OBJECTIVE ANALYSIS OF THE HURRICANE AND ITS ENVIRONMENT
Principal Investigator:
James L. Franklin
Collaborating
scientist(s):
Steven E. Feuer
John Gamache
Objective:
Diagnosis of the structure of the tropical cyclone core and environment;
investigation of factors influencing tropical cyclone motion and
intensification.
Background:
Datasets obtained by the NOAA WP-3D research aircraft during the HRD Field
Program span a variety of spatial scales: Doppler radar data in the inner core
are available in 300 m gates, or bins; flight level state parameters are
measured once per second; Dropwindsonde soundings in the storm environment have
a spatial resolution of 150-300 km. Other sources of synoptic and asynoptic
data (satellites, rawinsondes, ships, commercial aircraft, etc.) are also
available to complement the WP-3D observations.
Analysis Methodology:
HRD has developed a nested objective analysis software package to assimilate
this wide array of observations, in the context of a relatively small hurricane
vortex embedded in a broad-scale surrounding flow. The objective analyses that
are produced are used to improve our understanding of tropical cyclone
structure, motion, and evolution. The objective analysis package is applied to
datasets obtained during the HRD Field Program's Synoptic Flow and Vortex Motion
and Evolution (VME) experiments.
Accomplishments:
Initial investigations with the analyzed wind fields of the first 16 Synoptic
Flow experiments focused on distinguishing potential vortex-environment
interactions (e.g., the "beta-gyres") from stronger environmental flow features.
To accomplish this, wind and vorticity asymmetries were calculated in two
coordinate systems: the normal earth-based geographical system, and a
coordinate system oriented parallel to the direction of storm
motion.
These analyses documented, for the first time, subtle features in the
environmental vorticity fields that were most readily interpreted as beta-gyres.
Vorticity asymmetries tended to cluster in geographical coordinates and
translate along with the vortex. The location (FIGURE
1) and motion of these asymmetries is consistent with an interaction between
the cyclone and the earth's vorticity gradient. This work is described in the
following publication:
Franklin, J. L., S. E. Feuer, J. Kaplan, and S. D.
Aberson, 1996: Tropical cyclone motion and surrounding flow relationships:
Searching for Beta-gyres in Omega dropwindsonde datasets. Mon. Wea.
Rev., 124, 64-84.
In FY97, wind analyses for an additional Synoptic Flow experiment, Hurricane
Emily (0000 UTC 30 August 1993), were completed. ODW data from the 1996
Hurricane Field Program were processed and made available to the appropriate
PIs.
During the summer of 1995, highly successful VME field experiments were
conducted in Hurricanes Iris and Luis. In these experiments, ODWs and airborne
Doppler radars were used together to obtain the most comprehensive
three-dimensional kinematic data sets ever obtained in the core and near
environment (within 300 km) of a hurricane. Preliminary analyses of the Luis
wind field have been completed, incorporating ODW, aircraft, and satellite data.
Doppler radar wind sets were prepared for incorporation into the analyses.
Work has begun on the enhancement of analysis product graphical output. A
postscript driver is under development.
Plans:
Analysis of the Luis wind fields will continue in FY98. If the opportunity
presents, an additional data set using GPS dropwinsondes in an enhanced VME
pattern will be obtained during the 1997 Hurricane Field Program.
Related references:
Ooyama, K. V., 1987: Scale controlled objective analysis. Mon. Wea.
Rev., 115, 2479-2506.
Franklin, J. L., S. J. Lord, S. E. Feuer, and F. D.
Marks, Jr., 1993: The kinematic structure of Hurricane Gloria (1985)
determined from nested analyses of dropwindsonde and doppler radar data.
Mon. Wea. Rev., 121, 2433-2451.
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Last modified: 23 June 1997.
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