The Large-Scale Circulation Change at the End of the Baiu Season in Japan as Seen in ERA40 Data

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概要

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• The time evolution of the circulation change at the end of the Baiu season is investigated using ERA40 data. An end-day is defined for each of the 23 years based on the 850hPa θ_e value at 40°N in the 130-140°E sector exceeding 330K. Daily time series of variables are composited with respect to this day. These composite time-series exhibit a clearer and more rapid change in the precipitation and the large-scale circulation over the whole East Asia region than those performed using calendar days. The precipitation change includes the abrupt end of the Baiu rain, the northward shift of tropical convection perhaps starting a few days before this, and the start of the heavier rain at higher latitudes. The northward migration of lower tropospheric warm, moist tropical air, a general feature of the seasonal march in the region, is fast over the continent and slow over the ocean. By mid to late July the cooler air over the Sea of Japan is surrounded on 3 sides by the tropical air. It is suggestive that the large-scale stage has been set for a jump to the post-Baiu state, i.e., for the end of the Baiu season. Two likely triggers for the actual change emerge from the analysis. The first is the northward movement of tropical convection into the Philippine region. The second is an equivalent barotropic Rossby wave-train, that over a 10-day period develops downstream across Eurasia. It appears likely that in most years one or both mechanisms can be important in triggering the actual end of the Baiu season.

• 2009-02-25

著者

• SUZUKI Shin-ichi

  Storm, Flood and Landslide Research Department National Research Institute for Earth Science and Dis

• HOSKINS Brian

  Department of Meteorology, University of Reading

• Hoskins Brian

  Department Of Meteorology University Of Reading:grantham Institute For Climate Change

• Hoskins Brian

  Department Of Meteorology University Of Reading

• Suzuki Shin-ichi

  Storm Flood And Landslide Research Department National Research Institute For Earth Science And Disa

関連論文

• The Large-Scale Circulation Change at the End of the Baiu Season in Japan as Seen in ERA40 Data
• Impact of Tibetan Orography and Heating on the Summer Flow over Asia(125th Anniversary Issue of the Meteorological Society of Japan)
• The Seasonal and Wintertime Interannual Variability of the Split Jet and the Storm-Track Activity Minimum near New Zealand

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