عنوان مقاله [English]
Convective systems are meso-scale atmospheric phenomena which their intensity of activity is determined by atmospheric static stability indices (convective indices). The effect of large-scale teleconnections on the increase or decrease in the potential for occurrence of convective systems in the atmosphere is of particular importance. Therefore, study of the climatological distribution of atmospheric stability indices along with teleconnections can be important in predicting convective systems. Given the lack of a comprehensive study of the relationship between the two phenomena, the purpose of this study is to investigate the climatological distribution of some atmospheric stability indices and their relationships with some teleconnections over the West Asia.
In this study, first using JRA55 reanalysis data with a horizontal resolution of 1.25×1.25 degree during the period 1958 to 2018, four atmospheric stability indices including Convective Available Potential Energy (CAPE), K Index (KI), Lifted Index (LI) and Total Totals Index (TTI) were calculated. Then, in the first part of this study, the average seasonal distribution of these indices on the West Asian region in the range of 0 to 60 degrees north and 10 to 90 degrees east are presented. Next, in the second part of this study, the relationship between atmospheric stability indices and teleconnections is examined. For this purpose, by determining the critical phases of the four teleconnections, including the North Atlantic Oscillation (NAO), East Atlantic/West Russia (EA/WR), Indian Ocean Dipole (IOD) and Madden–Julian Oscillation (MJO), the difference in distribution of the average atmospheric stability indices for the positive and negative critical months of these teleconnections is investigated in spring season during the study period on the West Asia.
The results of the first part of this study showed that the seasonal distribution of atmospheric stability indices on the study area is affected by the seasonal cycles of temperature and humidity associated with the ITCZ displacement. The results also showed that the maximum values of the stability indices occur in summer over lowland areas and the minimum ones in winter and highlands. The results of the second part showed that generally the area in which the atmospheric stability indices have significant values over the most parts of the study area decreases (increases) during the positive (negative) phases of the two northern indices of NAO and EA/WR, but increases (decreases) during the positive (negative) phases of the two southern indices IOD and MJO. The highest increase of CAPE index during the negative phase of NAO (EAWR) compared to its positive phase on the Oman Sea (East India) exceeds +250 (+450) J/kg and also during the positive phase of IOD (MJO) compared to its negative phase on Western India (Oman Sea) exceeds +450 (+600) J/kg.