Vorticity and entropy budgets of tropical cyclones during IFEX 2005

We use dropsondes from NOAA P-3 and G-IV aircraft to estimate the

tendencies of circulation and moist entropy in developing and mature

tropical cyclones observed during the IFEX 2005 project. The

circulation around a system equals the area integral of vorticity

inside the circulation loop. The boundary layer circulation is

increased by the convergence of environmental vorticity and decreased

by surface friction. The former is estimated as the product of the

mass convergence obtained from the dropsonde data and the ambient

planetary vorticity while the latter is estimated by assuming that

surface stress is distributed uniformly through the planetary boundary

layer. The entropy flow through the lateral boundaries is

characterized as the sum of a part associated with the mass

convergence-divergence couplet and a part due to the ventilation of

the system by the ambient wind blowing relative to the moving cyclone.

The former contribution can only be computed from dropsondes deployed

from high altitude by the G-IV. However since the most important

ventilation is likely to occur in the low to middle troposphere, the

P-3 dropsondes (typically deployed from about 600 hPa) are useful in

computing the ventilation term. We will discuss results from storms

well-observed during IFEX, such as Dennis, as well as others for which

ample observations were made during the extraordinary summer of 2005.