I am taking a navigational course and part of it is about meteorology. There is one thing which is, although obvious, quite hard for me to grasp.

Looking at a global weather map like this: https://earth.nullschool.net I can see the High pressure area on the Atlantic pushing air towards Europe and into the Low pressure area in the North pole.

My understanding is that High pressure = Cold air, flowing clockwise and outwards. Viceversa for the Low pressure.

What I don't understand is why there is an area of High (cold) over the Atlantic in the tropics and Low (warm) in the Poles, while I would expect the Atlantic to be warmer than the North pole (and indeed it is, if you look at surface temperature). My expectation would be the opposite should happen.

  • $\begingroup$ You shoudn't really compare air masses between The Atlantic and the Arctic. A High on the Atlantic would mean colder temperatures locally, but it doesn't mean it's colder than the North Pole. $\endgroup$ – jgadoury Nov 11 '16 at 15:53
  • $\begingroup$ @jgadoury so you are saying that the HP on the Atlantic is there because the sea is locally colder that the surroundings (which I understand, being water slower to heat than land) and then it starts moving around and ending up towards the pole where (and I don't know why) it is locally hotter? Is it hotter because of the Iceland/Greenland landmasses? $\endgroup$ – Tallmaris Nov 11 '16 at 16:20
  • $\begingroup$ Pressure patterns are not generated locally, but the movement of air masses. As you know, the temperatures in the tropics are warmer than the poles, creating a temperature gradient. Due to physics, the atmosphere tries to redistribute this energy, resulting in atmospheric waves that move air masses and generate low or high pressure systems at the surface. This affects temperatures on a large scale. After that, local temperatues can be affected further by temperature advection due to the rotation of the weather systems moving air at the surface. Sorry if it's not clear, I'm trying to simplify $\endgroup$ – jgadoury Nov 11 '16 at 16:35

The Bermuda high is centered near the horse latitudes, where air from the tropical Hadley trade wind cell is sinking. This forced sinking of air can dynamically contribute to high pressure even if the air is warm --- warm air can be forced to sink against its own buoyancy in a Ferrel-type circulation. But the Bermuda high is helped thermally too, at least in summer, because the Atlantic Ocean at those latitudes, at least in summer, is cooler than North America and much cooler than the Sahara at the same latitudes. It is certainly easier for a Ferrel-type circulation to work against cooler surface temperatures than against warmer ones.


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