Which statement below best explains the cause of global winds? A. The equator has a larger area than the North Pole causing uneven heating of the earth. B. The equator is closer to the Sun than the North Pole causing uneven heating of the earth. C. The equator has more daylight hours per year than the North Pole causing uneven heating of the earth. D. The equator receives more direct sunlight than the North Pole causing uneven heating of the earth.

D. The equator receives more direct sunlight than the North Pole causing uneven heating of the earth.

Explanation:

At a global level, it occurs unequal warming of the atmosphere, which depends on many factors and varies with latitude. This effect occurs because solar radiation reaches the earth differently at different latitudes. Unequal warming of the atmosphere results in convective atmospheric circulation cells: Hardley cell, Ferrel cell, and Polar cell.

The term convective cell refers to air getting warm, expanding, and ascending. As it gets to higher altitudes, it gets colder and thicker, and hence descends again.    

In each hemisphere, warm air ascends at the equator and approximately at 60º latitude. Cold air descends at approximately 30º latitude and at the poles. These air masses circulation generates superficial winds that blow toward the equator between 0º-30º latitude and toward the poles between 30º-60º latitude.

Hardley cell occurs between 0º and 30º latitude (north and south). While the tropical air gets warmer, it ascends and produces a low atmospheric pressure area over the equator. The dense air coming from the north and south moves to a low-pressure area and forms the superficial winds that blow toward the equator.

As the warmed air ascends, it is pushed by new masses of warm air that are also rising. The equator turns to be the divergence point where warm masses of air rise and get separated as they get colder and pushed to the different poles.      

When the air gets cold enough, it descends again at approximately 30º latitude (north and south). This is the horse´s latitude. And the cycle starts all over again.  

Ferrel cell occurs between 30º and 60º latitude, and the polar cell occurs between 60º and the poles.  

High-pressure zones send cold winds from the poles to higher latitudes toward the equator. As these winds go to lower latitude they get warmed, and they start accumulating humidity. Approximately at 60 degrees latitude, they meet with warm winds coming from the horses' latitude (30 degrees latitude). They both ascend while getting cooled. They cannot maintain humidity, so it precipitates. Then winds move back to the poles, where they get cold again, so the cycle continues.