From the discussion mentioned above:
<font face="Verdana, Arial, Helvetica" size="2">Question: So, you are landing at Madrid, 2000' AMSL, DH 200', is the correction based on 200' of cold air, or 2200' of cold air?
Ans: If you are using the Madrid QNH (as I expect you would) then that QNH is not the "actual" pressure at sea level.
If it was you would require a 2200' correction, and indeed the altimeter would not read 2000' when sitting on the taxiway. The Airport QNH is adjusted, so that an altimeter reads the airport elevation when you are at the airport.
The correction from sea level up to the airport elevation has already been done for you, so you only need to apply a density correction to the height above the airport elevation. (ie 200' in the question).</font>
That probably answers the bit you mention about ATC correcting for cold temperatures.
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Tech Log forum moderator