On the observational and numerical aspects of explosive East coast cyclogenesis.

摘要

An explosively deepening storm or 'bomb' (hereafter quotes omitted) is defined by Sanders and Gyakum (1980) as an extratropical cyclone whose central mean sea-level pressure falls at least 1 mb per hour for 24 hours. The composites constructed from the daily global analyses generated and archived at the European Center for Medium Range Weather Forecasts (ECMWF) accurately describe the three-dimensional kinematic and thermodynamic structure of bombs over the entire depth of the troposphere. Furthermore, a regional ;Numerical experimentation of explosive east coast cyclogenesis is performed using the Florida State University Global Spectral Model (FSUGSM). The three cases examined here are the Presidents' Day storm of 18-19 February 1979 and the North Atlantic and Pacific bombs of 18-20 January 1979 which formed off the east coasts of the United States and Japan respectively. The use of a global model provides a framework for studying the phenomena on the 3-5 day time scale and for examining the sensitivity of the forecasts to data analysis in regions several thousand km upstream of the storm domain. A technique is developed to uniquely partition and quantify the role of the dynamical and physical processes in the explosive cyclogenetic process. Additionally, the complete model-generated four-dimensional data sets are used to compute residual-free Eulerian vorticity budgets.;The results of this work reveal that explosive cyclogenesis is a baroclinic phenomena in which the rapid intensification in the presence of pronounced middle and upper tropospheric forcing is enhanced by a highly destabilized lower troposphere that is strongly heated and moistened by upward (positive) oceanic sensible and latent heat fluxes. The focus of the ongoing research is shifting away from the problem of actually predicting explosive cyclogenesis toward improving the skill of bomb forecasts and simultaneously extending the range of predictability of such events.