Climatology
Masoud Jalali; Ali SHahbai; Vahab Kamrian
Abstract
In this paper, we attempted to identify the synoptic patterns of Summer heavy rainfall in the southern coast of the Caspian Sea by using environment- to- circulation method. To attain this aim , by using statistics of daily Precipitation of 40 synoptic and climatology stations located in the region for ...
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In this paper, we attempted to identify the synoptic patterns of Summer heavy rainfall in the southern coast of the Caspian Sea by using environment- to- circulation method. To attain this aim , by using statistics of daily Precipitation of 40 synoptic and climatology stations located in the region for periods of 20 years of 1991 to 2010 and by percentile method , 29 days have rain more than 15 mm which have occurred in at least 30 percents of region stations , were determined as days with heavy rain. By using factorial analysis and cluster analysis methods , 3 synoptic patterns were determined as agent of creating rain in 29 days that the first pattern 48.3 percent , second pattern , 30 percent and the third pattern have allocated 21.7 percent of days of heavy rain in the studied region. In order to synoptic analysis of these patterns , maps of sea level pressure , 500 hectopascal level , omega (atmosphere vertical motions) , vorticity and moisture flows of level of 850 hectopascal related to two days before rain was used until rain day and finally it is determined that the main cause of occurring heavy summer rainfall in southern coast of the Caspian Sea is the penetration high-pressure system and after that formation of cool and moist northern flows as well as incidence of vast convection in the region. Each three patterns emphasize on occurrence of this condition and their difference is the place of deployment of high-pressure system and consequently the number of rainy days and severity of rain in these days.
Mitra Amini; Hasan Lashkary; Mostafa Karampour; Zahra Hojaty
Volume 17, Issue 43 , October 2013, , Pages 1-20
Abstract
The aim of present study is the synoptic analysis of systems having by heavy precipitation on the Kashkan basin. After study of 34-years statistics from stations for basin and its environments three storms by maximum precipitation were selected. The results of study of weather maps, humidity, earth surface ...
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The aim of present study is the synoptic analysis of systems having by heavy precipitation on the Kashkan basin. After study of 34-years statistics from stations for basin and its environments three storms by maximum precipitation were selected. The results of study of weather maps, humidity, earth surface pressure difference and 850 hPa of 48 hours before and after storms, showed that with regard to the fact that three selected storms have out of heavy storms during statistics period occurred in various seasons of the year, their generating system was equal and Sudan-Mediterranean merger system pattern generated maximum precipitation. Synoptic conditions in three chosen storms are: 1-High pressure over Europe northwest and influx of the cold weather in higher latitudes toward low pressure that is situated in east Mediterranean, 2-Sudan low pressure nutrition and motion toward northeast. 3-Days that maximum precipitation has occurred in the basin. These low pressure systems are merged with each other in east of Iraq, and high pressure situated on east of Iran with influx of cold weather over Oman and Arab seas on the one hand and presence of anticyclone in Arabia have caused humidity transfer inside low pressure system situated over west of Iran and generated maximum precipitation.
Faramarz Khoshakhlagh; Seaed omid Nabavi; Esmail Abbasi
Volume 16, Issue 40 , September 2012, , Pages 97-118
Abstract
The presented study aims to investigate synoptic atmospheric conditions along with heavy precipitation in Khorasan Razavi and Khorasan Shomali provinces. The identification of temporal and spatial distribution of heavy precipitation associated with these extreme conditions is another goal of this study. ...
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The presented study aims to investigate synoptic atmospheric conditions along with heavy precipitation in Khorasan Razavi and Khorasan Shomali provinces. The identification of temporal and spatial distribution of heavy precipitation associated with these extreme conditions is another goal of this study. The amount of precipitation greater than 20 mm was chose to distinguish heavy rainfall from others. The parameters such as sea level pressure, temperature, relative humidity, specific humidity at the level of 700 hPa and wind direction were analyzed to identify sources of heavy precipitation moisture. Geopotential height at the level of 500 hPa was considered to determine heavy precipitation synoptic patterns. Wind speed and direction at the level of 300 HPA were evaluated to track the high-speed wind (jet stream). Then, these parameters were averaged monthly to investigate the general behavior of the atmosphere status associated with heavy precipitation in the studied area. The results show that in cold period of year the foci of heavy precipitation are located in KhorasanRazaviCounty. Mediterranean deep trough and Red Sea were identified as synoptic pattern and the main moisture source of heavy precipitation, respectively. Subtropical jet stream also recognized along with almost all heavy precipitation cases at level of 300 hPa.
Hossein asakereh
Volume 16, Issue 39 , May 2012, , Pages 73-88
Abstract
Understanding the heavy precipitation behaviors tend toward easy planning, designing, act and management of the water recourses. There are many definitions on heavy precipitation in different professional references. Two important extreme indices are maximum precipitation and five highest precipitations ...
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Understanding the heavy precipitation behaviors tend toward easy planning, designing, act and management of the water recourses. There are many definitions on heavy precipitation in different professional references. Two important extreme indices are maximum precipitation and five highest precipitations in a year. One characteristic of heavy precipitation is variation in time and space. Accordingly’ it is important to study this phenomenon by high resolution in time and space. To investigate heavy rains in Zanjan, daily precipitation during 1961-2006 have been analyzed. The trends of maximum precipitation and their ratio to annual precipitation, the trends of five highest precipitations and their ratio to annual precipitation have been modeled by Non-parametric methods. The results in two scales (annual and monthly) show no trends in time series, while there are high fluctuation periods during 1961-1973 and low fluctuation periods during 1974-2006.
