Latitude vs. Cloudiness

Here we can see nearly all of Earth's surface is covered by clouds to some extent, though there is a lighter concentration just south of the equator. According to Nasa's Earth Observatory, clouds tend to form in abundance between latitudes 60 degrees north and south of the equator, as this is where "the edges of polar and mid-latitude (or Ferrel) circulation cells collide and push air upward, fueling the formation of the large-scale frontal systems that dominate weather patterns in the mid-latitudes. While clouds tend to form where air rises as part of atmospheric circulation patterns, descending air inhibits cloud formation. Since air descends between about 15 and 30 degrees north and south of the equator, clouds are rare and deserts are common at this latitude."