The Circulation of the Tropical Stratosphere in the Years 1954–1960

Abstract

The circulation is described in terms of three components: the long-term mean, the annual cycle and a newly-discovered 26-month cycle, referred to as the equatorial stratosphere wind oscillation. Mean winds are everywhere easterly, except that very weak westerlies may possibly exist near the equatorial tropopause. The easterlies increase with height and are strongest between latitudes 10N and 15N. The amplitude of the annual cycle rises from near zero at the equator to a maximum of about 10 m/sec at approximately 25N and undergoes little change with height. Peak easterlies occur in late July or early August. The amplitude of the 26-month cycle is greatest near the equator, attaining a value in excess of 20 m/sec at the 25-mb level. Below this level the amplitude decreases, and the oscillation fades away in the vicinity of the tropopause. In the poleward direction it is still faintly detectable near 30N. The phase varies with height, each band of easterly or westerly winds appearing first at the highest levels observed (about 30 km) and progressing downward at a speed of slightly greater than 1 km/mo.