Hi Rik,

Pressure is usually quoted with the figure corrected to sea level so that a
meaningful comparison can be made between different locations. If you don't
do this then the pressure pattern is just a chart of height because, as you
point out, the pressure gradient is very much greater in the vertical than
the horizontal.
ICAO and WMO have different rules for the correction so there are two sea
levels pressures at airfields and the station level pressure as well!!

Frankie


"Rik O'Shea" wrote in message
om...
Hello,
my understanding is that air pressure [mb] or [hPa] (metric units
please) descreases with altitude. A rough rule of thumb that I've seen
cited is that the correction is 1 millibar for each 8 meters of
altitude gain.

Looking at the weather for Mixico city in the links below I see an
Air-Pressure 1011.2 hPa or Millibar.

I would have though that the measured air-pressure in Mexico city
(2300 m) would
be of the order of ~ 800 hPa. Can someone enlighten me on this issue ?

Thanks & regards

http://www.wetter.com/home/cooperati...18 2&type=WMO

http://www.bbc.co.uk/weather/5day.shtml?world=0300