Impact of Soil Moisture Data Assimilation on the Numerical Simulation of Landfalling Hurricanes

Surface heat and moisture fluxes are important to the evolution of a tropical storm after its landfall. Soil moisture is one of the essential components that influence surface heating and moisture fluxes. In the previous sensitivity study by Zhang and Pu (2019), the impact of soil moisture on a pre-landfall numerical simulation of Tropical Storm Bill (2015) was investigated. It is found that increased soil moisture before storm’s landfall tends to produce a weaker storm after landfall and negatively impacts storm track simulation. Further diagnoses indicate that the increase in soil moisture inside the storm corresponds to a strengthened vertical mixing within the storm boundary layer, which is conducive to the decay of the storm and has negative impacts on storm evolution. In addition, surface diabatic heating effects over the storm environment are also found to be an important positive contribution to the storm evolution over land, but their impacts are not so substantial as boundary layer vertical mixing inside the storm. The overall results highlight the importance and uncertainty of soil moisture in numerical model simulations of landfalling hurricanes and their further evolution over land.

Those previous results and conclusions were further evaluated with a strongly coupled land-atmosphere data assimilation using NASA unified WRF (NU-WRF) and NCEP GSI data assimilation system. Soil moisture data derived from NAS SMAP and CYGNSS satellites were assimilated. Some new case studies with recent hurricanes (e.g., Hurricane Ida 2021) were performed. The new findings will be presented at the conference.