A Note on the Magnitude of Jet-stream Winds East of Japan as Derived from Transosonde Data

A comparatively unbiased set of wind statistics at jet-stream level from Japan eastward to the 180th meridian may be obtained from the United States Navy constant level balloon (transosonde) flights launched from Japan in 1957-59. Wind speeds so derived are presented as a function of time of year and longitude at pressure surfaces of 300 and 250 mb. At these longitudes and heights the average speed is 103 kt. in fall, 123 kt. in winter, and 101 kt. in spring. A comparison with mean meridional cross sections indicates tha t at these levels in this area of the northwestern Pacific the mean wind speed heretofore may have been underestimated by an amount exceeding 25 kt.