HR: 0800h
AN: A21C-0646    [Abstracts]
TI: Vortex Rossby Waves in Hurricanes Katrina and Rita (2005)
AU: * Judt, F
EM: fjudt@rsmas.miami.edu
AF: RSMAS/University of Miami, 4600 Rickenbacker Causeway, Miami, FL 33149, United States
AU: Chen, S S
EM: schen@orca.rsmas.miami.edu
AF: RSMAS/University of Miami, 4600 Rickenbacker Causeway, Miami, FL 33149, United States
AB: Radar observations in hurricanes reveal inner spiraling rainbands emanating from the eyewall and propagating outward. Theoretical analysis indicated that these inner bands are azimuthally and radially propagating vortex Rossby waves (VRW). The outward propagating waves convey PV from the inner core to outer regions and thus lead to PV redistribution within a hurricane. It has been hypothesized that the outward propogating VRWs may play a role in interacting with an existing secondary PV ring in the outer region of a hurricane, which could lead to a development of concentric eyewalls. However, the lack of simultaneous observations over the inner-core and rainband regions is a major difficulty in our understanding of the complex interaction. The importance of VRWs in hurricane intensity change remains to be a question. This study aims to address the question using high- resolution model (MM5) forecasts of Hurricanes Katrina and Rita during the Hurricane Rainbands and Intensity Change Experiment (RAINEX) in 2005. The two major hurricanes went through a similar rapid intensification over the Gulf of Mexico. Both RAINEX observations and model forecast fields showed that Rita developed a secondary eyewall and went through an eyewall replacement before landfall, whereas Katrina did not. We analyze the model output at 1.67 km grid-resolution with 12-min time intervals. Azimuthally and radially propagating VRWs were found in the PV, rainrate, and vertical velocity fields in both storms. In the case of Katrina, no secondary PV maximum exists due to the lack of highly circular rainbands. Thus the VRWs propagate outward smoothly over a relatively long distance. No VRW activity has been found beyond 80-100 km radius in Katrina. This result indicates that interaction between the VRWs and outer PV disturbance must take place within this region, otherwise no effect concerning the importance of VRW would occur. The stagnation radius depends on the background PV- gradient which itself can be changed by wave-redistributed PV. It is also a function of the azimuthal wavenumber. Higher wavenumbers generally propagate farther and are thus more likely to interact with outer PV disturbance in the first place. In contrast, Rita developed a PV ring in the outer rainband region. Detailed analysis of Rita is underway. The comparison between the two hurricanes may shed some lights on the interaction of VRWs and rainbands as well as its implication on hurricane intensity change.
DE: 3354 Precipitation (1854)
DE: 3355 Regional modeling
DE: 3374 Tropical meteorology
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting