aaaThe role of lower tropospheric circulation of Arabian high pressure in Iran's Precipitation

Atmospheric circulation patterns leads to different weather conditions and rainfall regime change is controlled by seasonal and irregular variations of atmospheric circulation pattern.
Variety and climate change, such as drought and flood result in changes in the spatio-temporal of precipitation, one of the important parameters conditions mentioned, heterogeneity in moisture transmission and injection in the systems rainy of iran. One component of the atmospheric circulation of moisture transmission is the high pressure centers and the most important point is their location on the water's surface.
Saudi Arabian high pressure is one of the main elements of the general circulation on the lower level of the atmosphere which affects climatic characteristics of the region. Therefore, the main aim of recent study was to investigate Saudi Arabian High Pressure circulation patterns and its impact on the moisture and precipitation by using cluster analysis.
In order to assess the role of Saudi Arabian high pressure patterns on the rainfall and moisture of Iran, the hourly data viz., 00, 06, 12 and 18 global standard geopotential height of 850 hPa for 11 years during the period 2000 to 2010 in the range of 30° to 80° longitude and 5° to 30° latitude with a spatial resolution of 1° * 1° of data re-analysis of the ERA interim center of Europe medium-term forecasts (ECMWF).
By scripting in MATLAB software, use of cluster analysis to correlation method and performed Clustering Based on the threshold correlation coefficient of 0.5 and Initially obtained the 160 groups, in from which the greater number of days whose the higher correlation were more than 0.5 have been placed in one group.
In the later steps to reduce the the group between correlation to less than the The correlation coefficient threshold, with calculation and integration of the average of any of days of the each cluster groups that has been made and the number of groups in each step using reiteration of operation were reduced and finally the 5 large pattern was obtained.
In order to evaluate the resulting patterns all the days in each pattern were pulled out. Traced maps, the mean geopotential height, zonal and meridional component of the wind were obtained through the scripting GrADS software. In addition, rain and moisture advection based on the total days of each pattern on a large scale were maped and frequency of the monthly patterns were calculated as well.
In this study, 5 large patterns were detected such that 2 of them were rare patterns and 5 dominant patterns. The 4 patterns in the cold season and 1 pattern in the heat season have been more abundant. The second pattern of the cold season is the highest and most pervasive precipitation of iran, and fourth pattern are in second order. The Summer pattern is lowest rainfall pattern during the 11 years studied.
The transfer and placement of center core of high pressure over the seas in the south of the country, especially over the Arabian Sea, With southwest flows the Many moisture injection into the country and Number of more seas are involved. It is clear that the moisture injection could be observed in, the second and fourth pattern of high precipitation and high pressure core with the stretching on the sea. Moreover, the exisrance of an trough 500 mb level over country has additional impact on the recent condition.
The first and second patterns have less rainfall With the high pressure displacement to the Western and northern parts. In the warm season of the year with the expansion of the Ganges low pressure at the lower level and integration and expansion of the subtropical high pressure and Saudi Arabian high pressure at the higher levels over the country, And consequently reduction of the activity of this high pressure result in Sharply decrease of the amount of moisture and precipitation in the country. While there are other atmospheric systems in the higher latitudes Such as the blocking system and its link with Saudi Arabia high pressure behavior leads to specific situations that caused different precipitation conditions in various parts.
The results showed that the spatio-temporal behavior of Saudi Arabian high pressure such as east-west, north-south displacement and even center core stretching has very significant role in the infusion of moisture and consequently the precipitation over iran. The spatial distribution of precipitation in the country depends to the location, shape and area circulation of high pressure. Generally, the high pressure has more impact at cold season together with remarkable role in moisture and precipitation of iran. However, in the warm seasons the role of high pressure greatly reduced due to its integration with subtropical high pressure and transfer to the North over the country's and Increase air stability in the region.