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SOME EFFECTS OF WAVE-LENGTH VARIATIONS OF THE LONG WAVES IN THE UPPER WESTERLIES

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  • 1 University of Chicago
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Abstract

In an attempt to use the equation developed by Rossby for the motion of waves in a single-layer barotropic atmosphere as a prognostic tool, the effect of the upstream variation of wave length is studied. With the aid of the concept of group velocity an expression is obtained for trough displacement which takes into account the change of wave length with time and the acceleration of the long waves. Tests of the results indicate that the inclusion of the upstream wave-length variation in the forecast of trough displacement gives a significant improvement in the forecast verification. The results can be expressed qualitatively as follows: If the wave length of the long waves increases upstream at the initial moment, the eastward speed of the wave under consideration decreases with time. If the wave length decreases upstream at the initial moment, the eastward speed of the wave increases with time.

Abstract

In an attempt to use the equation developed by Rossby for the motion of waves in a single-layer barotropic atmosphere as a prognostic tool, the effect of the upstream variation of wave length is studied. With the aid of the concept of group velocity an expression is obtained for trough displacement which takes into account the change of wave length with time and the acceleration of the long waves. Tests of the results indicate that the inclusion of the upstream wave-length variation in the forecast of trough displacement gives a significant improvement in the forecast verification. The results can be expressed qualitatively as follows: If the wave length of the long waves increases upstream at the initial moment, the eastward speed of the wave under consideration decreases with time. If the wave length decreases upstream at the initial moment, the eastward speed of the wave increases with time.

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