AN ANALYSIS OF OPERATIONAL 300-MB TRANSOSONDE FLIGHTS FROM JAPAN IN 1957–58

Abstract

This paper summarizes the operational 300-mb constant-level balloon or transosonde flights made by the United States Navy from Iwakuni, Japan during 1957–58. On the average, the transosondes reached the west coast of the United States 3 days after release in winter and 4 days after release in spring and fall. The trajectories traversed the United States farther to the north in winter than in spring or fall. For these flights, the zonal standard deviation of position increased approximately linearly with time since transosonde release, whereas the meridional standard deviation of position remained practically constant after the transosondes had been aloft 3 days. The mean transosonde-derived wind speed, at 300 mb was 71 kn while the mean cross-contour flow was 7.5 kn and the mean deviation between wind and geostrophic wind speed was 12.4 kn. Zonal and meridional ageostrophic winds derived from the transosondes suggest that, at 300 mb, six or seven per cent of the northward transport of momentum at 37 N is brought about by ageostrophic flow. Power spectrum analysis shows that the meridional wind tends to oscillate with a 54-hr period, corresponding to the average time it takes the transosondes at 300 mb to pass through a typical long wave in the westerlies. The wind speed and zonal wind component tend to oscillate with a period exceeding 5 days, a result of strong winds being found over Japan and off the east coast of the United States. Not as clear-cut is the tendency for the cross-contour flow to oscillate with a period of 30 to 36 hr. Cross-spectrum analysis shows that for oscillations of period exceeding 2 days the maximum zonal wind is to be found near the pre-trough inflection point along the wave-shaped trajectories while the maximum flow toward low pressure occurs near the trough line. However, for oscillations of period 36 to 16 hours the maximum zonal wind is found in the northerlies and the maximum flow toward low pressure occurs on the ridge. Temperatures interpolated to the 300-mb transosonde positions suggest the presence of ascending air motion across the Pacific Ocean and descending air motion across the United States. Contour heights interpolated to the 300-mb transosonde positions suggest the presence at 300 mb between Japan and the east coast of North America of a northward ageostrophic flow of magnitude 2 kn. “Abnormal” flow is discussed briefly, and an example thereof is given.