Dynamical Analysis of the Winter Middle East Jet Stream and Comparison with the East Asian and North American Jet Streams

Abstract

Abstract The wintertime Middle East jet stream (MEJS) is an important upstream signal for the East Asian winter monsoon and the subsequent Asian summer monsoon. Thus, the maintenance and interannual variations of the MEJS as well as its similarities and differences with the East Asian jet stream (EAJS) and the North American jet stream (NAJS) are studied dynamically using the geopotential tendency equation and empirical orthogonal function analysis. Analysis reveals that the MEJS is mainly maintained by tropical diabatic heating and the low-frequency transient eddy (TE) vorticity forcing. It is different from the EAJS, which is maintained by both tropical diabatic heating and high-frequency TE vorticity forcing, and the NAJS, which is mainly sustained by high-frequency TE vorticity forcing. Furthermore, while temperature advection plays a considerable role in the maintenance of EAJS and NAJS, it is less important for the MEJS. On interannual time scales, the meridional shift of the MEJS is related to low-frequency TE heating, while the variation of the jet’s intensity is associated with temperature advection. For both EAJS and NAJS, the interannual variations are mainly contributed by high-frequency TE vorticity forcing, although temperature advection also promotes their meridional shifts. These results suggest that whether or not the maintenance of the jet streams is related to tropical diabatic heating, their interannual variations are not directly induced by this forcing. Significance Statement The wintertime Middle East jet stream (MEJS) is a narrow and strong westerly wind belt over the Middle East whose variations in intensity and location can affect the Asian monsoon significantly. However, little effort has been devoted to investigating the MEJS. Thus, dynamical diagnosis and statistical analysis are applied in this study to understand the MEJS and its variability comprehensively. Analysis reveals that low-frequency transient eddies, which are the mobile atmospheric systems with a lifespan longer than 10 days, are important for both the maintenance and the interannual variability of the MEJS. This phenomenon is apparently different from the East Asian and North American jet streams, in which synoptic transient eddies (lifetime shorter than 10 days) play an essential role.