Date Published:

Abstract:

We developed an entraining parcel approach that partitions parcel buoyancy into contributions from different processes, e.g. adiabatic cooling, condensation, freezing, and entrainment. Applying this method to research quality radiosonde profiles provided by the Atmospheric Radiation Program (ARM) at six sites, we evaluated how atmospheric thermodynamic conditions and entrainment influence various physical processes that determine the vertical buoyancy structure across different climate regimes as represented by these sites. The differences of morning buoyancy profiles between the deep convection/transition cases (DC) and shallow convection/non-transition cases (SC) were used to assess pre-conditions important for shallow-to-deep convection transition. Our results show that for continental sites such as the U.S. Southern Great Plains (SGP) and the West-Central Africa, surface condition alone is enough to account for the buoyancy difference between DC and SC cases, although entrainment further enhances the buoyancy difference at SGP. For oceanic sites in the Tropical West Pacific, humidity dilution in the lower-to-mid free troposphere (~1-6km) and temperature mixing in the mid-to-upper troposphere (>4km) have the most important influences on the buoyancy difference between DC and SC cases. For the humid Central Amazon region, entrainment in both the boundary layer and the lower free troposphere (~0-4km) have significant contributions to the buoyancy difference; the upper tropospheric influence seems unimportant. In addition, the integral of the condensation term, which represents the parcel's ability to transform available water vapor into heat through condensation, provides a better discrimination between DC and SC cases than the integral of buoyancy or the Convective Available Potential Energy (CAPE).