Identification of the Steering Flow for Tropical Cyclone Motion from Objectively Analyzed Wind Fields

Johnny C. L. Chan Department of Meteorology, Naval Postgraduate School, Monterey, CA 93943

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Abstract

The flow patterns at various levels in the atmosphere around northwest Pacific tropical cyclones are studied using objectively-analyzed wind fields produced by the United States Navy. The results show large differences in the flow fields among groups of cyclones moving in different directions. Appreciable baroclinity is found in cyclones moving northward or northeastward. The results also demonstrate the impotence of stratifying cyclones by their characteristics and synoptic environment in the study and prediction of tropical cyclone motion

The relationships between tropical cyclone motion and the midtropospheric flow averaged around the 5–7° latitude radial band are also investigated using both the composite and individual cases. The composite results are generally consistent with those obtained from individual cases. In most cases, these relationships also agree with those derived in previous studies from rawinsonde composites and objectively-analyzed height fields. Since the objectively-analyzed wind fields used in this study are available for individual cases, the results suggest possible application of these fields to additional research studies of tropical cyclone motion as well as to development of short-term prediction techniques.

Abstract

The flow patterns at various levels in the atmosphere around northwest Pacific tropical cyclones are studied using objectively-analyzed wind fields produced by the United States Navy. The results show large differences in the flow fields among groups of cyclones moving in different directions. Appreciable baroclinity is found in cyclones moving northward or northeastward. The results also demonstrate the impotence of stratifying cyclones by their characteristics and synoptic environment in the study and prediction of tropical cyclone motion

The relationships between tropical cyclone motion and the midtropospheric flow averaged around the 5–7° latitude radial band are also investigated using both the composite and individual cases. The composite results are generally consistent with those obtained from individual cases. In most cases, these relationships also agree with those derived in previous studies from rawinsonde composites and objectively-analyzed height fields. Since the objectively-analyzed wind fields used in this study are available for individual cases, the results suggest possible application of these fields to additional research studies of tropical cyclone motion as well as to development of short-term prediction techniques.

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