Sensitivity of Tropical West Pacific Oceanic Squall Lines to Tropospheric Wind and Moisture Profiles

Abstract

Two-dimensional experiments using the Goddard Cumulus Ensemble model are performed in order to examine the influence of environmental profiles of wind and humidity on the dynamical and microphysical structure of mesoscale convective systems (MCSs) over the tropical oceans. The initial environments used in this study are derived from the results of a cluster analysis of the TOGA COARE sounding data. The model data are analyzed with methods and measurements similar to those used in observational studies. Experiments to test the sensitivity of MCSs to the thermodynamic profile focus on the role of humidity in the free troposphere. In the experiments, a constant amount of relative humidity is added to every level above the boundary layer. As humidity is increased, model storms transition from weak, unsteady systems with little precipitation to strong, upshear-tilted systems with copious rainfall. This behavior is hypothesized to be the result of the entrainment of environmental air into the updraft cores. Experiments to test the sensitivity of MCSs to the kinematic profile focus on the amount of vertical wind shear in the midlevels, between approximately 2 and 10 km. Five kinematic profiles are used. The dynamical and microphysical characteristics of the runs changed dramatically in different shear environments. Shear in the midlevels affects the convective systems by altering the perturbation pressure field. Stronger shear results in a broader and deeper mesolow below the updraft and a more intense dynamic high above the leading edge.