Ok,
Reading the Australian BAE 146incident analysis of met conditions contributing to the cause of the engine rollbacks we have the Fohne effect at altitude. The same effect that caused a 15 deg temp rise in my garden in Bergamo, south of the Alps one December afternoon, within less than 30 mins.
The dynamic effect of the tropopause causing air to rapidly descend, with a modified moisture content, and now drier that the surrounding air mass and rapidly heating as it goes until it runs out of energy.
And I always thought hot air rises! God knows how I got my Siver C!