The sensitivity of tropical squall lines to surface fluxes: Three‐dimensional cloud‐resolving model simulations

Abstract

AbstractTwo tropical oceanic squall lines, from the Tropical Ocean–Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE) and the Global Atmospheric Research Program Atlantic Tropical Experiment (GATE), that developed over the west Pacific and east Atlantic, respectively, are simulated using a three‐dimensional cloud‐resolving model to examine the impact of surface fluxes on tropical squall line development and associated precipitation processes. The important question of how convective available potential energy (CAPE) is maintained in clear and cloudy areas in the tropics is investigated. The boundary‐layer structure and evolution in the clear inflow area are also discussed. Although the cloud structure and precipitation intensity are different between the TOGA COARE and GATE squall line cases, the effects of the surface fluxes on the amount of rainfall and on the cloud development processes are quite similar. The area where surface fluxes originated was categorized into clear and cloudy regions according to whether there was cloud in the vertical column. The model results indicated that the surface fluxes from the large clear‐air environment are the dominant moisture source for tropical squall line development, even though the surface fluxes in the cloud region display a large peak. The high‐energy air from the boundary layer in the clear area is what feeds the convection, while the CAPE is removed by the convection. Trajectory and water budget analyses also indicate that most of the moisture (90%) is from the boundary layer of the clear‐air environment. Copyright © 2003 Royal Meteorological Society