some ideas on hurricane katrina’s wind expansion · • convergence of ram gave a possible...
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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