Synergistic Impacts of Surface Heterogeneity and Cold Pools on Tropical Convection

Tropical convective initiation and convective properties are tied to boundary layer processes, such as cold pools and other circulations impacted by surface features like land surface heterogeneity. Understanding land surface and boundary layer influences on tropical convection characteristics is essential to better characterize potential changes in convective properties with anthropogenic activities like land use / land cover change, the role of tropical convection in the global circulation and hydrologic cycle, and convective fluxes of mass, water, and aerosols. It is known that land surface heterogeneity can enhance the propensity for convection initiation via mesoscale circulations and influence convective properties like intensity and depth by creating local regions of higher boundary layer temperatures and/or moisture. Cold pools are also known to initiate convection and hasten the transition from shallow to deep convection. However, the mutual impacts of cold pools and land surface heterogeneity on convective initiation and characteristics have not been previously explored.

In this study, we use idealized, high-resolution, large-eddy simulations to examine the individual and synergistic impacts of cold pools and land surface heterogeneity on convective initiation and intensity. We initialize the simulations with an environmental sounding and land surface characteristics representative of the Amazon rainforest region from the TRMM LBA campaign. We conduct an ensemble of simulations including (1) control simulations with a heterogeneous surface and cold pools, (2) homogenized surface properties, (3) suppressed cold pools by turning off rain evaporation below cloud base; and (4) both effects (homogeneous surface and suppressed cold pools). We use the factor separation technique to analyze the individual contributions and nonlinear interactions between surface heterogeneity and cold pools on convective properties. Preliminary results indicate that while each individual effect reduces convective intensity, nonlinear interactions between surface homogenization and suppressed cold pools further suppresses intensity beyond the additive individual effects. Convective clouds are tracked through their lifecycles to explore physical mechanisms explaining these results.