The Hadley cell is a pattern of atmospheric circulation in which warm air rises near the equator, moves towards the poles above the surface of the Earth, cools and descends at around 30 degrees latitude, and then moves back towards the equator.

Option 1: Incorrect. The Intertropical Convergence Zone is where the trade winds of the northern and southern hemispheres converge. This is not where the air descends but where it rises, leading to its exclusion as a possible answer.

Option 2: Incorrect. Doldrums are regions near the equator with a lack of wind due to the air rising. Again, this is not where the air descends in the Hadley circulation.

Option 3: Correct. Subtropical high-pressure cells, found roughly at the 30 degrees latitude in both hemispheres, are precisely the sites where air descends in the Hadley Cell. This downward motion creates a zone of high pressure.

Option 4: Incorrect. Equatorial troughs are areas of low pressure near the equator where air tends to rise, not descend. Thus, this option is wrong.