A WACCM-PMC attribution study investigating why the solar cycle signal disappeared in the polar mesospheric clouds

The response of the polar mesosphere to decadal variability (11-year solar cycle, greenhouse gases) is investigated using satellite observations and attribution studies using NCAR’s Whole Atmosphere Community Climate Model (WACCM). 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, temperature and water vapor observation record to track variability in the summer polar mesosphere. The mesospheric satellite observation records span between 1978- 2023 and indicate that PMCs, temperature and water vapor vary with the 11-year solar cycle and show evidence of long-term trends that could be associated with greenhouse gas increases. PMC observations showed a clear anti- correlation with the solar cycle before 2004, however, the solar cycle response is curiously absent between 2005-2020 but appears to be recovering in the last few years. To untangle why the solar cycle seems to have disappeared over ~two decades, we conduct attribution studies using the WACCM-PMC model (WACCM coupled to a PMC parameterization) to isolate and quantify decadal influences to the PMC, temperature and water vapor data record. This talk will present the data and model results which show that a perfect combination of green-house gas increase and decreased solar activity caused the solar cycle signal in the PMC data record to disappear.