The correct option is D Northward shift of the subtropical westerly jet stream
Many scientists believe that the northward shift of the subtropical westerly jet stream is the first indication of the onset of the monsoon over the Indian subcontinent. If the jet stream withdraws earlier, the monsoon also arrives early. If the jet stream withdraws later then monsoon is also delayed. The timing of the withdrawal of the jet stream affects the onset of monsoon in the Indian Subcontinent.