Kinematic and Thermodynamic Structure of Hurricane Isabel (2003) Michael M. Bell Michael T. Montgomery NCAR/Colorado State University Michael L. Black Sim D. Aberson NOAA/AOML/Hurricane Research Division This research was supported by ONR Grant N 00014 -02 -1 -0474 and NSF Grant NSF-ATM-0132006.
Introduction ● ● Hurricane Isabel was at or near Category 5 intensity on the Saffir-Simpson scale from September 11 – 14 th, 2003 A comprehensive dataset was obtained as part of the ONR sponsored CBLAST Experiment. – ● NCAR GPS Dropwindsondes, Doppler Radar, in situ flight level data, and more Isabel's structure suggests it could be “superintense” as described by Persing & Montgomery (2003)
Hurricane Maximum Potential Intensity (MPI) ● What intensity can a hurricane attain for a given set of environmental conditions? – – ● Sea Surface Temperature Relative Humidity Outflow Temperature CAPE? Miller (1958) and Holland (1997) – – ● ● CAPE Dependent Moist Neutral, Carnot Engine – Carnot ‘turbocharger’ Emanuel (1986), Rotunno & Emanuel (1987) Persing and Montgomery (2003)
MPI and Superintensity
Storm Relative Dropsonde and Flight-level Trajectories 85 dropsondes & 3 aircraft tracks QCed and composited relative to moving storm center ●
Mean Kinematic and Thermodynamic Structure
Perturbation Pressure
12 th 13 th 14 th
Mean Boundary Layer Structure
Sea Surface Temperature
Outflow Temperature
“Superintense” Isabel? ● MPI theory predicts mean Vmax of < 56 m/s, but observations estimate intensity at 76 m/s • The estimated range of the bulk transfer coefficient ratio from 0. 5 to 1. 0 changes the E-MPI intensity prediction by 30 knots. • Additional effects of dissipational heating and ocean cooling are assumed to offset
Summary ● Kinematic structure – – ● Thermodynamic structure – – ● Axisymmetric tangential intensity at the top of the BL on the 13 th was likely 76 m s-1 or greater. Intense, shallow inflow penetration into eye region. Reservoir of high e air inside eye Indications of eye/eyewall mixing Observed structure and intensity 20 m s-1 above MPI predictions and suggest that Isabel was superintense, but uncertainty in the bulk transfer coefficients gives varying degrees of superintensity.
Consequences My parent’s house after Jeanne (2004)
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