Investigation of changes in spatial high-pressure intercontinental spatial autocorrelation on Iran during the years 1979 to 2018

From a climatic point of view, the main cause of drought at latitudes of 30 degrees north is subtropical high pressure. Temporal and spatial changes of subtropical hypertension cause anomalies in regional and global circulation and consequently climatic anomalies. These changes are important.

In this study, the changes of subtropical high pressure spatial autocorrelation on Iran from daily geopotential altitude data of 500 hPa during the years 1979-1979 for the warm period of the year, i.e. June 22 to September 22, were used. The data was taken with a pixel size of 0.25 by 0.25 degrees for the Era-Interim version, from the European Center for Medium-Term Weather Forecast database.

The results showed that according to the global Moran index, subtropical high pressure changes over Iran have a high cluster state. The index showed that in all periods, there were cold spots on the northern, northwestern and northeastern strip, and hot spots on the west, southwest and areas of the south and center of the country. In the second and third periods, the distribution of the standard oval pattern was circular, but in the first period it was elongated and this state reached its maximum in the fourth period and reached a northwest-southeast state, which indicates the further expansion of subtropical hypertension over the regions to the west and the upward trend to the north and the lack of expansion of this system over the eastern regions of Iran. Changes in cold spots on Iran have an increasing trend, especially in the fourth period in the eastern regions of the country it has reached its peak, which indicates a change in the location of hot spots on Iran and its spread to the west and north compared to other periods.

This paper aims to investigate subtropical high pressure changes using spatial statistics methods. The advantage of this study over other studies on the study of subtropical hypertensive changes is the use of spatial statistics methods, so that the result is very consistent with synoptic research conducted by other researchers such as Hejazizadeh (1993), Movahedi and Et al. (2012), Asakereh and Fattahian (2015), Alipour et al. (2015), Alijani et al. It shows the changes of two surface indices (positive local Moran index) and subtropical hypertension intensity (Getis-Ardji index at 99% level) and the output of the work is increasing the surface index and subtropical hypertension intensity on Iran from the first period to the fourth period, which shows a tendency to the west and northwest. The results of descriptive statistics analysis showed that the average height of geopotential level of 500 on Iran from the first to the fourth period has increased and its maximum has occurred in the fourth period.