Replace the atmosphere parameters with more accurate ones from ARPC

[francobfort]

@RufousJayes

To be fair, they cannot do such a change based on 2 screenshots.

XP12 has it already with plenty of screenshots, looks pretty convincing

https://www.avsim.com/forums/topic/636337-xp1206b1-is-out/?do=findComment&comment=4992922