Invited Speaker: Numerical modeling of air-sea interaction in tropical cyclones

We will discuss the progress in developing coupled tropical cyclone-wave-ocean models for operational implementations at NOAA and Navy. The key element of our coupled modeling approach is the air-sea interface model (ASIM) developed by the URI research group that consists of the wave boundary layer model and the air-sea heat and momentum flux budget model. The ASIM is embedded into the TC-wave-ocean coupled model and calculates all the flux boundary conditions for the atmospheric, wave and ocean models.

As part of the coupled model development we evaluated the performance of the NOAA's operational WAVEWATCH III under a very strong tropical cyclone wind forcing. We compared the model results with field observations of the surface wave spectra from a scanning radar altimeter, NDBC time series and satellite altimeter measurements in Hurricane Ivan (2004). The results suggest that the operational model tends to overestimate the significant wave height and the dominant wave length, and produces a wave spectrum that is higher in wave energy and narrower in directional spreading. When an improved drag parameterization is introduced and the wave-current interaction is included, the model yields improved forecast of significant wave height and wave spectral energy, but underestimates the dominant wave length.

We will discuss the results of numerical simulations of the hurricane-ocean in the vicinity of a warm core eddy, also known as a warm core ring (WCR). The anticyclonic circulation around a WCR, may impact hurricane intensity by advecting the sea surface temperature towards or away from the storm core. Here, a coupled hurricane-ocean model is used to investigate the change in hurricane intensity when a warm ocean eddy is located to the left, right, and center of the storm track. Numerical simulations are performed using a one and three-dimensional version of the ocean model component, only the latter of which accounts for advection. The results indicate the location of the warm ocean eddy relative to the storm track impacts both the storm-core sea surface temperature and hurricane intensity. These simulations also provide evidence for the importance of horizontal advection due to the WCR's anticyclonic circulation when the WCR is located to the left or right of the storm track.