OBJECTIVE ANALYSIS OF THE HURRICANE AND ITS ENVIRONMENT

Principal Investigator: James L. Franklin
Collaborating scientist(s):
Steve Feuer
John Gamache
Objective: Diagnosis of the structure of the tropical cyclone core and environment; investigation of factors influencing tropical cyclone motion and intensification.
Rationale: 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; Omega dropwindsonde (ODW) 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.

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.

Method: The basic methodology involves application of a nested objective analysis package to datasets obtained during the HRD Field Program's Synoptic Flow and Vortex Motion and Evolution (VME) experiments.

Wind fields for the first 16 Synoptic Flow experiments have been analyzed. Initial investigations with the analyzed wind fields 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.

Accomplishment: Documentation, for the first time, of 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.

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. Data reduction of the Luis data set is currently in progress.

Key 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.

Last modified: 9/10/96