Earth's weather is controlled by intricate patterns of convection and circulation. There are three convection cells in each of the northern and southern hemispheres; these circulate air from the top to the bottom of the atmosphere. In addition, there are bands of winds similar to those seen in much larger scale on Jupiter. Near the equator, the prevailing winds blow westward and toward the equator. In the mid-latitude bands of both hemispheres the winds travel eastward and toward the poles. The atmosphere over the North pole circulates clockwise while the air over the South pole circulates counter-clockwise. In addition to this mass motion in the atmosphere, smaller cyclonic, or spiraling, motions are very common. These can range in size and intensity. The clouds in the atmosphere, composed of water vapor, are tracers of all of this motion. At any given time, a large percentage of the surface is hidden from view by satellites by these clouds.
