Mesospheric temperature trends at mid-latitudes in summer, Berger et al, 11/2011; ``... This large cooling is primarily caused by long - term changes of ozone in the upper stratosphere in combination with a CO2 increase.» (notrickszone.com)
A more frequent positive phase is associated with a more active Sun due to cooling of the polar stratosphere (less mesospheric ozone descending through the polar vortex) and consequent lifting of the polar tropopause. (newclimatemodel.com)
It is also proposed that, over time, the changes at the higher mesospheric level dominate because the higher level effect gradually filters down to lower levels through the descending column of air within the polar vortices as described above. (newclimatemodel.com)