Rain Shadow of the Himalayas

The picture above is a satellite view of the Tibetan plateau, found north of the Himalayas. The green land to the south of the Himalayan mountains is India, which receives enough precipitation to support a tropical rainforest. North of the mountain range you can see a great plains region and the Gobi Desert; areas that receive very little rainfall. How can we account for such a change in the amount of precipitation each place receives? The short answer is "rain shadow", and it happens in the United States as well. It is largely the reason that Western South Dakota receives approximately 5 less inches of rain per year than we do here in Sioux Falls.
In your response on Classmarker (it will be on the Fronts and Air Masses Standard Check), explain what happens to the air mass that initially forms over the Indian Ocean as it travels north. Why does this process leave so much precipitation on the south (windward) side of the Himalayas, and hardly any to the north of them?
Note: You should answer this question on Classmarker. It will be worth 4 points.