気象集誌. 第2輯
Online ISSN : 2186-9057
Print ISSN : 0026-1165
ISSN-L : 0026-1165
Articles
Projections of Future Changes in Precipitation and the Vertical Structure of the Frontal Zone during the Baiu Season in the Vicinity of Japan Using a 5-km-mesh Regional Climate Model
Sachie KANADAMasuo NAKANOTeruyuki KATO
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2012 年 90A 巻 p. 65-86

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Future changes in precipitation and the vertical structure of the frontal zone around Japan during the Baiu season are investigated using regional climate experiments with a 5-km-mesh non-hydrostatic model, driven for the present-day (1979-2003) and future (2075-2099) climates by output from global warming experiments using a 20-km-mesh atmospheric global circulation model under the SRES-A1B scenario.
Significant increases are projected for the future climate relative to the present-day in daily precipitation amounts around western Japan during the late Baiu season. The percentage of precipitation occurring in intense precipitation (over 100 mm day-1) increases with statistical confidence above the 98% confidence level. In the present-day climate, 9% of the 25-year-mean precipitation amount during early July in the region within 30°N-35°N and 127°E-137°E is estimated to be dominated by intense precipitation; this value rises to 15% in the future climate.
Changes in the Baiu front and in environmental conditions around western Japan are investigated. In the future climate, a delay in the northward march of the Baiu front is projected, and the mean location of the front during the late Baiu season is 33.0°N, compared with 33.5°N in the present-day. The mean amount of water vapor on the southern side of the front at a 500 m height increases to 19.7 g kg-1 in the future climate, an increase of 2.8 g kg-1 relative to the present-day. Mean vertical cross-sections of the front reveal tall structures of intense vertical vorticity (> 1.0 × 10-5 s-1) along an intensified frontal zone with intense mean updrafts and large amounts of rainwater in the future climate. Two of the characteristic jets associated with the Baiu front, located at a 700 hPa level on the southern side of the front and at a 200 hPa level on the northern side, are also intensified. The increases in the supply of water vapor and the intensified convective activity along the Baiu front could contribute to the projected increase in the occurrence of intense daily precipitation.

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© 2012 by Meteorological Society of Japan
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