NOAA/AOML/HRD's Hurricane Ensemble Data Assimilation System (HEDAS): A comparative analysis of a Hurricane Paloma (2008) case using simulated vs. real vortex-scale aircraft observations

The Hurricane Ensemble Data Assimilation System (HEDAS) was developed at the Hurricane Research Division (HRD) of NOAA, in conjunction with an experimental version of the Hurricane Weather and Research Forecast model (HWRFx) at nested 9/3-km horizontal resolution. The primary goal of this effort is to improve the initial representation of the hurricane vortex by utilizing high-resolution in-situ data collected during NOAA's Hurricane Field Program. HEDAS implements the “ensemble square root “ filter of Whitaker and Hamill (2002) using a 30-member ensemble, where the assimilation is performed on a 3-km nest that contains the hurricane vortex. As part of NOAA's Hurricane Forecast Improvement Program (HFIP), HEDAS will be run in a semi-operational mode for the first time during the 2010 Atlantic hurricane season and will assimilate airborne Doppler radar wind, dropwindsonde and flight level wind, temperature, pressure and relative humidity, and Stepped Frequency Microwave Radiometer (SFMR) surface wind observations as they become available. The results from the semi-operational implementation will be presented in another talk by Sellwood et al., at the 15-th Conference on Integrated Observing and Assimilation Systems for Atmosphere, Oceans, and Land Surface (IOAS-AOLS, AMS Annual Meeting, 2011). Meanwhile, Vukicevic et al. will focus on the vortex evolution in short-range forecasts initialized from HEDAS analyses for a case of Hurricane Bill 2009.

In this talk, we will present a detailed analysis of HEDAS' performance comparatively with simulated and real observations for a Hurricane Paloma (2008) case. Hurricane Paloma was a 2008 late-season major hurricane (7 November 00Z – 9 November 06Z) in the Western Caribbean Sea. Operationally, Paloma was well-observed at the vortex scale by the NOAA P-3 aircraft with 3 missions that sampled the rapid intensification period of 7-8 November. In the first half of the talk, results from experiments where aircraft observations simulated from a high-resolution (nested 4.5/1.5-km resolution) HWRFx nature run are assimilated into HEDAS are analyzed and the dynamical properties of the nature run and HEDAS short-range forecasts and analyses are compared during the cycling of observations. Then, these findings are compared to the performance of HEDAS when real P-3 observations from the 8 November 00Z flight mission are assimilated.