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February 5th, 20082008 TRMM Conference
The 3-D Reflectivity Structure of Intense Atlantic Hurricanes as seen by the TRMM PR
Deanna Hence, Robert Houze and Stacy Brodzik
University of Washington
February 5th, 20082008 TRMM Conference
Objectives of the Study
• To develop a three-dimensional climatology of precipitation structures within tropical cyclones
• To characterize the dynamics of the rainbands—are they more like ordinary convection or eyewall convection?
February 5th, 20082008 TRMM Conference
Statistics of Precipitation Structure• Suggest higher
reflectivities aloft in eyewall and outer rainband region
• More intense brightband signature in inner rainband region
• Contoured Frequency by Altitude Diagrams (CFADS, Yuter and Houze 1995)
• Show frequency of occurrence of reflectivity values as a function of height
• Distinguishes precipitation type and vertical structure
Yuter and Houze (1995)
Cecil et al. (2002)
February 5th, 20082008 TRMM Conference
Annuli and Quadrant Definition
• Based on eye diameter
• Ring 1 = Reye + 17 km • Ring 2 = 2R1• Ring 3 = 3R1• Ring 4 = 4R1• Quadrants counted
counterclockwise from storm track vector
180.4Distance (km)
TRMM PR Vertical Slice
12
4
8
16
Hei
gh
t (k
m)
00.0 45.1 90.2 135.3
48.6
43.2
37.8
32.4
27.0
21.6
16.2
10.8
5.4
dBZ
eye
TRMM PR Reflectivity at 03:36 on 28 August 2005
79°W
51
45
39
33
27
21
dBZ
15
9
3
808190 89 88 87 86 85 84 83 82
3
2
25
241
4
28°N
26
27Storm motion
February 5th, 20082008 TRMM Conference
TCSP and RAINEX
• Initial study includes Hurricanes Dennis, Emily, Katrina, and Rita of 2005
• Analysis of overpasses when storms are hurricane strength
• Quadrant analysis revealed lack of consistent asymmetry
February 5th, 20082008 TRMM Conference
Outer Region
• Broad distribution of reflectivities below melting level
• Bright band signature• Relatively broad
distribution above melting level reaching to 11 km
• Resembles ordinary buoyant convection
Annulus 5
February 5th, 20082008 TRMM Conference
Middle Region
• Narrower distribution of reflectivity below melting level
• Strong brightband signature
• Sharp dropoff of reflectivity above melting level reaching to just below 10 km
• Looks more like an eyewall CFAD
Annulus 3
February 5th, 20082008 TRMM Conference
Eyewall
• Relatively narrow but intense distribution below melting level
• Weak brightband signature
• Mostly narrow distribution above melting level
• Outliers suggest occasional intense convective towers reaching over 12 km
Annulus 1
February 5th, 20082008 TRMM Conference
Annulus 1 Annulus 3Annulus
5
Initial Conclusions• Outer region has distinct ordinary convective signature with
some stratiform• Middle region rainbands have structure more similar to
eyewall than to ordinary convection• Eyewall CFAD is not like that of classic stratiform or
convective precipitation- it is intense, deep, AND uniform• Eyewall has intermittent deep convective elements• No distinctive quadrant asymmetry, but will further test with
larger dataset
February 5th, 20082008 TRMM Conference
Further Data
• First expansion is into the overpasses of all hurricanes between 1997-2007 that reach Category 4 and 5 intensity
• Overpasses are stratified into when the storm is Cat 1 or 2 and when Cat 3, 4, and 5
• Category 5 overpasses are also looked at separately
February 5th, 20082008 TRMM Conference
Further Data
• Generally consistent with the four 2005 storms, but differences between annuli are less when weaker storms are included.
• Eyewall distribution is broader when weaker storms are included
Annulus 1 Annulus 3 Annulus 5
February 5th, 20082008 TRMM Conference
Future work
• Continue expansion of database to all Atlantic Basin hurricanes, and eventually to all basins
• Stratify overpasses based on track speed, wind shear, and other factors known to influence storm structure and intensity
• Develop method of quantitatively sorting CFADs