Final answer:
The Monsoon season, with its reversal of winds and heavy rainfall, controls the surface flow of the Northern Hemisphere portion of the Indian Ocean. This seasonal pattern greatly affects the region's currents, weather, and agriculture.
Step-by-step explanation:
The seasonal change that controls the surface flow of the Northern Hemisphere portion of the Indian Ocean is the Monsoon. The summer monsoon is characterized by a reversal of winds that bring heavy rainfall to South Asia. A significant portion of this rainfall comes from the warm moist air that is pulled from the Bay of Bengal and the Indian Ocean, due to the vacuum created by the rising hot air over the continent. Conversely, during the winter, the monsoon system is marked by cool, dry winds blowing from the north as a result of the cold, dry air above the Asian continent moving south.
This seasonal airflow reversal heavily influences the currents and weather patterns in the region. The monsoon delivers necessary moisture that feeds rivers and is critical for agricultural practices in these areas. Understanding the interactions of the monsoon system with surface ocean flows is essential for predicting weather patterns and preparing for agriculture and water management.