Institute of Geophysics, University of TehranJournal of the Earth and Space Physics2538-371X35420100121Detection of thermal infrared (TIR) anomalies related to the Ms=5.1 earthquake on Oct.14, 2004 near Ravar (SE Iran)Detection of thermal infrared (TIR) anomalies related to the Ms=5.1 earthquake on Oct.14, 2004 near Ravar (SE Iran)21441FAGhasemAskariNaserHafeziMohammad RezaRahimi TabarAbdolrezaAnsariJournal Article19700101Over the last two decades there have been numerous reports from different seismically active regions of the world that thermal infrared (TIR) anomalies can be identified around the epicentral areas before major earthquakes [e.g. (Tronin et al., 2002)]. The TIR anomalies reportedly appear as early as 14 to 7 days before the seismic events and affect areas as large as 1000s to 100,000s km2 in size. Our case study for detection of TIRs using NOAA -AVHRR data(Band 4) is an Ms = 5.1 earthquake that occurred on 14th October 2004 near Ravar in Kerman province located in Loot and Tabas deserts, southeast-central Iran. The area is part of the Golbaf-Sirj seismogenic zone. It includes major faults comprising regional geology of cenozoic granitic to intermediate igneous rocks in the north and east, but cretaceous shales, sandstone (Shemshak Formation) and limestone in the center and west. The epicentral region is surrounded by the Nayband fault to the east, the Lakarkuh fault in the center, and the Kuhbanan fault to the west. To find TIR anomalies we surveyed the night-time satellite data of the epicental area representing the period of 2 ½ years before the Ravar earthquake checking the background noise, cloud cover and other meteorological conditions to ensure stable, high quality data. Finally we selected 14 dates of which the first 8 cover 2 ½ years prior to the earthquake to establish a reference TIR background. The remaining 6 dates cover the period from 11 days to 2 days before the event. The last day before and the day of the earthquake were not included due to regional cloudiness. To optimize the information extracted from the available satellite data, three methodologies were designed. Since this is a post-event analysis, we have the advantage of knowing the location of the epicenter.
1- Square Array Method (SAM): We superimpose over the epicenter a series of squares with their edges increasing from 10, 20, 30, 40, 60, 80, 120, to 200. We integrate the TIR intensities over each of these squares.
2- Rectangle Array Model (RAM): We superimpose rectangles over the epicenter with their longest edges aligned along the trace of the N–S trending Lakar Kuh fault, up to a maximum length of 200 km and an aspect ratio of about 5. We integrate the TIR intensities over the area of each of these rectangles.
3- Geologic Square Array Method: we divided the largest square in SAM model into 9 equivalent squares to detect geologic effects spatially igneous rocks item on the appearance TIR anomalies. We integrate the TIR intensities over the area of each of these rectangles.
Results showed the NOAA (AVHRR) band 4 is suitable for detecting thermal anomalies before earthquakes. In this research the abnormal increase of TIR radiation around the epicentral region was detected using three slightly different methodologies, SAM, RAM and GSAM. The primary results indicate that the area emitting enhanced TIR radiation was aligned along the Lakarkuh fault, which ruptured during the event. The results further indicate that the TIR anomaly reached its highest intensity six nights before the Ravar earthquake. Also the GSAM model extracted small differences in the TIR intensity emitted from igneous rocks and sand or gravel surfaces of which the maximum anomaly was allocated to igneous ones. Finally this study has shown that, given near-ideal weather conditions and a barren desert land surface, a TIR anomaly can be clearly identified for a relatively modest seismic event such as the M5.1 Ravar earthquake using NOAA (AVHRR) data.Over the last two decades there have been numerous reports from different seismically active regions of the world that thermal infrared (TIR) anomalies can be identified around the epicentral areas before major earthquakes [e.g. (Tronin et al., 2002)]. The TIR anomalies reportedly appear as early as 14 to 7 days before the seismic events and affect areas as large as 1000s to 100,000s km2 in size. Our case study for detection of TIRs using NOAA -AVHRR data(Band 4) is an Ms = 5.1 earthquake that occurred on 14th October 2004 near Ravar in Kerman province located in Loot and Tabas deserts, southeast-central Iran. The area is part of the Golbaf-Sirj seismogenic zone. It includes major faults comprising regional geology of cenozoic granitic to intermediate igneous rocks in the north and east, but cretaceous shales, sandstone (Shemshak Formation) and limestone in the center and west. The epicentral region is surrounded by the Nayband fault to the east, the Lakarkuh fault in the center, and the Kuhbanan fault to the west. To find TIR anomalies we surveyed the night-time satellite data of the epicental area representing the period of 2 ½ years before the Ravar earthquake checking the background noise, cloud cover and other meteorological conditions to ensure stable, high quality data. Finally we selected 14 dates of which the first 8 cover 2 ½ years prior to the earthquake to establish a reference TIR background. The remaining 6 dates cover the period from 11 days to 2 days before the event. The last day before and the day of the earthquake were not included due to regional cloudiness. To optimize the information extracted from the available satellite data, three methodologies were designed. Since this is a post-event analysis, we have the advantage of knowing the location of the epicenter.
1- Square Array Method (SAM): We superimpose over the epicenter a series of squares with their edges increasing from 10, 20, 30, 40, 60, 80, 120, to 200. We integrate the TIR intensities over each of these squares.
2- Rectangle Array Model (RAM): We superimpose rectangles over the epicenter with their longest edges aligned along the trace of the N–S trending Lakar Kuh fault, up to a maximum length of 200 km and an aspect ratio of about 5. We integrate the TIR intensities over the area of each of these rectangles.
3- Geologic Square Array Method: we divided the largest square in SAM model into 9 equivalent squares to detect geologic effects spatially igneous rocks item on the appearance TIR anomalies. We integrate the TIR intensities over the area of each of these rectangles.
Results showed the NOAA (AVHRR) band 4 is suitable for detecting thermal anomalies before earthquakes. In this research the abnormal increase of TIR radiation around the epicentral region was detected using three slightly different methodologies, SAM, RAM and GSAM. The primary results indicate that the area emitting enhanced TIR radiation was aligned along the Lakarkuh fault, which ruptured during the event. The results further indicate that the TIR anomaly reached its highest intensity six nights before the Ravar earthquake. Also the GSAM model extracted small differences in the TIR intensity emitted from igneous rocks and sand or gravel surfaces of which the maximum anomaly was allocated to igneous ones. Finally this study has shown that, given near-ideal weather conditions and a barren desert land surface, a TIR anomaly can be clearly identified for a relatively modest seismic event such as the M5.1 Ravar earthquake using NOAA (AVHRR) data.https://jesphys.ut.ac.ir/article_21441_99c2ab41db613639374e895c4849e697.pdfInstitute of Geophysics, University of TehranJournal of the Earth and Space Physics2538-371X35420100121Geological, geotechnical and geophysical characteristics of the Tus Fault located North of Mashhad, North-eastern IranGeological, geotechnical and geophysical characteristics of the Tus Fault located North of Mashhad, North-eastern Iran21442FAAsgharAzadiGholamJavan DoloeiNaserHafezi MoghadasKhaledHesami AzarJournal Article19700101The NW-SE trending Tus fault is one of the active faults in the north-east of Iran . Geomorphologic evidences indicate that this fault is active and goes through Mashhad city from near Tus town. Since the population and number of pilgrims in this city are high, the study of the Tus fault is of great importance. Hence, we have carried out a new investigation to evaluate the hazardous potential of this fault. This study includes analysis of geomorphologic evidence (such as offset streams recognized in aerial photos and geological maps), geophysical, geodesy and geotechnical surveys.
The Copeh Dagh area includes active fold mountains in the north-east of Iran in contact with the aseismic cratons of Eurasia . The NW-SE trending Tus fault is one of the active faults in Copeh Dagh in the north-east of Iran near Mashhad , the capital of Razavi Khorasan province. Studies of aerial photos detected tracing of this fault on alluvial deposits. Hafezi Moghaddas et al. (2007) showed that the change of path streams in the valleys of Mashhad is correlated with the Tus fault trend. This fault enters into Mashhad from the north- west near the town of Tus and passes through Khajeh-rabee and then exits from Golshahr complex in the eastern part of Mashhad.
Occurrences of some earthquakes north of Mashhad may be related to this fault. Since Mashhad is a heavily populated city and there are old buildings in the city, the investigation of the characteristic of the fault is very important. From 1982 to 1983 an electrical resistivity study was done by the water organization of Khorasan province in order to determine the water level in mashhad area. These data were again reprocessed for tracing the fault and some cross sections were prepared again and interpreted. A land subsidence study was carried out in Mashhad during 1995 to 2005 (Motagh et al., 2007). In this study the three methods of InSAR, leveling and GPS measurements were used. The results indicated that the valley floor with a north-western-south-eastern trend subsided at a rate of 15 cmyr?1 during 2003 to 2005. In this paper we have considered an assessment of the geological characteristics and historical earthquake seismicity of the area. These investigations show that some of the powerful, historic earthquakes in Iran took place in Khorasan province at the north-eastern part of the Iranian plateau, the epicenters of some of which were located in Mashhad city (Ambrasys and Melville, 1982; Berberian et al., 1999).
The seismic exploration technique has been carried out for determining shear wave velocity, through six boreholes along the Tus fault. The results of this study show a composition of typical marls around the first borehole, while geological setting around other boreholes were composed of alluvial material such as sand, silt with traces of gravel and clay. Moreover, our results have shown that the least shear wave velocity is about 500 m/sec along BH#10.
Microtremore studies have been carried out for deriving the background vibration of the earth's surface from artificial sources such as traffic, industrial machinery and so on. In this method usually a three-component seismometer is installed for recording noise during a period of about 20 minutes. Then horizontal to vertical spectral ratio is calculated to extract the predominant period. This type of measurement is repeated for many points around the Tus fault and finally, the iso-predominant period map is prepared for the area of study. For completing the study and defining the fault some general electrical resistivity sounding point and three-dimensional electrical resistivity surveys have been taken and then measurement data are processed and interpreted. For defining the deep geometry of the fault an array of deep electrical soundages has been designed and tested. The results of the deep electrical resistivity test showed that the Tus fault has a reverse mechanism with dip direction to the south-west, towards the populated area of the city.
After revising and correlating these studies, a supplementary study with the electrical resistivity method has been conducted in the area along the Tus fault. Results show that this fault is a reverse fault and has a dip direction to south-west. The activity of this fault during the Quaternary Period is evident from displaced alluvial deposits. These results show it is necessary to prepare a suitable legal order for limiting construction near this fault and it is recommended that the present buildings should be reinforced as well.The NW-SE trending Tus fault is one of the active faults in the north-east of Iran . Geomorphologic evidences indicate that this fault is active and goes through Mashhad city from near Tus town. Since the population and number of pilgrims in this city are high, the study of the Tus fault is of great importance. Hence, we have carried out a new investigation to evaluate the hazardous potential of this fault. This study includes analysis of geomorphologic evidence (such as offset streams recognized in aerial photos and geological maps), geophysical, geodesy and geotechnical surveys.
The Copeh Dagh area includes active fold mountains in the north-east of Iran in contact with the aseismic cratons of Eurasia . The NW-SE trending Tus fault is one of the active faults in Copeh Dagh in the north-east of Iran near Mashhad , the capital of Razavi Khorasan province. Studies of aerial photos detected tracing of this fault on alluvial deposits. Hafezi Moghaddas et al. (2007) showed that the change of path streams in the valleys of Mashhad is correlated with the Tus fault trend. This fault enters into Mashhad from the north- west near the town of Tus and passes through Khajeh-rabee and then exits from Golshahr complex in the eastern part of Mashhad.
Occurrences of some earthquakes north of Mashhad may be related to this fault. Since Mashhad is a heavily populated city and there are old buildings in the city, the investigation of the characteristic of the fault is very important. From 1982 to 1983 an electrical resistivity study was done by the water organization of Khorasan province in order to determine the water level in mashhad area. These data were again reprocessed for tracing the fault and some cross sections were prepared again and interpreted. A land subsidence study was carried out in Mashhad during 1995 to 2005 (Motagh et al., 2007). In this study the three methods of InSAR, leveling and GPS measurements were used. The results indicated that the valley floor with a north-western-south-eastern trend subsided at a rate of 15 cmyr?1 during 2003 to 2005. In this paper we have considered an assessment of the geological characteristics and historical earthquake seismicity of the area. These investigations show that some of the powerful, historic earthquakes in Iran took place in Khorasan province at the north-eastern part of the Iranian plateau, the epicenters of some of which were located in Mashhad city (Ambrasys and Melville, 1982; Berberian et al., 1999).
The seismic exploration technique has been carried out for determining shear wave velocity, through six boreholes along the Tus fault. The results of this study show a composition of typical marls around the first borehole, while geological setting around other boreholes were composed of alluvial material such as sand, silt with traces of gravel and clay. Moreover, our results have shown that the least shear wave velocity is about 500 m/sec along BH#10.
Microtremore studies have been carried out for deriving the background vibration of the earth's surface from artificial sources such as traffic, industrial machinery and so on. In this method usually a three-component seismometer is installed for recording noise during a period of about 20 minutes. Then horizontal to vertical spectral ratio is calculated to extract the predominant period. This type of measurement is repeated for many points around the Tus fault and finally, the iso-predominant period map is prepared for the area of study. For completing the study and defining the fault some general electrical resistivity sounding point and three-dimensional electrical resistivity surveys have been taken and then measurement data are processed and interpreted. For defining the deep geometry of the fault an array of deep electrical soundages has been designed and tested. The results of the deep electrical resistivity test showed that the Tus fault has a reverse mechanism with dip direction to the south-west, towards the populated area of the city.
After revising and correlating these studies, a supplementary study with the electrical resistivity method has been conducted in the area along the Tus fault. Results show that this fault is a reverse fault and has a dip direction to south-west. The activity of this fault during the Quaternary Period is evident from displaced alluvial deposits. These results show it is necessary to prepare a suitable legal order for limiting construction near this fault and it is recommended that the present buildings should be reinforced as well.https://jesphys.ut.ac.ir/article_21442_c5410a5896e0e65cf8f21a7089b2cc9a.pdfInstitute of Geophysics, University of TehranJournal of the Earth and Space Physics2538-371X35420100121Trace reconstruction by Parabolic Radon TransformTrace reconstruction by Parabolic Radon Transform21443FAMohammad AliRiahiNaserBani HasanNavidAminiJournal Article19700101Due to some difficulties during seismic data acquisition, like natural obstacles (high voltage electricity cable, bad coupling of geophones with the ground) some of the traces cannot be recorded. Since bad traces make the final stack unclear, usually bad traces go mute while processing. The final image of the earth’s crust is highly dependent of the quality and resolution of acquired data and muting these traces may cause lack of resolution. In this paper, parabolic radon transform is utilized to restore data. Radon transform is a method in which data is transferred to t-q domain from t-x domain. One of the remarkable features in this domain is that data with irregular spacing can be used as input. If these data transfer to t-q domain and transfer back to t-x domain, they will be partially restored. If we carry out this process in an iterative algorithm, the entire missed data will be reconstructed. This method uses an interpolation and extrapolation approach so that it predicts the wavelength and amplitude of each missed trace using adjacent traces.
There are some algorithms for which we do not need pre-information in order to make weighted coefficients as these coefficients are defined automatically. The algorithm offered here uses this approach and weighted coefficients metrics are defined using the Haber norm. Based on this method, this equation should be solved for each frequency component, meaning that this method utilizes the iterative least square approach. Our experience shows that solving the equation forward and backward, maximum 10 times restores the missed traces.
Some assumptions have been made in order to simplify the question. We assumed that there is no lateral velocity variation in layers. Moreover, the length of the receiver array is small compared with the depth of the target. With this assumption we can approximate the events to hyperbola. To apply the parabolic transform, we need to approximate the hyperbolic events to parabolic events. Thus, we applied a partially NMO correction on the data. The data will be corrected to the original hyperbolas, the same amount of initial NMO correction right after the reconstruction. The algorithm is run on a couple of synthetic models with various locations missed traces. We modeled parabolic and hyperbolic CMP gathers with 50 traces in which 11 traces are missed in near offset as well as in middle offset. After running the algorithm on the model, the traces were restored very well. However, far offset missing data cannot be extrapolated completely. We applied a white noise in the middle offset; the result was in agreement with the original wiggle synthetic CMP gather. Since the parabolic transform is used, the data is fully restored providing the events are completely parabolic.
The reconstruction algorithm is applied on real marine data afterwards. This CMP gather contains 51 traces irregularly spaced and sampled by 4ms rate. Some of the traces from the middle and near offsets were muted arbitrarily. After applying a set of forward and inverse Radon transform, the data were restored remarkably and concentration of energy in semblance panel became much better.
This method makes no artifact as this is interpolation and/or extrapolation of existing hyperbolic events. Although hyperbolic algorithm is our convention (since the events are hyperbolic), this is not applicable due to computational difficulties. It is possible to perform parabolic Radon transform in frequency domain quite fast. Since the L matrix (inverse radon transform matrix) contains full information about traces and their distribution, lack of a trace or irregular spacing of them does not play an important role.Due to some difficulties during seismic data acquisition, like natural obstacles (high voltage electricity cable, bad coupling of geophones with the ground) some of the traces cannot be recorded. Since bad traces make the final stack unclear, usually bad traces go mute while processing. The final image of the earth’s crust is highly dependent of the quality and resolution of acquired data and muting these traces may cause lack of resolution. In this paper, parabolic radon transform is utilized to restore data. Radon transform is a method in which data is transferred to t-q domain from t-x domain. One of the remarkable features in this domain is that data with irregular spacing can be used as input. If these data transfer to t-q domain and transfer back to t-x domain, they will be partially restored. If we carry out this process in an iterative algorithm, the entire missed data will be reconstructed. This method uses an interpolation and extrapolation approach so that it predicts the wavelength and amplitude of each missed trace using adjacent traces.
There are some algorithms for which we do not need pre-information in order to make weighted coefficients as these coefficients are defined automatically. The algorithm offered here uses this approach and weighted coefficients metrics are defined using the Haber norm. Based on this method, this equation should be solved for each frequency component, meaning that this method utilizes the iterative least square approach. Our experience shows that solving the equation forward and backward, maximum 10 times restores the missed traces.
Some assumptions have been made in order to simplify the question. We assumed that there is no lateral velocity variation in layers. Moreover, the length of the receiver array is small compared with the depth of the target. With this assumption we can approximate the events to hyperbola. To apply the parabolic transform, we need to approximate the hyperbolic events to parabolic events. Thus, we applied a partially NMO correction on the data. The data will be corrected to the original hyperbolas, the same amount of initial NMO correction right after the reconstruction. The algorithm is run on a couple of synthetic models with various locations missed traces. We modeled parabolic and hyperbolic CMP gathers with 50 traces in which 11 traces are missed in near offset as well as in middle offset. After running the algorithm on the model, the traces were restored very well. However, far offset missing data cannot be extrapolated completely. We applied a white noise in the middle offset; the result was in agreement with the original wiggle synthetic CMP gather. Since the parabolic transform is used, the data is fully restored providing the events are completely parabolic.
The reconstruction algorithm is applied on real marine data afterwards. This CMP gather contains 51 traces irregularly spaced and sampled by 4ms rate. Some of the traces from the middle and near offsets were muted arbitrarily. After applying a set of forward and inverse Radon transform, the data were restored remarkably and concentration of energy in semblance panel became much better.
This method makes no artifact as this is interpolation and/or extrapolation of existing hyperbolic events. Although hyperbolic algorithm is our convention (since the events are hyperbolic), this is not applicable due to computational difficulties. It is possible to perform parabolic Radon transform in frequency domain quite fast. Since the L matrix (inverse radon transform matrix) contains full information about traces and their distribution, lack of a trace or irregular spacing of them does not play an important role.https://jesphys.ut.ac.ir/article_21443_b30067910df7581506f98db35172f141.pdfInstitute of Geophysics, University of TehranJournal of the Earth and Space Physics2538-371X35420100121Suppression of ground roll in seismic reflection data using slowness adaptive f-k filterSuppression of ground roll in seismic reflection data using slowness adaptive f-k filter21444FAAliJelvehgar FilbandMohammad AliRiahiJournal Article19700101One of the common problems in reflection seismic records in the land is the existence of surface waves with high amplitude and low frequency which cause the most important parts of reflective signals to be masked. Therefore, it is necessary to attenuate them by processing and acquisition methods. As it is impossible to attenuate the surface waves completely, and sometimes it is likely to damage reflective event signal content, using the complement processing techniques is vital. These methods are based on the properties and assumptions of surface waves. In this paper, we employed a new method called the slowness adaptive f-k filter to attenuate surface waves instead of using the conventional frequency f-k filter. The advantage of the slowness adaptive f-k filter compared with the f-k filter is that in this method, by selection of a space-variant narrow reject-band f-k which is variant with time and space and applying it on data, the flaws of the f-k filter that consist of smoothing the main signal, distortion of the signal and insufficient attenuation of coherent noise, are removed and data frequency content are less influenced.
Finally, both techniques were applied on real and synthetic data. Comparison between the obtained results from both methods showed that these results are nearly similar in some aspects. But overall, the results from the slowness adaptive f-k filter were more accurate.
Ground roll is usually present on reflection seismograms with velocity values between 100 to 1000 m/sec (Telford et al., 1990). In seismic data acquisition, generated by sources like dynamite and vibrators we usually face coherent noises. These types of waves will mask the reflection signals produced in the deeper part of the earth's layers, due to their inherent scattering and low velocity (Saatcilar and Canitez, 1988). Generally the ground role has to be suppressed during the data acquisition operations.
Suppression of the coherent noises during data acquisition will not be complete, therefore elimination processes are subject to application of signal processing sequence procedures (Coruh and Costain, 1983). To suppress surface wave phenomena we have applied the slowness adaptive filtering and have presented its successful results compared to the conventional f-k filtering.
To reduce distortions of the recorded seismic signals, it is recommended to apply a time and space dependent f-k filter. The filter that has been applied here consists of two steps as follows;
1- Apparent slowness of the coherent noise was calculated from the seismograms.
2- With respect to the obtained apparent slowness values, the filter was applied in time and space domain on the seismograms. To do this, the instantaneous apparent slowness must be calculated.
The obtained results showed that the slowness adaptive f-k filter is capable of automatically adapting itself with lateral variations of the apparent slowness. The filtering operation is based on the depth of the seismic events. Some of the filter's characterizations are as follows;
1- Since the slowness adaptive f-k filter is a band compared to the conventional f-k therefore the shape of the signal will remain intact.
2- The slowness adaptive f-k filter will be applied on the specific deep like velocity of the linear coherent noise for which their energy will be deduced. This will preserve the energy of the main reflection signal and reduce the energy of the coherent noises like ground roll.One of the common problems in reflection seismic records in the land is the existence of surface waves with high amplitude and low frequency which cause the most important parts of reflective signals to be masked. Therefore, it is necessary to attenuate them by processing and acquisition methods. As it is impossible to attenuate the surface waves completely, and sometimes it is likely to damage reflective event signal content, using the complement processing techniques is vital. These methods are based on the properties and assumptions of surface waves. In this paper, we employed a new method called the slowness adaptive f-k filter to attenuate surface waves instead of using the conventional frequency f-k filter. The advantage of the slowness adaptive f-k filter compared with the f-k filter is that in this method, by selection of a space-variant narrow reject-band f-k which is variant with time and space and applying it on data, the flaws of the f-k filter that consist of smoothing the main signal, distortion of the signal and insufficient attenuation of coherent noise, are removed and data frequency content are less influenced.
Finally, both techniques were applied on real and synthetic data. Comparison between the obtained results from both methods showed that these results are nearly similar in some aspects. But overall, the results from the slowness adaptive f-k filter were more accurate.
Ground roll is usually present on reflection seismograms with velocity values between 100 to 1000 m/sec (Telford et al., 1990). In seismic data acquisition, generated by sources like dynamite and vibrators we usually face coherent noises. These types of waves will mask the reflection signals produced in the deeper part of the earth's layers, due to their inherent scattering and low velocity (Saatcilar and Canitez, 1988). Generally the ground role has to be suppressed during the data acquisition operations.
Suppression of the coherent noises during data acquisition will not be complete, therefore elimination processes are subject to application of signal processing sequence procedures (Coruh and Costain, 1983). To suppress surface wave phenomena we have applied the slowness adaptive filtering and have presented its successful results compared to the conventional f-k filtering.
To reduce distortions of the recorded seismic signals, it is recommended to apply a time and space dependent f-k filter. The filter that has been applied here consists of two steps as follows;
1- Apparent slowness of the coherent noise was calculated from the seismograms.
2- With respect to the obtained apparent slowness values, the filter was applied in time and space domain on the seismograms. To do this, the instantaneous apparent slowness must be calculated.
The obtained results showed that the slowness adaptive f-k filter is capable of automatically adapting itself with lateral variations of the apparent slowness. The filtering operation is based on the depth of the seismic events. Some of the filter's characterizations are as follows;
1- Since the slowness adaptive f-k filter is a band compared to the conventional f-k therefore the shape of the signal will remain intact.
2- The slowness adaptive f-k filter will be applied on the specific deep like velocity of the linear coherent noise for which their energy will be deduced. This will preserve the energy of the main reflection signal and reduce the energy of the coherent noises like ground roll.https://jesphys.ut.ac.ir/article_21444_23dfd25452dc9a605be66806cb2235a7.pdfInstitute of Geophysics, University of TehranJournal of the Earth and Space Physics2538-371X35420100121Investigation of the magnetosphere`s response to changes of solar wind parameters with MHD simulationInvestigation of the magnetosphere`s response to changes of solar wind parameters with MHD simulation21445FABarataliFeizabadyMahmodMirzaeiNaserHosseinzadeh GuyaJournal Article19700101The global computer simulation based on the magnetohydrodynamic (MHD) theory describes the evolution of physical conditions in the simulation domain based on measurements for each point in the solar wind. Considering the size of magnetosphere and strong spatial variation of the energy transfer process, the amount of transferred energy cannot be directly measured on the surface of magnetosphere, called the magnetopause. Therefore, simulation can provide a unique opportunity to calculate quantitatively the amount of solar wind energy transfer to the magnetosphere and to determine where the energy transfer process mainly takes place. Only a small amount of the transferred energy is consumed in the earth’s polar ionosphere and in its two sinks: part of the energy is converted to Joule heat , which is caused by the ionospheric closure of the electric currents flowing between the magnetosphere and the ionosphere and the remainder of the energy is left in the ionosphere as charged particles originating from the magnetosphere precipitate (these particles collide with atmospheric particles and produce auroral light).
In this paper, the energy related to the ionospheric processes was quantified by the magnetosphere`s structure of using a computer code based on MHD equations. Also, the amount and time variation of the total energy consumed by the ionosphere was correlated with solar wind parameters to predict the total ionospheric energy from a point measurement in the solar wind. The developed relationship can have practical significance in situations where the total ionospheric energy needs to be estimated quickly, for example, for space weather prediction purposes.
In this paper, the global MHD simulation is done in the GSE coordinates system.The origin is on the earth`s center and the direction of X-axis always pointing sunward. The Z-axis is normal to elliptic plane and its direction is northward, and the Y-axis completed the right-handed coordinate system and its direction is duskward. The location of the sunward simulation boundary is about from the earth`s center and is covered until on the midnight sector of the earth by cubic cells. The dimensions of the cells are selected about .The global computer simulation based on the magnetohydrodynamic (MHD) theory describes the evolution of physical conditions in the simulation domain based on measurements for each point in the solar wind. Considering the size of magnetosphere and strong spatial variation of the energy transfer process, the amount of transferred energy cannot be directly measured on the surface of magnetosphere, called the magnetopause. Therefore, simulation can provide a unique opportunity to calculate quantitatively the amount of solar wind energy transfer to the magnetosphere and to determine where the energy transfer process mainly takes place. Only a small amount of the transferred energy is consumed in the earth’s polar ionosphere and in its two sinks: part of the energy is converted to Joule heat , which is caused by the ionospheric closure of the electric currents flowing between the magnetosphere and the ionosphere and the remainder of the energy is left in the ionosphere as charged particles originating from the magnetosphere precipitate (these particles collide with atmospheric particles and produce auroral light).
In this paper, the energy related to the ionospheric processes was quantified by the magnetosphere`s structure of using a computer code based on MHD equations. Also, the amount and time variation of the total energy consumed by the ionosphere was correlated with solar wind parameters to predict the total ionospheric energy from a point measurement in the solar wind. The developed relationship can have practical significance in situations where the total ionospheric energy needs to be estimated quickly, for example, for space weather prediction purposes.
In this paper, the global MHD simulation is done in the GSE coordinates system.The origin is on the earth`s center and the direction of X-axis always pointing sunward. The Z-axis is normal to elliptic plane and its direction is northward, and the Y-axis completed the right-handed coordinate system and its direction is duskward. The location of the sunward simulation boundary is about from the earth`s center and is covered until on the midnight sector of the earth by cubic cells. The dimensions of the cells are selected about .https://jesphys.ut.ac.ir/article_21445_5eac44296bf8bb5e6c19d8832338d58b.pdfInstitute of Geophysics, University of TehranJournal of the Earth and Space Physics2538-371X35420100121Spatial distribution of the annual precipitation trend in Iran in the period 1960-2001Spatial distribution of the annual precipitation trend in Iran in the period 1960-200121446FAParvizIrannejadParisimaKatiraei BoroujerdiSohrabHajjamJournal Article19700101Many studies on precipitation trend have been performed in recent years (e.g., Brunetti et al., 2006; Rodrigo et al., 2007; Turkesh, 1996), but spatial analysis of the sign of trends is rarely carried out (Suppiah and Hennessy, 1998; De Luis et al., 2000). In the present paper we analyze the observational precipitation data from some oldest meteorological stations to investigate the possible systemic trend in precipitation across Iran. We then search for the spatial coherence of the precipitation change.
Daily precipitation data from 38 stations were selected from the Iranian Meteorological Organization (IRIMO) files for a 42-year period (1960-2001). The linear regression model is used to determine the signs and magnitudes of annual precipitation trends. The non-parametric Kendall-taw statistic (Sneyers, 1990) is applied to evaluate the statistical significance of trends.
To assess the spatial distribution of precipitation trends, we applied a statistical analysis similar to De Luis et al. (2000) which is based on the Cramer-von Misses non-parametric test (Zimmerman, 1993; Syrjala, 1996). The test is applied to three possible signs of trend: positive, negative and zero. The null hypothesis is that, there are no differences in the spatial distribution of signs of trend, implying that the signs are distributed randomly in the study area and only the local factors are responsible for the spatial variability of trends. If differences are significant, we may conclude that precipitation has evolved differently in different areas.
To compare distribution of signs, each station was categorized by the presence of each of the three trend signs (+, -, or 0). The Cramer-von Misses test is insensitive to differences in the total number of trends in the study area, but sensitive to differences of respective number of stations with a given sign of trend. Therefore, each pair of signs (+ versus -, + versus 0, - versus 0) was first normalized to eliminate the effect of differing sizes in population. The test statistic is based on the differences between two cumulative distribution functions that are calculated along spatial gradients. The spatial gradients used in the present study are those along the mean annual precipitation, altitude (one dimensional), longitude (east-west), latitude (north-south) and those parallel and perpendicular to the dividing heights of the Alborz and Zagros ranges (two dimensional).
The test determines whether the stations with significant local trends have occurred by chance. A modified version of the Cramer-von Misses non-parametric test is applied (De Luis et al., 2000) to test for spatial distribution of precipitation trends. The test statistic is calculated as the squared difference between the two cumulative distribution functions summed over all sampling locations. For application of the Cramer-von Misses test, data must be selected at random in space, but because locations of the stations are fixed, the sign of trend in each station is assumed as the random variable. The null hypothesis is that there are no differences in the spatial distribution of trends. Of the 38 stations studied, 18 showed positive trend, 16 showed negative trend and 4 showed zero trend on a yearly basis.
The results of the application of the Cramer-von Misses test along annual precipitation gradient indicate that stations with negative sign show a different distribution when compared with those with positive sign (99% significant). In contrast positive and zero stations, as well as negative and zero stations seemed to overlap along the precipitation gradient. It seems that semi-arid and humid regions show a significant decrease in annual precipitation, while the arid region shows a positive trend (1960-2001).
The results of the 2-dimensional test application show that on the east-westerly gradient positive trends are distributed differently from negative ones (95% significant). This means that the stations with these signs are not randomly distributed along the east-west direction. On the other hand the negative versus zero trends along the north-south gradient show a significant (90%) difference, indicating that the distribution of these signs is not random is space. Non-significant differences between other pairs along these gradients indicate that these pairs of trend signs are distributed randomly and overlapping in space. The results of the test to trend signs along the gradients parallel and perpendicular to the two main mountain ranges (Zagros and Alborz) show no significant difference, implying that the signs are distributed randomly.Many studies on precipitation trend have been performed in recent years (e.g., Brunetti et al., 2006; Rodrigo et al., 2007; Turkesh, 1996), but spatial analysis of the sign of trends is rarely carried out (Suppiah and Hennessy, 1998; De Luis et al., 2000). In the present paper we analyze the observational precipitation data from some oldest meteorological stations to investigate the possible systemic trend in precipitation across Iran. We then search for the spatial coherence of the precipitation change.
Daily precipitation data from 38 stations were selected from the Iranian Meteorological Organization (IRIMO) files for a 42-year period (1960-2001). The linear regression model is used to determine the signs and magnitudes of annual precipitation trends. The non-parametric Kendall-taw statistic (Sneyers, 1990) is applied to evaluate the statistical significance of trends.
To assess the spatial distribution of precipitation trends, we applied a statistical analysis similar to De Luis et al. (2000) which is based on the Cramer-von Misses non-parametric test (Zimmerman, 1993; Syrjala, 1996). The test is applied to three possible signs of trend: positive, negative and zero. The null hypothesis is that, there are no differences in the spatial distribution of signs of trend, implying that the signs are distributed randomly in the study area and only the local factors are responsible for the spatial variability of trends. If differences are significant, we may conclude that precipitation has evolved differently in different areas.
To compare distribution of signs, each station was categorized by the presence of each of the three trend signs (+, -, or 0). The Cramer-von Misses test is insensitive to differences in the total number of trends in the study area, but sensitive to differences of respective number of stations with a given sign of trend. Therefore, each pair of signs (+ versus -, + versus 0, - versus 0) was first normalized to eliminate the effect of differing sizes in population. The test statistic is based on the differences between two cumulative distribution functions that are calculated along spatial gradients. The spatial gradients used in the present study are those along the mean annual precipitation, altitude (one dimensional), longitude (east-west), latitude (north-south) and those parallel and perpendicular to the dividing heights of the Alborz and Zagros ranges (two dimensional).
The test determines whether the stations with significant local trends have occurred by chance. A modified version of the Cramer-von Misses non-parametric test is applied (De Luis et al., 2000) to test for spatial distribution of precipitation trends. The test statistic is calculated as the squared difference between the two cumulative distribution functions summed over all sampling locations. For application of the Cramer-von Misses test, data must be selected at random in space, but because locations of the stations are fixed, the sign of trend in each station is assumed as the random variable. The null hypothesis is that there are no differences in the spatial distribution of trends. Of the 38 stations studied, 18 showed positive trend, 16 showed negative trend and 4 showed zero trend on a yearly basis.
The results of the application of the Cramer-von Misses test along annual precipitation gradient indicate that stations with negative sign show a different distribution when compared with those with positive sign (99% significant). In contrast positive and zero stations, as well as negative and zero stations seemed to overlap along the precipitation gradient. It seems that semi-arid and humid regions show a significant decrease in annual precipitation, while the arid region shows a positive trend (1960-2001).
The results of the 2-dimensional test application show that on the east-westerly gradient positive trends are distributed differently from negative ones (95% significant). This means that the stations with these signs are not randomly distributed along the east-west direction. On the other hand the negative versus zero trends along the north-south gradient show a significant (90%) difference, indicating that the distribution of these signs is not random is space. Non-significant differences between other pairs along these gradients indicate that these pairs of trend signs are distributed randomly and overlapping in space. The results of the test to trend signs along the gradients parallel and perpendicular to the two main mountain ranges (Zagros and Alborz) show no significant difference, implying that the signs are distributed randomly.https://jesphys.ut.ac.ir/article_21446_43601442cebea43c8fdacb9c92459598.pdfInstitute of Geophysics, University of TehranJournal of the Earth and Space Physics2538-371X35420100121The study of the ENSO's effect on the seasonal precipitation of Iran in the period 1971-2000The study of the ENSO's effect on the seasonal precipitation of Iran in the period 1971-200021447FAFarhangAhmadi- Givi0000-0002-9487-4862DavoodParhizkarSohrabHajjamJournal Article19700101An analysis of seasonal rainfall over Iran for a period of 30 years (1971-2000) shows a significant variability in spatial and temporal distributions of rainfall as well as its frequency and intensity. In this paper, the likely effects of ENSO on the rainfall anomalies are investigated. The accumulated monthly and seasonal rainfalls from 43 synoptic stations are taken through the Islamic Republic of Iran Meteorology Organization (IRIMO) and the ENSO activity years are obtained from NOAA. Three cases of strong cold phase (La-Nina) and three cases of strong warm phase (El-Nino) of ENSO in the period of this study have been selected. Then, the distribution of seasonal rainfall anomalies for these cases is studied. Also, the relation between the seasonal rainfall anomalies and Oceanic Nino Index (ONI), from the sign and magnitude view point, for the selected cases is examined. These investigations have been done for both solar and agriculture (from autumn of one year to the next) years. In addition, the correlation between the ONI and the seasonal rainfall of the 43 stations for the total 30 year period at study is calculated.
The results of the distribution of seasonal rainfall anomalies for the above cases indicate that there is no certain relation between the rainfall anomalies over Iran and the different phases of ENSO activity. The comparison of total seasonal rainfall anomalies over Iran and the ONI anomalies shows that the signs and magnitudes of anomalies in all the cases are significantly inconsistent. For example, both positive and negative seasonal rainfall anomalies exist in the El-Nino years. The weak correlation between the ONI and the seasonal rainfall of the 43 stations for the period of 30 years confirms the above results.
The key result is that it is not possible to predict the sign and magnitude of seasonal rainfall anomalies having the phase of ENSO activity. The possible reason being that ENSO has a complex and nonlinear interaction with other phenomena such as monsoon, North Atlantic Oscillation (NAO), and Madden-Julian Oscillation (MJO).An analysis of seasonal rainfall over Iran for a period of 30 years (1971-2000) shows a significant variability in spatial and temporal distributions of rainfall as well as its frequency and intensity. In this paper, the likely effects of ENSO on the rainfall anomalies are investigated. The accumulated monthly and seasonal rainfalls from 43 synoptic stations are taken through the Islamic Republic of Iran Meteorology Organization (IRIMO) and the ENSO activity years are obtained from NOAA. Three cases of strong cold phase (La-Nina) and three cases of strong warm phase (El-Nino) of ENSO in the period of this study have been selected. Then, the distribution of seasonal rainfall anomalies for these cases is studied. Also, the relation between the seasonal rainfall anomalies and Oceanic Nino Index (ONI), from the sign and magnitude view point, for the selected cases is examined. These investigations have been done for both solar and agriculture (from autumn of one year to the next) years. In addition, the correlation between the ONI and the seasonal rainfall of the 43 stations for the total 30 year period at study is calculated.
The results of the distribution of seasonal rainfall anomalies for the above cases indicate that there is no certain relation between the rainfall anomalies over Iran and the different phases of ENSO activity. The comparison of total seasonal rainfall anomalies over Iran and the ONI anomalies shows that the signs and magnitudes of anomalies in all the cases are significantly inconsistent. For example, both positive and negative seasonal rainfall anomalies exist in the El-Nino years. The weak correlation between the ONI and the seasonal rainfall of the 43 stations for the period of 30 years confirms the above results.
The key result is that it is not possible to predict the sign and magnitude of seasonal rainfall anomalies having the phase of ENSO activity. The possible reason being that ENSO has a complex and nonlinear interaction with other phenomena such as monsoon, North Atlantic Oscillation (NAO), and Madden-Julian Oscillation (MJO).https://jesphys.ut.ac.ir/article_21447_f53b0c04d2ddeb924aa168c089691444.pdfInstitute of Geophysics, University of TehranJournal of the Earth and Space Physics2538-371X35420100121Effects of the annual variations in the positions of the sub-tropical high pressure belt and Siberian high on the Mediterranean cyclogenesis and precipitation in IranEffects of the annual variations in the positions of the sub-tropical high pressure belt and Siberian high on the Mediterranean cyclogenesis and precipitation in Iran21448FAAlirezaMohammadnejadFarhangAhmadi Givi0000-0002-9487-4862ParvizIrannejadJournal Article19700101The Mediterranean is one of the most important cyclogenesis regions in the Northern Hemisphere. The depressions occurring in specific areas of the Mediterranean region and cyclonic tracks have been the subject of extensive climatological research. The climate of the Mediterranean region is conditioned by its position in the transition area between the sub-tropical high pressure belt and the mid latitude westerlies. The seasonal positional shift of the sub-tropical high pressure belt to the south during winters and to the north during summers effects both the frequency of cyclogenesis over the Mediterranean and the cyclone tracks, which are towards the east during the winter months. Studies show that, during 1957 to 2002, the monthly cyclone frequency in the cyclogenesis zones of the Gulf of Geneva, southern Italy, Cyprus and East and West Mediterranean decreases in summer and increases in winter months. Also relationships between sea level pressure departures in the Mediterranean and monthly precipitation conditions in the East Mediterranean (EM) have been found. Dry (Wet) rainfall conditions in the East Mediterranean, were found to be characterized by positive (negative) pressure departures and /or southerly (westerly or northerly) circulation over the East Mediterranean.
Research showed that the atmospheric circulation is predictable when the SST and sea level pressure fields are persistent. The movement of the position of the sub-topical high pressure belt is slow. Therefore, it is expected that, similar to the SST, it acts as a low frequency signal, making the atmospheric circulation and surface condition predictable over the Mediterranean.
In the present paper, the effect of annual positional variation of the sub-tropical high pressure belt on the Mediterranean cyclogenesis and its combined effect with the position of the Siberian high on the annual precipitation in Iran are studied. The latitude of the sub-tropical high pressure belt on the meridian passing through Alexandria in the east of the Mediterranean Sea (STPSKJ) and the latitude of the Siberian high on the meridian passing through Tehran (STPIRJ) were determined in January (southern position) and July (northern position), each year. The annual latitudinal difference between northern and southern positions of sub-tropical high pressure on the Alexandrian meridian (DLSTPSK) and that of the Siberian high on the Tehran meridian (DlSTPIR) are calculated during the 1960 - 2002 period.
We found a significant coefficient of correlation (0.643) between DLSTPSK and the East Mediterranean cyclone frequency. The geographical distribution of correlation coefficients of precipitation in Iran with DLSTPSK and with DLSTPIR shows the significant influence of DLSTPSK in precipitation on the western and north -western parts of Iran, while DLSTPIR affects precipitation in the western, north-western and north-eastern parts of the country. The magnitude of the correlation coefficient of the Siberian index (DLSTPIR) and precipitation in these regions varies from 0.3 to 0.6. No significant correlation was found between DLSTPIR and cyclone frequency in the Mediterranean and the North Red Sea cyclogensis centers.
We also found significant correlation coefficients between DLSTPSK and the latitude of STPSKJ in January and July and between DLSTPIR and the position of STPIRJ in the two extreme months. The correlation coefficients are 0.477 and -0.548 for the sub-tropical high pressure belt position in the East Mediterranean and 0.731 and
-0.873 for the Siberian high pressure position in January and July, respectively. This means that the annual variation of the position of sub-tropical high pressure belt in the East Mediterranean meridian and that of the Siberian high pressure on the Tehran meridian are affected by variation of its first position in January and/or its end position in July.
Results show that precipitation in some regions of Iran is under the combined influence of DLSTPSK and DLSTPIR. The impact of DLSTPSK on precipitation in Iran is mostly because of its role in the frequency of cyclones generated in the East Mediterranean and that of DLSTPIR is through its effect on the flow of the cold air from the Siberian high to the lower latitudes in Iran. It seems, in this situation, that the warm, wet westerly flow from the Mediterranean hitting the cold Siberian air favors the formation of fronts and subsequent precipitation in the west of Iran. This is manifested by the wet years in Iran being associated with positive anomalies of both DLSTPSK and DLSTPIR and the dry years with negative anomalies of DLSTPSK and DLSTPIR. We also found that the seasonal cycles of precipitation are similar in the wet and dry years in the regions that are under the influence of DLSTPSK and DLSTPIR (i.e. the west of Iran), but different in the eastern parts of the country.The Mediterranean is one of the most important cyclogenesis regions in the Northern Hemisphere. The depressions occurring in specific areas of the Mediterranean region and cyclonic tracks have been the subject of extensive climatological research. The climate of the Mediterranean region is conditioned by its position in the transition area between the sub-tropical high pressure belt and the mid latitude westerlies. The seasonal positional shift of the sub-tropical high pressure belt to the south during winters and to the north during summers effects both the frequency of cyclogenesis over the Mediterranean and the cyclone tracks, which are towards the east during the winter months. Studies show that, during 1957 to 2002, the monthly cyclone frequency in the cyclogenesis zones of the Gulf of Geneva, southern Italy, Cyprus and East and West Mediterranean decreases in summer and increases in winter months. Also relationships between sea level pressure departures in the Mediterranean and monthly precipitation conditions in the East Mediterranean (EM) have been found. Dry (Wet) rainfall conditions in the East Mediterranean, were found to be characterized by positive (negative) pressure departures and /or southerly (westerly or northerly) circulation over the East Mediterranean.
Research showed that the atmospheric circulation is predictable when the SST and sea level pressure fields are persistent. The movement of the position of the sub-topical high pressure belt is slow. Therefore, it is expected that, similar to the SST, it acts as a low frequency signal, making the atmospheric circulation and surface condition predictable over the Mediterranean.
In the present paper, the effect of annual positional variation of the sub-tropical high pressure belt on the Mediterranean cyclogenesis and its combined effect with the position of the Siberian high on the annual precipitation in Iran are studied. The latitude of the sub-tropical high pressure belt on the meridian passing through Alexandria in the east of the Mediterranean Sea (STPSKJ) and the latitude of the Siberian high on the meridian passing through Tehran (STPIRJ) were determined in January (southern position) and July (northern position), each year. The annual latitudinal difference between northern and southern positions of sub-tropical high pressure on the Alexandrian meridian (DLSTPSK) and that of the Siberian high on the Tehran meridian (DlSTPIR) are calculated during the 1960 - 2002 period.
We found a significant coefficient of correlation (0.643) between DLSTPSK and the East Mediterranean cyclone frequency. The geographical distribution of correlation coefficients of precipitation in Iran with DLSTPSK and with DLSTPIR shows the significant influence of DLSTPSK in precipitation on the western and north -western parts of Iran, while DLSTPIR affects precipitation in the western, north-western and north-eastern parts of the country. The magnitude of the correlation coefficient of the Siberian index (DLSTPIR) and precipitation in these regions varies from 0.3 to 0.6. No significant correlation was found between DLSTPIR and cyclone frequency in the Mediterranean and the North Red Sea cyclogensis centers.
We also found significant correlation coefficients between DLSTPSK and the latitude of STPSKJ in January and July and between DLSTPIR and the position of STPIRJ in the two extreme months. The correlation coefficients are 0.477 and -0.548 for the sub-tropical high pressure belt position in the East Mediterranean and 0.731 and
-0.873 for the Siberian high pressure position in January and July, respectively. This means that the annual variation of the position of sub-tropical high pressure belt in the East Mediterranean meridian and that of the Siberian high pressure on the Tehran meridian are affected by variation of its first position in January and/or its end position in July.
Results show that precipitation in some regions of Iran is under the combined influence of DLSTPSK and DLSTPIR. The impact of DLSTPSK on precipitation in Iran is mostly because of its role in the frequency of cyclones generated in the East Mediterranean and that of DLSTPIR is through its effect on the flow of the cold air from the Siberian high to the lower latitudes in Iran. It seems, in this situation, that the warm, wet westerly flow from the Mediterranean hitting the cold Siberian air favors the formation of fronts and subsequent precipitation in the west of Iran. This is manifested by the wet years in Iran being associated with positive anomalies of both DLSTPSK and DLSTPIR and the dry years with negative anomalies of DLSTPSK and DLSTPIR. We also found that the seasonal cycles of precipitation are similar in the wet and dry years in the regions that are under the influence of DLSTPSK and DLSTPIR (i.e. the west of Iran), but different in the eastern parts of the country.https://jesphys.ut.ac.ir/article_21448_6c37f7f2886c6bc7c0618d69ae45bc87.pdfInstitute of Geophysics, University of TehranJournal of the Earth and Space Physics2538-371X35420100121Study of the effect of horizontal resolution of MM5 mesoscale model on simulation of precipitation of October 2004 synoptical system over IranStudy of the effect of horizontal resolution of MM5 mesoscale model on simulation of precipitation of October 2004 synoptical system over Iran21449FAMajidMazraeh FarahaniAhadVazifehMajidAzadi0000-0002-5991-9703Journal Article19700101In this research the effect and importance of horizontal resolution in mesoscale numerical model of MM5 on quality and magnitude of some atmospheric variables has been discussed. A case study was also carried out to verify the results of the findings. The case occurred in an unusually cold winter. This case was activated in the north of Iran during 12-15 October 2004. The main reason for selecting this case is its heavy fall in temperature (10-15 ?c) and precipitation on the southern coast of the Caspian Sea and the northern side of the Alborz Mountain Range. The effect of horizontal resolution of MM5 has been studied by simulating this atmospheric system. The main variables that have been focused on are mean sea level pressure and predicted precipitation by MM5 model . These variables which are achieved from a run of MM5 with 60, 20, and 15 km, are compared with those of synoptical maps and precipitation observatories. The high resolution effect of model has been considered extensively for precipitation values.
The results revealed that the numerical model is able to simulate the mesoscale and synoptic scale characteristics such as precipitation in synoptic scale quite well. By reducing the horizontal grid size to 15-20 km which fell into mesoscale distance, the precipitation could be simulated reasonably . No distinguishing differences exist in changing the horizontal grid size from 20 to 15 km. The effect of land-use in the surface and its coverage are considered. Special attention is paid to the height fluctuations in the surface and also to the slope of the surface because of their intensive effect on precipitation but since the available data of surface topography was in a single resolution, model is run with same topography data for different grid sizes. The different options of model configurations for physical and dynamical conditions have been tested and the present results are based on the best (based on agreement with observation) output of predictions of variable with emphasis on precipitation. There are some differences in some parts and these differences are discussed and evaluated. The main reasons for disagreement of predicted variables and observations are: disagreement in methods of measurements , various instruments of measurements and different managements from different organizations.In this research the effect and importance of horizontal resolution in mesoscale numerical model of MM5 on quality and magnitude of some atmospheric variables has been discussed. A case study was also carried out to verify the results of the findings. The case occurred in an unusually cold winter. This case was activated in the north of Iran during 12-15 October 2004. The main reason for selecting this case is its heavy fall in temperature (10-15 ?c) and precipitation on the southern coast of the Caspian Sea and the northern side of the Alborz Mountain Range. The effect of horizontal resolution of MM5 has been studied by simulating this atmospheric system. The main variables that have been focused on are mean sea level pressure and predicted precipitation by MM5 model . These variables which are achieved from a run of MM5 with 60, 20, and 15 km, are compared with those of synoptical maps and precipitation observatories. The high resolution effect of model has been considered extensively for precipitation values.
The results revealed that the numerical model is able to simulate the mesoscale and synoptic scale characteristics such as precipitation in synoptic scale quite well. By reducing the horizontal grid size to 15-20 km which fell into mesoscale distance, the precipitation could be simulated reasonably . No distinguishing differences exist in changing the horizontal grid size from 20 to 15 km. The effect of land-use in the surface and its coverage are considered. Special attention is paid to the height fluctuations in the surface and also to the slope of the surface because of their intensive effect on precipitation but since the available data of surface topography was in a single resolution, model is run with same topography data for different grid sizes. The different options of model configurations for physical and dynamical conditions have been tested and the present results are based on the best (based on agreement with observation) output of predictions of variable with emphasis on precipitation. There are some differences in some parts and these differences are discussed and evaluated. The main reasons for disagreement of predicted variables and observations are: disagreement in methods of measurements , various instruments of measurements and different managements from different organizations.https://jesphys.ut.ac.ir/article_21449_8468b8e6f7db1e29926f7bac0d6ff02b.pdfInstitute of Geophysics, University of TehranJournal of the Earth and Space Physics2538-371X35420100121Two case studies to introduce a method for thunderstorm forecastingTwo case studies to introduce a method for thunderstorm forecasting21450FASaharTajbakhshParvinGhaffarianEbrahimMirzaeiJournal Article19700101Thunderstorm is one of the most dangerous phenomena in aviation because the greatest number weather hazards such as icing, turbulence, wind shear, lightning hail are combined in one single source, the thunderstorm. Spatial characteristics of thunderstorms which can be associated with irreparable outcomes are known by most of the forecasters. Tornadoes, microbursts, very strong winds and flash floods are some of the accompanying hazardous atmospheric conditions with thunderstorm. Therefore, its prediction is one of the elementary duties of forecasting centers to rectify aeronautical problems.
Typical horizontal and vertical extents of thunderstorm are in order of tens of kilometers and 30,000 feet (up to and pushing into the tropopause at times) respectively, and typical duration in time is in the order of 30 minutes. The life cycle of a thunderstorm is divided into three stages. In the first, the towering cumulus stage, warm moist unstable air feeds the cloud’s vertical growth and updraft increases in strength. The second stage is known as the mature stage where the cumulonimbus top glaciates and down drafts become significant. In the third, dissipating, Stage, the anvils are well developed and the down drafts diminish. Associated clouds include cumulus cloud (Cu), towering cumulus (TCu), cumulonimbus (Cb) thunderstorm cloud. Often low-level stratus (St) forms in the precipitation at the base of a thunderstorm, The morning appearance of altocumulus castellans, turrets of middle-level cloud, are the precursor to thunderstorm activity later in the day.
Several methods have been presented for thunderstorm forecasting since 1951. Most of them are applicable when an active atmospheric system on a large scale is dominant. But many strong storms cannot be monitored on the synoptic scale. Therefore, some other forecasting methods were introduced by Dvorak et al. (1975).These methods have been known as decision tree. Colquhoun was the first one who used decision tree for thunderstorm forecasting. He tried to solve some problems of thunderstorm forecasts using skew-t data and NWP outputs. Then, in 1998 Miles and Colquhoun (1998) modified the tree, so that all parameters could be computed automatically from numerical weather prediction outputs.
The method which is presented in this paper is the Colquhoun (1996) algorithm. It is a suitable guide for meteorologists for predicting thunderstorms using each numerical weather prediction output.
Two case studies are considered to survey the thunderstorm in the present research. Both of them occurred at 15 UTC at Mehr-Abad airport. One of them on 13th of May and another on 5th of June 2007 which are analyzed according to the decision tree. The surface and upper air synoptic patterns and satellite images are studied in events of storms. On the other hand some MM5 numerical weather prediction outputs are examined to determine the threshold values of vertical velocity in 850mb, relative humidity in 500-600mb and subsidence currents in 400-500 mb layers. It should be mentioned that the MM5 was run with 35km resolution in regional scale. To access better results, some of the most significant thermodynamic upward motion indices are calculated for Mehr-Abad airport such as LI, KI, SWEAT index, CAPE and BRN using the RAOB software.
Analysis of the MM5 outputs shows that the vertical velocity in 850 mb is not reliable because the observations confirm the passage of a cold front which is a reason for convergence in low level but the vertical velocity values do not correspond with them. The threshold values of relative humidity and sinking currents are the same as other studies in the world. Also, the LI, KI, SWEAT and CAPE values represented unstable conditions for thunderstorm occurrence.
Although most of decisions in the Colquhoun algorithm are designed for severe thunderstorms in tropical and subtropical regions, some boxes of the decision tree are denoted to ordinary storms which occur in mid latitudes of which 2 examples are shown in this research. So, it can be used in operational applications such as aeronautical meteorology in forecasting center of IRIMO. Large scale patterns are not suitable guides for the prediction of thunderstorms because there are no especial indexes for identifying the storms and they can show instability qualitatively. The thermodynamic indexes (LI, KI, SWEAT and CAPE) and their threshold values are appropriate signs to forecast storms in the Tehran area. MM5 vertical velocity at low level isn't reliable and needs to be modified but relative humidity and subsiding currents in mid levels give the acceptable results.Thunderstorm is one of the most dangerous phenomena in aviation because the greatest number weather hazards such as icing, turbulence, wind shear, lightning hail are combined in one single source, the thunderstorm. Spatial characteristics of thunderstorms which can be associated with irreparable outcomes are known by most of the forecasters. Tornadoes, microbursts, very strong winds and flash floods are some of the accompanying hazardous atmospheric conditions with thunderstorm. Therefore, its prediction is one of the elementary duties of forecasting centers to rectify aeronautical problems.
Typical horizontal and vertical extents of thunderstorm are in order of tens of kilometers and 30,000 feet (up to and pushing into the tropopause at times) respectively, and typical duration in time is in the order of 30 minutes. The life cycle of a thunderstorm is divided into three stages. In the first, the towering cumulus stage, warm moist unstable air feeds the cloud’s vertical growth and updraft increases in strength. The second stage is known as the mature stage where the cumulonimbus top glaciates and down drafts become significant. In the third, dissipating, Stage, the anvils are well developed and the down drafts diminish. Associated clouds include cumulus cloud (Cu), towering cumulus (TCu), cumulonimbus (Cb) thunderstorm cloud. Often low-level stratus (St) forms in the precipitation at the base of a thunderstorm, The morning appearance of altocumulus castellans, turrets of middle-level cloud, are the precursor to thunderstorm activity later in the day.
Several methods have been presented for thunderstorm forecasting since 1951. Most of them are applicable when an active atmospheric system on a large scale is dominant. But many strong storms cannot be monitored on the synoptic scale. Therefore, some other forecasting methods were introduced by Dvorak et al. (1975).These methods have been known as decision tree. Colquhoun was the first one who used decision tree for thunderstorm forecasting. He tried to solve some problems of thunderstorm forecasts using skew-t data and NWP outputs. Then, in 1998 Miles and Colquhoun (1998) modified the tree, so that all parameters could be computed automatically from numerical weather prediction outputs.
The method which is presented in this paper is the Colquhoun (1996) algorithm. It is a suitable guide for meteorologists for predicting thunderstorms using each numerical weather prediction output.
Two case studies are considered to survey the thunderstorm in the present research. Both of them occurred at 15 UTC at Mehr-Abad airport. One of them on 13th of May and another on 5th of June 2007 which are analyzed according to the decision tree. The surface and upper air synoptic patterns and satellite images are studied in events of storms. On the other hand some MM5 numerical weather prediction outputs are examined to determine the threshold values of vertical velocity in 850mb, relative humidity in 500-600mb and subsidence currents in 400-500 mb layers. It should be mentioned that the MM5 was run with 35km resolution in regional scale. To access better results, some of the most significant thermodynamic upward motion indices are calculated for Mehr-Abad airport such as LI, KI, SWEAT index, CAPE and BRN using the RAOB software.
Analysis of the MM5 outputs shows that the vertical velocity in 850 mb is not reliable because the observations confirm the passage of a cold front which is a reason for convergence in low level but the vertical velocity values do not correspond with them. The threshold values of relative humidity and sinking currents are the same as other studies in the world. Also, the LI, KI, SWEAT and CAPE values represented unstable conditions for thunderstorm occurrence.
Although most of decisions in the Colquhoun algorithm are designed for severe thunderstorms in tropical and subtropical regions, some boxes of the decision tree are denoted to ordinary storms which occur in mid latitudes of which 2 examples are shown in this research. So, it can be used in operational applications such as aeronautical meteorology in forecasting center of IRIMO. Large scale patterns are not suitable guides for the prediction of thunderstorms because there are no especial indexes for identifying the storms and they can show instability qualitatively. The thermodynamic indexes (LI, KI, SWEAT and CAPE) and their threshold values are appropriate signs to forecast storms in the Tehran area. MM5 vertical velocity at low level isn't reliable and needs to be modified but relative humidity and subsiding currents in mid levels give the acceptable results.https://jesphys.ut.ac.ir/article_21450_deee6434aa1cbbd3fadea5d642c9a7c6.pdfInstitute of Geophysics, University of TehranJournal of the Earth and Space Physics2538-371X35420100121The lithosphere-asthenosphere boundary in the North-West of
Iran from S receiver functionThe lithosphere-asthenosphere boundary in the North-West of
Iran from S receiver function21451FAFatanehTaghizadeh FarahmandForoghSodoudiMohammad RezaGheitanchiNargesAfsariJournal Article19700101Recently, the S receiver function method has been successfully developed to identify upper mantle interfaces. S receiver functions have the advantage of being free of s-wave multiple reflections and can be more suitable than P receiver function for studying mantle lithosphere. However, because of specific ray geometry of the S-to-P converted waves, the S receiver function method has some technical difficulties and limitations. We selected data from teleseismic events (Mb>5.7, epicentral distance between 60?- 85?) recorded since 1996 to present at 8 three component short period stations from the Tabriz Telemetry Network. Clear negative signals from the lithosphere-asthenosphere boundary (LAB) are observed. The average LAB depth is approximately 85 Km and varies from 77 to 103 km underneath the NW of Iran.Recently, the S receiver function method has been successfully developed to identify upper mantle interfaces. S receiver functions have the advantage of being free of s-wave multiple reflections and can be more suitable than P receiver function for studying mantle lithosphere. However, because of specific ray geometry of the S-to-P converted waves, the S receiver function method has some technical difficulties and limitations. We selected data from teleseismic events (Mb>5.7, epicentral distance between 60?- 85?) recorded since 1996 to present at 8 three component short period stations from the Tabriz Telemetry Network. Clear negative signals from the lithosphere-asthenosphere boundary (LAB) are observed. The average LAB depth is approximately 85 Km and varies from 77 to 103 km underneath the NW of Iran.https://jesphys.ut.ac.ir/article_21451_b0e19571f73c7caa0e005dc9521ffb3c.pdfInstitute of Geophysics, University of TehranJournal of the Earth and Space Physics2538-371X35420100121The crustal structure beneath the northwest of the Zagros (Kermanshah
Region) from teleseismic receiver functionsThe crustal structure beneath the northwest of the Zagros (Kermanshah
Region) from teleseismic receiver functions21452FANargesAfsariForoghSodoudiMohammad RezaGheitanchiAKavianiFatanehTaghizadeh FarahmandJournal Article19700101In this study, we used teleseismic data which was recorded by 5 stations (DHR, GHG, KOM, LIN and VIS) of the Kermanshah Seismic Network from 2003 to 2007 with Mb?5.5 and epicentral distances from 30° to 95°. The crustal structure beneath these stations was determined by the modeling of the P receiver functions. The main phases, which were observed in our final P receiver functions, are Moho conversions, their multiples in the crust, and conversions at the base of the sediments. We obtained a 2-layer model for the crust of the Kermanshah Region. The crust beneath this region is approximately 42 km thick and consists of a 9 to 18 km thick sedimentary layer overlying a 24 to 35 km thick layer. The average shear wave velocity was estimated to be 3.69 kms-1 in the crust and reaches to 4.80 kms-1 under Moho and those obtained from other geophysical studies.In this study, we used teleseismic data which was recorded by 5 stations (DHR, GHG, KOM, LIN and VIS) of the Kermanshah Seismic Network from 2003 to 2007 with Mb?5.5 and epicentral distances from 30° to 95°. The crustal structure beneath these stations was determined by the modeling of the P receiver functions. The main phases, which were observed in our final P receiver functions, are Moho conversions, their multiples in the crust, and conversions at the base of the sediments. We obtained a 2-layer model for the crust of the Kermanshah Region. The crust beneath this region is approximately 42 km thick and consists of a 9 to 18 km thick sedimentary layer overlying a 24 to 35 km thick layer. The average shear wave velocity was estimated to be 3.69 kms-1 in the crust and reaches to 4.80 kms-1 under Moho and those obtained from other geophysical studies.https://jesphys.ut.ac.ir/article_21452_db150b56cfa066d11e27e3d3d6cb4ad1.pdfInstitute of Geophysics, University of TehranJournal of the Earth and Space Physics2538-371X35420100121The exploration of gold by magnetic method in Hired Area, South Khorasan, a case studyThe exploration of gold by magnetic method in Hired Area, South Khorasan, a case study21453FAMohammad RezaHaidarian ShahriMohammad HassanKarimpourAzadehMalekzadehJournal Article19700101Hired is a large gold prospecting area which is located in South Khorasan province, in the east of Iran. Gold mineralization is found in 4 target areas covering about 24 km2. The host rocks are mainly Tertiary volcanics, some Jurassic and Cretaceous sediments. Sub-volcanic rocks are of magnetite series (gabbros to diorite) and ilmenite series (granite-granodiorite-monzonite) which have intruded the Tertiary and older rocks. Important styles of mineralization are: stockwork, skarn, vein, and replacement. Stockwork gold mineralization has only pyrrhotite and is found within or around the granite-granodiorite-monzonite. Detail core logging was carried out in 4 target areas with respect to gold content, mineral paragenesis, types of veinlets, rock types, and measuring the magnetic susceptibility. Within the stockwork mineralization at east of target 1, there is good correlation between gold grade, amount of pyrrhotite, and magnetic susceptibility. At Hired, sub-volcanic rocks of the ilmenite series (granite-granodiorite-monzonite) have susceptibility less than 40 × 10-5 SI. The magnetite series (gabbros to diorite) have susceptibility of 150 – 900 × 10-5 SI. Stockwork gold mineralization has susceptibility of 200-3500 × 10-5 SI. Therefore the host rocks, granite-granodiorite-monzonite, have low magnetic susceptibility. Based on this sharp magnetic contrast ground magnetic was selected as a suitable geophysical method. The aim was to use the magnetic method for drill target identification of gold ore east of target 1. The total magnetic field intensity (TMI) was measured in 780 points along 25 lines. Measurement spacing was 2 meter. magnetic lines, contour maps, and images revealed large anomalies at east of target 1 representing the magnetic responses of gold ore. The depth of the anomalies is estimated to be shallow as indicated by their expression on the first vertical derivative map. This prediction is consistent with mineralogical observation on the surface and the continued map. The locations of the anomalies on the Reduced To the Pole (RTP) map are proposed as suitable points for drilling target.Hired is a large gold prospecting area which is located in South Khorasan province, in the east of Iran. Gold mineralization is found in 4 target areas covering about 24 km2. The host rocks are mainly Tertiary volcanics, some Jurassic and Cretaceous sediments. Sub-volcanic rocks are of magnetite series (gabbros to diorite) and ilmenite series (granite-granodiorite-monzonite) which have intruded the Tertiary and older rocks. Important styles of mineralization are: stockwork, skarn, vein, and replacement. Stockwork gold mineralization has only pyrrhotite and is found within or around the granite-granodiorite-monzonite. Detail core logging was carried out in 4 target areas with respect to gold content, mineral paragenesis, types of veinlets, rock types, and measuring the magnetic susceptibility. Within the stockwork mineralization at east of target 1, there is good correlation between gold grade, amount of pyrrhotite, and magnetic susceptibility. At Hired, sub-volcanic rocks of the ilmenite series (granite-granodiorite-monzonite) have susceptibility less than 40 × 10-5 SI. The magnetite series (gabbros to diorite) have susceptibility of 150 – 900 × 10-5 SI. Stockwork gold mineralization has susceptibility of 200-3500 × 10-5 SI. Therefore the host rocks, granite-granodiorite-monzonite, have low magnetic susceptibility. Based on this sharp magnetic contrast ground magnetic was selected as a suitable geophysical method. The aim was to use the magnetic method for drill target identification of gold ore east of target 1. The total magnetic field intensity (TMI) was measured in 780 points along 25 lines. Measurement spacing was 2 meter. magnetic lines, contour maps, and images revealed large anomalies at east of target 1 representing the magnetic responses of gold ore. The depth of the anomalies is estimated to be shallow as indicated by their expression on the first vertical derivative map. This prediction is consistent with mineralogical observation on the surface and the continued map. The locations of the anomalies on the Reduced To the Pole (RTP) map are proposed as suitable points for drilling target.https://jesphys.ut.ac.ir/article_21453_b2d39627affaefbae55b10eb9d2fff5b.pdf