Kamal Omidvar; Nesa Sepandar; Shahab Shafiee
Abstract
Extended abstract
Among the natural disasters, floods involve the highesthuman casualties. The economic damages of flood in developing countries, including Iran, is much more, and its occurrence is very high particularly in the cold months of the year in the west of the country. By studying the synoptic ...
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Extended abstract
Among the natural disasters, floods involve the highesthuman casualties. The economic damages of flood in developing countries, including Iran, is much more, and its occurrence is very high particularly in the cold months of the year in the west of the country. By studying the synoptic maps of the Earth’s surface and the middle and upper levels of the atmosphere, many Earth-surface phenomena such as flood, based on the spatial arrangement of the pressurecurves or the height and the location of patterns on these maps, the pattern of daily weather conditions can be controlled and the origin of many of these phenomena can eventually be determined. Precipitation is the major climate phenomenon resulting from the complex interactions of the climate system and it has a complex behavior due to the bond with various components of the climate system. The occurrence of precipitation requires the provision of several conditions. The availability of moisture, deep instability and cooling, are the prerequisites for the occurrence of precipitation. All of these conditions must appear in its strongest state for the occurrence of super heavy rainfalls.The western region of Iran is a suitable area for exacerbating and extending rainfall and sometimes flooding due to the presence of mountains. This is because the role of mountains in in capturing air humidity plays a significant role in increasing the atmospheric precipitations.There are two types of approaches in synoptic studies: circulatory to environmental, and environmental to circulatory. In the study of precipitation, the environmental to circulatory classification and approach are used. The reason for thisis that, the temporal and spatial variations of rainfall are severe,and the environmental to circulatory method allows the researchers to concentrate on the precipitation and, consequently, on the synoptic patterns whichtheyintendtostudy.In this study, the heavy and pervasive rainfall in the province of Kermanshah on October 27-30, 2015, was selected and it was attempted to analyze the synoptic and thermodynamic conditions of the occurrence of this torrential rain. In this research, the environmental to circulatory approachwas used. To conduct such studies, two databases are required. In this paper, which was conducted with the aim of analyzing the heavy rainfall synoptic situation in Kermanshah province (on October 27-30, 2015), two databases have been used. First, the daily rainfall data from October 25 to 31, 2015 were extractedby referring directly to digital files sent by the stations to the Iranian Meteorological Organization, and then, the high atmospheric variables on the same date were used for synoptic and thermodynamic analysis of the aforementioned precipitation and to see how the synoptic systems entered the region. Data related to the station’s level pressure, geopotential height, orbital and meridional components of wind and moisture at different levels of the atmosphere from the database related to high atmosphere data were obtained from the United States National Oceanic and Atmospheric Administration’s (NOAA) National Center for Environmental Prediction, and National Center for Atmospheric Research (NCEP / NCAR) with a spatial resolution of 2.5 by 2.5 arc degrees. Then, for the synoptic analysis of the aforementioned rainfall, daily maps of the Earth’s surface and the levels of 850 and 500 hPa were plotted in the GrADS software. Drawings of these maps were carried out 48 hours prior to the start of the rainfall until the day of full stop. The instability indices KI, LI, SW and SI were also usedfor the thermodynamic analysis of the high atmosphere data of Kermanshah and obtaining the extent of instability in the study days. In the analysis of the Earth’s surface synoptic mapson the day of torrential rains, the southern system appearsas a low-pressure field and has the highest power in the Red Sea and Sudan region, and the low-pressurecurrent has been drawn to the center of Iran, and extends over a vast areafrom the east and south of the European high pressure to the west and center of Iran and the conditions of instability are dominant in these areas. The ascending currents have increased because of the intensity of pressure reduction. It seems that the intense pressure gradient between the Sudan’s low-pressure and the European high-pressure current is one of the causes of the occurrence of torrential rains during the studied period in the province of Kermanshah. All stations in Kermanshah province have reported rainfalls under this very strong pressure and moisture from the Persian Gulf and Oman Sea. Enhancement of the low level system of the Earth’s surface and the downfall of cold weatherin high latitudes by polar troughat the level of 500 hpa contributes to the occurrence of atmospheric instability and the onset of rainfall in the west of the country. The trough is located on the eastern Mediterranean in such a way that, its axis at the end of the Mediterranean trough passes over the Red Sea. on the eastern part of this trough’s axis (Red Sea descent), there is air turbulence from the west of the Red Sea to the north of the Caspian sea, which causes low pressure of the Earth’s surface to be raised to high latitudes. If this trough is strengthened while moving eastward, it will contain thunderstorm, rain and snow, in case of having enough moisture on its way, which is from southwest to the northeast, while passing over the heights. At the beginning of the heavy rainfall, the subtropical jet stream is onNorth Africa and the polar jet stream is on the areas located on the north of the Caspian and Black Sea. The amount of precipitation increase dramatically as these two jet streams get closer to each other, the polar jet stream changes position to the lower latitudes, and the subtropical jet stream moves towards the northeast. In the study of instability indices, there has been dispersed thunderstorm according to the LI instability index.The probability of dispersed shower on October 28 is very low according to the S1 index and the study area will witness very storms with low intensity on this day according to SW index. According to the KI index, this probability reaches to 60-80% in Kermanshah province on October 28 (peak day of precipitation).
Mahdi Modiri; Mahdi Khazaei; Mohammad Hasan Mahutchi
Volume 22, Issue 85 , May 2013, , Pages 27-42
Abstract
In this study have been paid on analysing Thunderstoms in a period of 25 years in Shiraz (1984-2008). Therefore, data on sea level pressure, geopotential height levels 850 and 500 hpa in the rainfall day of NCEP/NCAR databse prepared and extraction levels above the map drawing software environment GRADS ...
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In this study have been paid on analysing Thunderstoms in a period of 25 years in Shiraz (1984-2008). Therefore, data on sea level pressure, geopotential height levels 850 and 500 hpa in the rainfall day of NCEP/NCAR databse prepared and extraction levels above the map drawing software environment GRADS Were drawn. The extreme rainfall patterns Related to Shiraz have been identified and analyzed. By examining maps of sea level pressure, 850 and 500 hpa, three general patterns were identified for Shiraz thunderstorm rainfall. In the first pattern (1 March 1998), the low-pressure lingual of the Sudan country, large parts of the study area is located. The system In addition provides moisture, instability in the level do too. And in the level of 850 and 500 hpa, area studied the influence of anticyclonic centers are located in the western and ridges. In second type of the pattern (December 6,2003) at sea level, the area studied is affected by center anticyclone, and the level of 850 and 500hpa area at the front of the trpugh with a curved contour 1450 and 5720 geopotential meters located and the conditions are very unstable at this level. And the third pattern (26 March 2003) Low-pressure center with a central pressure of 1004hpa is located on the country. At this level, the currents are such that relatively moist air flows from the Caspian to the North West and the West. The levels of 850 and 500hpa area studied are located under the trough axis above and instability intensifies levels above.
Hasan Lashgari; Hooshang Ghaemi; Fatemeh Parak
Volume 22, SEPEHR , April 2013, , Pages 57-63
Abstract
Precipitation is the first important parameter in studying dry and wet years. It has a direct relation with precipitation systems entering Iran and the sources of humidity which inject humidity into those systems. Studies performed on Sudanese system indicate that precipitation in southern parts of the ...
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Precipitation is the first important parameter in studying dry and wet years. It has a direct relation with precipitation systems entering Iran and the sources of humidity which inject humidity into those systems. Studies performed on Sudanese system indicate that precipitation in southern parts of the country have a close relation with the activities of this system in cold days of the year and it plays the most important role in heavy rainfalls. Reviewing synoptic maps of high and low precipitation reveals that two different dominating patterns exist in the area. In the high precipitation pattern, Sudanese low pressure is located on the South West of the Red Sea and continues toward North East and influences South and South West of Iran. This pattern dominates South East of the Arabian Peninsula. It inject heat and humidity from the Oman Sea and the Arabian Sea on one hand and the Adan Gulf and the Red Sea on the other hand to the mentioned systems. Then, this heat and humidity enters Iran Southern area with the Sudanese system. Due to the deepening of east Mediterranean trough, and the falling of cold weather from eastern latitudes in the Sudanese system, the system becomes extremely powerful and changes into dynamic status, creating a heavy rainfall on the area. In the weak precipitation pattern, Sudanese low pressure system is extremely weak and it crosses the southern areas of the Arabian Peninsula in east-west direction. Moreover in this pattern, a cyclone system covers South Eastern areas of the Arabian Peninsula.
