MET-question concerning pressure levels

[austrianpilot]

Hey guys,

this is my first thread here and I hope there's someone that could help me with my problem. There's a question in the MET-exams, which answer I can't understand:

Q: "Flying from Marseilles (QNH 1012) to Palma (QNH 1015) at FL100. You don't reset the altimeter, why would the true altitude be the same throughout the flight?"
A: "Air at Marseilles is warmer than air at Palma"

I can't figure out, why that's the correct answer... Can someone help me please?

[hvogt]

If you fly from Marseilles to Palma at FL100 you will follow a surface of constant atmospheric air pressure. The true altitude of this surface will depend on the density of the air below. Flying from Marseilles, where the QNH is lower, to Palma, where the QNH is higher, you would normally expect your true altitude to increase. Since true altitude (height of FL100 above MSL) remains constant, it must be colder in Palma.

Does this help?

[ashdaman]

im only a ppl, is it anything to do with the atmosphere being thicker near the equator you go because of the rotation of the earth?

[austrianpilot]

@hvogt, thank you very much. I came to the same conclusion, but I was a bit confused... maybe I need a break and learn another subject for a while... ;-)

[mad_jock]

its trying to get you to think about density altitude.