What exactly do meteorologists mean by the term "high pressure"? Do they mean the <i>weight</i> of the column of air above ground or is it some other feature which they are measuring? In the winter, very cold clear air is associated with a high pressure area and the increased density of the cold air accounts for the "high" pressure.
But in the summer high pressure areas are associated with warmer air and this seems to contradict the logic of the first case, as the hot air is less dense and should therefore create relatively "lower" pressure. Please explain!
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