ON LOCATING JET STREAMS FROM TIROS PHOTOGRAPHS

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.