Trying to truly understand high- and low-pressure systems, I find explanations contradicting. The question is: Where is the mistake in my line of thoughts?

Looking from a surface point of view:

  1. More sun = more heat.
  2. More heat = higher ground pressure (just like heating a bottle)
  3. Higher ground pressure = Hot air wants to expend to all directions
  4. Expending air (also) the vertical axis = rising air, cloud formation.

That is coherent with the notions

  • that high-pressure areas come from the equator while low-pressure areas come from the poles
  • that there is a circulation of air rising around the equator and sinking at the poles.

But it conflicts with the notion

  • that air sinks into high-pressure areas and
  • hence high-pressure areas have fewer clouds than low-pressure areas.

If I flip everything, that conflict is solved while suddenly global circulation and "H from Equator" doesn't fit into the picture.

Additionally, it seems that sometimes air sinks, creating the higher pressure underneath, and other times it starts with the high pressure and air rises. So I might assume that both high and low pressure can origin from both high and low temperatures, and at both, air can rise or fall. Or in other words: whatever, it's free-for-all.

Where is my mistake?

  • $\begingroup$ Earthworm, thanks for your comment. "Differences in warming" seem to be exactly my point 2, "more heat=more ground pressure". $\endgroup$ – Zsolt Szilagy Apr 26 at 15:11
  • $\begingroup$ Nope, that deduction is not right, it is in many cases the other way round (see: thermal low). I don't know were to begin, wikipedia has two articles on high and low pressure, pls. try these. One needs to understand that there can be differences e.g. in insolation, that cause winds to equalize the differences, that are then deflected on a rotating sphere. Furthermore: there's a global circulation, and there are different processes on different scales and a 3-dimensional atmosphere. But the two wiki articles could be a start ... $\endgroup$ – user22279 Apr 26 at 15:48
  • $\begingroup$ Actually, I've spent several hours on the topic, reading Wikipedia, printed books etc. That's my problem: I found all stated sentences in one source or another, they just don't add up. Probably I either miss a step, or make an assumption I’m not aware of. Anyways, thank you. $\endgroup$ – Zsolt Szilagy Apr 26 at 16:12

Your logic is wrong. Do not think of the atmosphere as a closed system. Your analogy of heating a bottle is not appropriate.

In uncomplicated terms, the Sun heats the ground, the ground radiates thermal energy heating the air just above the ground and the heated air rises. In rising, the air heated has less density than the surrounding air. By rising it exerts less pressure on the ground than the surrounding and thus has a lower pressure relative to the air surrounding it - it is a low pressure system.

The rising air reaches the tropopause, around 10 to 15 km above sea level, where it is no longer buoyant. Forced by the continually rising air it travels away from the heated zone. As it moves at such elevations the air cools, increases in density and falls to the ground. As it falls the pressure it exerts on the ground is higher than the air surrounding it and it forms a high pressure system.

The system is best explained with Hadley Cells.

Air tends to rise around the equator and at latitudes 60° north and south, where most of the low pressure systems are located. Air tends to fall around latitude 30° north and south and the poles, where most of the high pressure systems are located.

  • 1
    $\begingroup$ Fred, thank you for your explanation. What confuses me: In Western and Central Europe, the most influential and recurring pressure areas are the southern warm "warm Azores highs" and the northern "cold polar lows". Following your explanation, it should be "warm Azores Lows" and "cold polar highs". Or is it that the latitude (your final paragraph) "overrides" the temperatures? $\endgroup$ – Zsolt Szilagy Apr 26 at 19:19
  • $\begingroup$ The Azores are located at 38.8° N, which is very close to "around latitude 30° north" where high pressure system tend to occur, as I stated in my answer. It is also consistent with "warm Azores highs". $\endgroup$ – Fred Apr 26 at 22:27

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.