Potential Vorticity Perspective of Vortex Structure Changes of Tropical Cyclone Bilis (2006) during a Heavy Rain Event following Landfall

Potential Vorticity Perspective of Vortex Structure Changes of Tropical Cyclone Bilis (2006)... AbstractTropical cyclone (TC) Bilis made landfall on the China coast at 0500 UTC 14 July 2006. Following the landfall, sudden and unforecast torrential rain commenced some 400 km southwest of the weakening circulation center at around 1200 UTC 14 July 2006. At least 843 people were killed and the direct economic loss was estimated at up to US$5 billion in this event.Prior to the rain event, as the environmental fields evolved, the vertical vorticity weakened and deformation increased around the Bilis circulation. We illustrate that a strong gradient wind imbalance (GWI) through midlevels became established over the northwestern quadrant of Bilis, from which a large quantity of air with high potential vorticity (PV) was re-distributed from the inner circulation to outer radii. Both backward and forward Lagrangian trajectories show this re-distribution as an outward bulge of midlevel PV towards the rainfall areas. The transport of midlevel PV from inner to outer radii provides a dynamical reason for the rapid decline in rainfall around Bilis’ center. It is also associated with large differential horizontal PV advection below 400 hPa over the rainfall area. Diagnostic analysis further demonstrates the re-distribution of high PV to over the rainfall areas is associated with a raising of the local isentropic surfaces and the formation of a cold dome in the mid-lower troposphere. This is not only a direct lifting mechanism but also establishes favorable conditions for warm advection and ascent on the raised isentropic surfaces. These adiabatic ascent mechanisms are considered to have released conditional instability, resulting in broadscale convection and heavy rainfall. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Monthly Weather Review American Meteorological Society

Potential Vorticity Perspective of Vortex Structure Changes of Tropical Cyclone Bilis (2006) during a Heavy Rain Event following Landfall

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Publisher
American Meteorological Society
Copyright
Copyright © American Meteorological Society
ISSN
1520-0493
eISSN
1520-0493
D.O.I.
10.1175/MWR-D-16-0276.1
Publisher site
See Article on Publisher Site

Abstract

AbstractTropical cyclone (TC) Bilis made landfall on the China coast at 0500 UTC 14 July 2006. Following the landfall, sudden and unforecast torrential rain commenced some 400 km southwest of the weakening circulation center at around 1200 UTC 14 July 2006. At least 843 people were killed and the direct economic loss was estimated at up to US$5 billion in this event.Prior to the rain event, as the environmental fields evolved, the vertical vorticity weakened and deformation increased around the Bilis circulation. We illustrate that a strong gradient wind imbalance (GWI) through midlevels became established over the northwestern quadrant of Bilis, from which a large quantity of air with high potential vorticity (PV) was re-distributed from the inner circulation to outer radii. Both backward and forward Lagrangian trajectories show this re-distribution as an outward bulge of midlevel PV towards the rainfall areas. The transport of midlevel PV from inner to outer radii provides a dynamical reason for the rapid decline in rainfall around Bilis’ center. It is also associated with large differential horizontal PV advection below 400 hPa over the rainfall area. Diagnostic analysis further demonstrates the re-distribution of high PV to over the rainfall areas is associated with a raising of the local isentropic surfaces and the formation of a cold dome in the mid-lower troposphere. This is not only a direct lifting mechanism but also establishes favorable conditions for warm advection and ascent on the raised isentropic surfaces. These adiabatic ascent mechanisms are considered to have released conditional instability, resulting in broadscale convection and heavy rainfall.

Journal

Monthly Weather ReviewAmerican Meteorological Society

Published: Mar 13, 2017

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