Tropical Cyclone Structure and Dynamics Based on Data from the Hurricane Rainband and Intensity Experiment (RAINEX)

University Of Washington, Seattle WA

Investigators

Abstract

The Hurricane Rainband and Intensity Change Experiment (RAINEX) documented the 2005 Hurricanes Katrina, Ophelia and Rita. In conjunction with NOAA's Intensity Forecasting Experiment, RAINEX was the first hurricane project to 1) combine the use of three Doppler radar-equipped aircraft, 2) use the high-definition NSF Electra Doppler Radar (ELDORA) in hurricanes, and 3) use real-time ground-based flight coordination to optimize the placement of aircraft within the storms. RAINEX also deployed dropsondes (released at 5 min intervals on each Doppler flight leg) and was guided by the use of real-time high-resolution numerical forecasts. RAINEX was unusually successful in that it documented some of the most interesting hurricanes in the history of the U.S. and the data set was of extremely high quality. This research will exploit the RAINEX data in studies aimed at understanding tropical cyclone phenomenology in relation to hurricane intensity changes. The ELDORA data and dropsondes will be analyzed to: 1) Document details of evolving storm structure during the eyewall replacement cycle of Rita; in particular, the relationship of convective-scale circulation anomalies to the developing wind maximum in the secondary eyewall and differences between the secondary and primary (inner) eyewalls. 2) Document and interpret the principal rainbands in Katrina and Rita when each storm was at Category 5 intensity. 3) Synthesize the circulation within a convective burst leading to the development of Hurricane Ophelia. The possible contribution of the extremely deep, wide, and persistent updraft in the burst to cyclogenesis will be evaluated. 4) Analyze the influx of dry air into the rainbands of Hurricane Ophelia to determine if the dry air intrusion takes the form of a mesoscale unsaturated downdraft. 5) Analyze how the pattern of small-scale structures observed by ELDORA changed as Rita came under the influence of large-scale shear. 6) Compare the convective structures of outer rainbands in all three storms to interior rainbands that are more strongly affected by the primary vortex. The analysis of ELDORA and dropsonde data in the above studies will include determination of the three dimensional (3D) latent heating structures associated with the slantwise convection of eyewalls, the discrete convective cells of rainbands and within a secondary eyewall, the stratiform regions of rainbands, and the ordinary convection of far outer rainbands. From these calculations, the implications of the 3D latent heating pattern to the storm circulation structure and associated rainband and eyewall dynamics will be inferred. This study will include collaborative efforts to assimilate RAINEX Doppler radar and dropsonde analyses into numerical forecasts and ultimately to transfer RAINEX experience to operational forecast centers. Intellectual merit: The study builds on the PI's previously established expertise in the dynamics and physics of tropical convection, tropical cyclones, and other types of atmospheric clouds and precipitation systems. Results will provide valuable new information to increase basic understanding related to prediction of hurricane intensity changes. Broader impacts: This study will contribute to the societal goal of improving predictions of hurricanes and associated extreme wind, coastal storm surge and flash flood events that have a devastating impact on life and property in coastal regions.