THE DIRECT AND INDIRECT EFFECTS OF LATENT HEAT RELEASE ON EXTRATROPICAL CYCLONE DEVELOPMENT (HEIGHT TENDENCY, LFM MODEL, KINETIC ENERGY, AVAILABLE POTENTIAL)
Abstract
The effects of latent heat release on the development of extratropical cyclones are proposed to be of two types, direct and indirect. The former is represented in diagnostic equations by any term which is expressed in terms of diabatic heating, while an indirect effect can occur through any of the other terms. The National Meteorological Center's LFM model is used to simulate a winter cyclone case over North America for varying conditions of latent heating. Direct effects were computed from model latent heating rates; indirect effects were found by comparing forecasts made with and without latent heating. The first diagnostic equation used was a new formulation of the height tendency equation called the extended height tendency equation. The extended equation is more general than the quasi-geostrophic form, using actual winds and vorticities in place of geostrophic, unsimplified coefficients, and two additional terms, the differential heating term, and the vertical advection of static stability term. Results of this diagnosis show that latent heat release indirectly alters height tendencies ahead of the cyclone by decreasing height falls due to vorticity advection, decreasing (increasing) height falls due to differential thermal advection at low (high) levels, and decreasing height rises due to vertical advection of stability. The differential heating term, representing the direct effect of latent heating, was negligible when such heating was omitted from the forecasts but achieved values comparable to the other terms when the heating was included. This term yielded height falls at low levels and height rises at upper levels. Eddy available potential energy (AE) and the eddy kinetic energy (KE) budgets were also calculated. Latent heat release was found to generate AE directly. However, the indirect effects overwhelmed this source giving an enhanced decrease in AE with time. This was accompanied by an enhanced generation of KE and larger net increases in KE in the forecasts which included latent heat release.
Degree
Ph.D.
Subject Area
Atmospheric sciences
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