3:30 PM - 3:45 PM
[AAS03-07] A Mechanism for the Maintenance of Sharp Tropical Margins
Keywords:Tropical dynamics, Satellite data analysis, Conceptual theory
Major findings are summarized as follows. (1) CWV increases equatorward from the subtropics for all CWV thresholds but eventually converges to 48 mm deep into the tropical side. Precipitation abruptly intensifies on the tropical side of the margin but declines equatorward to 85 W/m2 regardless of the CWV thresholds. (2) The diabatic forcing to the atmosphere (radiative heating plus surface heat fluxes) changes its sign across the CWV=48 mm border, being positive on the tropical side and negative on the subtropics. This contrast is owing to the meridional gradient of radiative heating, principally the longwave effect of high clouds. (3) Vertical mode decomposition reveals a transition from bottom-heavy to top-heavy subsidence on the subtropical side of the margin. These observed features are interpreted in terms of a simple theory from the moisture and heat budget perspectives. The model explains the abrupt moistening at the margin as a singularity where the vertical displacement of air costs little energy within a column.