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[B-5.3 Mass Circulation Variations due to Seasonal and Longer Term Variations in the Middle Atmosphere Circulation]

[Contact Person]

Kiyotaka Shibata, Senior Researcher
Climate Research Department, Meteorological Research Institute
Japan Meteorological Agency
Nagamine 1-1, Tsukuba, Ibaraki, 305, Japan
Tel +81-298-53-8602, Fax +81-298-55-2552
E-mail:kshibata@mri-jma.go.jp

[Total Budget for FY1994-1996]

18,511,000 Yen (FY1996 5,798,000 Yen)

[Abstract]

　Off-line transport experiments are made with general circulation models(GCMs) in order to investigate the details of the air mass inflow from the troposphere into the stratosphere in low latitudes. At first, the effect of vertical and horizontal resolutions on the simulated middle atmosphere was investigated with GCMs extending from the surface to the middle mesosphere. The numerical experiments with four GCMs(R13L23, R13L92, R24L92 and R74L92) revealed that the increase in horizontal or vertical resolution induces westerly wind in the equatorial middle stratosphere, and that the westerly region goes down similarly to the real quasi-biennial oscillation. However, there seems no downward propagation of easterly region. Next, passive-tracer transport experiments are made with R24L92 and R74L92 GCMs. 10,000 tracers, initially located in 200-150 hPa over the equator, are transported by off-line GCM winds for two-months. This experiment are made every month for 2 and half years. It is found that the tracer inflow into the stratosphere shows an anti symmetric property . In particular, major inflow occurs in southern hemisphere in northern summer and autumn. In addition, there are favorable region for the inflow, where two conditions must be satisfied simultaneously:large diabatic heating and small-circulation wind.

[Key Words]

Middle Atmosphere, Seasonal Variations, Mass Circulation, Numerical Simulation