294 ANNUAL REPORT SMITHSONIAN INSTITUTION, 195 7 



over Japan. The air speeds at that time were such that a high-level 

 bombing run from east to west under such conditions meant that 

 an aircraft would present a stationary target for the antiaircraft 

 batteries below. Here, then, was a meteorological phenomenon whose 

 military significance could not be ignored. 



The impact of this discovery on the meteorological world left little 

 time for serious reflection on the nature of these strong, high-level 

 air currents, which were later to be named "jet streams." Many 

 questions remained unanswered. For instance, where are jet streams 

 found? What is their structure? How do they behave? To an- 

 swer these and other questions, the Office of Naval Research of the 

 United States Navy sponsored a general atmospheric circulation 

 project at the University of Chicago in 1946. Dr. C.-G. Eossby, one 

 of the world's leading meteorologists, was called upon to direct the 

 project. His colleagues were Palmen, Riehl, and many other out- 

 standing meteorologists. Since then, research activities related to 

 jet streams have spread to all parts of the world. 



For a period of time, attention was focused on meteorological 

 analyses of upper winds and temperatures obtained by radiosondes, 

 which consist of meteorological instruments coupled with a small 

 transmitter carried aloft by hydrogen- or helium-filled balloons. 

 Winds were obtained by tracking the balloons with radar equipment. 

 Out of these studies emerged a fairly complete large-scale picture of 

 jet streams which has remained substantially unchanged in the light of 

 subsequent research. In more recent years, research has been directed 

 to the finer details of the wind field. A large part of jet-stream re- 

 search is still being conducted by the United States Navy, Bureau 

 of Aeronautics Project AROWA (Applied Research Operational 

 Weather Analysis), at various locations in the United States and 

 other regions of the world. Also actively engaged in this field is the 

 Geophysics Research Directorate, Air Force Cambridge Research Cen- 

 ter, which is sponsoring Project Jet Stream. The main task is to 

 determine precisely the horizontal and vertical distribution of wind in 

 jet streams in a large number of cases. For this purpose, specially 

 instrumented aircraft are flown through jet streams, taking contin- 

 uous observations whose analyses will yield details unobtainable in 

 any other way. 



STRUCTURE OF THE JET STREAM 



As a result of the intensive preliminary studies at the University 

 of Chicago and other institutions throughout the world, a relatively 

 clear picture of the jet stream began to emerge. It was found that 

 jet streams are worldwide features of the atmosphere. That is, they 

 are essentially high-speed rivers of air that encircle the earth in the 



