Air Motions in the Tropical Stratosphere Deduced from Satellite Tracking of Horizontally Floating Balloons

Abstract

Between June and November of 1970, 26 GHOST-type constant-level balloons were released from Ascension Island (8S) for flight at 30 and 50 mb. The balloons were positioned by the Interrogation, Recording and Location System (IRLS) aboard the Nimbus D satellite. Eight of the flights at 50 mb and three of the flights at 30 mb were tracked for more than one month, and one 50-mb flight was tracked continuously for more than five months while making seven circumnavigations of the earth. During the period June 1970 to March 1971, the 50-mb flights drifted northward at a mean speed of ?0.1 m sec?1. The northward drift was a maximum in the Northern Hemisphere winter, suggesting a weak upward extension of the Hadley cell to at least 50 mb (the 30-mb data were insufficient for such an analysis). Superimposed an this drift were oscillations in meridional velocity having an approximate two-month period, with these oscillations also being most pronounced in the Northern Hemisphere winter. Small (1?3 m set?1) short-period fluctuations in meridional velocity were evident directly above the equator at 50 rob. Thew waves appear to move wesiwaid at speeds of 30?40 m sec?1 and to have a wavelength of about 90? longitude. They were responsible for transporting small amounts of westerly momentum into the winter hemisphere. Kelvin waves were also delineated by flights near the equator. These waves appear to move eastward at speeds of 30?40 m sec?1 and to have a wavelength of 360° longitude. Some comparisons are made between these IRLS data and those obtained from GHOST balloon flights at the same heights in early 1969.