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Extratropical Transition of Southwest Pacific Tropical Cyclones. Part II: Midlatitude Circulation Characteristics

Extratropical Transition of Southwest Pacific Tropical Cyclones. Part II: Midlatitude Circulation... This second of two papers on extratropical transition (ET) over the southwest Pacific Ocean focuses on the variability of ET. A climatology of ET onset based on a previously described objective technique shows that ET commences 15°° of latitude nearer the equator on average than similar cases from the Northern Hemisphere. Characteristic midlatitude circulation patterns accompanying ET near 30°°S are identified by means of empirical orthogonal function (EOF) analysis of 50 storms. The first eigenvector pattern, explaining nearly half the circulation variability, expresses relaxed and enhanced pressure gradients south of the storm that define composites similar to ““cradled”” and ““captured”” classifications previously described for the southeast Indian Ocean. The second EOF distinguishes redeveloping from weakening storms. Reintensifying storms were located beneath strong cyclonic vorticity advection (CVA) near the equatorward entrance region of an upper jet whereas the upper jet was well to the west of weakening storms. A survey of factors responsible for modulating central sea level pressure change during ET was conducted for the 50 storms. The quantity most strongly correlated with surface development was found to be CVA at the jet level. Extratropical reintensification occurred when the surface cyclone was located beneath the equatorward entrance region of an upper jet for storms between 28°° and 34°°S, and beneath the poleward exit jet region for storms farther south. Strongest examples of redevelopment each occurred beneath a potent double jet signature aloft, with maximum storm-relative upper-level CVA located directly above the surface low and net vorticity fluxes reflecting amplification of the upper wave. Weakening storms featured a weakening upper trough directly above the storm, with CVA to the east. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Monthly Weather Review American Meteorological Society

Extratropical Transition of Southwest Pacific Tropical Cyclones. Part II: Midlatitude Circulation Characteristics

Sinclair, Mark R.
Monthly Weather Review , Volume 132 (9) – Apr 23, 2003
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References (55)

Publisher
American Meteorological Society
Copyright
Copyright © 2003 American Meteorological Society
ISSN
1520-0493
DOI
10.1175/1520-0493(2004)132<2145:ETOSPT>2.0.CO;2
Publisher site
See Article on Publisher Site

Abstract

This second of two papers on extratropical transition (ET) over the southwest Pacific Ocean focuses on the variability of ET. A climatology of ET onset based on a previously described objective technique shows that ET commences 15°° of latitude nearer the equator on average than similar cases from the Northern Hemisphere. Characteristic midlatitude circulation patterns accompanying ET near 30°°S are identified by means of empirical orthogonal function (EOF) analysis of 50 storms. The first eigenvector pattern, explaining nearly half the circulation variability, expresses relaxed and enhanced pressure gradients south of the storm that define composites similar to ““cradled”” and ““captured”” classifications previously described for the southeast Indian Ocean. The second EOF distinguishes redeveloping from weakening storms. Reintensifying storms were located beneath strong cyclonic vorticity advection (CVA) near the equatorward entrance region of an upper jet whereas the upper jet was well to the west of weakening storms. A survey of factors responsible for modulating central sea level pressure change during ET was conducted for the 50 storms. The quantity most strongly correlated with surface development was found to be CVA at the jet level. Extratropical reintensification occurred when the surface cyclone was located beneath the equatorward entrance region of an upper jet for storms between 28°° and 34°°S, and beneath the poleward exit jet region for storms farther south. Strongest examples of redevelopment each occurred beneath a potent double jet signature aloft, with maximum storm-relative upper-level CVA located directly above the surface low and net vorticity fluxes reflecting amplification of the upper wave. Weakening storms featured a weakening upper trough directly above the storm, with CVA to the east.

Journal

Monthly Weather Review – American Meteorological Society

Published: Apr 23, 2003

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