A Study of the subtropical high pressure 500 hPa level changes in the Iran's atmosphere with emphasis on climate change

Abstract

Azores subtropical high pressure is accounted as the most striking and permanent features of tropospheric circulation in the Northern Hemisphere subtropical region and Iran. Assessing the published sources about the subtropical high-pressure variations showed that a comprehensive research of the high-pressure changes is needed in different seasons of the year. Increase or decrease in the severity index and eastern and northern extension index of the subtropical high pressure of 500 hPa level, is a major determinant index of the arid and wet periods in Iran. Therefore, the main goal of this research was to determine the tempo-spatial changes of subtropical high pressure or in the other words determining the northern and eastern borders spread and also the intensity of this system in different seasons over Iran. For this purpose, the data with NC format and geopotential height of 12GMT over a period of 68 years (1948_2015) were downloaded from the databases of National Center for Atmospheric Prediction (NCEP) and the National Center for Atmospheric Research (NCAR) NOAA and for seasonal classification and drawing the intended maps, they were converted to standard and intended formats Intended in the next stage. The maps and time series charts of mean STHP of Iran’s atmosphere indicate an increase in the severity and surface index during all the seasons of the year. The slope of the trend line has been increased for all the seasons and the average of geopotential height in Iran increased at a rate of 5.87 Geopotential meter per every 10 years and in 2015 reached to the maximum positive anomaly.

Keywords

• iran
• azores subtropical high pressure
• severity and surface index
• trend