A Numerical Study on the Coastal Kelvin Wave Features about the Cold Surges around the Tibetan Plateau

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  • Nakamura Hajime
    Geophysical Institute, University of Tokyo Numerical Prediction Division of Japan Meteorological Agency
  • Doutani Tadayasu
    Geophysical Institute, University of Tokyo Institute of Space and Astronautical Science

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Other Title
  • チベット高原のまわりのコールド•サージのケルヴィン波的性質に関する数値的研究
  • A numerical study on the coastal Kelvin wave features about the cold surge around the Tibetan Plateau

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Detailed structure of the edge front associated with the cold surge discussed by Nakamura and Murakami (1983) and Murakami and Nakamura (1983) was investigated using a higher resolution model with 1°×1°horizontal grid interval and 16 vertical levels. (Here edge' is applied to the disturbances attached to the mountain boundary.)<br>The increase of the resolution made the edge front more intensified. A strong cold front was formed at the northeast corner of the model elliptic shaped mountain. Temperature gradient became about 15°K/100km. The ageostrophic northerly wind with magnitude of 20-25m/s appeared across the cold front. This edge front was trapped along the mountain boundary and propagate clockwise with the speed of 20-25m/s. One day later it moved to the south of the mountain and then reached west of the mountain where it dissipated. This behavior indicates the feature of gravity waves, being similar to the coastal Kelvin waves.<br>During the propagation, the wind and pressure fields behind the edge front hold well geostrophic balance. Cross isobaric wind is found only at the head of the edge front. Wind velocity behind the front was about 20m/s, while the propagating speed of the edge front was about 25m/s. Nonlinear advection was dominant in the propagation of the edge front. We also demonstrated the generation of the Kelvin waves by a shallow water equation model. It indicated that the generation of the Kelvin waves is one of major factors for the initiation of the edge front. However, there is a possibility that the shelf waves (topographic Rossby waves) may work in geostrophic adjustment during the propagating stage of the edge front and in determining its lateral scale.

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