Transcript 080502Orlando_TropConf_TRMM_Hence.ppt

Three-Dimensional Precipitation Structure
of Tropical Cyclones
Deanna A. Hence and Robert A. Houze, Jr.
University of Washington
What is the typical
vertical structure of
these mesoscale
features?
Willoughby (1988)
AMS Hurricane and Tropical Meteorology Conference
May 2nd, 2008
Idealized vertical structures suggested
by past studies
Outer
rainband
Inner
rainband
Deep
Restricted
Inner
rainband
Deep
Outer
rainband
Objectives of this study
• Determine statistically the vertical
structures of the mesoscale precipitation
features of hurricanes
• Determine how these structures vary from
eyewall to inner rainband to outer rainband
regions
TRMM Precipitation Radar (PR)
• 13.8 GHz (2.17 cm)
radar
• 17º (from nadir)
scanning angle
• 215 km swath width
• 4.3 km horizontal
resolution
• 250 m vertical resolution
From NASA TRMM website
(http://trmm.gsfc.nasa.gov/)
Annuli and Quadrant Analysis
TRMM PR Reflectivity at 03:36 on 28 August 2005
28°N
dBZ
51
RF
27
Stor
m
26
45
39
m ot
RR
ion
33
27
25
21
15
LF
24
9
LR
90
89
88
87
86
85
3
84
83
82
81
80
79°W
• Center location, eye diameter and storm motion provided
in the National Hurricane Center (NHC) best track data
Primary Analysis Tools
Relative frequency of
occurrence
• Contoured Frequency by
Altitude Diagrams (CFADS,
Yuter and Houze 1995)
• NCAR Zebra software
Ordinary Deep Convection CFAD
Convective
component
Stratiform
component
Total
Vertical Structure Analysis with CFADS
• Analyze CFADs of all overpasses of
hurricanes that reached Category 4 or 5.
• Atlantic/Gulf of Mexico/Caribbean basin
storms from 1998-2007
• Determine how structures of eyewall,
rainbands, and outer bands vary with
radius and storm quadrant
CFADS by Annulus-Outer Region
• Resembles ordinary
buoyant convection
Outer Region
Annulus 5
– Broad distribution of
reflectivities below
melting level
– Bright band signature
– Relatively broad
distribution above
melting level reaching
to 11 km
CFADS by Annulus -- Rainband Region
• Strong brightband
signature
• Sharp dropoff of reflectivity
above melting level
reaching to just below 10
km
• But… Narrower distribution
of reflectivity below melting
level…not like ordinary
convection
• Looks more like an eyewall
CFAD
Rainbands
Annulus 3
CFADs by Annulus– Eyewall Region
• Relatively narrow but
intense distribution
below melting level
• Weak if any brightband
signature
• Mostly narrow & sharp
distribution above
melting level
• Outliers suggest
occasional intense
convective towers
reaching over 12 km
• Not like convective or
stratiform CFADs of
ordinary convection
Eyewall
Annulus 1
Eyewall CFADs by Quadrant —
All Overpasses
LF Quad 1
RF 4
Quad
Quad 1
Quad 2
Storm motion
LRQuad 2
Quad 4
Quad
RR 3
Quad 3
Rainbands CFADs by Quadrant —
All Overpasses
RF
Quad 1
Quad 4
LR
Quad 2
Storm motion
LF
RR
Quad 3
Conclusions
• Outer region CFADs
– convective-like distribution
• Rainband CFADs
– Vertically limited
– Narrow distribution
– CFADs similar in all quadrants
• Eyewall CFADs
– Deep
– Intense reflectivities
– Relatively narrow distribution with extreme outliers
– Right side stronger than left side
Ongoing and Future Work
• Continue expansion of database to all Atlantic
Basin hurricanes, and eventually to all basins
• Stratify overpasses based on intensity, track
speed, wind shear, sea surface temperature,
and other factors known to influence storm
structure and intensity
• Perform EOF analysis to objectively sort CFADs
• Use technique to analyze model simulations