AMS Hurricane

and Tropical Meteorology Conference

Tucson

May 9, 2010

Vertical distribution of radar reflectivity in eyewalls observed by TRMM

Deanna A. Hence and Robert A. Houze, Jr.University of Washington

Idealized vertical structures suggested by past studies

Inner rainband

Outer rainband

Outer rainband

Inner rainband

DeepDeep Restricted

From Houze et al. (2007)

How does the eyewall structure change with storm evolution and environmental

conditions?

Primary Analysis Tools

• TRMM Precipitation Radar (PR)

• NCAR Zebra software

• Contoured Frequency by Altitude Diagrams (CFADs)

Yuter and Houze 1995, Houze et al. 2007 R

ela

tiv

e f

req

ue

nc

y o

f o

cc

urr

en

ce

Fro

m N

AS

A T

RM

M w

eb

site

(http

://trmm

.gsfc.n

asa

.go

v/)

Annuli and Quadrant Analysis

Re

flectivity (d

BZ

)

TRMM PR Maximum Reflectivity at 03:26 on 28 August 2005

She

ar

Vec

tor

DLDL

ULUL

URUR

DRDR

From the National Hurricane Center (NHC) best track data

• Center location

• Eye diameter

• Storm motion

Raw Number CFADs, Not Normalized, All Overpasses

URUL

DL DR

peak of low-level distribution 120

60

10

Track

She

ar

How shear affects the eyewall

shear

From Black et al. (2002) From Braun et al. (2006)

Updrafts initiating just upwind of the downshear-left quadrant

shear

ULUL DLDL

URUR DRDR

ULUL

DLDL

DRDR

URUR

Vertical structure in weaker and stronger storms

• Greater reflectivity overall• More extreme outliers

intermittent intense cells

CAT4,5CAT1,2

Total Eyewall Annulus, Normalized

• Majority of distribution similar

High SST (>28 °C)

Vertical structure over cooler and warmer water

• Outliers much stronger and higher in high SST cases

Marginal SST (26-28 °C)

Total Eyewall Annulus, Normalized

Vertical structure by quadrant relative to shear

Brightband appears

Weaker overall, no distinct peak

No brightband, broad upper levels

Normalized CFADs, All Overpasses

Track

She

ar

1.0

0.5

0.2Brightband intensifies

DLDL

ULUL URUR

DRDR

Normalized CFADs, High SST

Tighter DistributionDLDL

WeakeningULUL StrengtheningURURT

rack

She

ar

WeakeningDRDR

1.0

0.5

0.2

More distinct brightband

• Vertical wind shear • Determines echo placement around the eyewall

• Cat. 4 and 5 storms • More intense• More intermittent intense cells

• Lower SST values • Suppress intense outliers• Doesn’t change the mean reflectivity distribution

• Track motion ≥ shear, opposite in direction• echo formation region shifts upshear right

Conclusions

Ongoing Work

• Expand analyses to rainband and outer regions

• Expand analyses to intense cyclones in worldwide basins

Normalized CFADs, High SST

Tighter DistributionDL

WeakeningUL StrengtheningURT

rack

She

ar

WeakeningDR

1.0

0.5

0.2

More distinct brightband

Normalized CFADs, Low Shear

Tra

ck

Narrowing of upper levels

She

ar

1.0

0.5

0.2

Tighter DistributionDL

WeakeningUL StrengtheningUR

DR

More distinct brightband

This research was supported byNSF Grant ATM-0743180 and NASA Grants NNX07AD59G and NNX10AH70G