Enthalpy Fluxes during Tropical Cyclones in the Caribbean Sea Relative to Ocean Variability

Several studies have shown the importance of sea-to-air latent and sensible heat flux as an energy source for tropical cyclones (TC) and their intensification. Recent studies show the important contribution of near-surface moisture disequilibrium to air-sea flux, which modulates boundary layer buoyancy, inducing fluctuations in storm intensity, independent of wind-induced air-sea flux. Additionally, moisture disequilibrium is observed to be correlated and collocated with deep, warm ocean features such as warm core eddies during TC rapid intensification (RI). Thus, these eddies provide a source of sustained moisture to the boundary that increases buoyancy and thus storm intensity. This hypothesis is being tested using global positioning systems sonde data for Ivan (2004), Emily (2005), Dean (2007), and Felix (2007) during their time over the Caribbean Sea basin.

The Caribbean Sea is home to large warm core eddies which propagate through the basin as part the complex ocean circulation. Each of these hurricanes encountered one of these eddies and attained category 4 or 5 status. Preliminary results show that the maximum momentum and enthalpy fluxes are collocated within the inner two radii of maximum winds (Rmax) for all different oceanic regimes during a nearly steady-state storm. However, it is found that moisture disequilibrium and latent heat flux structure are more similar to ocean heat content (OHC) when the storm is over areas of high OHC (> 80 kJcm^-2) for areas outside of 2 Rmax during steady intensification periods (non-RI). Furthermore, enthalpy fluxes over the entire storm are significantly greater over areas of high OHC (~150 kJcm^-2) compared to areas of relatively lower OHC (~60 kJcm^-2) for the same wind stress. The relationships between OHC, wind stress, and air-sea variables for all four hurricanes are quantified using a regression analysis. The slopes and regression coefficients are compared to assess the sensitivity of the air-sea variables to both OHC and wind stress variability. These coefficients are then used to form a relationship between different oceanic regimes and total enthalpy flux in non-dimensional space in an attempt to build a predictive capability.