ON THE ANNUAL VARIATION OF THE MONTHLY MEAN MERIDIONAL CIRCULATION

Abstract

Abstract Data for a 5-yr period from a dense network of upper air stations have been used to determine the annual cycle in the mean meridional circulation north of 15°S. Only during the transition months April, May and October, November is there some degree of symmetry with respect to the Equator. During the other months of the year, the Hadley cell of the winter hemisphere with a maximum strength of about 23 × 1013 gm sec–1 appears always to dominate the circulation. The Hadley cell of the summer hemisphere practically disappears, except possibly near the surface. Maximum meridional velocities connected with the winter Hadley cell are about 2.5 m sec–1 near 1000 mb and over 3 m sec–1 near 200 mb. Mean vertical velocities attain values of about 5 and 8 mm sec–1 in the downward and upward branches of the winter Hadley cells. A rather weak Ferrel circulation (about 4 × 1013 gm sec–1) and a very weak polar circulation (about 1 × 1013 gm sec–1) are computed in middle and high latitudes throughout the year. Wi...