300 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1957 



strong wind could be maintained by flying along the same isotherm. 

 He further states : 



An amazingly accurate guide for calculation of wind strength on either side 

 of the jet stream (within altitude limits normally flown; viz, 15,000-25,000 ft.) 

 was that the wind decreased some 8 knots for every degree Centigrade drop in 

 temperature on the polar (or cold) side; and it decreased some 16 knots for 

 every degree Centigrade rise on the equatorial (or warm) side. 



N. E. Davis, writing in the September 1954 issue of the Meteorolog- 

 ical Magazine, described a successful trans- Atlantic crossing in a 

 jet stream by a B. O. A. C. Stratocruiser, under Capt. L. V. Messen- 

 ger and Navigating Officer M. H. Sutcliff, on August 2-3, 1953. By 

 the judicious use of their outside air thermometer, they were able to 

 locate and fly for three hours (about 1,000 miles) in the strong winds 

 below a jet stream. The penetration of the jet stream from the cold 

 side was indicated by a sudden rise in air temperature. 



Therefore, to maintain strong tail winds when flying below the jet 

 axis, one should endeavor to stay in the warm air. Above the jet 

 stream, one should try to stay in the colder air to the right of the 

 jet axis. In a similar manner, the temperature field can be used to 

 detect and maintain a track along which the headwinds will be more 

 favorable, if one is flying into the wind. 



Research flights across jet streams have revealed some interesting 

 details of the wind field in the vicinity of their axes. The results of 

 several such flights under project AROWA have recently been pub- 

 lished. v They have shown that the wind speed is rather variable with- 

 in a jet-stream core. Winds have also been found to vary consider- 

 ably with time at a fixed point. For instance, Lt. Col. R. C. Bund- 

 gaard, U. S. A. F., reported that the wind speed changed from 120 

 knots to 60 knots, and again to 120 knots, within 4 hours at 34,000 

 feet over Dayton, Ohio, on March 5, 1954. On another occasion, five 

 B-47's observed a wind change from 200 to 72 knots at 40,000 feet 

 over Alabama during a 3-hour period on April 14, 1953. Such varia- 

 tions are impossible to forecast at the present state of knowledge. It 

 is hoped that further research into the mechanics of air motion will 

 provide answers in the future. 



CLOUD FORMS OF THE JET STREAM 



Through the work of Dr. Vincent J. Schaefer, of the Munitalp 

 Foundation, Inc., and many military as well as commercial pilots, 

 there has now been gathered considerable information on cloud forms 

 associated with jet streams. This knowledge can be used as an auxili- 

 ary tool to locate jet streams. 



Dr. Schaefer has found four main cloud types associated with jet 

 streams. They are cirrus, cirrocumulus, lenticular altocumulus, and 



