THERMAL FORCING IMPACTS OF THE EASTERLY VORTEX ON THE EAST-WEST SHIFT OF THE SUBTROPICAL ANTICYCLONE OVER WESTERN PACIFIC OCEAN

By employing the NCEP/NCAR reanalysis data sets (1 000 to 10 hPa, 2.5°×2.5°), the thermal forcing impacts are analyzed of an easterly vortex (shortened as EV) over the tropical upper troposphere on the quasi-horizontal movement of the Western Pacific Subtropical Anticyclone (shortened as WPSA) during 22-25 June 2003. The relevant mechanisms are discussed as well. It is shown that the distribution and intensity of the non-adiabatic effect near the EV result in the anomalous eastward retreat of the WPSA. The WPSA prefers extending to the colder region, i.e., it moves toward the region in which the non-adiabatic heating is weakening or the cooling is strengthening. During the WPSA retreat, the apparent changes of non-adiabatic heating illustrate the characteristics of enhanced cooling in the east side of the EV. Meanwhile, the cooling in the west side exhibits a weakened eastward trend, most prominently at 300 hPa in the troposphere. The evidence on the factors causing the change in thermal condition is found: the most important contribution to the heating-rate trend is the vertical transport term, followed in turn by the local change in the heating rate term and the horizontal advection term. As a result, the atmospheric non-adiabatic heating generated by the vertical transport and local change discussed above is mainly connected to the retreat of the WPSA.