Latent Heating and Mixing Due to Entrainment in Tropical Deep Convection
March 26, 2013
Clayton McGee
Committee: Sue van den Heever (advisor), Eric Maloney, Richard Eykholt (Physics)
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Abstract
Recent studies have noted the role of latent heating above the freezing level in reconciling Riehl and Malkus' Hot Tower Hypothesis (HTH) with evidence of diluted tropical deep convective cores. This study evaluates recent modifications to the HTH through Lagrangian trajectory analysis of deep convective cores in an idealized, high-resolution cloud-resolving model (CRM) simulation. A line of tropical convective cells develops within a high-resolution nested grid whose boundary conditions are obtained from a large-domain CRM simulation approaching radiative-convective equilibrium (RCE). Microphysical latent heating processes and equivalent potential temperature (θe) are analyzed along trajectories ascending within convective regions of the high-resolution nested grid. Changes in θe along backward trajectories are partitioned into contributions from latent heating due to ice processes and a residual term. This residual term is composed of radiation and mixing. Due to the small magnitudes of radiative heating rates in the convective inflow regions and updrafts, the residual term is treated as an approximate representation of mixing within these regions. The simulations demonstrate that mixing with dry air decreases θe along ascending trajectories below the freezing level, while latent heating due to freezing and vapor deposition increase θe above the freezing level. The latent heating contributions along trajectories from cloud nucleation, condensation, evaporation, freezing, deposition, and sublimation are also quantified. Finally, the source regions of trajectories reaching the upper troposphere are identified; it is found that two-thirds of backward trajectories with starting points within strong updrafts or downdrafts above 10 km have their origin at levels higher than 2 km AGL. The importance of both boundary layer and mid-level inflow in moist environments is underscored in this study.
