Ensemble transform sensitivity and tropical cyclone targeted observation: An OSSE case study

Unmanned aerial system (UAS) for improving tropical cyclone track forecasts has been studied under the NOAA joint OSSE system. Due to the limited number of dropsondes, adaptive observation schemes have to be considered in these experiments in order to fully take advantages of this observation system. Among the existing adaptive observation schemes, we investigated ensemble transform (ET) methods and proposed a new ET based method for better performance in both computational efficiency and analysis quality. The prosposed ET-based sensitivity (ETS) method, which calculates the gradient of forecast error variance reduction to analysis error variance reduction, is proposed to specify regions for possible adaptive observations. The ETS method was applied in a UAS OSSE for calculating sensitivity regions for UAS dropsonde deployment. The impact of the adaptive dropsonde data assimilation on analyses and forecasts of a simulated hurricane will be presented