Heat Budgets of Analyses and Forecasts of an Explosively Deepening Maritime Cyclone

Abstract

Diagnosis of the conditions associated with explosive maritime cyclogenesis is hindered by the lack of observations. A heat budget approach with analyses and forecasts for a rapid cyclogenesis event during the FGGE period is used in this study. An explosively deepening cyclone in the western North Pacific during 12–15 January 1979 is selected from the analyses by the European Centre for Medium-Range Weather Forecasts. A fairly good numerical prediction of the cyclogenesis is available from the UCLA 9-layer general circulation model. Synoptic feature comparisons and quasi-Lagrangian heat budget results show that the model captured the major mechanisms of the explosive maritime cyclogenesis event. Use of the forecast fields in combination with the analyses allows the inference of heating field distributions during rapid cyclogenesis that are not available from budget studies based on analyzed fields. For both analyzed and predicted cyclogenesis, diagnosed diabatic heating rates are much larger than found in earlier studies of less intense cyclogenesis. Diabatic heating (latent heat release) at 600–700 mb is the primary process to maintain strong vertical motion during the most rapid deepening period. The cyclone deepening rate and the inferred diabatic heating rate are found to be highly correlated, with correlation coefficients of 0.83 and 0.65 for the forecast and analyzed cyclogenesis, respectively. An experimental integration of the UCLA model without latent heat release indicates that 75% of the deepening in this cyclogenesis event can be explained by dry dynamics alone. The latent heat release serves to enhance and modulate the rapid cyclogenesis.