What causes a decline in atmospheric pressure?
Well, yes a low pressure decreases the atmospheric pressure, it’s in the name! But why and when does it happen? The sun heats the earth and the sea. That heats a layer of air right above it. Warmer air is less dense and therefore lighter. Lighter air rises. Because of the lesser pressure aloft, that air cools down by the so-called adiabatic effect. Once as cold as the surrounding air, it stops rising. But, in the process of rising, it creates a void at the base that must be replaced by incoming air: the wind! That can happen in so many different places; for example the black surface of a parking lot will see a tiny low pressure and a thermal parcel rising. This is what I use to climb when I fly a glider. During a sunny day, near a coast, the land gets warmer than the sea and the entire land region works as a low pressure, bringing moist air from the sea that rises to form nice cumulus clouds. This is called a sea breeze. Near the tropic, it can get much bigger. We are now talking about
