What causes low and high pressure in the atmosphere?

Question

What causes low and high pressure in the atmosphere?

Answer 1

Heat. When air molecules warm, they become excited and move around hitting each other and bouncing around. This makes the air less dense and it rises up.  Cold air molecules do not move very much and they close in tightly together causing the air to be denser and flow downward.  So, there is a relationship between air temperature and air density.

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Answer 2

I'll narrow down what you're asking by explaining the basic formation of surface low and high pressure systems over land.

Strong surface heating causes the formation of shallow low pressure systems.  These low pressure systems extend only up to about 3000 metres in altitude.   In general, heat lows form over the hottest parts of the landmass.  The higher the temp, the lower the atmospheric pressure will be over that region.   The surface low forms in response to the air being less dense over that area.

Above these surface lows you have high pressure systems that complete the circulation.

Whereas a high pressure system near the surface is located over the coldest regions of the landmass.  Typically the colder the surface temperatures, the higher the surface atmospheric pressure will be since the air is more dense over that region.   A classic example would be the Siberian highs.  The eastern part of Russia is one of the coldest regions in the northern hemisphere.  For this reason, it's very common for a intense high pressure system to lay stationary over that region for months on end.   Any cold fronts and other types of low pressure systems simply move around this high.   Only warm surface heating is able to weaken the high, and it's only then that it's forced to move out of the area.  

I hope this wasn't too basic.  I could give you more advanced information if you need to learn more about it.   I hope it helps in the mean time.

Answer 3

Weather forecasters measure air pressure with a barometer. Barometers are used to measure the current air pressure at a particular location in "inches of mercury" or in "millibars" (mb). A measurement of 29.92 inches of mercury is equivalent to 1013.25 millibars.

Cooler air is heavier, but the skies could be clearer than when warmer air prevails, which is lighter than colder air. Winds flow from the cold high pressure air mass toward the low pressure air mass.

Answer 4

The unequal heating of the earth's surface(both land and sea) by the solar radiation is the main reason for the formation of low and high pressure systems.