Trends and Solar Irradiance Effects in the Mesosphere

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Friday, March 29, 2019

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.

Graph of Monthly mean global average temperatures
Monthly mean global average temperatures (red lines), their multiple linear regression fittings (black lines), temperature trends (K per decade), the standard deviations of the trends (sigma, in kelvins per decade), and solar effects on temperatures (the relation between temperature and solar irradiance, kelvins per 100 sfu), at six different altitudes from 105 to 55 km, simulated by Whole Atmosphere Community Climate Model‐eXtended, for the period of 1980–2014. The bottom panel shows the corresponding 81‐day average F10.7 index.

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.

Publication Name: JGR

First HAO Author's Name: Liying Qian