A Case Study of Variations in Structure and Circulation about Westerly Jet Streams over Europe

Abstract

This paper contains a case study of multiple wind maxima over western Europe during January 1951. One stratospheric and two tropospheric jet streams (600 km apart) are shown over the British Isles, where the flow was almost zonal and quite steady latitudinally for the period discussed. The northernmost tropospheric jet stream rises locally as much as 3,000 meters in height and 13 degrees in potential temperature during a 12-hour period. The southernmost maximum curves sharply southward downstream to pass over the Mediterranean where it is associated with a wave train separate from that over northern Europe. Two 30-hour mean cross sections (means of six observation times), at longitude 4° West and at longitude 10° East, show the space changes in wind, temperature and potential temperature in the exit region of the jet stream. Mean vertical velocities over the same 30-hour period are computed using several different techniques, and the errors in the computations due to restrictive assumptions are discussed. Neglect of ageostrophic components may change the vertical motion results by as much as 50%. The vertical-motion patterns are significantly different from those suggested by some previous studies, with rising motions on the right side of the jet in the difluence region.