A STUDY OF THE IMPACT OF DIABATIC HEATING ON THE EVOLUTION OF EXTRATROPICAL CYCLONES
Abstract
A diagnostic energetics analysis is used to study the effects of moisture-related processes on three numerically simulated cases of cyclone development. Both kinetic and available potential energy budgets are partitioned into zonal and eddy quantities in order to focus more effectively on cyclone-scale processes. Moist and dry versions of the Drexel University Limited Area Mesoscale Prediction System (LAMPS) are used. In addition, moist and dry energetics of a linear, quasi-geostrophic, analytical model are evaluated for comparative purposes. Results from the LAMPS forecasts show that the baroclinic process of cyclone development is noticeabely enhanced by both convective and stable latent heat release. Conversion of zonal available potential energy (AZ) to eddy available potential energy (AE) is strengthened in the moist forecasts through increased horizontal transport of sensible heat. Generation of available potential energy (GE) is often the same size as the conversion of AZ to AE. Release of AE and subsequent conversion to eddy kinetic energy (KE) is enhanced by condensational processes in all three cases. In addition, virtually all of the AE release due to moist processes is realized as KE. Resulting KE contents are consistently higher in the moist forecasts. Specific aspects of KE modification by diabatic heating are revealed through analyses of point values of energetics quantities. Typically, KE is enhanced north of (on the cold air side of) the region of precipitation at upper levels. Conversely, KE at lower levels (600-700 mb) is enhanced on the warm side of the precipitation region. These dynamic responses to the heating represent adjustment by the large scale flow toward hydrostatic and geostrophic equilibrium. The changes in KE structure are, thus, diagnosed by the thermal wind relationship. Qualitative agreement between the linear model and the LAMPS results is striking. The increase in baroclinic growth rate is largest near the short wave cutoff according to linear theory. Accordingly, the LAMPS forecast with the smallest zonal wavelength exhibits the largest component of baroclinic growth (conversion of AE to KE).
Degree
Ph.D.
Subject Area
Atmosphere
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