Seasonal transition of the lower-level circulation systems around the Baiu front in China in 1979 and its relation to the northern summer monsoon

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Abstract

The seasonal transition of the characteristics of the lower-level circulation systems around the Baiu front in China from spring to summer and their relation to the Northern Summer Monsoon are examined by using the observational data of 1979. The Baiu front in May (stage (A)) is the system within the baroclinic zone in middle latitudes. The surface high pressure belt with cooler air and large divergence is located just to the north of it and the subtropical high at the surface level to the south of the Baiu front is not so clearly found. The subtropical high with a strong lower-levels outherly wind toward the Baiuuf ront around China was enhanced abruptly in the middle of June, nearly simultaneously with the onset of the Northern Summer Monsoon (the beginning of stage (C)). In stage (C) the low OLR area (intense heat source area) expands widely in South Asia (EQ~25ºN/60ºE~105ºE)T. he pressure in the lower layer decreases there, which results in the geostrophic enhancement of the southerly wind in the subtropical high area around 120ºE by producing the eastward pressure gradient. At the same time the belt-shaped low OLR area extending from India to Western Pacific region (~10ºN/60ºE~140ºE) is formed, which intensifies the local Hadley cell with strong lower-level divergence around 20ºN as its northern branch. It is concluded that the change in the lower-level wind structure of the subtropical high to the south of the Baiu front in the middle of June is due to the superposed effect of the two characteristics of the heat source distribution associated with the Northern Summer Monsoon. The additional analysis by using the pentad mean data from 1979 to 1983 supports this conclusion.

Original languageEnglish
Pages (from-to)249-265
Number of pages17
JournalJournal of the Meteorological Society of Japan
Volume67
Issue number2
DOIs
Publication statusPublished - Apr 1 1989
Externally publishedYes

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monsoon
summer
heat source
divergence
Hadley cell
surface pressure
pressure gradient
air

ASJC Scopus subject areas

  • Atmospheric Science

Cite this

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title = "Seasonal transition of the lower-level circulation systems around the Baiu front in China in 1979 and its relation to the northern summer monsoon",
abstract = "The seasonal transition of the characteristics of the lower-level circulation systems around the Baiu front in China from spring to summer and their relation to the Northern Summer Monsoon are examined by using the observational data of 1979. The Baiu front in May (stage (A)) is the system within the baroclinic zone in middle latitudes. The surface high pressure belt with cooler air and large divergence is located just to the north of it and the subtropical high at the surface level to the south of the Baiu front is not so clearly found. The subtropical high with a strong lower-levels outherly wind toward the Baiuuf ront around China was enhanced abruptly in the middle of June, nearly simultaneously with the onset of the Northern Summer Monsoon (the beginning of stage (C)). In stage (C) the low OLR area (intense heat source area) expands widely in South Asia (EQ~25ºN/60ºE~105ºE)T. he pressure in the lower layer decreases there, which results in the geostrophic enhancement of the southerly wind in the subtropical high area around 120ºE by producing the eastward pressure gradient. At the same time the belt-shaped low OLR area extending from India to Western Pacific region (~10ºN/60ºE~140ºE) is formed, which intensifies the local Hadley cell with strong lower-level divergence around 20ºN as its northern branch. It is concluded that the change in the lower-level wind structure of the subtropical high to the south of the Baiu front in the middle of June is due to the superposed effect of the two characteristics of the heat source distribution associated with the Northern Summer Monsoon. The additional analysis by using the pentad mean data from 1979 to 1983 supports this conclusion.",
author = "Kuranoshin Kato",
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N2 - The seasonal transition of the characteristics of the lower-level circulation systems around the Baiu front in China from spring to summer and their relation to the Northern Summer Monsoon are examined by using the observational data of 1979. The Baiu front in May (stage (A)) is the system within the baroclinic zone in middle latitudes. The surface high pressure belt with cooler air and large divergence is located just to the north of it and the subtropical high at the surface level to the south of the Baiu front is not so clearly found. The subtropical high with a strong lower-levels outherly wind toward the Baiuuf ront around China was enhanced abruptly in the middle of June, nearly simultaneously with the onset of the Northern Summer Monsoon (the beginning of stage (C)). In stage (C) the low OLR area (intense heat source area) expands widely in South Asia (EQ~25ºN/60ºE~105ºE)T. he pressure in the lower layer decreases there, which results in the geostrophic enhancement of the southerly wind in the subtropical high area around 120ºE by producing the eastward pressure gradient. At the same time the belt-shaped low OLR area extending from India to Western Pacific region (~10ºN/60ºE~140ºE) is formed, which intensifies the local Hadley cell with strong lower-level divergence around 20ºN as its northern branch. It is concluded that the change in the lower-level wind structure of the subtropical high to the south of the Baiu front in the middle of June is due to the superposed effect of the two characteristics of the heat source distribution associated with the Northern Summer Monsoon. The additional analysis by using the pentad mean data from 1979 to 1983 supports this conclusion.

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