Geopotential height and pressure relationship

[03jtrickey]

Hi,

I have a probably fairly basic question about geopotential height, which has bugged me for a while.

What is confusing me is that...if pressure falls, this means that the atmosphere is less dense and therefore thicker. Therefore by my logic, since pressure would fall more slowly one would need to travel higher in the atmosphere in order to reach, say, the 500mb pressure level under low pressure conditions than under high pressure conditions. This seems to suggest that high heights ought to be associated with low pressure and low heights with high pressure.

However, on the charts, low pressures seem to have low heights and high pressures typically higher heights, e.g. height rises over Greenland are associated with the establishment of high pressure in that area etc. Can anyone help to put me out of my confusion and explain why this is the case? I feel like there is something really obvious that I am missing!

Thanks

[03jtrickey]

Thank you very much, weather09! That makes sense!

For some reason I had envisaged low pressure as the atmosphere expanding in terms of thickness above a point, rather than thinking about the rising motion of the air.