Impacts of Airborne Doppler Radar Data Assimilation on Hurricane using WRF-Var

Most available satellite data over the hurricane inner-core region are unfortunately contaminated by heavy precipitation and thus produce unreliable initial fields for the region. However, the airborne Doppler radar observations can properly resolve these inner-core features. The data distributed in the hurricane eye region with a very high spatial resolution: 2-km in horizontal and 0.5-km in vertical respectively. Both the wind and reflectivity are available. It makes the detailed inner wind and moisture structure of hurricane can be represented by airborne Doppler radar observation. Using the newly developed Advanced Research WRF (ARW) and its variational data assimilation system (WRF-Var), this study demonstrate that the assimilation of airborne Doppler radar measurements can enhance the definition of hurricane inner core structures. The forecast skill of the storm's intensity and structure are therefore improved with the initialization using Airborne Doppler radar data.

The airborne Doppler radar data from NOAA P-3s are provided by HRD. We made three cases to evaluate the impact of the airborne radar data on the hurricane. They are hurricane Jeanne (2004), Katrina (2005) and Rita (2005). The radar winds and/or reflectivity are assimilated into the hurricane initializations, and compared with GFS analysis. Numerical forecasts are conducted on two-way nested, 3 domains with resolutions of 12, 4 and 1.333-km. The airborne Doppler radar data assimilation are performed on Domain 2 (4 km resolution) and Domain 3 (1.33 km resolution), while only conventional data are assimilated in Domain 1 (12 km resolution).

The significance of our experimental results is that the forecast of storm intensity is significantly improved with airborne Doppler radar data assimilation using WRF variational (WRF-Var) data assimilation system. The encouraging impact on these three cases prove airborne Doppler radar data assimilation has great potential in our research to explore the hurricane structure, intensity and intensity change.