Impacts of Model Physical Parameters at the Air-Sea Interface on the Background Ensemble of HAFS-MOM6 EnVar Data Assimilation for Hurricane Fiona (2022)

As a first step to achieve the fully coupled ocean-atmosphere data assimilation (DA) system for the Hurricane Analysis and Forecast System (HAFS) and Modular Ocean Model version 6 (MOM6), the current study aims to improve the background ensemble quality at the air-sea interface by examining physical parameters associated with the air-sea interaction. The experiments are conducted for Hurricane Fiona (2022) with the self-cycled EnVar DA system for HAFS. The impacts of model physical parameters at the air-sea interface on the background ensemble are examined using novel observations for both the ocean and atmosphere, such as saildrone observations, Dropsondes, Airborne Expendable Bathy-Thermograph (AXBT) probes, and Stepped Frequency Microwave Radiometer (SFMR) winds. The baseline experiment is equipped with the default settings for the physical parameters. Initial results for the 6-h background of the control member show that HAFS-MOM6 has cold biases in the temperature, dry biases in the specific humidity, and underestimation of the surface wind speed. Experiments to test the sensitivity of the background ensemble to the physical parameters at the air-sea interface are being conducted and will be presented at the conference.