NEXRAD-In-Space: the potential for spaceborne Doppler radar observations to improve forecasts of tropical cyclones

NEXRAD-In-Space (NIS) is to be a 35-GHz Doppler radar in geosynchronous orbit. By providing hourly observations of reflectivity and vertical velocity over a disc of diameter 5300-km at the earth's surface, NIS will open a new vista on tropical cyclone observation and prediction. Never before has it been possible to observe the precipitation and vertical motion fields with such regularity, and it is anticipated that the NIS data will have large positive impacts on both the theoretical and numerical weather prediction (NWP) aspects of the tropical cyclone problem.

The focus of this study is the latter. In particular, a series of observing system simulation experiments (OSSEs) is conducted to gauge the impact of NIS data on tropical cyclone simulations performed with the University of Wisconsin Nonhydrostatic Modeling System (UW-NMS). Previous work by the authors has demonstrated the power of the Ensemble Kalman Filter (EnKF) in convective-scale data assimilation, and so the EnKF is the assimilation framework of choice. It is demonstrated that the type, density and frequency of observations anticipated to be provided by NIS can indeed be expected to result in significant improvement in tropical cyclone prediction. In particular, significant reduction in track, intensity and precipitation forecast errors are demonstrated.