Some Ideas on Hurricane Katrina’s Wind Expansion · • Convergence of RAM gave a possible...

Some Ideas on Hurricane Katrina’sWind Expansion

Pat Fitzpatrick, Chris Hill, Yongzuo Li, Nam Tran, Yee LauGeoResources Institute

Mississippi State UniversityStennis Space Center branch

Qingnong XiaoNCAR

Boulder, CO

Radius tropical storm-force winds

100

150

200

250

300

350

400

Rad

ius

(km

) East

North

West

South

26.5 27.0 27.5 28.0 28.5

Land effect from FloridaNorth, west, east side increasedbetween 70-100 km in first 6 h. Doubledin size by the 28th.

I. Some mechanisms forstorm size growth

Angular momentum budget

( )

C B A

12

2

rFrfururv

rtM

frrvM

rrt

t

+−∂

∂−=∂∂

+=

A – convergence of RAMB – Coriolis torqueC – friction torque

Vortex merger ideas(Lander, Holland, Dietachmayer 1993, 1994)

Ritchie and Elsberry 2000Kuo, Chen, and Lin 2000

Oct 10, 00Z

Oct 11, 00Z

Oct 12, 12Z

II. Wind and satelliteobservations

26 Aug 2005 00 UTC

27 Aug 2005 12 UTC 28 Aug 2005 00 UTC

26 Aug 2005 12 UTC 27 Aug 2005 00 UTC

28 Aug 2005 12 UTC

6-hourly multi-satellite blended sea winds source: http://www.ncdc.noaa.gov/oa/rsad/blendedseawinds.html

L

NAM analysis

L

August 26, 08Z

August 26, 11Z

August 26, 14Z

August 26, 17Z

August 26, 20Z

August 26, 23Z

August 27, 02Z

August 27, 04Z

August 27, 07Z

August 27, 10Z

August 27, 12Z

August 27, 15Z

August 27, 18Z

August 27, 21Z

August 28, 00Z

August 28, 03Z

August 28, 07Z

Angular momentum budget by quadrant using RUC data, r=460 km------- Convergence RAM------- Coriolis torque------- Friction torque

8/27 8/28 8/29 8/27 8/28 8/29

8/22/05 8/28/05

8/30/05

8/28/05

8/31/058/28/05

Interaction with loop current

III. Very TentativeConclusions

• Convergence of RAM gave a possible kickstart onAugust 27th• Coriolis torque provided continuous angularmomentum throughout the period• Overall, it appears two low-level jets, in combinationwith loop current interaction, contributed to thewind expansion• A barotropic model simulation (not shown) showsInteraction with these jets, especially on the north side• Some kind of merger process may have contributedto wind field expansion

Future plans include WRF modeling withsensitivity runs to test some of these ideas