While the pressure gradient force is from north to south, i.e. from the subtropical high pressure to the equator in the northern hemisphere, why are the winds north easterlies in the tropics.
The pressure gradient force causes air to flow from the subtropical high pressure belt (around 30°N) towards the low pressure at the equator. This would naturally create a wind blowing from north to south.
However, the rotation of the Earth creates the Coriolis force, which deflects the wind to the right direction in the northern hemisphere. As a result, the wind that would have blown directly southward gets deflected towards the right.
Due to this deflection, the wind flows from the northeast towards the southwest in the tropics. Hence, these winds are called north easterlies or trade winds in the northern hemisphere.
Explanation
The textbook explains that while pressure gradient force moves air from high to low pressure (north to south in this case), the Coriolis force deflects winds to the right in the northern hemisphere. This combined effect causes the winds to flow from the northeast direction rather than directly from the north. The context also mentions that air from subtropical highs flows towards the equator as easterlies.
Solution Steps
Step 1: Identify the pressure gradient direction - from subtropical high (30°N) to equator (southward)
Step 2: Apply Coriolis force effect - deflects wind to the right in northern hemisphere
Step 3: Combine both forces - southward flow gets deflected rightward, resulting in northeast to southwest flow