Vertical structure of variabilities in the tropical easterly jet and associated factors

Abstract

The tropical easterly jet (TEJ) is an easterly jet stream that occurs from the upper troposphere to lower stratosphere in boreal summer. Owing to its wide vertical extension from 300 to 70 hPa, the TEJ may exhibit distinct characteristics at different levels, the details of which remain thus far unclear. In this study, two empirical orthogonal function (EOF) modes of the year-to-year variability in the vertical structure of the TEJ were investigated. The leading EOF mode represents a consistent strengthening or weakening of the TEJ's main body in the vertical direction and varies on both interannual and interdecadal time scales. It has been suggested that ENSO can modulate this vertically consistent mode interannually, whereas the Atlantic Multidecadal Oscillation and Pacific Decadal Oscillation can influence its interdecadal variability. In contrast, the second EOF mode exhibits an out-of-phase relationship between the zonal wind anomalies of the upper troposphere and lower stratosphere, linked with the changes in the TEJ's vertical movement and dominating on the quasi-biennial time scale. The Quasi-Biennial Oscillation could contribute to variations in the TEJ's vertical movement by changing the tropopause winds as a direct pathway and inducing anomalous convection over the tropical Indian Ocean and Maritime Continent as an indirect pathway.