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.
This project has used aircraft and satellite measurements to improve knowledge of hurricanes. Project RAINEX collected data with a very special high resolution radar (called ELDORA) in Hurricanes Katrina, Rita, and Ophelia in 2005. The data collected in these storms, which included the historic storm Katrina, have led to better understanding of how intense "convective bursts" can lead to the initiation of a hurricane. The radar data collected in RAINEX further has shown the detailed air motions that occur inside the eyewall of a hurricane, how a new eyewall forms around an older dying eyewall. The RAINEX data further show how intense up and downdrafts occur in the spiral rainbands outside the main eyewall, and how air moves along and across the rainbands in ways that can affect the intensity of the hurricane. The general representativeness of the RAINEX results were determined by examining over 10 years of data collected by the precipitation radar aboard the TRMM satellite and by the Doppler radars collected in hurricanes investigated by NOAA P3 aircraft. It was found the convective clouds in eyewalls and rainbands bear a systematic relationship to the environmental wind shear, with clouds forming downshear right, maturing downshear left, and weakening upshear. It is a longstanding problem that forecasting the intensity changes that hurricanes undergo is difficult and has not improved over the last few decades. It is thought that these intensity changes are related to the internal dynamics of the storms. The intellectual merit of this study is that its results regarding the details of hurricane genesis, eyewalls, and rainbands will contribute strongly to a better understanding of these internal dynamics. The broader impacts of the study are that this new understanding will contribute to better prediction and forecasting of, and hence preparedness for, potentially damaging hurricanes.
