حسن لشکری

The formation and occurrence of any climatic phenomenon require conditions that, when the sum of these atmospheric and environmental conditions occur simultaneously, make it possible for the phenomenon to form and occur. Depending on the type of phenomenon, some of these atmospheric or environmental factors are formed in the atmosphere alone, while others are formed in the physical environment under it. A phenomenon like a dust storm is a combined atmospheric-environmental phenomenon. The existence of dry and highly fragmented soils provides favorable conditions for the rise of dust. For this reason, dry deserts, bare plains with soft and granular soils are always prone to this phenomenon as sources of dust production. Therefore, physical substrates with this feature should always be studied and investigated as potential places for dust phenomenon to occur. What is related to atmospheric conditions, severe instabilities without moisture or with little moisture are the basis of dust storms. This weather pattern is more likely to appear in arid and semi-arid climates. It is not possible to control or change the structure of atmospheric phenomena with current human technology. Therefore, the best way to reduce the effects of destructive phenomena such as dust storms in a geographical area is to first identify the source and path of dust storms.

The selected study area for this research is the southwest of Iran, an area that has experienced an increasing trend in the frequency and intensity of dust storms in recent decades. The study area includes the three provinces of Kohgiluyeh, Boyer Ahmad, Chaharmahal and Bakhtiari.In the first step of the research, all synoptic stations with complete statistics for 33 years (1986-2019) in the study area were identified and extracted. .In the second step, using the data (number of reports of dust phenomenon (nhz), number of reports with dust phenomenon (ndu), number of reports with sand and dust storm phenomenon (nbdu), wind speed and horizontal visibility less than 1000 meters and codes (06.07, 08.09, 30.31, 32.33, 34.35, 98) days with dust were extracted from the data of Meteorological Organization. In the next step, using the website [https://www.ready.noaa.gov/HYSPLIT, ↗] (https://www.ready.noaa.gov/HYSPLIT,) the origin of dust storms in the southwest of Iran was plotted using the backward method from the GDAS data system with a resolution of 0.5 degrees. This data is available from 2007. Therefore, for all the dust reports with the above characteristics from each of the sample stations, the origin of the storm has been determined.

Statistical analysis of dust storm reports from selected stations showed that 3027 cases of dust storm have been reported during the 33-year statistical period from a total of selected stations. In terms of monthly distribution, the months of January, February and December respectively have reported the highest number of dust storms. In terms of seasonal distribution, the highest number of pollen reports were from winter (1153 cases, 38.1%) and spring (711 cases, 23.5%) respectively. The highest number of dust storms was reported from the two dry years of 2008 (225 cases) and 2009 (243 cases). In terms of stations, the highest number of dust storms was reported from Ahvaz and Abadan stations. Based on the routing performed in this study, the input dust storms came from six areas:Iraq (from four parts), eastern Mediterranean countries, Saudi Arabia, central and northeast Africa, distant sources in eastern Europe, and local sources within the study area.The origin of 93.25% of the input dust storms to the study area was from sources in central Iraq, and about 20% of the dust storms originated from eastern Mediterranean countries, while 16% of the dust storms were from local sources in Khuzestan province. The origin of dust storms in high-altitude stations in the eastern part of the study area, such as Shahr-e Kord, Yasuj, and Kuhrang, was from distant sources in Syria and Jordan or northeastern Africa.

Given that, 84% of the dust storms entering the region originate from outside the border. Considering that the two sources of the west and the center of Iraq are the source of 35% of the storms entering the region. Diplomatic efforts for the cooperation of the country of Iraq to stabilize the soil in these resources are very necessary.

Precipitation is the most important and effective source of water in a watershed, which changes with uneven spatial and temporal distribution in the basin. In this research, two heavy rains that led to floods in 2016 and 2019 were investigated in order to know and understand the mechanisms affecting the occurrence of these rains and to identify the relationship between the intensity of the rainfall and the flow rate. In order to analyze these relationships, an environmental approach was chosen. After drawing the maps of the upper atmospheric levels and identifying the effective system in causing super heavy rains, the flood discharge caused by the mentioned systems was extracted from the recorded data. The most effective system in causing heavy rains is the Sudanese low pressure system. The peak flow of floods has been delayed by 12 to 24 hours from the day of peak rainfall and the increasing trend of runoff is closely related to the increase in intensity and continuity of rainfall. Due to heavy rains with total rains of more than 160 to 120 mm in some stations, the discharge values have been recorded geometrically exponentially in hydrometric stations. The importance of investigating the phenomenon of precipitation is more obvious when a place witnesses a small or significant fall or suddenly a large amount of precipitation. In recent years, several studies have been conducted in relation to heavy rains, heavy rains and flood potential in the synoptic method and with the help of maps of different levels of the atmosphere in the world and in Iran. Considering the importance of rainfall and its impact on various economic, agricultural and social sectors, the need to investigate and identify the synergistic patterns of rainfall in the study area for use in planning and optimal management of water resources is evident. Ecosystems and physical structures of human societies are adjusted to normal climatic conditions, and when extreme climatic phenomena occur, they can rarely equip and prepare themselves. Therefore, the temporal variability of precipitation, especially extreme precipitations, has many economic effects.

The study method in this research is a combination of field method and statistical-analytical method. Research is of applied type. Obtaining atmospheric data of pressure, omega, specific humidity and flow for the indicated atmospheric levels during a 33-year period (1990-2017) from the website (NCEP/NCAR) and European Center for Medium-Range Forecasting (ECMWF) Determining the heaviest precipitations that occurred in the Dez River basin with the index method 98% percentile base and then determining the most durable rain waves (indicator waves) in each year and taking into account the duration of rainy days during the 33-year statistical period (1990-2017) and drawing weather maps using GRADS and SURFER software and performing factor analysis method and Clustering and visual analysis to identify the atmospheric patterns of heavy and long-term rainfall occurrences and synoptic analysis of the atmospheric patterns of heavy and long-lasting cloud precipitations and the investigation and analysis of the historical course of heavy and long-term cloud precipitations and the investigation and analysis of the degree of correlation or the relationship between the intensity of rainfall and the intensity of surface runoff and choosing the factor that expresses the highest intensity of rainfall.

The findings of this research are presented in two separate sections. In the first part, synoptic patterns leading to selected super heavy rains will be presented. In the second part, the flood discharge resulting from these extremely heavy rains has been analyzed. Based on the spatial arrangement and the functioning of the systems in the lower and middle layers of the atmosphere, synoptic patterns leading to the formation of these super heavy rains were identified. In the analysis of the flood hydrograph, while showing the flow of the flood caused by this rainfall during the flooding of the river in the water year, the hourly hydrograph of the flood caused by this rainfall has also been drawn and analyzed.

In the investigation of the middle layer of the Wardspehr in all the systems that led to the flood of 2019, it was observed that the Saudi Wacharkhand cell has been established over the Arabian and Oman seas and the east of the Arabian Peninsula by moving eastward. And the formation of a low-altitude center over Iraq is the most suitable pattern for heavy cloud precipitation in the Dez basin. On the synoptic maps of the lower and middle levels of the 2016 Wardspehr system, the African Watcher Khand has blocked the west of Iran with its significant northward expansion over eastern Europe. As a result, the activity period of the system has increased by more than 4 days. Therefore, the African cycle and its stop in Eastern Europe is the main reason for prolonging the activity period of rainfall systems leading to flooding in the area. Therefore, the Azureverse system has not played a significant role in prolonging the activity period of the systems on the field. In the investigation of the flood discharge of super-heavy rainfall systems, it was observed that in all the selected rainfall systems of Dubai, the peak floods have caused very severe floods with a delay of 12 to 24 hours from the day of the peak rainfall of the Dubai system. So that in the floods of 2019 with a peak discharge of 4503 cubic meters per second, the flood of 2016 with a peak discharge of 10510 cubic meters per second, while they were among the very heavy floods of the study period. Flow values due to short-term super heavy rains with intensities of more than 160 to 120 mm in some stations have been recorded in geometrical exponential form in hydrometric stations. Therefore, the increasing trend of surface runoff is an exponential trend compared to the increasing intensity of rainfall.

Aridity and drought are inseparable features of every climate. But in arid and semi-arid climates, tarsal is an ideal opportunity to restore or compensate for the lack of water in the region. The southern part of Iran has a dry climate despite access to the huge moisture resources of the warm southern seas. To conduct the research, first, the daily rainfall data of all the synoptic stations of the southern provinces of the country, which had complete statistics in the 33-year statistical period (1986-2019), were extracted. Then, using ZCI, ZSI, and SPI indicators, droughts and droughts were identified. Finally, the years that were in extreme poverty in all three above indicators were selected as samples. In the next step, the data of specific humidity, orbital and meridional wind, geopotential height and omega for all atmospheric levels in the lower and middle layers of the Verdosphere were received from the NCEP/NCAR site for all rainy days. Examining the maps of subsurface levels of the Verdspehr (sea, 1000 and 925 hectopascals) showed that three main systems control the pattern of the subsurface layer of the Verdspehr. The Siberian, Tibetan and Mohajer high-pressure fronts spread over the warm waters of the Oman and Arabian seas from 3 to 7 days before the start of the system's rainfall and spread the necessary moisture into the Sudanese system. It plays a very important role in determining the entry path of the system, the expansion pattern of the Mediterranean trough and the duration of the activity of the precipitation system in the middle layer of the Arabian Wardspehr

In global meteorological literature, atmospheric rivers are defined as long and narrow pathways of intense water vapor transport towards the polar regions in the middle latitudes, typically associated with low-level jet streams along the leading edge of extratropical cyclones. In this study, to identify the origins of the incoming atmospheric rivers to the study area, precipitation systems that occurred at more than half of the region's stations were selected. Then, using vertically integrated water vapor flux data from the east and north of the study area with a spatial resolution of 0.5 x 0.5 degrees, the magnitude of the water vapor flux was calculated. To calculate the magnitude of the flux, data including specific humidity and meridional and zonal winds at pressure levels from 1000 to 300 hPa were used. showed that these rivers have entered northwest and west of Iran from four moisture sources. The sources are the warm southern seas (the Sudan - Red Sea low-pressure pattern), the convergence zone region, the combined source of the Sudan low-pressure system and the Mediterranean circulation, and the Mediterranean Sea. Among these sources, the warm seas of Arabia and Oman and the Red Sea had the largest share in the incoming rivers to the region. These atmospheric rivers have been the strongest in terms of both temporal continuity and moisture flux. They first enter southwest Iran and then into the study area. The atmospheric rivers with the convergence zone source rank second in terms of their contribution to the region's precipitation.

The occurrence of heatwaves, even in short time periods, can disrupt daily life and many social activities for residents. This phenomenon, when it persists for longer durations, may cause environmental and agricultural damage. The objective of this research is to extract and introduce synoptic patterns that lead to the creation of heatwaves in the southern coastal cities over the past 33 years. To achieve this goal, using the Z-score index and other selected criteria, heatwave samples were extracted for all selected stations. Based on the selected criteria, 90 heatwave samples were extracted for the 33-year statistical period. Then, using the factor analysis method and visual inspection with 1000 hPa weather data, dominant and frequent synoptic patterns were extracted. The results of this research showed that seven factors and 14 frequent patterns are the most dominant synoptic patterns that create heatwaves during the cold season in southern Iranian cities. Among these patterns, the first factor of the Sudan-Turkmenistan low-pressure pattern and, among the effective systems in creating high heatwave temperatures, the Sudan low-pressure system had the most significant role in the structure of synoptic patterns. In this pattern, the Sudan low-pressure system is combined with a northeast expansion towards the South and the warm air movement of the Hadley cell, causing an abnormal rise in temperatures at coastal stations. The core heat of this pattern is located over Sudan and Saudi Arabia. In the boundary layer to the middle troposphere, the Arabian trough rotates over the region, creating dynamic

The purpose of this research is to determine the best deployment position and stretching pattern of the side-to-side jet to create tarsal in the southwest of Iran, as well as to select the most frequent synoptic pattern in this region.

The daily rainfall data of stations in the southwest of Iran (Khuzestan, Chaharmahal, Bakhtiari, Kohgiluyeh, and Boyer Ahmad) during the statistical period in three solar cycles (1986-1997), (1997-2008) and (2008-2019) were received from the National Meteorological Organization. Orbital and meridional wind component data, geopotential height at 250 and 300 hPa levels, slp, specific humidity and omega from the US National Center for Oceanography and Environment (NCEP/NCAR) with a spatial resolution of 2.5 × 2.5 degrees. received. Then, using factor analysis and visual inspection, the most frequent patterns were determined for all three solar cycles.

The examination of the maps of the lower, border and middle level of the troposphere showed that in the severe droughts of southwest Iran, the establishment of high pressure Arabia over the Arabian and Oman seas and the movement of moisture from these seas to the low-pressure eastern slope of Sudan and the formation of a deep trough in the west of Iran from Europe to southern Sudan and Cold subpolar advection on the western low pressure slope of Sudan is the most suitable pattern for heavy rains and its continuation for several days in the southwest of Iran. The best location of the subtropical jet to strengthen the rain systems is the area between Egypt and the western coast of the Persian Gulf in southern Iraq, if the core of the jet is located in northwestern Saudi Arabia. And the main source of system moisture in all precipitation samples is the Arabian, Oman and Mediterranean seas.

The importance of heavy rainfall and its consequences have caused this phenomenon to be of special importance in environmental planning and water resources management. Using statistical methods and the discharge data of the Dez river, the heavy floods of this river were extracted to identify the effective factors in their creation. Among all systems leading to heavy rains, the Sudanian system has been the main factor of moisture advection in the lower layer of the troposphere with its expansion to the north and northeast. Due to its thermal characteristics, this system has been prone to receive considerable moisture from the surrounding warm seas. This system has provided the necessary conditions for the creation of surface instabilities in most transitional systems independently and in a smaller number in the integrated state with the Mediterranean system. In the investigation of the middle layer of the troposphere in all the systems that led to the floods of 1993 and 2005, it was observed that the anticyclone cell of Arabia was established over the Arabian and Oman seas and the east of the Arabian Peninsula by moving eastward. In this situation, a very deep trough has formed in the west of Iran, and the southern end of the trough has extended to southern Sudan and northern Ethiopia. The eastward movement of high pressure in Arabia and the significant southward expansion of the Mediterranean trough and the formation of a low-altitude center over Iraq is the most suitable pattern for the heavy cloud rains in the basin.

In terms of geographic location, the Dez basin is limited between 48°10' to 50°21' east longitude and 31°34' to 33°7' north latitude. The studied area is a part of the Dez river basin, which is located almost in the middle part to the end part. After the Karun branch of one of the largest and longest Dez rivers, Dez is formed from two main branches named Caesar and Bakhtiari, and after leaving the mountainous region north of Andimeshk and Dezful, it enters the plain of Khuzestan. For comprehensive and accurate interpretation of pressure systems and assessment of their environmental effects on the earth, the maps of the earth's surface and level of 500 hPa are very efficient. In most cases, the wind direction and temperature distribution at the 500 hPa level are completely affected by the topographic arrangement of the geopotential height at the 500 hPa level. Geopotential height maps are one of the most important and efficient atmospheric maps in synoptic analysis and interpretation. Heavy rains on representative days are analyzed, interpreted, and explained. Two statistical and synoptic methods were used for a more detailed investigation of the synoptic situation of heavy rains in the Dez river basin. In the statistical part, factor analysis, which is one of the widely used statistical methods in climatology, was used, and in the synoptic part, maps of different atmospheric levels were extracted and analyzed using Gardes software for the specified days. To determine the members of each group, the correlation of the scores of each factor with the sea level pressure map in the time period (1964-2020) was calculated, and the members of each group were determined. To determine the representative days, the correlation of the SLP maps of the days of each group was used, and the day that had a high correlation with more days was selected as the representative day. To perform factor analysis, the elements of the database were transferred from the Excel environment to the S-Plus2008 software environment, and then by performing various inferential analysis calculations, the most suitable method was selected to identify the main and effective factors.

As can be seen, the heavy rains of 2013 lasted for 6 days, and the system of 2011 lasted for 7 days. Of course, as mentioned, in some systems, days before or after the end of the activity period of the main system, scattered rains, even with high intensity, have been recorded in some stations. But these scattered rains are considered local rains. The highest peak flow rate of 8556 m3 belongs to the system in February 2013. This system has lasted for 4 days. It took 31 hours to reach the peak of the flood.

In the investigation of the middle layer of the troposphere in all the systems that led to the floods of 1993 and 2005, it was observed that the Arabian anticyclone has been established over the Arabian and Oman seas and the east of the Arabian Peninsula by moving eastward. In this situation, a very deep trough has formed in the west of Iran, and the southern end of the trough has extended to southern Sudan and northern Ethiopia. Therefore, the eastward displacement of the high pressure in Arabia and the significant southward expansion of the Mediterranean trough, and the formation of a low-altitude center cut over Iraq is the most suitable pattern for heavy cloud precipitation in the Dez basin. The peak discharge of floods with a delay of 12 to 24 hours from the day of peak rainfall has created a very intense discharge system. So, the floods of 2005 with a peak discharge of 8556 m3 s-1 and the flood of 1993 with a peak discharge of 4022 m3 s-1, while they were very heavy floods, there were two study periods.

Introduction:

Dust storms with visibility of less than 200 meters are dangerous storms for human life and activity. By knowing the behavioral characteristics and how these storms form and spread over the sources of dust production, it is possible to reduce its many damages or adapt to it by creating the necessary infrastructure.

According to the purpose of the research, to investigate the historical trend of the occurrence of severe storms and the synoptic patterns that cause such storms, a statistical period of 33 years (corresponding to the last three solar cycles) was selected. Based on this statistical basis, 16 synoptic stations were selected as sample stations. All codes with visibility less than 200 meters were extracted for all selected stations. The days in which code was reported in at least two observatories with visibility less than 200 meters were selected as a day with a storm. To select synoptic systems, the days when this phenomenon was reported in at least one third of the sample stations were selected as a dust system. In this way, 68 study samples were extracted. These samples were tested using the method of factor analysis and visual inspection to select the dominant patterns.

The highest number of dust storms with visibility less than 200 meters occurs in two turbulent seasons in terms of weather, i. e. winter (593 cases) and autumn (426 cases). In monthly terms, the highest number of dust storms of this type occurred in January (352 cases) and December (236 cases). In terms of historical trends, from the beginning of the period (1987) to 2007, the number of storms has been almost constant. Since 2008, the number of such storms has increased significantly and this process continued until 2012. Since 2012, the number of storms has decreased slightly, but it has not returned to the conditions before 2007. In terms of spatial distribution, the highest number of storms occurred in the cold period of the year, in the eastern stations of the region, on the contrary, in the warm period of the year, the highest number of storms occurred in the western part of the study area.

Two recurring patterns are the main cause of dust storms in the cold period of the year. In the African gyre pattern, the significant northward expansion of this anticyclone ridge and the cold advection of the subpolar latitudes over the western region of Asia creates a severe temperature and pressure gradient in the entire lower and middle layer of the troposphere. Such storms generally start after the end of rain in the west of Iran. In the Sudan low pattern, with the significant expansion of the Sudan low pressure tongue over the western region of Asia and the formation of a deep trough in the middle layers, it causes the instabilities to intensify over the dust sources of Syria and Iraq. Most summer dust storms have followed a general pattern. In these patterns, three low pressure systems, Saudi Arabia, Pakistan and sometimes Lut desert, are the main cause of dust storms in the lower layer (up to the level of 850hpa). The strong winds resulting from this surface instability are the main cause of dust rising from dust sources in the region. Meanwhile, in the middle layers, calm atmosphere generally dominates the western region of Iran.

The result of this research showed that storms with visibility of less than 200 meters are increasing in the western region of Iran. In terms of spatial distribution, the highest number of such storms occurs in the cold period of the year in the eastern part of the region. From a synoptic point of view, dust particles rise from dust sources in Syria and western Iraq and enter the eastern part of the study area along the atmospheric currents of the middle layer of the troposphere. That is, during the cold period of the year, highland areas are affected by severe dust storms. Meanwhile, the western part of the study area is affected by the highest number of dust storms in the hot period of the year. Dust storms this time of the year are not very deep.

In the Ethiopian-Sudan range forms the low pressure system without front in the cold and transition seasons that is affecting the climate of the adjacent regions by crossing the Red sea. Based on the evidence in the context of Iran, studying Sudan low was first begun by Olfat in 1968. Olfat refers to low pressures which are formed in northeastern Africa and the Red Sea and then pass Saudi Arabia and the Persian Gulf, enter Iran, and finally, cause rainfall. The most comprehensive research specifically examining Sudan low, was the work carried out by the Lashkari in 1996. While he studying the floods that occurred in southwestern of Iran, he was identified Sudan low by the most important cause of such flooding and he explained how they are formed, and how these low-pressure systems were deployed on the southwest of Iran.

The study period with long-term variations was considered from 9.5 to 11 years based on solar cycles. Precipitation data for 13 synoptic stations are considered above 5 mm in south and southwestern Iran. With three criteria were determined for the days of rainfall caused by each type of atmospheric system. The visual analysis of high and low altitude cores and geopotential height at 1000 hPa pressure level (El-Fandy, 1950a; Lashkari, 1996; 2002) were considered based on the aim of the study. Accordingly, the approximate locations of activity centers, as well as the range of the formation and displacement of the Sudan system were initially identified based on the location of the formation of low and high-pressure cores. Then, the rainy days due to the Sudan system in January were separated from the precipitation of the other atmospheric system.

According to the selected criteria in the forty-year statistical period, 507 precipitation systems were identified with different continuities that led to precipitation in the northern coast of the Persian Gulf. The pattern of independent Sudan low rainfall was responsible for 77% of the precipitation in the Persian Gulf. Decade frequency share of Sudan low was lower in the first decade (16%) compared to the next three decades. This system of rainfall was more activated during the second and third decades compared to the first decade. However, rainfall changes were not evident in the mid-decade. Independent Sudan low precipitation provide 25% and 27% of the cold season precipitation of the Persian Gulf during the second and third decades respectively. In accordance with the 24th solar cycle, at the end of the study period, the Sudan low was more effective on the Gulf coast than ever before. During this decade, 125 cases of Sudan low rainfall was recorded for the Persian Gulf. Thus, the frequency of Sudan low during the fourth decade was about 31%, which was higher than in the rest of the decade. Overall, the Sudan low rainfall was repeated 151 times for 2 days rainfall, during the statistical period studied. This Precipitation has increased over the last decades compared to other periods.

The severe variability of rainfall along the timing and location of the permanent Persian Gulf coasts can have a significant impact on the economic and agricultural behavior of the Gulf population in the three provinces of Ahwaz, Bushehr and Hormozgan.The purpose of this study was to evaluate the precipitation changes due to Sudan low in the Persian Gulf coastal region during the cold period. The results of this study showed that the role of integration patterns in influencing the precipitation of the Persian Gulf coast has decreased with the strengthening and further activation of the Sudan low system during the last two decades. That way, about 77percent of the region's rainfall is provided by independent Sudan low. At the end of the course (in accordance with 24th solar cycle activity) the Sudan low system was more active than before. Although the Sudan low activity was different at each station during the period studied, but in the historical passage incremental and decade's positive behavior of Sudan low was common to all stations. Evaluation of changes in rainfall duration shows that the pattern of precipitation with 2days duration is more frequent than the patterns of one to several days.

Heavy rains are a risk factor for natural disasters such as floods. Therefore, identifying and predicting their occurrence is one of the measures that can reduce the damage caused by it. This study was with purpose analyze and explain heavy rainfall using statistical-synoptic methods. For this purpose, precipitation data from 14 synoptic and rainfall stations of Karkheh and Dez basins in a period of 60 years (1959-2019) were used. In this regard, first, using the probability distribution function of the final limit of type one (Gamble), the heavy rain threshold was determined. The results obtained from heavy rainfall thresholds showed that the average rainfall of more than 40.7 mm in Karkheh basin and the average rainfall of more than 47 mm in Dez basin are considered as heavy rainfall. The average number of days of heavy rainfall in Karkheh basin is 118 days and Dez basin is 81 days. The flood threshold of Karkheh basin is lower than Dez basin. Therefore, Karkheh rains occur more suddenly and irregularly, while the rains in the Dez basin have more normal time series. As a result, Karkheh basin is more vulnerable to floods than Dez basin in terms of increased heavy rainfall. The results of synoptic analysis showed that in all models, synoptic systems of Sudanese and Sudanese-Mediterranean integration systems have played an effective role in creating heavy rainfall simultaneously in both Karkheh and Dez basins. The deepening of the Mediterranean submarine also activates the humid low-pressure system on Sudan and the Red Sea. The Sudanese system causes heavy rainfall by moving north and northeast of the Mediterranean coast over the study area. The main source of moisture is the Arabian Sea, the Oman Sea, the Red Sea and the Mediterranean.Heavy rains are a risk factor for natural disasters such as floods. Therefore, identifying and predicting their occurrence is one of the measures that can reduce the damage caused by it. This study was with purpose analyze and explain heavy rainfall using statistical-synoptic methods. For this purpose, precipitation data from 14 synoptic and rainfall stations of Karkheh and Dez basins in a period of 60 years (1959-2019) were used. In this regard, first, using the probability distribution function of the final limit of type one (Gamble), the heavy rain threshold was determined. The results obtained from heavy rainfall thresholds showed that the average rainfall of more than 40.7 mm in Karkheh basin and the average rainfall of more than 47 mm in Dez basin are considered as heavy rainfall. The average number of days of heavy rainfall in Karkheh basin is 118 days and Dez basin is 81 days. The flood threshold of Karkheh basin is lower than Dez basin. Therefore, Karkheh rains occur more suddenly and irregularly, while the rains in the Dez basin have more normal time series. As a result, Karkheh basin is more vulnerable to floods than Dez basin in terms of increased heavy rainfall. The results of synoptic analysis showed that in all models, synoptic systems of Sudanese and Sudanese-Mediterranean integration systems have played an effective role in creating heavy rainfall simultaneously in both Karkheh and Dez basins. The deepening of the Mediterranean submarine also activates the humid low-pressure system on Sudan and the Red Sea. The Sudanese system causes heavy rainfall by moving north and northeast of the Mediterranean coast over the study area. The main source of moisture is the Arabian Sea, the Oman Sea, the Red Sea and the Mediterranean.Heavy rains are a risk factor for natural disasters such as floods. Therefore, identifying and predicting their occurrence is one of the measures that can reduce the damage caused by it. This study was with purpose analyze and explain heavy rainfall using statistical-synoptic methods. For this purpose, precipitation data from 14 synoptic and rainfall stations of Karkheh and Dez basins in a period of 60 years (1959-2019) were used. In this regard, first, using the probability distribution function of the final limit of type one (Gamble), the heavy rain threshold was determined. The results obtained from heavy rainfall thresholds showed that the average rainfall of more than 40.7 mm in Karkheh basin and the average rainfall of more than 47 mm in Dez basin are considered as heavy rainfall. The average number of days of heavy rainfall in Karkheh basin is 118 days and Dez basin is 81 days. The flood threshold of Karkheh basin is lower than Dez basin. Therefore, Karkheh rains occur more suddenly and irregularly, while the rains in the Dez basin have more normal time series. As a result, Karkheh basin is more vulnerable to floods than Dez basin in terms of increased heavy rainfall. The results of synoptic analysis showed that in all models, synoptic systems of Sudanese and Sudanese-Mediterranean integration systems have played an effective role in creating heavy rainfall simultaneously in both Karkheh and Dez basins. The deepening of the Mediterranean submarine also activates the humid low-pressure system on Sudan and the Red Sea. The Sudanese system causes heavy rainfall by moving north and northeast of the Mediterranean coast over the study area. The main source of moisture is the Arabian Sea, the Oman Sea, the Red Sea and the Mediterranean.

In this research, the historical trend and effectiveness of rainfall anomalies during severe and extremely severe droughts in southern Iran have been investigated. For this purpose, the daily and annual rainfall data of the synoptic stations of the study area were extracted from the data of the Meteorological Organization. The statistical base has been chosen to adapt to the solar cycles of a 33-year period corresponding to the years 1986-2019. Based on this, 34 synoptic stations of the region were consistent with this statistical period. First, the state of droughts was investigated based on Standard Rainfall Index (SPI), Chinese Z (CZI), and ZSI (ZSI) score. RAI index has been used to check precipitation anomaly. The selection criteria of 7 years were chosen as examples of extreme and extreme droughts. The historical trend of the occurrence of droughts showed that, firstly, in the last three cycles, in 26 years out of 33 years of the statistical period, the southern region of Iran has more or less faced the phenomenon of drought. The number of droughts in the last two cycles has increased greatly. So that in cycle 23 out of 11 years, 9 years and in cycle 24 out of 11 years, 10 years, many parts of the region were affected by drought. In both cycles in 4 years in more than half of the stations severe and super severe drought occurred. In terms of rainfall-related phenomena, severe anomalies have also occurred in the southern region during droughts, the average daily rainfall is greatly decreasing compared to the long-term average rainfall of the region. In other words, the distribution of rainfall per unit of time has decreased. So that the average daily rainfall in the rainy season has decreased from two millimeters to less than one millimeter.

In this study, the impact of precipitation anomalies during the occurrence of severe and extremely severe Wet in southern Iran has been investigated. The research design involves the following steps. 1- The daily and annual rainfall data of the synoptic stations of the study area were extracted from the data of the Meteorological Organization. 2- The statistical base has been chosen to adapt to the solar cycles of a 33-year period corresponding to the years 1986-2019. 3- The number of 19 synoptic stations that had these conditions were selected. 4- Wet years were determined based on standard precipitation indices (SPI), Chinese Z (CZI), Z score (ZSI). 5- To check the anomaly of precipitation RAI index is used. 6- Based on the declared indicators, with the criteria of 30% repetition in selected stations, 6 severe wet and based on 50% repetition in selected stations, three severe wets have occurred in the statistical period of 33 years. 7- In this research, two seasons of 1992-1993 and 1995-1996 have been examined in terms of anomaly indices and other rainfall characteristics. In the wet and extremely severe years, the annual rainfall was more than two and sometimes three times the long-term average in many stations. In terms of the number of rainy days in the years 1993-1992 in 10 stations and in the wet years 1996-1995 in 17 stations, rainy days over 30 days have been recorded. However, the number of rainy days in both wet years does not show a proportional

The Siberian high-pressure system is one of the components of atmospheric circulation affecting the climate of Iran, especially in the cold season of the year. In this research, the place of the initial formation of this system and its synoptic features have been investigated. For this purpose, the lower tropospheric levels of atmospheric data for the three months December to February data from NCEP / NCAR were received for 22 years. Systems with thermal characteristics were isolated. Then, the central core of this system was determined daily for all months and their geographical coordinates were calculated. The results show that in the vast majority of the months from December to February, the main Siberian high-pressure core is located in the lower atmosphere of the Altai Mountains. The study also found that more than half of the days of Siberian high-pressure had two central nuclei. Thus, contrary to popular belief, the Siberian high-pressure core forms not on the low Siberian plains but the high altitudes of the Altai and Sayan Mountains. Adaptation of isothermal, isobaric, and height maps also showed that the core of the cold in the cold three months was generally on the north or northeast of the Siberian desert. However, the high-pressure core was located on these two high mountains for almost a day. Therefore, in addition to cold, the topographic factor (northwest-southeast extension) plays a very important role in the formation of the high-pressure core. According to the general results of research, this high pressure, directly or indirectly, is the cause of colds and cold waves in the cold period of the year, as well as early and late waves in the country.

The purpose of this study is detection of climate change trend in 3 selected stations namely Abadan, Ahvaz and Dezful in the south of Khuzestan province,Iran during the baseline period of (1980-2010) and investigation the possible effect of climate change on the wheat crop calendar in Dezful region based on the RCP 2.6 scenario. The future projected climatic data with temporal resoulution of 5 mintues were retrived from CCAFS and WorldClim1.4 climate databases and downscaled using SDSM weather generator, till 2040. The precipitation, minimum and maximum temperature variables maps were produced by ArcGis10.4 software using the IDW . The possible effect of climate change on growing season length in Dezful station was assesed.The results showed that, on average,the beginning of all phenological stages from planting to harvest would occur about 15 days earlier by the end of future period.This sift for the heading phase is projected to be 8 to 10 days. For the physiological maturity stage, a different trend was observed, so that during near future period, i.e., 2021 to 2031, the maturity stage will occur between April 11th to April 22nd,but during 2031 to 2041, the date of maturity varies between 21 March to 11 th April. In other words, It is projected that by the middle of the century, the wheat crop maturity would happen sooner between 10 and 15 days in the study station.

Variation of rainfall origin in different parts of Iran along with latitude, distance and proximity to moisture sources, etc. causes rainfall behaviors such as intensity and continuity to have temporal and spatial changes .Using statistical methods and discharge data of Dez river, severe floods of this river were extracted to identify the effective factors in their creation.In this research, the information of all effective atmospheric levels has been analyzed using a combination of illustrative and appropriate maps.And Synoptic and thermodynamic properties of heavy cloud precipitation in Dez catchment At the same time, the synoptic patterns lead to the prolongation of the systems on the catchment And its effect on flow rate was identified and presented.The purpose of this study was to identify the pattern or patterns of durable rainfall systems in the Dez River Basin. There is a deep landing in the eastern Mediterranean that has caused the cold European air to fall in the west of the ship, as well as the transfer of moisture from the Arabian Sea and the Persian Gulf in the east. And the conditions for creating an ascent in the Dez River Basin are the most important elements of the pattern of heavy and durable rainfall in this basin. Water resources planning, prevention and timely information, and flood control and control are among the results that can be expected from this research.

Introduction Dust storms are one of the significant phenomena in the desert areas of the world. It is internationally agreed that days with visibility below 1000 metres due to dust present in the air are a result of strong winds. This atmospheric phenomenon causes damage or environmental, social and economic damage. Dust storms with visibility of fewer than 200 meters are the most severe storms that can occur in an area. Such storms disrupt the normal life of the residents and cause damage. In this research, the temporal and spatial distribution, as well as the occurrence of such storms in the two regions of southwest and west of Iran, have been investigated. Preliminary evidence indicates an increase in the frequency of these storms. On the other hand, these two regions are important regions of Iran in terms of agricultural and industrial production and population centers. The increase of such storms can cause serious damage to the economy, agriculture and health of the two population poles of the country. For analytical comparison of dust storms in Iran, two regions, 1- southwest including (Khuzestan, Kohkiluyeh and Boyer Ahmad and Chaharmahal and Bakhtiari provinces); 2- west including (Ilam, Kermanshah, Kurdistan, Hamedan and Lorestan provinces) it's been chosen. To select sample stations, after receiving dust data from all synoptic stations of 8 provinces from the Meteorological Organization, including (88 synoptic stations), the data were analyzed. According to the aim of the study, which was to investigate the trend of changes in the phenomenon of severe dust in the last three solar cycles (33-year statistical base), 28 stations of the above stations had the desired conditions. Then, the data with horizontal visibility less than 200 m were sorted. Frequency of dusty days in Excel environment; Extracted daily, monthly, seasonally and annually. SPSS software was used to investigate the traits and data scatter. Finally, from ArcGis10.6 software to draw maps, as follows; The topography of the area is shown as a zoning map and quantitative characteristics of dust events are displayed as a Bar / Column.

Precipitation is important climatic varibles which is directly involved the hydrological cycle. Iran is considered the most arid and semi – arid regions of the world due to lack rainfall and their inappropriate distribution, which has always faced water shortage important limitations of natural resources.Therefore, the present study was conducted with the aim of extracting scale behavior and identifying (long – term and short – term) precipitation memory of two Karkheh and Dez catchment. For this purpose, Precipitation data of two Karkheh and Dez catchment were used over a period of 60 years (1959 – 2019). The results showed that the stations both areas have 2 rainfall regimes. In the study precipitation regimes all stations, two basins were identified. The small – scale precipitation regime has a long – term memory and a stable time series. However the large – scale precipitation regimes has a short – term memory and its time series is static except Doab and Darreh Takht station. both precipitation regimes show completely different scale behavior. the relationship between precipitation scale behavior and topography of the study area was calculated using pearson correlation test. The results show that there is no significant relationship between Karkheh basin both precipitation regimes. but in Dez basin, there is a significant correlation the small – scale precipitation regime, but there is no significant correlation the large – scale precipitation regime. This can be due to the conflicting and heterogeneous topographic situation in different parts of the region in Karkheh

Rainfall is the most important source of water supply in the south and southwest of Iran. The Sudanese system is the most important cause of rain in these areas, which occurs mainly in the short and severe. Optimal survival is directly and indirectly related to the quantity and quality of these precipitations. As mentioned earlier, one of the most important characteristics of Sudanese systems in the south and southwest of Iran is their intensity. In the study of rainfall regime in the south and southwest of Iran, The lack of study of the intensity of rainfall in Sudanese systems, especially in recent decades, is quite evident. Therefore, in the present study, the trend of rainfall intensity of Sudanese systems from three independent input routes of Khuzestan, Bushehr and Hormozgan, which corresponds to the three main routes (A, B and C) of Lashkari (2002) research, is investigated. To use its findings in the management of water resources and atmospheric events such as floods and droughts.

In the present study, in order to analyze the trend of rainfall intensity of Sudanese systems in the triple routes of Khuzestan, Bushehr and Hormozgan, first 43 study stations were separated in the form of three routes. In the entrance route of Khuzestan included: 23 stations from the provinces of Khuzestan, Ilam, Kohgiluyeh and Boyer-Ahmad, Chaharmahal and Bakhtiari and Lorestan, in the entrance route of Bushehr included; 15 stations from Bushehr, Fars, Kohgiluyeh and Boyer-Ahmad provinces and at the entrance of Hormozgan, including; 7 stations of the province itself. Then, based on the rainfall incidence index of 1 mm and more in 50% of the stations of each route, the frequency of annual, monthly and continuous rainfall periods of Sudanese systems were identified using daily rainfall data (1995-2017) and then their average rainfall was extracted. Finally, after validating the data, the trend of rainfall intensity in Sudanese systems (2017-1995), using the methods; line of best fit, Man-Kendall and Sen’s slop estimator and based on the annual average, monthly and rainfall continuity periods, at 95% confidence level, it was checked in Visual Basic Excel environment and SPSS software

Sudanese systems operate in the cold period of the year in Iran (from the entrance routes of Khuzestan, Bushehr and Hormozgan). The rainfall of these systems in the triple routes is more 1 to 3 days, and rarely have rainfall of 5 days or more. The study of the trend of rainfall intensity of Sudanese systems (1995-2017) in the triple routes showed; the trend of rainfall intensity of these systems based on the annual average in the triple routes has a slope of decreasing changes of -0.04 to -0.1 mm during the period .However, these trends and the slope of changes are significant only in the rainfall of Bushehr route systems with a slope of very small decreasing changes (-0.1 mm during the period). The trend of rainfall intensity in Sudanese systems based on the monthly average of rainfall in the triple routes, is decreasing in some months and increasing in some. The slope of changes in these trends is in most cases zero and in some cases from 0.55 to -0.58 millimeters during the period, fluctuating. But in the meantime, only the increasing trend of November in Bushehr entrance route (0.55 one mm during the period) and the decreasing trend of February in Khuzestan entrance route (-0.21 mm during the period) is significant. The trend of rainfall intensity of Sudanese systems in the three routes is based on the average rainfall of different periods of continuity, in most cases decreasing and in some cases increasing. The slope of changes in these trends is in most cases zero and in some cases from 0.12 to -0.43 mm during the period. But in the meantime, only the decreasing trend of 2-day systems of Bushehr route with a slope of changes of -0.26 mm during the period is significant.

Despite the trend and slope of decreasing and increasing changes in the rainfall intensity of Sudanese systems, but due to the lack of significant trends and slope of changes (less than 0.6 ∓ one millimeter during the period), it can be concluded; The rainfall intensity of Sudanese systems in the entrance routes of Khuzestan, Bushehr and Hormozgan, lacks the trend and slope of significant changes at the 95% confidence level. But in general, Sudanese systems in most cases have short and heavy rainfall, and rarely light and long rainfall. As a result, the occurrence of heavy rains caused by Sudanese systems in the entrance routes of Khuzestan, Bushehr and Hormozgan should still be accepted as a principle. Therefore, floods are still one of the most important threats facing the study areas.

     In the last decade, the volatile region of the Middle East, along with all other natural hazards, has been plagued by dust storms. More than anywhere else in the world, global warming and climate change have affected the natural ecosystems of this vulnerable and fragile region. From a synoptic meteorological point of view, storm is a unique destructive phenomenon on synoptic maps that includes a combination of pressure, cloud, rain, wind, et.c (Alijani, 2006; Hosseini, 2000). Dust can be a reaction to changes in land vegetation, according to which the role of human activities along with the natural conditions of geographical environments should be considered (Arimoto, 2000). Burial of residential areas under sand, destruction of agricultural lands and expansion of desert areas (Wang 2005), creation of colored rainfall, disruption of transportation system, disruption of agricultural fields and orchards (Koren et al., 2015), air pollution, respiratory problems and diseases, and the prevalence of infectious diseases are the most important complications and problems caused by dust storms (Goudie and Midelton, 2002). Therefore, it is necessary to identify and analyze dust-generating patterns of prognostic aspects.

     In this research, the synoptic analysis of dust in Kermanshah province has been studied. For this purpose, dust codes for 12 synoptic stations over a period of 30 years (from 1990 to 2017) were received from the Iranian Meteorological Organization. Then, in order to perform the classification operation and further calculations, sea level pressure (SLP) and geopotential height of 500 hPa level data were extracted for grading days by programming in GrADS software. In the next step, in order to classify sea level pressure data and identify representative days, cluster analysis was performed on dusty days and dust generating atmospheric patterns were extracted, and finally the synoptic and dynamic analysess and interpretation of these patterns were performed.

     By performing cluster analysis on sea level pressure events, five patterns for dust occurrence in the western region of Iran can be identified as follows:Pattern1: Indian monsoon low pressure - European migratory high pressure: A study of this model shows that all regions located in southwest Asia to the center of the Mediterranean have become the convergence of currents originating from the monsoon region of South and Southeast Asia. Summer monsoon rotation, the region of South-Southeast Asia, has acted as a large-scale energy source. The regions located in Southwest Asia and the Eastern Mediterranean are the main area of ​​convergence of this flow and, in fact ,are heat wells.
Pattern2: Indian monsoon low pressure integration, Oman Sea - North Caspian high pressure: Like the first pattern, Indian monsoon low pressure system is formed on the northwestern regions of India and on the border with Pakistan, which moves in orbit through the Oman Sea and the Persian Gulf. It has entered the regions of Southwest Asia and covers a large area from the Middle East to North Africa, and has strengthened its coverage of the central to eastern Mediterranean.
Pattern3: Sudan low pressure, European low pressure - North African high pressure: A study of this model shows that at sea level, the Sudanese low pressure system travels from the southern and central parts of the Red Sea to cyclonic and meridional directions. The interior region of Saudi Arabia and the desert of Ruba'at al-Khali have moved and covered all the desert areas of Saudi Arabia, Iraq and Syria in such a way that it has caused the bottom convergence and vertical ascent of the currents over the dust centers. In addition, in the orbital direction and in the vicinity of this system in North Africa (Libya, Egypt and Algeria), a high-pressure system with a central pressure of 1016 hPa prevails, which leads to severe pressure differences and increased instability in dust centers and over-activation. It has resulted in dust hotspots in Saudi Arabia and North Africa.
Pattern4: Sudan low-pressure integration Sudan, Saudi Arabia - Siberian high-pressure: Sudan-origin low-pressure system with high spatial and spatial expansion across the Red Sea is integrated with Saudi low-pressure on one side and on the other; moving northwards with expanded tabs and Indian influence in the eastern and southern parts of Iran has created a huge expanded belt of low pressure centers. In addition, a weak high-pressure system with a central pressure of 1016 hPa over the Mediterranean Sea and North Africa has created atmospheric instability due to the pressure difference created over desert areas.These areas are the focal points of dust and the main generator of dust storms in the Middle East.
Pattern5: Polar low pressure, Sudan low pressure - European high pressure: A study of this model shows that the polar low pressure system along with Sudan and Red Sea penetration low pressure are the main controllers of Iran's atmosphere at sea level in such a way that the cyclonic movement of cold currents in the polar regions towards the lower latitudes and its penetration from the northeast into Iran and then the integration of its tabs with the low pressure tabs of the Red Sea and Sudan cause the corridor to have unstable currents in the polar and tropical regions, or in other words, the polar and subtropical regions, which have dominated the upward vertical currents in a very large area of ​​Iran. However, the dominance of the European high pressure system and its penetration to eastern Turkey in the orbital direction and North Africa in the meridional direction and its confrontation with the infiltration low pressure cause severe compression pattern, instability and transport of dust into the low pressure Sudan and the Red Sea.

   Studying and understanding the synoptic and dynamic state of the atmosphere as well as understanding the local conditions and geomorphology of each region is one of the key topics of interest in atmospheric studies. Dust storms in the western part of Iran are mainly caused by certain weather conditions. Thus, the components of the atmospheric circulation scale at the lower levels play a major role in the occurrence of dust storms. In the patterns of the warm periods of the year, the dominance of the west current with the monsoon origin of India has created the following convergence around the dust centers of southwest and west Asia, which are intensified by the upper convergence caused by the high pressure of the Azores or the western wave. This issue is accompanied by the activation and rising of dust in the dust centers of the region, which eventually extends to the western region of Iran by eastward and orbital currents.  On dusty days occuring in the cold seasons, Sudan and Red Sea thermal low pressures on Saudi Arabia, Iraq and Syria at sea level, and low-lying nuclei and western waves on Europe and the Mediterranean Sea at mid-atmospheric level are the main controllers of climatic conditions in the region. Therefore, in the cold period of the year, due to the heaviness of the cold weather in these days, they are allowed to penetrate to low offerings and place the eastern part of trough on the deserts of North Africa, Saudi Arabia, Iraq and Syria. By creating instability and moving to the east, they direct the generated dust to the west of Iran. However, whenever tabs of Indian monsoon low pressure and Sudan low pressure enter the West Asian region at sea level and the Mediterranean subtropical or high-pressure submarine operates in mid-atmosphere, the upper convergence and the dynamic decrease of air flow causes the amplification and over-activity of surface low pressures, which is accompanied by the activation of dust centers and the rise of dust in the area. In general, Azores high pressure along with migratory systems of western winds is the most important synoptic factor in dust systems in the western regions of Iran. Comparison of research findings showed that thermodynamic processes in the hot season and dynamic processes in the cold season are the most important factors in the formation and transfer of dust to the western half of the country (Kermanshah). Thus, the establishment of low thermal pressure at ground level and low altitude of 850 to 500 hPa in the vicinity of western Iran is effective in generating identified dust during the warm periods of the year, which is consistent with the findings of Azizi et al (2012) in the synoptic study of dust in the western part of the country.

Precipitation is one of the most important and complex climatic elements. This vital element, on which the lives of living organisms and fauna depend, has highly variable temporal and spatial distributions in the world. While limited areas of the planet have an excess precipitation, a large part of it is facing the shortage of this vital element. Therefore, its spatial distribution on the Earth is not at all satisfactory to the inhabitants. In the subtropical regions, this limitation is of great significance. For this reason, officials and users are so willing to receive more precipitation during the cooler months and minimize water loss from evaporation and transpiration. Winter precipitation can be very useful and effective in these areas. Several studies conducted on the trend of monthly precipitations in the cold periods of the year in the southern regions of Iran have found significant decreases in February precipitations compared to those of the two previous and following months recorded at most of the south and southwest stations. Considering that southern regions are among the few regions in Iran where the precipitation periods correspond to the cultivation periods, this problem was studied and analyzed as the main issue of this research. 

As stated, the purpose of this study was to identify the synoptic factors of decreasing precipitations in the southern half of Iran in February compared to March. To find the cause of this phenomenon, first, the data provided by the representative stations during the statistical period of 1986-2017 were selected. The ERA-Interim data from the European Center for Medium-Range Weather Forecast (ECMWF) with the spatial resolution of 0.5×0.5 degrees were used to investigate the synoptic patterns. For synoptic analysis, several samples were chosen from the statistical period. Moreover, various assumptions were examined to determine the cause of this phenomenon.To study moisture changes in February and March, changes in the moisture transfer from the Arabian and Oman Seas with negative values for the outflow of moisture fluxes and the relevant changes from the south and southwest regions of Iran with positive values of the inflow of moisture fluxes in the lower atmosphere were calculated. Displacements and fluctuations in pressure patterns and systems lead to significant changes in the meteorological phenomena. Therefore, due to the very important role of the Arabian subtropical high-pressure system in transferring moisture from the Arabian and Oman Seas to the Arabian Peninsula and towards Sudan low-pressure system, the locations and displacements of the high-pressure cores were extracted at the level of 850 hPa. Also, due to the more important role of Mediterranean troughs in the moisture advection transfer from these warm seas in the study area, their locations and depths were extracted from the selected samples at the level of 700 hPa in February and March within the statistical period. Subtropical jets play a crucial role in the dynamic structure of Sudan low-pressure precipitation systems. Therefore, another component studied in this research was the changes in the positions and structures of subtropical jets throughout the selected samples at the levels of 300 and 250 hPa in February and March. 

Winter precipitation in the southern part of Iran is of special importance due to its coincidence with the cultivation period and supplying part of the water needed for agriculture. The results obtained by Mohammadi & Lashkari (2020) and Esfandiari & Lashkari (2020) showed that the amount of precipitation and number of the input systems in this region in February compared to the months before and after it had significantly decreased.  Evaluation of moisture fluxA comparison of the amount of moisture released from the Arabian Sea with the moisture entering the region revealed the very significant difference of February precipitation, while the difference was very small in March, which was perfectly compatible in many cases. Hence, there must have been barriers to the transfer of moisture from the surrounding seas into the region in February.  Evaluation of the position of Saudi ArabiaIn terms of the latitude, there was no significant difference in the positions of Arabian subtropical high-pressure systems between the two months. However, the oscillations of their cores were much more intense in terms of longitude. In some years, the cores had moved up to about 70 degrees east longitude. In March, the displacements of the cores were quite noticeable compared to those of the other two months. During this month, most of the cores were located in Oman and its eastern coast. An interesting phenomenon was that the high-pressure cores of all the sample years were located in Oman and sometimes in the waters of the Arabian Sea at a distance from the coast. 3. Evaluation of the position of Mediterranean troughsThe axes of Mediterranean troughs did not show a significant difference in both the depth and longitudinal position. In this way, the troughs were in a good position in terms of transferring instabilities to the region every two months. They also had a suitable depth for transferring and injecting sufficient vorticities into the heating systems of this region.  Evaluation of the position of the subtropical jetsThe longitudinal and latitudinal positions of the subtropical jets were very different in February and March. Three features could be seen in the axes of the February jets. First, the jets had significant northward displacements in all the selected samples and thus, the jets located at this latitude did not create suitable dynamic conditions for the instabilities of southern and southwestern Iran. Second, the longitudinal axes of the jets in this month had been shortened. Most of the jets were coming from the east and center of Egypt. Third, most of the axes tended to be orbital. This feature caused the jets not to have a suitable vorticity.The expansion patterns of the jets in March were completely different from those of February. During this month, the subtropical jets had relocated to lower latitudes and were distributed between northwestern Iran and southern Saudi Arabia. Therefore, the southern and southwestern parts were exposed to the instabilities caused by the subtropical jets. Another notable change was in the lengths of the subtropical jets. Most of the jets had started in the southwest-northeast direction at a distance from behind Egypt and over Chad and even farther back of it. The jets had a more meridional pattern in March compared to February. 

The main purpose of this study was to find the cause of reduced precipitations in February compared to March in the southern regions of Iran. The results of this research revealed that the two factors of spatial displacement of the Arabian subtropical high-pressure system, especially at the level of 850 hPa and the lower layer of the atmosphere, and the displacements of subtropical jets in the northern and southern parts were the most important factors for lowering precipitations in February compared to the other months of the cold period of the year in the south of Iran. The subtropical jets showed a noticeable northward movements in February. This pattern of establishment had caused precipitation systems to enter the region from the south, move towards higher northern latitudes and western longitudes, and frequently enter Iran from the west in the form of integrated systems. At the same time, this had caused the Arabian subtropical high-pressure system to move westward and settle on the lands of eastern Saudi Arabia, preventing the entry of Sudanese systems into southern Iran and moving westward. 

In this research, the microclimatic effect of large parks in Tehran in summer has been studied. For this purpose, 7 large parks in Tehran have been selected as a sample. To show the effect of green cover in adjusting the temperature of the environment under the tree and the surrounding areas. In this study, using Landsat 8 data, the surface temperature of 7 large parks in Tehran for a hot summer day has been extracted and the temperature changes in the park have been investigated based on density and less density and bare areas. Then, by selecting a cross section between the covered part inside the park to the residential area around the park, the temperature changes have been evaluated. The results of this study showed that the temperature difference caused by radiation from green surfaces and leaves of trees and shade that is created under the tree compared to soil surfaces without asphalt depending on the height of the park between 15 to 9 degrees Celsius, this study also showed that broadleaf species have a much higher role in reducing surface temperature than coniferous species. Regarding the role of the park in regulating the ambient temperature around Lavizan and Sorkheh Hesar parks, the highest temperature adjustment and Chitgar Park had the least adjustment effect on the surrounding residential spaces.In terms of thermal gradient created between the dense area to the residential area around the parks of Kuhsar and Lavizan had the highest thermal pattern.

Sudanese low-pressure is a system with tropical characteristics. Its precipitation characteristics are very similar to that of tropical systems. This is especially evident in the countries on the southern shores of the Persian Gulf and in the southern and southwestern parts of Iran. Heavy rainfall of this system results in high moisture potential and access to the resources of the warm southern seas. Some researchers believe that the system originated in the northward expansion of the Inter-Tropical Convergence Zone (ITCZ) in the range of 25 to 35° east (in East Africa) and created a thermal nucleus in southern Sudan and Ethiopia (Lashkari, 1996; 2001). The aim of this study is to identify the adaptation of northward expansion of the Sudanese low-pressure trough with the ITCZ northward expansion pattern during pervasive and severe rainfall in the cold season in the southern half of Iran.

Two categories of data were used for this study. These data included daily precipitation data from the Iranian Meteorological Organization and the ERA interim gridded data which included sea level pressure and the specific humidity of the 700 HP of the ECMWF. Second category data with horizontal resolution of 0.5 × 0.5° during 1997-2017 statistical period were prepared. Subsequently, based on the selected criteria, 86 pervasive and severe rainfall systems were identified. Then, the ITCZ's average monthly position, the central core pattern, the area of the first closed curve, and the expansion of the Sudanese low-pressure trough for all 86 days of rainfall were plotted. In the final step, the position of the ITCZ was identified using a special humidity variable of 700 HP in the tropical region for the systems of each month.

This study has been examining the degree of adaptation and the role of the ITCZ in the formation, expansion and moisture supply of rainfall by Sudanese systems in three general forms for selected precipitation samples.Expansion pattern of the Sudanese low-pressure core During all months, the region between the eastern border of Sudan and Ethiopia is the focus of Sudan's low-pressure core. In November, December, March and April the pattern of distribution of low-pressure cores show very good adaptation with the expansion pattern of the ITCZ. However in January and February, the cores become condensed in the southeastern part of Sudan. Expansion pattern Sudanese low-pressure first closed curve The pattern of expansion of Sudanese low-pressure first closed curve shows very good adaptation with the trough pattern of the ITCZ in all months. The adaptation of the ITCZ trough and the pattern of expansion of the low-pressure internal core indicate that it plays a significant role in the strengthening and flowing pattern of Sudanese low-pressure.Synoptic expansion pattern of Sudanese low-pressure trough axis In all cases and all months, the extension of the low-pressure trough, especially over the Red Sea and the Bab al-Mandeb Strait, and even part of the Arabian Peninsula is in adaptation with the extension of the ITCZ trough.

During all the months of the rainy season, an ITCZ trough with a southwest-northeast direction extends from the Horn of Africa to northern Yemen. The pattern of expansion of Sudanese low-pressure trough, the pattern of nucleus distribution and the extent of expansion of the first closed curve are fully in adaptation with the monthly pattern of ITCZ expansion. This shows the undeniable role of ITCZ in the formation, expansion and moisture supply of rainfall systems. In January, in all three cases, the number of precipitation systems, the distribution effect area and the penetration depth of the input systems to the southern half of Iran are of primary importance. This could be related to the weaker thermodynamics of the Sudanese system at the beginning of its activity, the weak expansion of ITCZ in the region due to the westward position of the Arabian anticyclone at the beginning of the rainy season and the westward return at the end of the rainy season.

The atmospheric river is an almost emerging phenomenon in the modern scientific literature of the world that has been studied due to its association with weather extreme events, especially heavy rainfall and floods.In this study, the integrated vertical vapor transport data were used to identify atmospheric rivers, and the criteria were determined for its separation from daily fluxes. The 90th percentile of daily precipitation was then considered as the criterion for heavy precipitation across the country. Dates associated with heavy precipitation in the presence of atmospheric rivers were obtained, and its patterns were extracted by factor analysis after preparation of a 107×1190 matrix from 1000 level Geopotential height. The results showed that the first three factors account for nearly about 70% of the total variance. Overall, Sudan's low-pressure system has an undeniable role in the formation of atmospheric rivers and heavy precipitation. In Sudan's low-pressure and the Mediterranean combination pattern, the most effect was on south-west and west of the country. Sudan's low-pressure and Eastern Europe cyclone combination patterns encompass the wider parts of the country. The influence of such systems on the country was more than other patterns. In the low-pressure combination pattern of Sudan and the migratory cyclone, the rivers and heavy precipitation zones did not much extend to the northern latitudes. In terms of formation, in all patterns, the Sudan low-pressure and the Siberian High Pressure were played a major role in the gradient generation and moisture transfer to the atmospheric rivers, in the low levels of the troposphere. The sources of moisture in these layers were the Oman-Arabian Sea.

A quick look at the form of housing in the country and other countries reveals this effect well. Today, architects and housing engineers make every effort to harmonize housing with the climate of the region to create a calm environment with bio-comfort for residents. In modern architecture, due to the increase in the price of energy carriers and the very high cost of cooling and heating buildings, many efforts are made to adapt and adapt housing to climatic conditions. In cold and tropical regions, this phenomenon has a strong effect on the household budget. Despite government efforts to help people cover some of the costs by reducing electricity tariffs and energy carriers, the burden remains on households. Therefore, the best thing to do is to try to adapt the houses to the climatic conditions of the region. Saqez city is one of the cities in the cold region of Iran that special attention should be paid to the compatibility of buildings with the climatic conditions of the region. In this research, the most compatible architectural model with the climatic conditions of the region will be identified and introduced using conventional scientific indicators in Iran and the world, and at the same time the degree of compliance of old and new architecture in Saqez with the compatible model will be examined and evaluated.

The main purpose of this study is to detect precipitating clouds and to analyze their vertical structures in the south and southwest of Iran using CALIPSO and CloudSat satellite observations. At First, events with high precipitation rates using the daily precipitation data of the synoptic stations in the area of interest during the statistical period from 2006 to 2016 were selected. The selection of these samples is based on two parameters: the average precipitation of the synoptic system and the number of stations involved in precipitation. The average precipitation of the system was calculated by the ratio of the total precipitation of all stations in one day to the number of stations involved in precipitation on the same day. In order to eliminate light precipitating samples, a precipitation threshold was set for the mentioned parameters. So that at least in one of the days of precipitating system activity, the number of stations involved in precipitation is not less than 15 stations and the average precipitation of the system is not less than 15 mm. This threshold is defined as the day of peak precipitation. In total, 74 precipitating systems that lasted from one day to one week were determined and 107 days of precipitation with the above specifications were selected. In order to ensure the occurrence of precipitation at the same time as the satellite orbit passing through the area, TRMM satellite level 3B precipitation data was used. These data have precipitation values in a temporal interval of 30 minutes and spatial resolution of 0.1 by 0.1 degrees. Considering the network precipitation values of peak days, three precipitating samples in three different paths where the precipitation occurred along the satellite path, were selected to analyze their cloud structures. Precipitation characteristics of the mentioned systems were extracted based on station and network precipitation values. In the next stage, three features including the total attenuated backscatter at 532 nm, the depolarization ratio and the color ratio were obtained by the use of CALIOP lidar level 1B data. The radar reflectivity feature was also extracted using data of CPR sensor of CloudSat. Then, using layers extracted from CALIOP and CPR sensors, the clouds of these samples were compared and analyzed in terms of cloud thickness and precipitation intensity. The results of the analysis showed that in the first sample (Path A), despite the large thickness of the cloud (approximately 10 km), the amount of precipitation is less than the other two samples. The cloud of this sample is different from the other two samples. Cloud layers in the vertical direction are not dense and integrated enough. Also, aerosol particles and ice crystals in the cloud are fewer and smaller. While in the other two samples, especially in path C, while the thick and dense cloud covers the atmosphere of the region, the concentrations of aerosols and ice crystals are much higher.