A description of tropical cyclone recurvature in terms of isentropic potential vorticity
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Authors
Boerlage, Andrew P.
Subjects
Isentropic Potential Vorlicity
Bogus Vortex Structure
Bogus Vortex Structure
Advisors
Elsberry, Russell L.
Date of Issue
1989-06
Date
Publisher
Monterey, California. Naval Postgraduate School
Language
en_US
Abstract
Isentropic potential vorticity (IPV) fields calculated from the Na\7 Operational
Regional Atmospheric Prediction System are analyzed to determine their usefulness as
an aid to tropical cyclone recurvature forecasts. The IPV fields associated with Typhoon
Nelson are calculated on a 80 km grid for the period 0000 UTC 4 October to 0000 UTC
7 October 19S8. In this preliminar>- study, IPV advection fields and the horizontal and
vertical structure of the bogus vortex are examined to determine their contributions to
the model forecast. The extremely broad bogus vortex is found to distort the IPV fields
and cause regions of negative IPV, which is believed to result in inertial instability.
Approximately 36 h are required for the model to adjust to the initial imbalance in the
mass and wind fields. It appears that the unrealistic bogus vortex representation may
have degraded the early portions of the model forecast. Analysis of IPV advection fields
each 12 h during the NORAPS model integration showed that storm movement is primarily
due to the influence of self-advection and the large-scale steering fiow. During
later periods other advective features associated with adjacent synoptic systems begin to
influence the storm movement. Forecasters with access to such IPV fields may be able
to evaluate the likely validity of the model forecast of recurvature. The usefulness of the
IPV representation from the NORAPS prediction in this single case study suggest that
additional cases of tropical cxclone recurvature be examined in terms of IPV concepts.
Type
Thesis
Description
Series/Report No
Department
Meteorology
Organization
Naval Postgraduate School
Identifiers
NPS Report Number
Sponsors
Funder
Format
60 p.
Citation
Distribution Statement
Approved for public release; distribution is unlimited.