Investigation of the relationship between Euro-Atlantic and West Asia blockings and major stratospheric sudden warmings in the period of 1959-2018

The main aim of this paper is to investigate and compare the possible connection between tropospheric blocking events and major stratospheric sudden warmings (SSWs) in the two periods of 1959-1988 and 1989-2018 to present a dynamical insight into the blocking formation and behaviors. After identifying and characterizing two types of SSWs including wavenumber-1 (W-1) and wavenumber-2 (W-2) in both the periods, the behaviors of blocking events coincided with major SSWs are examined and compared in the two periods. Then, the relationship between blockings and major SSWs is discussed applying the Empirical Orthogonal Function (EOF) method. In general, 18 and 16 major SSW events were identified in the first and second periods, respectively. The investigation of planetary wave activities indicates that the maximum anomalies of geopotential height amplitude and meridional eddy heat flux in the PRE-SSW phase of both types of SSWs, particularly major W-2 warmings, in the second period occurred earlier than those in the first period. The peaks of blocking activities in the second period have also been moved eastward compared with the first period in both prior to and after the onset of SSWs. Moreover, the frequency of blocking event during the PRE-SSW phase of major W-1 warmings in EuroAtlantic and a large part of West Asia in the second period is less than that of the first period, while the occurrence of blocking during the PRE-SSW phase of major W-2 warmings in Eastern Europe and West Asia has been increased in the second period. In the POST-SSW phase, blocking activity associated with major W-2 warmings is enhanced in West Asia during the second period. In addition, the maximum blocking activities preceding major SSWs in the second period was occurred 5-days prior to the first period. The results of cross-correlation coefficients between blockings and SSWs show significant relationship between them with time lag of about 10-days prior to the onset of warmings in both the periods, especially in the recent years.