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L. F. Hubert and A. Timchalk

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S. FRITZ, L. F. HUBERT, and A. TIMCHALK

Abstract

The degree of organization and the size of the cloud patterns in TIROS pictures of tropical disturbances are good indicators of the maximum wind speed as observed by airplanes. The organization varies from unorganized bright cloud patterns, to highly organized spiral arrays of clouds with additional characteristic features, such as the sharp edge of cirrus clouds. Poorly organized clouds are associated with weak disturbances, the most highly organized ones with intense storms.

In addition, within each category a relationship exists between the size of the cloud pattern and the maximum wind speed. Both the organization category and the size of the overcast cloud pattern are related statistically to the maximum wind speed, so that the maximum wind speed can be estimated from the picture of the storm alone. Tests with independent data show that a useful relationship has been obtained. Theoretical justification for the results obtained is necessary but is not yet available.

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L. F. WHITNEY Jr., A. TIMCHALK, and T. I. GRAY Jr.

Abstract

The purpose of this study is to evaluate the reliability of locating jet streams by means of certain cloud patterns in TIROS pictures, and to determine the most definitive characteristics of those patterns. It would be very useful operationally, especially in data-sparse regions, if the jet stream could be accurately located from satellite pictures.

Jet stream positions over the United States estimated from TIROS pictures are compared with positions from operational analyses during a 3-month period. Initially agreement is achieved in about half the cases. The cases are re-examined to determine under which conditions agreement did or did not occur.

Jet streams can be accurately located in about 80 percent of the cases whenever clearly defined cloud characteristics occur under favorable viewing conditions. The most definitive cloud characteristics are (1) an extensive cirrus shield having a sharply defined poleward edge, often outlined by a shadow cast on lower cloud surfaces or on the earth, and (2) transverse banding in the cloud shield. The jet axis is located on the poleward cloud edge. Further, cirrus streaks alone prove to be undependable detectors. The greatest danger exists in confusing frontal cloudiness with jet stream cloudiness. There is the suggestion that operational jet analysis can benefit from satellite pictures even in data-rich areas.

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