Trends and Solar Irradiance Effects in the Mesosphere

We investigate trends and solar irradiance effects in the mesosphere using the Whole Atmosphere Community Climate Model with eXtended thermosphere and ionosphere (WACCM-X) and radar measurements of winds at Collm (51°N, 13°E), for the period of 1980–2014. We found that in the mesosphere, dynamics significantly impact temperature and wind trends, as well as how solar irradiance affects the temperature and winds. The global average temperature trends are negative, with a maximum of ~−1 K per decade in the middle to lower mesosphere. Solar irradiance effects on the global average temperature are positive and decrease monotonically with decreasing altitude, changing from ~3 K/100 solar flux units (sfu) near the mesopause to ~1 K per 100 sfu in the lower mesosphere. In the summer upper mesosphere, temperature trends can become near 0 or positive, likely due to dynamical effects. Both wind trends and solar effects on the winds show dynamical patterns with negative and positive values, indicating that they are predominantly controlled by dynamics. The wind trends and solar effects on the winds are on the orders of ~±5 m/s per decade and ~±5 m/s per 100 sfu, respectively, and they are not as statistically significant as their temperature counterparts. At Collm (51°N, 13°E), the observed zonal winds at 90 km have a larger trend of 1.98 m/s per decade compared to the simulated zonal winds and it is statistically significant, but both the simulated and observed meridional winds do not have statistically significant trends.