Note on the Structure of the Stratospheric Easterlies of Midlatitude1

Journal/Book: Reprinted from JOURNAL OF APPLIED METEOROLOGY Vol. 2 No. 3 June 1963 pp. 427-429. 1963;

Abstract: University of Minnesota 9 November 1962 and 10 January 1963 1This work was made possible by Contract Nonr-710(22) sponsored by the Office of Naval Research. 1. Introduction The steady nature of the easterly current of the summer stratosphere is now well known but defies quantitative description because the error in conventional wind observations is of the same magnitude as the observed variability. It is the purpose of this note to call attention to the magnitude of the true wind variability as determined from an analysis of accurately positioned constant altitude balloon trajectories. The trajectories not only demonstrate the low variability of easterlies but show that the wind patterns in which the major portion of the variability occurs are considerably smaller scale than the typical patterns of the troposphere. 2. Data and analysis The basic data consist of 15-min-average winds determined from the trajectories of some 60 stratospheric balloon flights made in Minnesota during June through August over a ten-year period. Fights varied in altitude from 80 000 to 115 000 ft and in duration from hours to as long as two days. Most of the flights were made for cosmic ray studies and many of the trajectories have appeared in technical reports of the Atmospheric Physics Group of the University of Minnesota.2 The mean easterly current is assumed to increase linearly with altitude from 18 kt at 80 000 ft to 25 kt at 115 000 ft and in view of the low overall variability variance of the zonal component has been computed about the mean seasonal speed for the same altitude. The mean seasonal meridional wind is zero within the accuracy of the measurements. The variance of the winds measured from balloon trajectories as computed about the seasonal mean is shown in Table 1 (without Table). Two sets of wind variance measured by conventional radiosonde techniques are given to illustrate the greater variance of these measurements. The most complete summary of wind variance at these altitudes has been given by Murakami.3 Unfortunately for this comparison he has included the month of September (a month in which the stratospheric easterly current frequently breaks down at midlatitudes) and his data therefore include a variance due to seasonal changes that is absent in the balloon trajectory data. ... ___MH

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