistivity and induced polarization forward responses is carried out using simulation of the current flow into the earth’s surface through solving the Poisson’s equation. In this contribution, a finite-difference algorithm is applied to discretize the simulated models restricted by a mixed boundary condition. To account for the 3D source characteristic, a spatial Fourier transform of the partial differential equations with respect to a range of wave numbers is performed along the strike direction. Then, an inverse Fourier transformation is conducted to obtain the potential solutions in the spatial domain. The present package provides a user-friendly interface designed to understand and handle for various conventional electrical configurations in the frame of the MATLAB programming language. To verify the program, initial responses of some simple models are compared with those of analytic solutions, which proved satisfactory in terms of accuracy. For further evaluation, the code is also examined on some complicated models.  }, keywords_fa = {RESIP2DMODE,Resistivity,Chargeability,Forward modeling,MATLAB,finite-difference}, url = {https://www.ijgeophysics.ir/article_104784.html}, eprint = {https://www.ijgeophysics.ir/article_104784_e091a345fcf0c8f9b4f8295f81c270ac.pdf} } @article { author = {Barazesh, Mohammad and Motavalli-Anbaran, Seyed-Hani}, title = {Estimation of Source Location Using Curvature Analysis}, journal = {Iranian Journal of Geophysics}, volume = {13}, number = {4}, pages = {79-92}, year = {2020}, publisher = {Iranian Geophysical Society}, issn = {2008-0336}, eissn = {2783-168X}, doi = {10.30499/ijg.2020.104786}, abstract = {A quadratic surface can be fitted to potential-field data within 3×3 windows, which allow us to calculate curvature attributes from its coefficients. Phillips (2007) derived an equation depending on the most negative curvature to obtain the depth and structural index of isolated sources from peak values of special functions. They divided the special functions into two categories: Model-specific special functions (including Horizontal Gradient Magnitude (HGM) and absolute value) and Model-independent special functions (including Local Wavenumber (LW) and Total Gradient (TG)). We used the normalized source strength (NSS) as a new model-independent special function to estimate depth and shape factor of gravity and magnetic sources. It has its peak directly over the potential field sources (even for dipping sources), and is independent of magnetization direction in magnetic cases. Spurious results are removed by applying a threshold on the shape index attribute and the shape factor.    In this study, the method has been applied on noisy and noise-free synthetic models. For depth estimation of complex sources, we first estimated the depth and structural index from local wavenumber special function. Then, it was used as input to TG and NSS special functions. Finally, this method was tested on real data from Safoo Manganese ore, Northwest of Iran.}, keywords = {Potential field,Curvature attributes,Special function}, title_fa = {Estimation of Source Location Using Curvature Analysis}, abstract_fa = {A quadratic surface can be fitted to potential-field data within 3×3 windows, which allow us to calculate curvature attributes from its coefficients. Phillips (2007) derived an equation depending on the most negative curvature to obtain the depth and structural index of isolated sources from peak values of special functions. They divided the special functions into two categories: Model-specific special functions (including Horizontal Gradient Magnitude (HGM) and absolute value) and Model-independent special functions (including Local Wavenumber (LW) and Total Gradient (TG)). We used the normalized source strength (NSS) as a new model-independent special function to estimate depth and shape factor of gravity and magnetic sources. It has its peak directly over the potential field sources (even for dipping sources), and is independent of magnetization direction in magnetic cases. Spurious results are removed by applying a threshold on the shape index attribute and the shape factor.    In this study, the method has been applied on noisy and noise-free synthetic models. For depth estimation of complex sources, we first estimated the depth and structural index from local wavenumber special function. Then, it was used as input to TG and NSS special functions. Finally, this method was tested on real data from Safoo Manganese ore, Northwest of Iran.}, keywords_fa = {Potential field,Curvature attributes,Special function}, url = {https://www.ijgeophysics.ir/article_104786.html}, eprint = {https://www.ijgeophysics.ir/article_104786_c4ca51953132825acb912781546e9a17.pdf} }