The Decadal Changes of Spatial Heterogeneity of the Subtropical Westerly Jet in Boreal Summer

Abstract The subtropical westerly jet (SWJ), a fundamental element of the midlatitude atmospheric circulation that greatly impacts global weather and climate, exhibits multiple centers with relatively high wind speed on the hemispheric scale. It manifests pronounced spatial heterogeneity when these jet centers experience asynchronous variations. However, previous researches about this heterogeneity are still limited. This study examines the long‐term variability of the spatial heterogeneity of SWJ during boreal summer (July–August) over recent 40 years, particular for the decadal changes. Three centers with high wind speed along SWJ, respectively located over Atlantic, West Asia and East Asia (short for ATJ, WAJ and EAJ) exhibit marked spatial heterogeneity in their temporal evolution. Both of ATJ and WAJ demonstrate the equatorward shifts, while EAJ shows poleward shift. This zonal heterogeneity is particularly pronounced on the decadal time scale, with all three centers have phase transitions in their meridional displacements around 1998. The decadal changes in the atmospheric circulation before and after 1998 encompass the circulation anomalies caused by the individual meridional displacements of the three jet centers. Meanwhile, the combined circulation anomalies caused by these jet centers closely match the decadal change of the atmospheric circulation. This provides compelling evidence for a strong dynamical connection between the atmospheric circulation and the heterogeneous variation of SWJ. The phase transitions of the Interdecadal Pacific Oscillation and Atlantic Multidecadal Oscillation, combined with the rapid retreat of Arctic sea ice, influence the decadal changes in the spatial heterogeneity of SWJ by modulating the meridional temperature gradient.