NEXRAD in space and tropical cyclones: observations and impacts

In those regions of the world where they occur, tropical cyclones (TCs) represent an ever present threat to life and property. In the North Atlantic basin, where TCs receive the most intensive scrutiny, the past two decades have seen dramatic advances in the skill with which TC track is forecast. However, any corresponding improvement in intensity forecasting has remained elusive, this despite increasing sophistication and resolution of the underlying numerical guidance. While numerous factors figure in this discrepancy, the role played by inadequate representation of the TC in the model initial condition represents a major obstacle. To that end, a novel remote sensing technology has been proposed: Doppler RADAR in geostationary orbit. NEXRAD in space (NIS) would operate at 35-GHz and provide hourly coverage of a 5300-km disk on the earth's surface. Such a deployment would provide heretofore unimagined capability to observe the evolution of TCs from genesis to dissipation, and, via advanced data assimilation techniques, the potential for dramatically improving TC intensity forecasts in NWP models.

This study focuses first on demonstrating the type and frequency of observations capable of being delivered by NIS, namely reflectivity factor and Doppler radial velocity. The usefulness of these observations in estimating the current intensity of TCs will be illustrated and compared to currently available tools and methodologies used for this purpose.

The second part of the study examines the utility of NIS in the data assimilation context. In particular, the value-added impact of NIS relative to current conventional observations (RAOB, ACARS, satellite winds, dropsondes, etc.) will be examined using the University of Wisconsin Non-hydrostatic modeling system (UW-NMS) in concert with an ensemble Kalman filter (EnKF).