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Influence of the Tibetian Plateau on Cumulative and Diurnal Changes of Weather and Climate in Summer

H. L. KuoDepartment of Geophysical Sciences, The University of Chicago, Chicago, IL 60637

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Y. F. QianDepartment of Geophysical Sciences, The University of Chicago, Chicago, IL 60637

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Abstract

The influences of the Tibetian Plateau on the cumulative and diurnal changes of the meteorological fields in July are investigated by the use of a five-layer primitive equation model which includes the effects of solar and longwave radiation, cumulus convection, topography, internal and surface friction and a mean flow field. It is found that prominent diurnal variations in the meteorological fields are created by the special influence of the plateau on the distribution of solar energy. The vertical circulation so created is such that at 1800 LST at 90°E the motion is upward over the entire Plateau and its surroundings from the surface to the 100 mb level except in a very narrow region close to the eastern edge of the Plateau. At 0600 downward motion prevails over the Plateau and along the surrounding slopes up to the 300 mb level, but above 300 mb ascending motion still persists. The daily mean vertical circulation is characterized by ascending motion over the entire region of the Plateau and its surroundings, which is in general agreement with the mean July flow pattern obtained from observations by Yeh and Gao (1979).

In addition, the distribution of rainfall rate obtained from the simulation also is in fair agreement with the observed distribution in July, with cumulus rainfall contributing to more than three-fourths of the total rainfall in the tropics.

Abstract

The influences of the Tibetian Plateau on the cumulative and diurnal changes of the meteorological fields in July are investigated by the use of a five-layer primitive equation model which includes the effects of solar and longwave radiation, cumulus convection, topography, internal and surface friction and a mean flow field. It is found that prominent diurnal variations in the meteorological fields are created by the special influence of the plateau on the distribution of solar energy. The vertical circulation so created is such that at 1800 LST at 90°E the motion is upward over the entire Plateau and its surroundings from the surface to the 100 mb level except in a very narrow region close to the eastern edge of the Plateau. At 0600 downward motion prevails over the Plateau and along the surrounding slopes up to the 300 mb level, but above 300 mb ascending motion still persists. The daily mean vertical circulation is characterized by ascending motion over the entire region of the Plateau and its surroundings, which is in general agreement with the mean July flow pattern obtained from observations by Yeh and Gao (1979).

In addition, the distribution of rainfall rate obtained from the simulation also is in fair agreement with the observed distribution in July, with cumulus rainfall contributing to more than three-fourths of the total rainfall in the tropics.

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