A Comparison of Quasigeostrophic and Nonquasigeostrophic Vertical Motions for a Model-simulated Rapidly Intensifying Marine Extratropical Cyclone

Abstract

Abstract Large-scale departures from quasigeostrophic vertical motions are diagnosed for a model simulation of the QE II storm (9–11 September 1978). The simulation was performed by the Limited-Area Mesoscale Prediction System (LAMPS), initialized at 1200 UTC 9 September 1978. The model cyclone intensified from a central pressure of 1003 mb to 976 mb in 24 h, considerably short of the 59 mb (24 h)−1 observed deepening but reasonable in comparison to other model simulations of this storm. This diagnosis centers on a hydrostatic generalized omega equation, which scales to the quasigeostiophic omega equation for small Rossby number. Vertical motions were computed both from this generalized omega equation and the quasigeostrophic omega equation in order to examine the importance of nonquasigeostrophic effects. The high correlation of vertical motions from a control experiment (using most of the terms in the generalized omega equation) with the vertical motions predicted by the model establishes the validity o...