(a) Fill in the blanks with appropriate words.
When air _______________(heats/cools), the air molecules _____________(spread out/come closer) so that there are fewer air molecules in the same space. _______________(Warm/Cool) air weighs less than _______________ (Warm/Cool) air, which means that warm air presses down on the earth less than cool air. Less pressing means _____________ (less/more) pressure. Thus, a mass of warm air creates an area of low pressure. Warm air rises and produces clouds. So, _______________ (low/high)pressure areas usually bring rain or storms.
(b) Now, explain how high pressure areas are associated with clear skies.