i. The north east trade winds blowing in the northern hemisphere and the south east trade winds blowing in the southern hemisphere lead to the formation of monsoon winds. Monsoon winds are winds that change direction in accordance with season. Monsoon is the seasonal reversal of wind in a year.
The factors responsible for the formation of monsoon winds are the apparent movement of the sun, Coriolis force and difference in heating. During the summer in the Northern Hemisphere, high temperature is experienced along the region through which the Tropic of Cancer passes. The pressure belts shift slightly northwards. The south east trade winds also cross the equator and move towards the north.
As the trade winds cross the equator, they get deflected and transfer into south west monsoon winds under the influence of the Coriolis effect. The low pressure formed over the land due to the intense day temperature attracts these sea winds and further contributes to the formation of south west monsoon winds. As a result of the formation of high pressure zones over the Asian landmass during winter and low pressure zones over the Indian Ocean, the north east trade winds get strengthened. These are the north east monsoon winds
ii. Global pressure belts in the northern hemisphere.
- Equatorial low pressure belt: between 5°N and 5°S.
- Subtropical high pressure belt: 30°N
- Subpolar low pressure belt: 60°N
- Polar high pressure belt: 90°N
- Planetary winds in the Northern hemisphere:
- Trade winds: Blow from subtropical high pressure belt to equatorial low pressure belt.
- Westerlies: Blow from subtropical high pressure belt to subpolar low pressure belt.
- Polar winds: Blow from polar high pressure belt to subpolar low pressure belt.