65th IHC Booklet/Program (pdf - 4.9MB) - Office of the Federal ...

On the Characteristic Height Scales of the Hurricane Boundary Layer: Dropsonde
Composite Analysis for the Purpose of Model Diagnostics
Jun Zhang 1 Robert Rogers 2 , David Nolan 3 , Frank Marks 2
(Jun.Zhang@noaa.gov)
1 UM/CIMAS & NOAA/HRD, 2 (NOAA/HRD), 3 UM/RSMAS
In this talk, we present composite analysis results using hundreds of GPS dropsonde data from
13 hurricanes. We focus on the investigation of the characteristic height scales of the hurricane
boundary layer. The height scales are defined in a variety of ways: the height of the maximum
total wind speed, the inflow layer depth, and the mixed layer depth. The height of the maximum
wind speed and the inflow layer depth are referred to as the dynamical boundary layer heights,
while the mixed layer depth is referred to as the thermodynamical boundary layer height. The
data analyses show that there is a clear separation of the thermodynamical and dynamical
boundary layer heights. Consistent with previous studies on the boundary layer structure in
individual storms, the dynamical boundary layer height is found to decrease with decreasing
radius to the storm center. The thermodynamic boundary layer height, which is much shallower
than the dynamical boundary layer height, is also found to decrease with decreasing radius to the
storm center. The results also suggest that using the traditional critical Richardson number
method to determine the boundary layer height may not accurately reproduce the height scale of
the hurricane boundary layer. These different height scales reveal the complexity of the hurricane
boundary layer structure that should be captured in hurricane model simulations. Methodology
and preliminary results of using the dropsonde composites to evaluate the PBL scheme used in
the Hurricane Weather Research and Forecast (HWRF) model are discussed.
Session 7 – Page 8