The effect of planetary-scale divergent circulation on the interannual variation of the summertime stationary eddies: the tropical easterly jet

Abstract

The tropical easterly jet is primarily composed of summertime stationary eddies over the monsoon region. Thus, the interannual variation of the former follows the interannual variation of the latter. Analysing the 200-mb wind fields generated by the Global Data Assimilation System of the National Meteorological Center for the past decade, we found that the weakening (or strengthening) tropical easterly jet and stationary eddies are coincident with the weakening (or strengthening) of planetary-scale divergent circulation. The streamfunction budget analysis was performed to infer the possible link between interannual variations of stationary eddies and divergent circulation. A simple barotropic model with the forcing derived from the divergence of the vorticity flux of long-term climatology and summers of the weak and strong tropical easterly jet was used to simulate summer-time stationary eddies. The numerical results demonstrate the argument that the weakening (or strengthening) and of the tropical easterly jet of summer-time stationary eddies over the monsoon region is caused by the weakening (or strengthening) of the planetary-scale divergent circulation, which may be attributed to the interannual variation of tropical diabatic heating.