Thermodynamic and Flux Observations of the Tropical Cyclone Surface Layer

Observed tropical cyclone (TC) near-surface pressure, temperature, and dew point temperature are obtained from buoy, C-MAN, and dropsonde observations of 42 Atlantic hurricane events; specific humidity, relative humidity, and specific entropy are calculated from these data. Radial profiles of the observed and derived variables are expressed in terms of radius and in terms of multiples of RMAX (radius of maximum winds). Composite profiles are created from the 42 TC events and are compared to the results from a previous observational study (Cione et al. 2000; hereafter CBH00) and to the idealized profiles assumed in the Potential Intensity Theory (EPI) of Emanuel (1986, 1988, 1995).

Observed radial profiles of the thermodynamic variables are found to be in substantial agreement with CBH00 and to deviate markedly from many aspects of the EPI idealized boundary layer. Further, the results analyzed here provide new insights into the temperature, moisture, and surface flux variations in the TC inner core that were not available to CBH00.

Finally, surface flux budgets are calculated based on the observed boundary layer characteristics. To complete these budgets, it is necessary to include spray calculations. Two published spray models are examined and a third model, developed from aspects of the original two, is also tested. Intercomparison of these three budgets highlights a substantial sensitivity of the flux budget to the spray treatment; this sensitivity is particularly evident in the Bowen Ratio of fluxes.