With observations made in northern Norway in the article Seasonal variation of the turbopause' One year of turbulence investigation at 69°N by the joint University of Tromso/University of Saskatchewan MF radar (Hall et al. 1998) showing that the levels at these latitudes decreasing in summer months.

However, long term changes seem to be occurring at high latitudes, with the Hall et al. (2008) observing

the classical radar turbopause has been at constant altitude at 52°N during the last decade. At 70°N, on the other hand it appears to be moving upward at a rate of between 2 and 7 km decade$^{−1}$.

Although the authors suggest that there may be an anthropogenic cause, the observed reasons for the high latitude change appears to be due to:

the trend we report at 70°N is commensurable with an observed cooling of the mesosphere (and in turn a lowering of the ionospheric E region altitude) and an increasing average electron density in the ionospheric D-region.