Observational and Modeling Study of
Hurricane Rainbands and Intensity Change
Shuyi S. Chen, Robert A. Houze
Bradley Smull, David Nolan, Wen-Chau Lee
Frank Marks, and Robert Rogers
RAINEX Planning Meeting, Miami, Florida, 15-17 November 2004
Science Objectives

Use airborne observations to examine
simultaneously the dynamic and thermodynamic
structures of hurricane inner core and outer
rainband regions where the positive potential
vorticity associated with deep convective cores
are located.

Use numerical model to investigate the
interactions of the rainbands and primary
hurricane vortex circulation and their role in
hurricane intensity change.
Schematic
Reflectivity Structure
(Hugh Willoughby)
Hurricane Floyd (1999)
12 Sep 2230-2300 UTC
13 Sep 2300-2330 UTC
Four characteristic tropical cyclone
rainband/eyewall structures
Factors Controlling Intensity Change

Inner core (eyewall) dynamics

Environmental conditions, including vertical wind
shear, moisture distribution, and sea surface
temperature (upper ocean heat content), etc.
Inner core
Rainbands
Environment
Evolution of a
single primary
eyewall (Kossin
et al. 2000)
Primary + Secondary Eyewalls (Kossin et al. 2000)
Hypothesis:
In the convective
rainband region
outside of the
hurricane inner core,
convectively induced
potential vorticity may
be “axisymmetrized”
by high wave number
Rossby waves.
MM5
Floyd (1999)
Hurricane Floyd (1999)
Floyd (1999)
Hurricane Floyd (1999)
Eyewall Replacement
TRMM TMI
NOAA/HRD&AOC Radar Composites in Hurricane Isabel (2003)
9/12/03 1700 UTC
9/13/03 1800 UTC
9/12/03 2000 UTC
9/14/03 1600 UTC
9/13/03 1600 UTC
9/14/03 2000 UTC
Isabel (2003)
Floyd (1999)
Isabel (2003)
Floyd (1999)
Environment
• Vertical wind shear
• Moisture distribution
Rainbands
Inner Core
Chen&Desflots (UM/RSMAS)
Intensity
(a) pressure
(b) wind speed
NOAA/HRD&AOC Radar Composites in Hurricane Lili (2002)
10/02
0600
10/02
0900
10/02
1700
10/02
1800
10/02
1900
10/03
1500
Chen&Desflots (UM/RSMAS)
Chen&Desflots (UM/RSMAS)
Eyewall Evolution in Lili (2002)
pressure
Mean RH Profiles
Derek and Chen (2004):
NOAA/G-IV GPS dropsondes (49
flights and 1002 dropsondes, mostly
taken in the TC environment outside
of 300 km radius from TC centers)
Rainfall
Dry simulation
Control run
Moist simulation
Summary
• TC inner core PV structure seems to have a significant
influence on the evolution of rainbands and eyewall
replacements.
• Environmental moisture distribution and vertical wind shear
affect TC inner core (and intensity) through rainbands in
some cases.
• Future high-resolution hurricane prediction models (e.g.,
HWRF) must be able to resolve the rainbands and inner core
as well as their interactions correctly.
RAINEX will provide the 1st high-res 3-D wind data covering
simultaneously both outer rainbands and inner core regions to
validate/evaluate the model results and, ultimately, improve the
TC intensity forecast.