Cyclone Fences around Humberto (2001)

The deployment of 200 Global Positioning System dropwindsondes (GPS sondes) over three consecutive days in Tropical Cyclone Humberto (2001) allows for the creation of azimuth-height (Φ-z) surfaces (aka cyclone fences) from sea-level to 3 km altitude at .25° and .5° latitude distance from the storm center. We estimate the radial flow and  equivalent potential temperature (θe) along these Φ-z  surfaces to diagnose the mass and energy fluxes through said surfaces (cyclone fences) as Humberto deepens from 1000 hPa to 983 hPa, then fills to 992 hPa by the third day.

As the TC intensifies the width, depth and rate of inflow increase. The inflow remains a wave number one pattern throughout the 3 days and rotates clockwise following the tropical cyclone motion and deep layer shear vectors. Net vertical mass and energy flux, based on continuity within a given volume, is correlated with TC intensity changes only for the inner .25° Φ-z surface. At subtly larger scales, only 50-60 km in radial distance from the circulation center, large values of net vertical mass and or energy flux, associated with rainbands, do not result in a lower central surface pressure. The θe along the .25° Φ-z surface and changes in θe from the outer to the inner Φ-z  surface lead intensity change by as much as a day. This behavior supports our conjecture that the energy content of the boundary layer builds in the eye, is exhausted, and then recovers, leading the observed intensity variations by many hours. The net mass and energy flux for the innermost volume is indicative of current TC intensity while θe along the innermost Φ-z surface has the possibility of being useful for forecasting intensity.