Convective Cold Pool Responses to Changes in Sea-Surface Temperature

Cold pools forming in association with convective clouds are common occurrences in tropical maritime regions. They occur when melting and evaporation combine with hydrometeor loading to create regions of locally denser air. This air descends to the surface, forming a cold pool: a region of cool air bounded by a gust front. The gust front enhances surface fluxes and also lifts the air ahead of it. Therefore, cold pools have implications for the formation and organization of subsequent convection.

Given cold pools' importance, it is useful to ask how surface and environmental attributes affect cold pool properties. To this end, this study investigates the role of sea-surface temperature (SST) in modulating cold pool properties. Of particular interest are the size and strength of the cold pools (as quantified by density potential temperature perturbations, wind speeds, and gust front convergence strength), as well as the structure of cold pools’ associated water vapor perturbations.

Multiple idealized simulations are run using the Regional Atmospheric Modeling System (RAMS). Each simulation has a different, fixed SST within the range 298 K to 304 K. The simulations are performed on a 150 km × 150 km × 26 km domain. First, preliminary, long-duration (~20 d) simulations are conducted with 1 km horizontal grid spacing in order to obtain profiles that are in quasi-equilibrium with each SST. Then, each simulation is re-initialized using the mean atmospheric profile at the end of its corresponding long-duration simulation. The re-initialized simulations are run using 250 m horizontal grid spacing and approximately 100 vertical levels.

Cold pools in all simulations are identified and tracked using a novel cold pool analysis algorithm. This algorithm generates statistics of cold pool area and strength, as well as composite cold pools constructed from the ensemble of cold pools identified in each simulation. Trends in the cold pool area, strength, and water vapor structure as a function of SST will be discussed. Furthermore, the implications for convective organization, SST-surface flux-cold pool interactions, and ultimately climate will be explored.