The Application of Global Positioning System (GPS) Sondes to Hurricane Intensity Evolution

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The Principal Investigator will study hurricane intensity changes using the substantial archive of Global Positioning System sondes (GPS sondes) deployed since 1997 from NOAA, NSF and NASA sponsored aircraft. These sondes will be combined with the aircraft radar and aircraft in-situ sensors for several hurricanes that were sampled over a considerable portion of their life. The GPS sondes provide wind and thermodynamic data from just below aircraft altitude to the sea surface in the inner core of the hurricane (eye to 300 km radial distance). Exploitation of the GPS sonde archive, maintained by the Hurricane Research Division of NOAA, is an economical approach to hurricane intensity research given the high cost of a research mission. The Principal Investigator has developed a cubic spline analysis that allows for the efficient construction of cross-sections (e.g., inflow distance-height, azimuth-height and radial distance-height) that provide unprecedented views of the lower troposphere and low-level inflow. These cross-sections will be applied at several stages of a hurricane's life to determine how the inner core wind and thermodynamic structures vary as the storm intensifies or weakens. With theses analyses the Principal Investigator will be able to determine mass and moisture inflow to the eyewall, and where the inflow layer acquires the energy necessary to create and sustain the hurricane circulation. Multiple cross-sections will allow for the detection of mesoscale asymmetries in the flow due to either environmental differences or rainbands and how they impact hurricane intensity. The derived fields will serve as a benchmark for numerical simulations of hurricanes. High energy air residing in the lower portion of the eye has been argued to boost instability in the eyewall and contribute to intensity levels that exceed those predicted from maximum potential intensity theory. A comparison between eye structure as seen with the GPS sondes jettisoned throughout the storm's life and aircraft in-situ measurements in the eyewall will increase understanding of how the lower eye thermodynamics affect intensity. The GPS sondes deployed from both the high altitude NOAA G-IV and the WP-3Ds in hurricanes a day or two prior to landfall will be used to identify the instability and the vertical shear of the horizontal winds while the storm is offshore. These critical indices will be compared to conditions diagnosed with the National Weather Service rawinsondes launched in the circulation at and after landfall. The purpose is to determine which hurricanes will spawn numerous tornadoes and how the wind and thermodynamic fields evolve at landfall. This is the first time that the GPS sondes deployed from the G-IV will be used for work beyond hurricane track improvement. The broader impacts of the research include the development of efficient sampling strategies to better probe the inner core of hurricanes undergoing intensity change, leading to improved forecasts of intensity that result in substantial safety and economic benefits to the United States. The proposal addresses issues identified by the NSF National Science Board, the NOAA Scientific Advisory Board, the American Meteorological Society, and the U.S. Weather Research Program Prospectus Development Teams. Educational benefits of the work include the training of graduate students and the continued development of hurricane classes for undergraduates and graduates. The work enhances the partnership between the University of Hawaii and NOAA's Hurricane Research Division.