Analyzed potential vorticity fields for explosive and non-explosive cyclogenesis events during FGGE.

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Author
Kirchoffer, Peter J.
Date
1986-09Advisor
Elsberry, R.L.
Second Reader
Wash, C.H.
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Show full item recordAbstract
Potential vorticity and jet streak properties associated with 23 explosive and
non-explosive cyclones from the western North Atlantic and western North Pacific
Oceans are analyzed for the period 17 January to 23 February 1979. ECMWF analyses
with FGGE data are used to represent the 300 mb wind fields over these ocean areas.
Relative maxima in potential vorticity are present upstream of all cyclones. Storm
tracks with respect to the potential vorticity maxima are counter-clockwise with the
greatest sea-level pressure decreases occurring when the storm is to the east or
southeast of the maximum, whereas pressure falls diminish when the cyclone is north
of the maximum. Only five of the 23 cases have a pre-existing potential vorticity lobe
that becomes superposed with the surface feature and enhances cyclogenesis. In the
remaining cases, the cyclone and potential vorticity lobe propagate and develop
concurrently. The presence of a jet maxima over the storm is a major factor in storm
development with large pressure falls being directly related to higher 300 mb wind
speeds. In 20 of 23 cases, the storm is in the left-front jet quadrant at some time
during its development. A statistical analysis demonstrates that forecasting the actual
values of 12-h pressure falls from the potential vorticity and wind fields is difficult.
However, forecasting development within one of three intensity categories using a
discriminate analysis technique may approach 90% accuracy for explosive cyclones.
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This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.Collections
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