The Impact of Model Moist Processes on the Energetics of Extratropical Cyclones

Abstract

A diagnostic energetics analysis is used to study the effects of moisture-related processes on two numerically simulated cases of extratropical cyclone development. Model output is derived from moist and dry versions of the Drexel University Limited Area Mesoscale Prediction System (LAMPS). Both kinetic and available potential energy budgets are partitioned into zonal and eddy quantities in order to focus more effectively on cyclone-scale processes. Results from the LAMPS forecasts show that the baroclinic aspects of cyclone development are significantly enhanced by both convective and stable latent heat release. Although generation of available potential energy (GE) is an important source of eddy available potential energy (AE), diabatic heating produces substantial modifications to eddy energy conversion terms. Transformation of zonal available potential energy (AZ) to AE is strengthened in the moist forecasts through increased horizontal eddy transport of sensible heat. Although conversion of AZ to AE maximizes in the lower troposphere where eddy heat transport is largest, moist forecasts show systematically larger conversions in the middle troposphere where latent heating maximizes. Release of AE is nearly twice as strong in the moist forecasts. A significant portion of the additional AE release due to moist processes results in increased generation or decreased destruction of eddy kinetic energy (KE) via altered ageostrophic flow. Resulting KE contents are found to be larger for the moist forecasts. An analysis of growth rates agrees qualitatively with previous theoretical and numerical results which indicate that heating effects are more critical to short baroclinic waves.