the role of Saudi Arabian sub - tropical high pressure on the south and south - West of Iran rainfall systems

Subtropical high pressure is one of the main elements of the general circulation of the atmosphere that it’s annual motion plays an important role in move path of pressure systems and westerly waves. Because of that a large parts of the planet are affected directly and indirectly by this system. Sometimes the high pressure called the subtropical high pressure belt. It’s shown as several cells within Latitude15 - 35 north and south degree on the atmosphere map. According to the seasons, the high pressure could be divided into 5-6 single cell or be merged. Saudi Arabia cell is one of the high-pressure cells in the cold period which generally is an independent cell over the Red Sea to the Indian subcontinent area and appears in warm period over the North-West of Arabian Peninsula, South West Iran and southern Iraq independently or merged cells with Africa desert and Azores. To determine the role of Saudi high- pressure on the southern part of the country rainfall, daily rainfall data for all synoptic stations in Khuzestan, Kohkilooyeh, Char Mohall Bakhtaran, Fars, Busher and hormzgan provinces were extracted in 10 years period (2000-2009). In southern parts of the country rainfall is generally regional. 41 extremely rainfall systems have been determined, if 50% of selective stations have precipitation. Then position of the Saudi high pressure center were determined in peak rainy day of system on the 500, 700, 850, 1000 h Pa level maps. To determine the more precise high pressure centers, contour distances of 5 geopotential meters were selected on geopotential maps. Next, to analyze the dominated patterns in systems arrangement, and the Saudi high pressure role on the precipitation area, one synoptic patterns type which was more similar with other systems in more detailed was analyzed. In this analysis, 500, 700, 850 hpa sea level pressure and elevation maps, and 500،700،850،1000 hpa zonal (U) and meridinal (V) wind components and specific humidity quadruplet level maps were used. The overall results of the study is as follows: 1 - Saudi Arabian high pressure, on the Sea Level Map, just in half of cases had closed center and for other cases doesnt appear on the map and mostly shown as ridge of high pressure on Tibet. 2 – Saudi Arabian high pressure specified on the 500 700 850 hPa maps level and sometimes comes with 4 - 5 closed counter. 3 –Generally high pressure Centers are in 15 - 30 north degree latitudes and 75-60 east degree longitudes (on the Oman and Arab sea). 4-vertical axes the center of anticyclones from 1000hps to 500hpa declination south east word. 5- Abetment anticyclones the prevailing machomise is the air subsidence from upper level of trophesphere to lower level caused the air temperature by debating heating Increased and potential 6 – By Saudi Arabian pressure Eastward movement, Eastern Mediterranean trough developed in lower latitudes and often extended to 10 north degree latitudes. 7 - Zonal currents had East and meridinal current in all levels on Arabian and sea north, while in Saudi Arabia, Red Sea and eastern Egypt and Sudan was south and west. These conditions shows adductive moisture by Arab and Oman warm seas into Sudan systems. 8- U wind over Saudi Arabia is west and V wind is south. This flow indicated a humid fluex in upper level. 9- in all case study the high specific humidity cell are located on Etoupi and south of Sudan. This humidity by divergence fluxed from arabnd Oman warm sea adverted west an south warm then by convection fluxed suddan low received so that specific humidity map showed that this humidity suddan low trough advected over Iran. Saudi Arabia high pressure is one of a subtropical high pressure systems for that affected rainfall area and periods in Iran. Zonal (west - east) and meridional displacement (North - South) is a very important factor in the development, strengthening and accession of Sudan system in cold period. In years that pattern of Saudi Arabia high pressure system movement prevents of formation, strengthening and accession of Sudan system to Iran. the main parts of country is prevented and country is faced with decreasing rainfall while its good position will result in Mediterranean trough deepening ability and Sudan system strengthening.