The Impact of ENSO Phase Transition on the Atmospheric Circulation, Precipitation and Temperature in the Middle East Autumn

Abstract

The impact of El Nino–Southern Oscillation (ENSO) phase transition on the atmospheric circulations, precipitation and temperature in the Middle East (ME) during the period of 1950–2018 autumn seasons were analyzed. ENSO events were selected based on the Oceanic Nino Index (ONI) and its phase transition from El Nino to La Nina (type 1) and from La Nina to El Nino (type 2) events during the study period. Monthly and climate means of data for precipitation, temperature, geopotential height, wind components (u and v) and Sea level pressure (SLP) obtained from National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis. Composites of the means and anomalies were derived from selected case studies of the ENSO phase transitions. Finally, the student’s t test is used to determine the significance of the composite means in each grid point. The results show during transitions, the SLP structure over the Atlantic region changes, in a way that pressure differences between Iceland low and the Azores high during type 1 (type 2) is minimum (Maximum) and also statistically significant at 95% confidence level which, these conditions are accompanied by statistically significant enhancing (decreasing) rainfall over the most parts of the ME. In addition, the variability of upper level geopotential height and zonal wind were found over the region which lead to favorable or less favorable conditions for infiltration of planetary Rossby waves to the ME in type 2 and type 1, respectively. Also this study reveals that, moisture flux transport from the adjoining seas to the ME is extremely different in both types, so that during type 2 (type 1), the ME receives significant (insignificant) amounts of moisture. This study therefore identified that most parts of the ME experienced statistically significant positive (negative) anomalies of precipitation during type 2 and type 1 respectively.