Abstract
A comparison of the mean winter and summer flow patterns at 8 km in the vicinity of India shows that a trough located to the east of India in winter has shifted westward by summer. A study of the onset of the summer monsoon during 1946 shows that this movement is comparatively rapid and coincides with the “burst of the monsoon” over India. The movement of the trough is explained as being due to changes in the long-wave pattern brought about by the presence of the Himalayan mountain complex combined with seasonal variations in the latitude of the circumpolar jet stream of the northern hemisphere.