Tropical Convective System and Cold Pool Interactions

Tropical convective systems leave imprints on the state of the tropical atmosphere, and so it is important to understand processes governing their behavior and evolution. However, mechanisms influencing the behavior of tropical convective systems are not as well studied as for midlatitudes. Although cold pools play a key role in the classic midlatitude system archetype, cold pools in the tropics are generally weaker due to greater boundary layer humidity and may not interact with tropical convective systems in the same way as in midlatitudes. The goal of this research is to assess cold pool and tropical convective system interactions and to determine the physical mechanisms by which cold pools influence tropical convective system characteristics, including rainfall production and propagation.

An idealized simulation of tropical convection in radiative-convective equilibrium (RCE) has been conducted to address this goal. The RCE simulation, which included an ocean SST of 300 K and 1 km horizontal grid spacing, utilized a large (3000 km by 200 km) domain such that multiple convective systems could develop. Two long-lived, mesoscale-organized systems, one a weaker cluster and the other a more intense linear system, were selected and simulated at 250 m horizontal resolution. In order to elucidate the cold pools’ influence on the convective systems’ behavior, sensitivity tests were conducted in which cold pool strengths were altered by changing sub-cloud evaporation rates.

Contrary to expectations, the sensitivity tests showed that when cold pools were weakened or eliminated, convection became more intense and produced more rainfall. Additionally, changing the cold pool strengths did not alter the propagation speeds of either system. Mechanisms responsible for the rainfall differences and for the lack of response in system propagation speeds have been explored through composite, streamline, and tracer analysis, and will be presented.