LINKS BETWEEN TROPICAL CONVECTION AND VARIATIONS OF THE EXTRATROPICALCIRCULATION DURING TOGA COARE

Data from the Intensive Observation Period of the Tropical Ocean Globa l Atmosphere Coupled Ocean-Atmosphere Response Experiment (November 19 92-February 1993) have been used to investigate the links between intr aseasonal variations in tropical convection and those in forcing of up per-tropospheric Rossby waves in the extratropics. The primary databas es are Geostationary Meteorological Satellite imagery and tropical win d analyses from the Bureau of Meteorology, Australia. A number of 5-da y periods showing convection in different locations were chosen. For e ach period, mean fields of divergence, cloud-top temperature, and uppe r-tropospheric Rossby wave source are presented. Vorticity budgets are used to demonstrate the processes responsible for the Rossby wave sou rce patterns. The approach follows earlier studies of links between in terannual variations of tropical convection associated with the Southe rn Oscillation and variations of the extratropical circulation. It is shown that the regions of tropical convection correspond to longitudin ally localized Hadley cells. in the subtropics, at the higher-latitude end of each cell, there is a Rossby wave source dipole with anticyclo nic and cyclonic forcing. The anticyclonic forcing of Rossby waves is associated with advection of vorticity by the divergent outflow, while the cyclonic forcing is due to the region of convergence immediately above the downward branch of the local Hadley cell. Hence, the authors provide a dynamical basis for tropical-midlatitude interactions assoc iated with intraseasonal variations of tropical convection.