1. Halley’s Thermal concept: Indian monsoon is because of contrast between Indian Subcontinent and adjoining Indian Ocean. Halley’s theory, suggested in 1686, considers the summer monsoon to be a regional phenomenon.
  2. Aerological concept: This was suggested by R. Scherhag in 1948. According to this theory, monsoon circulation develops due to changes in air temperature at all levels over the Indian Subcontinent and adjoining Indian Ocean.