Implementation of the JMA Typhoon Bogus in the BMRC Tropical Prediction System

Abstract

A modified version of the typhoon bogus developed at the Japan Meteorological Agency has been installed in the Australian Bureau of Meteorology's tropical prediction system. The construction of the bogus vortex is described and the impact on forecasts during several tropical cyclone events is illustrated. Improvements in prediction are obtained in nearly all cases. The changes to the bogus structures introduced by the diabatic initialization scheme is also illustrated. It is shown that the method of initialization can have a large effect on the imposed structure and can affect the quality of prediction of both the tropical cyclone itself and the large scale flows quite remote from the storm center. It is suggested that without careful initialization occasional erratic behaviour can result from mass-wind imbalance, inconsistency between the imposed vortex structure and the grid resolution, and rejection of the vortex by the forecast model. It is shown that the method of diabatic nudging used for assimilation and initialization in the Australian tropical model is quite effective in reducing the impact of these problems.