Etesian winds outbursts over the Greek Seas and their linkage with larger-scale atmospheric circulation features: Two real time data case studies

Abstract

There are significant differences in the way that researchers have defined “Etesian wind days”. An attempt is made here to establish common definitions of the various types of Etesian winds from the weather forecaster’s viewpoint. These definitions are based on objective criteria adopted from the frequency of atmospheric circulation features associated with the occurrence of the Etesian winds and their physical characteristics. The presence of fairly constant northerly winds over the Greek Seas in summer are called Etesian winds. When a new spell of Etesian winds is established with no diurnal variation of the wind direction for consecutive days (maximum of seven), these winds are called “type B” Etesian winds or “Etesian outbursts”. The atmospheric circulations associated with the occurrence, origin and evolution of the type B Etesian winds and the accompanying weather are revealed utilizing data for the period 1975-2015 and focusing on two case studies on July 21-22, 1983 and July 3-4, 2017. The presence of the Subtropical Jet Stream (SJS) over the Greek territory and its interaction with the Polar Jet Stream (PJS) are dominant factors. Large-scale atmospheric circulations are studied to identify simultaneous direct links to the Indian Summer Monsoon (ISM), El Niño-Southern Oscillation (ENSO), Madden-Julian Oscillation (JMO), deep convective activity in the Hadley circulation in the tropics, and West Africa Monsoon (WAM).