Observed “long-term” temperature change in a midlatitude mesopause region in response to external perturbations

Analysis of seven years (1990–1997) of measured temperature profiles in the mesopause region (84 to 102 km) at Fort Collins, CO (41°N, 105°W), shows that, after removing seasonal variations, there was an episoidic temperature excursion with an amplitude ranging from 7 K to 14 K. Observable increases began in 1992, maximum temperatures occurred during the first half of 1993, and the excursion was over by about 1996. Since this excursion followed the Mount Pinatubo eruption by a time scale consistent with published model simulations of the effect of stratospheric aerosol on the mesopause region, we attribute the temperature excursion to that eruption. In addition the data is consistent with a background cooling of roughly 1 K per year, most of which may be attributable to variability in the solar flux. Continued observation towards the coming solar maximum promises to quantify (assess) the “long-term” change in mesopause temperatures resulting from solar variability (anthropogenic effect).