The Tropical Dynamical Response to Latent Heating Estimates Derived from the TRMM Precipitation Radar

Abstract

A 3-yr (1998?2000) climatology of near-surface rainfall and stratiform rain fraction observed by the Tropical Rainfall Measuring Mission (TRMM) precipitation radar (PR) was used to calculate the four-dimensional distribution of tropical latent heating on seasonal-to-annual time scales. The TRMM-derived latent heating was then used to force an idealized primitive equation model using an initial value approach in order to obtain the quasi-steady-state, nonlinear, zonally asymmetric atmospheric response to precipitating tropical cloud systems. In agreement with previous studies, an increase in stratiform rain fraction elevates circulation centers and strengthens the upper-level response. Furthermore, horizontal variations in the vertical heating profile implied by the PR stratiform rain fraction pattern lead to circulation anomalies of varying height and vertical extent that are not present when the model is forced with a vertically uniform heating field. During El Niño, the trans-Pacific gradient in stratiform rain fraction that is normally present becomes more pronounced and the model response becomes even more sensitive to the horizontal variability of the latent heating vertical structure. When the heating field is modified to take into account the effects of nonprecipitating cumulus and cloud radiative forcing within the regions of tropical precipitating cloud systems, the overall pattern of the model response to the TRMM-derived latent heating is reinforced, as is the model's sensitivity to the variability in the latent heating vertical structure.