A diagnostic case study of Mei-yu frontogenesis and development of wavelike frontal disturbances in the subtropical environment

George Tai Jen Chen, Chung-Chieh Wang, Sau Wa Chang

Research output: Contribution to journalArticle

18 Citations (Scopus)

Abstract

During 6-7 June 2003, a mei-yu front over southern China, with active mesoscale convective systems (MCSs) along it and to its south, intensified rapidly in 24 h to possess a strong cyclonic circulation with relative vorticity centers reaching 1.7 × 10-4 s-1 and a low-level jet (LLJ) of 22.5 m s-1 at 850 hPa. Moreover, both the mass and wind fields and convection developed a wavelike structure at meso-α scale along the front. Using mainly gridded analyses from the European Centre for Medium-Range Weather Forecasts (ECMWT), the present study documented the evolution of this case and diagnosed the mechanisms responsible for its rapid intensification and the development of mesoscale disturbances using methods including the piecewise potential vorticity (PV) inversion. Results indicate that this mei-yu front was characterized by strong horizontal shear and moderate temperature gradient, and its development was not baroclinic in nature. The initiation of a wavelike structure along the frontal shear zone was consistent with barotropic: instability. The growth of mesoscale frontal disturbances (cyclogenesis) was a result of the nonlinear mechanism similar to the conditional instability of the second kind (CISK) in which the frontal PV centers and cumulus convection reinforce each other through a positive feedback process. As the MCSs were both intense and persistent, the latent heating was highly efficient and caused significant enhancement of the mei-yu frontal system, even at latitudes below 25°N. The vorticity budget analysis indicates that the front was maintained mainly by a stretching effect, while its gradual eastward extension and slow southward migration were linked to horizontal advection and a tilting effect, respectively. Induced by the MCSs, the transverse circulation south of the front was exceptionally strong, and the LIJ developed within its lower branch of northward-directed ageostrophic flow through Coriolis torque.

Original languageEnglish
Pages (from-to)41-61
Number of pages21
JournalMonthly Weather Review
Volume136
Issue number1
DOIs
Publication statusPublished - 2008 Jan 1

Fingerprint

frontogenesis
convective system
disturbance
potential vorticity
vorticity
ageostrophic flow
convection
barotropic instability
cyclogenesis
cumulus
torque
wind field
temperature gradient
shear zone
advection
heating
weather

ASJC Scopus subject areas

  • Atmospheric Science

Cite this

A diagnostic case study of Mei-yu frontogenesis and development of wavelike frontal disturbances in the subtropical environment. / Chen, George Tai Jen; Wang, Chung-Chieh; Chang, Sau Wa.

In: Monthly Weather Review, Vol. 136, No. 1, 01.01.2008, p. 41-61.

Research output: Contribution to journalArticle

@article{80def7aaa8de46cea3ee384210117461,
title = "A diagnostic case study of Mei-yu frontogenesis and development of wavelike frontal disturbances in the subtropical environment",
abstract = "During 6-7 June 2003, a mei-yu front over southern China, with active mesoscale convective systems (MCSs) along it and to its south, intensified rapidly in 24 h to possess a strong cyclonic circulation with relative vorticity centers reaching 1.7 × 10-4 s-1 and a low-level jet (LLJ) of 22.5 m s-1 at 850 hPa. Moreover, both the mass and wind fields and convection developed a wavelike structure at meso-α scale along the front. Using mainly gridded analyses from the European Centre for Medium-Range Weather Forecasts (ECMWT), the present study documented the evolution of this case and diagnosed the mechanisms responsible for its rapid intensification and the development of mesoscale disturbances using methods including the piecewise potential vorticity (PV) inversion. Results indicate that this mei-yu front was characterized by strong horizontal shear and moderate temperature gradient, and its development was not baroclinic in nature. The initiation of a wavelike structure along the frontal shear zone was consistent with barotropic: instability. The growth of mesoscale frontal disturbances (cyclogenesis) was a result of the nonlinear mechanism similar to the conditional instability of the second kind (CISK) in which the frontal PV centers and cumulus convection reinforce each other through a positive feedback process. As the MCSs were both intense and persistent, the latent heating was highly efficient and caused significant enhancement of the mei-yu frontal system, even at latitudes below 25°N. The vorticity budget analysis indicates that the front was maintained mainly by a stretching effect, while its gradual eastward extension and slow southward migration were linked to horizontal advection and a tilting effect, respectively. Induced by the MCSs, the transverse circulation south of the front was exceptionally strong, and the LIJ developed within its lower branch of northward-directed ageostrophic flow through Coriolis torque.",
author = "Chen, {George Tai Jen} and Chung-Chieh Wang and Chang, {Sau Wa}",
year = "2008",
month = "1",
day = "1",
doi = "10.1175/2007MWR1966.1",
language = "English",
volume = "136",
pages = "41--61",
journal = "Monthly Weather Review",
issn = "0027-0644",
publisher = "American Meteorological Society",
number = "1",

}

TY - JOUR

T1 - A diagnostic case study of Mei-yu frontogenesis and development of wavelike frontal disturbances in the subtropical environment

AU - Chen, George Tai Jen

AU - Wang, Chung-Chieh

AU - Chang, Sau Wa

PY - 2008/1/1

Y1 - 2008/1/1

N2 - During 6-7 June 2003, a mei-yu front over southern China, with active mesoscale convective systems (MCSs) along it and to its south, intensified rapidly in 24 h to possess a strong cyclonic circulation with relative vorticity centers reaching 1.7 × 10-4 s-1 and a low-level jet (LLJ) of 22.5 m s-1 at 850 hPa. Moreover, both the mass and wind fields and convection developed a wavelike structure at meso-α scale along the front. Using mainly gridded analyses from the European Centre for Medium-Range Weather Forecasts (ECMWT), the present study documented the evolution of this case and diagnosed the mechanisms responsible for its rapid intensification and the development of mesoscale disturbances using methods including the piecewise potential vorticity (PV) inversion. Results indicate that this mei-yu front was characterized by strong horizontal shear and moderate temperature gradient, and its development was not baroclinic in nature. The initiation of a wavelike structure along the frontal shear zone was consistent with barotropic: instability. The growth of mesoscale frontal disturbances (cyclogenesis) was a result of the nonlinear mechanism similar to the conditional instability of the second kind (CISK) in which the frontal PV centers and cumulus convection reinforce each other through a positive feedback process. As the MCSs were both intense and persistent, the latent heating was highly efficient and caused significant enhancement of the mei-yu frontal system, even at latitudes below 25°N. The vorticity budget analysis indicates that the front was maintained mainly by a stretching effect, while its gradual eastward extension and slow southward migration were linked to horizontal advection and a tilting effect, respectively. Induced by the MCSs, the transverse circulation south of the front was exceptionally strong, and the LIJ developed within its lower branch of northward-directed ageostrophic flow through Coriolis torque.

AB - During 6-7 June 2003, a mei-yu front over southern China, with active mesoscale convective systems (MCSs) along it and to its south, intensified rapidly in 24 h to possess a strong cyclonic circulation with relative vorticity centers reaching 1.7 × 10-4 s-1 and a low-level jet (LLJ) of 22.5 m s-1 at 850 hPa. Moreover, both the mass and wind fields and convection developed a wavelike structure at meso-α scale along the front. Using mainly gridded analyses from the European Centre for Medium-Range Weather Forecasts (ECMWT), the present study documented the evolution of this case and diagnosed the mechanisms responsible for its rapid intensification and the development of mesoscale disturbances using methods including the piecewise potential vorticity (PV) inversion. Results indicate that this mei-yu front was characterized by strong horizontal shear and moderate temperature gradient, and its development was not baroclinic in nature. The initiation of a wavelike structure along the frontal shear zone was consistent with barotropic: instability. The growth of mesoscale frontal disturbances (cyclogenesis) was a result of the nonlinear mechanism similar to the conditional instability of the second kind (CISK) in which the frontal PV centers and cumulus convection reinforce each other through a positive feedback process. As the MCSs were both intense and persistent, the latent heating was highly efficient and caused significant enhancement of the mei-yu frontal system, even at latitudes below 25°N. The vorticity budget analysis indicates that the front was maintained mainly by a stretching effect, while its gradual eastward extension and slow southward migration were linked to horizontal advection and a tilting effect, respectively. Induced by the MCSs, the transverse circulation south of the front was exceptionally strong, and the LIJ developed within its lower branch of northward-directed ageostrophic flow through Coriolis torque.

UR - http://www.scopus.com/inward/record.url?scp=39749185476&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=39749185476&partnerID=8YFLogxK

U2 - 10.1175/2007MWR1966.1

DO - 10.1175/2007MWR1966.1

M3 - Article

AN - SCOPUS:39749185476

VL - 136

SP - 41

EP - 61

JO - Monthly Weather Review

JF - Monthly Weather Review

SN - 0027-0644

IS - 1

ER -