Characteristics of Cold Pools during the DYNAMO Field Campaign: Observations and SAM Simulations

Convectively-generated cold pools are efficient at further invigorating convection, thereby increasing overall convective variability, modulating the diurnal cycle, redistributing moisture, and ultimately organizing the overall structure of tropical convection. Previous studies consider the primary processes driving tropical cold-pool-driven convection to be mechanical lifting by cold density currents, anomalous specific humidity from either surface fluxes or rain evaporation, or some combination of the two. Here, we evaluate these processes with detailed observational information on the evolution of tropical cloud systems generating the cold pool and the accompanying thermodynamics, as well as the surface properties, using observations from the equatorial Indian Ocean. Different environments are considered along with clouds of varying extent, both horizontally and vertically., through synthesizing observations from the ARM mobile surface station, multiple radar platforms (both profiling and scanning), and the high-resolution soundings collected during the DYNAMO field campaign. Cold pools are identified based on the surface temperature time series, and changes in the surface properties are composited for different cloud types. The analysis primarily uses measurements from Gan Island, with a comparison made to shipboard R/V Revelle datasets. One finding is that cold pool edges are only slightly anomalously moist in the mean, so that the additional buoyancy is helpful, but not determining of, further convection. Two detailed case studies with slow and fast recoveries in the boundary layer properties are analyzed, complementing the composite statistics. The observed statistics are compared with the simulated cold pool statistics from a high resolution System for Atmospheric Modeling (SAM) model over the DYNAMO period (October 2011-February 2012). The similarities and differences between observed and simulated cold pool properties are documented and assessed.