What is a zone of weak, variable winds located at 30 degrees north and 30 degrees south?

Horse latitude, trade winds

Explanation:

The area of the low pressure or the calm consists of the variable light winds that blow near the equator are known to the marines as the doldrums and they form a circuital pattern near the earth atmosphere.Forms at a center of the near the higher pressure systems called as the horse latitudes where the  trade winds at the surface are weak and variable and this zone is found generally in latitudes of the 30° North and South of the equator and move in an east to west direction.