Abstracts for the 6th International GAME Conf.
3-5 December 2004
Kyoto Japan
Mechanisms of westward and northward movement of sub-monthly scale disturbances over Asian monsoon regions.
YOKOI, Satoru (1), SATOMURA, Takehiko (1)
(1) Graduate School of Science, Kyoto University
Submonthly-scale disturbances, which have timescales between 10 and 25 days, are found frequently at various places in the Asian monsoon region during northern summer. They have strong cyclonic circulation anomaly in the lower troposphere and move west-northwestward or northwestward with its speed about a few meters per second. We discuss the mechanisms for westward and northward components of the movement and their differences among locations that centers of the disturbances exist. The westward component mainly results from balance between advection of the planetary and relative vorticity. The advection of the planetary vorticity (the beta effect) contributes to the westward movement of the disturbance, like the Rossby wave dynamics. On the other hand, the advection of the relative vorticity plays more complex role to the westward movement. Over the south Asia, advection of the relative vorticity strongly forces the disturbances move eastward mainly because of the strong environmental westerly jet in the lower troposphere, though its eastward forcing is slightly weaker than the westward forcing of the beta effect. As a result, the disturbances move westward slowly. Over the western Pacific, eastward forcing of the advection of the relative vorticity is weak, thus the westward speed of the disturbance is larger than that over the south Asia. For the northward component, tilting as well as the advection is an important effect. The tilting effect forces the disturbance northward, especially south of 15N. Over the south Asia, the advection of the relative vorticity and the tilting effect contribute to the northward movement at almost the same degree. On the other hand, over the western Pacific, the advection of the relative vorticity contributes more strongly to the northward movement than the tilting effect does, because of southeast-northwest tilts of the disturbances and environmental zonal wind. In vertical, the tilting effect works well in the middle and upper troposphere because anomalous vertical velocity has maximum amplitude there, while the advection works well in the lower troposphere.
Submittal Information
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Climate Physics Lab., Div. Earth and Planetary Sci. Graduate School of Science, Kyoto University | |
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Kitashirakawa-Oiwake cho, Sakyo, Kyoto 606-8502 | |
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