KINEMATIC EVOLUTION OF THE HURRICANE CORE
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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