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