Validity of Reported Extreme Wind Speeds in the Arctic Stratosphere at SST Altitudes

Abstract

Wind speeds of more than 100 m sec?1 (sometimes exceeding 150 m sec?1) were often recorded in the Canadian stratosphere prior to the winter of 1967?68, and occasionally recorded over Alaska, Greenland and Eurasian arctic regions. For the stations at which these extreme winds occurred, all values greater than 100 m see?1 were recorded at or near the termination level of the rawinsonde and/or at very small elevation angles, suggesting instrumentation error. Previous studies have established that the RMS wind speed error grows rapidly as elevation angles become small and as altitude of measurement increases above 20 km. Mathematical determinations of the horizontal temperature gradients at these altitudes over Canada, using the thermal wind relation and observed wind extremes, are shown to be at least 50% larger than the observed temperature gradients for distances of 150 to 300 mi. Also, speeds exceeding 100 m sec?1 in the Canadian arctic have rarely appeared in the records since the winter of 1966?67, probably a consequence of changes in Canadian upper-air sounding procedures. As a result, virtually all of these unusually strong winds which have been recorded by rawinsondes at altitudes above 20 km are considered unreliable. They should either not be used or used with extreme caution in developing climatologies related to the design and operation of the SST and other aerospace vehicles.