The effects of theTropical extratropical interaction (TEI) on the extreme and widespread precipitation of Iran

Abstract

This research was conducted with the aim of investigating the role of the interaction of tropical-extratropical circulation patterns on the extreme and widespread precipitation of Iran. To this end, 9 days with the extreme and widespread precipitation in Iran were investigated the 95th percentile index and their occurrence in 20 percent of stations and more during the statistical period of 31 years (1989-2019). Atmospheric data were extracted over 9 days. The data used are ERA5, which were extracted in the lower (850 and 800 hPa) and middle (700, 600, 500 hPa) levels. Geopotential hight jet stream maps show the tropical influence of extratropical dynamic factors, the amount of which is different in different levels of the atmosphere.Tropical and extratropical interaction have provided two factors for the occurrence of precipitation, i.e. humidity and atmospheric instability over Iran. The tropical influence of the Cut off low ,troughs and polar jet stream currents Their convergence with high-altitude subtropical centers have led to the transfer of tropical moisture to extratropical. On Iran, the influence of cut off low, the western trough and the polar jet stream provide suitable conditions for the ascent and instability of the atmosphere, which, with the entry of the tropical moisture of Iran, widespread and extreme precipitation occur.



Key Words: circulation patterns, tropical and extratropical regions, tropical extratropical interaction, extreme widespread rain, Iran