INNER CORE STRUCTURE AND INTENSITY CHANGE IN HURRICANE ISABEL (2003) Shuyi S. Chen and Peter J. Kozich RSMAS/University of Miami J. Gamache, P. Dodge, F. Marks NOAA/AOML/HRD 27 th AMS Tropical & Hurricane Conference, April 23-28, 2006, Monterey, CA.

12-14 Sept 2003 LF Radar Reflectivity (dBZ) Composite from NOAA-42 RF 9/ UTC9/ UTC9/ UTC 9/ UTC9/ UTC9/ UTC

What has been observed in Isabel? significant inner core structure changes concentric eyewalls mesovortices in the eye What role do they play in Isabel’s intensity and intensity change?

Model and Data PSU-NCAR MM5 (nested domains with 45,15,5, and 1.67 km grid resolution, 28 sigma levels, Chen and Tenerelli 2006) NCEP global analysis fields as initial and lateral B.C. Vortex relocation scheme (Liu et al 1997) NOAA/HRD airborne Doppler radar, flight-level, and GPS dropsonde data 45km

Isabel Tracks, from Best Track and MM5 Investigation focuses on time frame between arrows; observation and model times are different

Intensity (minimum SLP) Investigation focuses on time frame between arrows

Idealized barotropic model (Schubert et al. 1999, Kossin et al. 2000) (Kossin et al. 2000) Evolution of a single primary eyewall Evolution of primary + secondary eyewalls

Hovmoller Diagrams of Azimuthal Averaged MM5 Rainrate and Tangential Windspeed at 2km Level 14 th 13 th 12 th

9/12 9/13 9/14 Radar MM5 Observed and Model Simulated Tangential Wind Speed (ms -1 ) at 1-km level

9/ Azimuthally Averaged Reflectivity Radar MM5

Flight Level Wind (Blue) and MM5 Wind (Red) at 2km level 9/ mean

9/12 9/13 9/14 Radar MM5 Relative Vorticity (x s -1 ) at 1-km level

Potential Vorticity at 1-km Level 0600 Z 9/ Z 1800 Z 0000Z 9/ Z 1200 Z 1800 Z 0000Z 9/ Z 1200 Z 1800 Z 0000Z 9/14

Inertial Stability Analysis Hack and Schubert (1986): IS = [(f + 2V/r)(f +  )] 1/2 = [(f + 2V/r)(f + V/r +  V /  r)] 1/2

Intensifying storm Highest flight-level winds with a sharp bell-shaped profile High inertial stability (IS) inside of the eyewall Strong eyewall updrafts and convection Secondary wind max 9/12/03 IS V(r) RMW

9/13/03 Eyewall replacement Less sharp bell-shaped wind profile Lowered inertial stability (IS) inside of the eyewall Weakened eyewall updrafts and convection RMW

9/14/03 Weakened storm Linear-shaped wind profile Lower inertial stability (IS) Weak and broad eyewall updrafts and convection RMW

MM5 T (color - upper panels), T d (contour) and  e (color - lower panels) 9/ Mixing of the eye and eyewall

Conclusions Intensification is associated with storm’s ability to maintain strong eyewall convection, sharp bell- shaped wind profile and high inertial stability inside of the eyewall (i.e., eyewall contraction). Formation of secondary eyewall and eyewall replacement weaken the convection in the primary eyewall. Mixing of the eye and eyewall by vortex Rossby waves (mesovorties) contributed to the collapse of the inner eyewall and weakening of Isabel (before the vertical wind shear increased on 9/15/03).