Investigation of the Role of the Ocean Component in HWRF

The role of the ocean in hurricane intensity has been long recognized. To this date, in hurricane numerical modeling, however, only a few including GFDL(Geophysical Fluid Dynamics Laboratory) and HWRF (Hurricane Weather Research and Forecast) models are fully coupled to the ocean model. A recent report on coupled GFDL hurricane model (Bender et al., 2007) presents promising improvements of the hurricane intensity forecast skills over its non-coupled version. Similar to the GFDL, HWRF model runs are coupled for the Atlantic basin. However, HWRF runs are un-coupled for the Eastern Pacific basin, using the same values of air-sea flux parameters employed for the Atlantic basin. In this work, we conduct investigations on the pertinence of the surface physics parameterization. This would result in better understanding of parameterization of the flux transfer in the one and two-way feedback environments, and, eventually, its relationship to hurricane intensity. HWRF offers a choice of ocean models –HYCOM (HYbrid Coordinate Ocean Model) and POM (Princeton Ocean Model), providing advantage to examine sensitivity of the flux exchange to the ocean. Preliminary analyses show that non-coupled HWRF resulted in larger positive bias in intensity compared to its counterpart, suggesting that the adjustment of the air-sea exchange coefficients for heat and momentum is necessary in order to account for the feedback due to the ocean. Also shown are differences in the forecast intensity produced by the two ocean models for the same parameter values. We present results of further analysis, which include the physical processes governing the flux transfer and the state of ocean and atmosphere in and around the air-sea interface.