Investigating the response of the polar mesosphere to the 11-year solar cycle

Abstract:

The response of the polar mesosphere to the 11-year solar cycle is investigated using satellite observations and modeling runs from NCAR’s Whole Atmosphere Community Climate Model (WACCM). The long mesospheric satellite observation records (data spanning between 1978-2019) indicate that mesospheric ice clouds, temperature and water vapor vary with the 11-year solar cycle. Because polar mesospheric clouds (PMC) are excellent monitors of mesospheric conditions due to their extreme sensitivity to temperature and water vapor, we use the PMC observation record to track variability in the polar mesosphere. Solar maximum is expected to cause higher temperatures and lower water vapor in the upper mesosphere, thus reducing the amount of PMC ice. PMC observations showed a clear anti-correlation with the solar cycle before roughly 2002, however, this response is curiously absent during the recent Solar Cycle 24. The satellite observations suggest that the main cause of the diminished solar cycle in PMCs appears to be a dramatic suppression of the solar cycle response of water vapor in the last cycle.

To untangle this discrepancy, we conducted attribution studies using the WACCM-PMC model to isolate decadal influences to the PMC data record. Model results show an agreement with observations through Solar Cycle 23, with a clear solar cycle signature in PMCs and mesospheric temperature and water vapor. However, there is a divergence in the model/data agreement in Solar Cycle 24 indicating a possible change in the way the atmosphere responded to a weak solar maximum. Our attribution studies also examined the effect of large volcanic eruptions on conditions near the polar summer mesopause. We will discuss our results and the implications for mesospheric trend and variability studies.