Trade winds: It is the wind blowing steadily towards the equator from the north-east in the northern hemisphere or the south-east in the southern hemisphere, especially at sea. Two belts of trade winds encircle the earth. These winds are called trade winds because of the fact that they helped the sea merchants in sailing their ships as their (of trade winds) direction remain more or less constant and regular. There is more or less regular inflow of winds from subtropical high-pressure belts to the equatorial low-pressure belt.
Characteristics of Trade winds:
- According to Ferrel’s law (based on Coriolis force generated by the rotation of the earth), trade winds are deflected to the right in the northern hemisphere and to the left in the southern hemisphere.
- There is much variation in the weather condition in different parts of the trade winds. The poleward side of the trade winds or eastern sides of the subtropical anticyclones are dry because of the strong subsidence of air current from above.
- Because of the dominance of the anticyclonic conditions, there is strong atmospheric stability, strong inversion of temperature and clear sky.
- On the other hand, the equatorward part of the trade winds are humid because they are characterized by atmospheric instability and much precipitation as the trade winds while blowing over the oceans pick up moisture.
- Trade winds are more regular and constant over the oceans than over the lands. At some places on the lands (eg. S.E. Asia and the southern USA) the trade winds disappear during the summer season due to the formation of low-pressure cells because of high temperature but the trade winds are more constant and regular over the continents during the winter season.
- It may be pointed out that the zone of trade winds is called Hadley Cell on the basis of the convective model prepared by Hadley for the entire earth