Altimeter readings "mystery".
Hello
I am an Air Traffic Controller, currently being trained for a position in the Guadalajara Airport Radar for Terminal Control.
My question is regarding Meteorology, I hope someone will help me out on solving this "mystery".
We all know that air density, and thus atmospheric pressure, decreases at higher altitudes, given a certain temperature.
Here most of us don't think about this often, we just read our altimeters and transmit the reading to pilots, and that's it. Maybe sometimes we also think about worsening weather conditions based on our knowledge of pressure changes.
One member of our team insists that whenever you see a decrease in the altimeter reading, what is showing is an increase in pressure. He says so because we hear about altimeter readings on the aiports near or on the coast, always much lower readings than miles inland like in Guadalajara, and at higher elevations. So, he concludes, a lower pressure (in Puerto Vallarta for example, one of the nearest airports on the coast, fellow controllers tell us that they read 29.98 inches Hg) indicates a higher atmospheric pressure, whilst in Guadalajara, on a higer elevation and at the same time of day, teh altimeter reads, say, 30.22"Hg.
To me, that is contrary to intuition because as far as I know, the reading is based on the height of the mercury column inside a tube, so the higher the atmospheric pressure, the higher the column.
My guess is that temperature has a very clear influence on altimeter readings on the coast, usually a much higher temperature there than locally on Guadalajara, and that causes that discrepancy.
Any help? Thank you!