Convective heating and momentum transport associated with tropical disturbances

The thermodynamic and dynamic coupling processes between convection and large-scale tropical motions are investigated. Primarily with sounding and wind-profiler datasets from the Tropical Ocean Global Atmosphere (TOGA) Coupled Ocean Atmosphere Response Experiment (COARE) Intensive Observing Period (IOP), November 1992-February 1993, heat, moisture, and momentum budgets are derived with estimated surface fluxes as boundary conditions. In addition, a subset of European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA) and results from a Cloud Resolving Model (CRM) during the COARE IOP are used to verify the momentum budget computation. Moreover, satellite imagery and radar-derived rainfall are used as convective indices.

It is found that, over the western Pacific warm pool, the eastward-propagating deep convection associated with the Madden-Julian Oscillation (MJO) accelerates the westerlies between 850 and 300 hPa before the climax of the Westerly Wind Burst (WWB). Concurrently, the effect of increasing surface drag is seen below 850 hPa. The results indicate upgradient transport of zonal momentum by convection and enhancement of the baroclinicity of MJO during its convective phase. It is further noticed that, in some cases, the upgradient transport of momentum seems to be coincident with linear convective organizations in large scale, which should be considered when developing cumulus momentum parameterization.