Impacts of Assimilating Airborne Tail Doppler Radar Observations using the GSI-based Hybrid Ensemble-Variational Data Assimilation System for HWRF to Improve Operational High-Resolution Tropical Cyclone Prediction

Tropical cyclones (TCs) are among the most costly forms of natural disaster. While steady progress has been made in improving TC track forecasts, difficulties still remain especially for intensity forecasts. Accurate intensity forecasts will require high-resolution models that can accurately simulate inner-core processes, and data assimilation systems that can make effective use of available observations that sample the TC core. High resolution airborne TC observations onboard reconnaissance aircrafts such as Tail Doppler radar (TDR) data have been collected for many years and provide value observations to sample the inner core of the TC. The primary goal of this study is to improve the effective utilization of these TDR data through using advanced data assimilation method to improve operational high resolution tropical cyclone forecasts.

Recently, a hybrid EnKF–variational data assimilation system was developed for HWRF based on the US National Weather Service operational data assimilation system, GSI. Experiments with the assimilation of TDR data have been conducted with a detailed study of hurricane Sandy (2012) and with cases during 2012-2014 hurricane seasons. Ingesting the radial velocity data from TDR onboard NOAA P-3 aircrafts properly, the hybrid system was able to correct both the wind and mass fields in a dynamically and thermodynamically coherent fashion compared to NoDA. Hybrid using self-consistent HWRF EnKF ensemble improved the track, minimum sea level pressure and Maximum wind forecasts relative to GSI-3DVar and the hybrid ingesting GFS ensemble. The impact of the TDR data was dependent on the data assimilation method. Among all the assimilation methods examined, the newly hybrid data assimilation system provided the largest positive impact of the TDR data for hurricane forecasts. In addition to the assimilation of TDR data, the HWRF hybrid data assimilation system was further developed to include storm following, continuous cycling capability using a new moving strategy, dual resolution data assimilation capability, and vortex relocation capability. This system will be run in near real time during the 2015 hurricane season. The findings of the impact of TDR data on the forecast of 2015 hurricanes will also be presented in the conference.