Principal Investigator: John F. Gamache
Collaborating scientist(s):
Hugh E. Willoughby
James Franklin
Frank Marks, Jr.
Michael Black
Christopher Samsury
Objective: To analyze the evolution of the flow fields in the cores of hurricanes and relate them to environmental and internal dynamics and thermodynamics.
Rationale: The structure and intensity of a hurricane is clearly related to sea surface temperature, atmospheric environmental forcing, eye thermodynamics, and internal dynamics. We need to determine these relationships to hurricane core changes. Part of this process is to document the nature of wind field changes. Thus, analyses of rapid Doppler scans of the hurricane inner core structure are a necessary though insufficient requirement to understanding hurricane intensification.
Method: Analyses of observations of the hurricane core with approximately 30 minute resolution are performed. The data are obtained from two NOAA WP-3D aircraft flying simultaneous orthogonal flight tracks through the hurricane center, while both aircraft sample a wind component with their airborne Doppler radar. The data are then synthesized using the variational technique described in the Project entitled "THREE-DIMENSIONAL VARIATIONAL ANALYSIS OF DOPPLER WIND OBSERVATIONS". The changes in the wind field over a several hour period are then documented.
Accomplishment: Rapid (30 min) Doppler observations have been made in Hurricanes Gustav (1990), Claudette (1991), Jimena (1991), Olivia (1994), Iris (1995), and Luis (1995), as well as others. Analyses of the first four has been underway, with some of the results from Gustav and Claudette already reported. Since GPS navigation was added before Hurricane Olivia, and the most rapid dual-aircraft scans were done in Olivia, these data represent the best so far for studying inner core change. Analyses of flights on 25 September have mostly been completed and they show a remarkable change between the beginning and end of the mission (only about 3 hours). The central pressure increased by 10 mb, while the mean lower wind changed little. However, the mean tangential wind in the core decreased by over 10 m/s at the 9 km level. During the same period the lower-tropospheric vertical shear of the horizontal wind increased from approximately 1 to 2 m/s/km to as much as 3 to 4 m/s/km. The nature of these changes will be investigated further. The change in the tangential wind at 9 km during the three hour period is documented by the differences between figures one and two.
Key reference:
Gamache, J. F., F. D. Marks, Jr., and F. Roux, 1995: Comparison of Three Airborne Doppler Sampling Techniques with Airborne in situ Wind Observations in Hurricane Gustav (1990). J. Atmos. Oceanic Technol., 12, 171-181.

Roux, F., and N. Viltard, 1995: Structure and evolution of Hurricane Claudette on 7 September 1991 from airborne Doppler radar observations. Part I: Kinematics. Mon. Wea. Rev., 123, 2611-2639.

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