Upper thermospheric variability over Millstone Hill during the LTCS‐2 and LTCS‐6 Campaigns

Abstract

We report on winds and temperatures observed in the upper thermosphere over Millstone Hill during the coupling energetics and dynamics of atmospheric regions (CEDAR) Lower Thermosphere Coupling Study 2 (LTCS‐2) and LTCS‐6 campaigns conducted during December 6–11, 1988, and December 4–11, 1991, respectively. Comparable geophysical conditions which prevailed during these periods facilitate their intercomparison and our investigation of interannual and day‐to‐day variability. Our analyses suggest that variability in exospheric temperature is largely characterized by variations in both the diurnal mean and tidal harmonics. While there may be unresolved signatures of geomagnetic effects in these data, the observed variability appears to be correlated with changes in the EUV forcing as represented by the 10.7‐cm solar radio flux. Conversely, variations on shorter (< 6 hours) timescales characterize the day‐to‐day variability observed in the thermospheric winds for the periods. These signatures may be partially attributable to changes in aurorally driven circulation, but our results are not conclusive. Finally, the wind and temperature signatures that we observe confirm that upward propagating semidiurnal tides do not play a preeminent role in the energy and momentum budgets of the middle latitude upper thermosphere during solar maximum winter conditions.