A Numerical Study of a TOGA-COARE Squall-Line Using a Coupled Mesoscale Atmosphere-Ocean Model

An atmosphere-ocean coupled mesoscale modeling system is developed and used to investigate the interactions between a squall line and the upper ocean observed over the western Pacific warm pool during the Tropical Ocean/Global Atmosphere Coupled Ocean and Atmosphere Response Experiment (TOGA-COARE). The modeling system is developed by coupling the Advanced Regional Prediction System (ARPS) to the Princeton Ocean Model (POM) through precipitation and two-way exchanges of momentum, heat, and moisture across the air-sea interface. The results indicate that the interaction between the squall-line and the upper ocean produced noticeable differences in the sensible and latent heat fluxes, as compared to the uncoupled cases. Precipitation, which is often ignored in air-sea heat flux estimates, played a major role in the coupling between the mesoscale convective system and the ocean. Precipitation affected the air-sea interaction through both freshwater flux and sensible heat flux. The former led to the formation of a thin stable ocean layer underneath and behind the precipitating atmospheric convection. The presence of this stable layer resulted in a more significant convection-induced sea surface temperature (SST) change in and behind the precipitation zone. However, convection-induced SST changes do not seem to play an important role in the intsensification of the existing convective system that resulted in the SST change, as the convection quickly moved away from the region of original SST response.