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Mark Hedley and M. K. Yau

Abstract

A three-dimensional anelastic model is used to perform simulations of explosive cyclones. The major goals are 1) to investigate the importance of horizontal resolution on the simulation of mesoscale features during explosive cyclogenesis using a very high resolution nonhydrostatic model and 2) to determine the impact of the destabilization of the lower troposphere by strong surface fluxes on the development of the storm.

The results from six experiments are presented. The main conclusions are:

1) By using analytic initial conditions based on typical wintertime conditions prior to explosive cyclogenesis, it is possible to obtain very realistic simulations of rapid cyclogenesis.

2) The use of high horizontal resolution is important in simulating the mesoscale features of rapidly deepening cyclones. In particular, the structure of the intense warm front observed ahead of the cyclone is very sensitive to changes in horizontal resolution.

3) The destabilization of the lower troposphere prior to the period of rapid deepening is essential in the formation of an extremely intense frontal structure, which in turn is instrumental in the rapid spinup of the storm.

4) In the presence of strong surface fluxes, the development of the simulated cyclone is affected by the depth of the planetary boundary layer.

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Mark Hedley and M. K. Yau

Abstract

A two-dimensional anelastic model is used to study the propagation of errors arising from the use of open lateral boundaries. Reference experiments were performed using very large horizontal domains. Other experiments were carried out in smaller domains with various radiation boundary conditions. Direct calculation of the error fields demonstrates the mechanism for the generation, propagation, and growth of errors. It was shown that a fixed phase speed method resulted in runaway circulation while a floating speed scheme exhibited difficulties in regions where horizontal gradients in horizontal velocity are small. A hybrid scheme is proposed which was shown to work well in highly truncated spatial domains.

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