Sensitivity of tropical cyclone potential intensity to observed near-surface conditions

Open Access
- Author:
- Kowaleski, Alexander Michael
- Graduate Program:
- Meteorology
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- May 24, 2013
- Committee Members:
- Jenni Evans, Thesis Advisor/Co-Advisor
Michael Mann, Thesis Advisor/Co-Advisor
Ken Davis, Thesis Advisor/Co-Advisor - Keywords:
- hurricane
cyclone
entropy
flux
potential intensity - Abstract:
- Observed tropical cyclone (TC) thermodynamic variables including temperature, humidity, moist enthalpy, and specific entropy are obtained from buoy, C-MAN, and dropsonde data from 42 Atlantic hurricanes. Ocean-air energy fluxes are calculated for 31 hurricanes in the dataset for which SST data are available. Profiles constructed with these data are compared to the theoretical boundary layer profiles of Emanuel Potential Intensity (EPI) theory. It is determined that the boundary layer is not isothermal as in the idealized EPI profile, but decreases in temperature with decreasing radius between the environment and TC core. Also, in the composite TC profile, entropy increases more rapidly inside 2.5 times the radius of maximum winds (Rmax) than pressure decreases alone can account for. This indicates that ocean-air fluxes outside of Rmax can play a substantial role in TC entropy input. It is also determined that the scheme used in calculating spray fluxes impacts the total ocean-air turbulent energy flux, and has an even greater impact on the distribution between latent and sensible energy fluxes. In the second section of the study, the effects of environmental conditions and conditions in the storm on potential intensity (PI) are studied. Lower temperature and moisture in the unsaturated boundary layer at Rmax increases PI as measured by maximum sustained winds (Vmax). This occurs because lower temperature and moisture at Rmax allow greater entropy input into the TC at Rmax due to greater ocean-air temperature and moisture disequilibria. The PI increases from using observationally-derived profiles can be as great as 10 ms-1. This suggests that conditions within the TC are of comparable importance to environmental conditions in determining PI. It also suggests that Vmax may be higher than EPI theory currently predicts using its idealized boundary layer profiles. A further observation is that sufficiently dense observations of TC near-surface conditions may allow more accurate real-time PI calculations.