Abstract
In earlier papers it was shown that tropospheric vertical wind shear in the layer 850–200 mb decreases appreciably prior to formation of depressions in the Indian summer monsoon area. Further analysis reveals that this decrease in shear stems almost entirely from the upper troposphere between 400 mb (7.4 km) and 250 mb (10.5 km).
During the southwest monsoon period (June–September) the tropospheric wind shear over the Indian subcontinent is found to wax and wane in periods of 5–10 days in the latitudinal belt 9–27°N with an amplitude of the order of 35 m s−1 (650 mb)−1. These oscillations in wind shear thus appear to be a characteristic of the monsoon atmosphere. The phase of the shear oscillation south of about 16°N is opposite to that in the north.
