The influence of anthropogenic greenhouse gases emissions on noctilucent clouds and their response to the solar cycle

The increasing emissions of greenhouse gases, especially CO2  and CH4, have a significant impact on Earth’s climate as they contribute to global warming. In the upper atmosphere, however, the consequences are different. Understanding the impact of this phenomenon on the upper mesosphere is challenged by difficulties and limitations in measuring atmospheric properties. Noctilucent clouds (NLCs) have been proposed as important tracers in the summer mesopause region due to their high sensitivity to atmospheric background conditions such as temperature, water vapor concentration, and dynamics. Recently, we studied the long-term trends in the response of NLC properties and the background atmosphere to the solar cycle during the period 1849-2019, which covers 15 complete solar cycles (Solar Cycle 10 to Solar Cycle 24) with increasing concentrations of CO2 and CH4. We utilized model simulations from the Leibniz Institute Middle Atmosphere (LIMA) and the Mesospheric Ice Microphysics And tranSport (MIMAS) over 170 years. We found that background temperature and H2O show an apparent response to the solar cycle throughout the study period, which intensified after 1960 due to increased greenhouse gas emissions. The properties of NLCs, such as maximum brightness, mean radius of ice particles, and ice water content (IWC), respond to the solar cycle, and these responses increase with time mainly due to an increase in water vapor. NLC altitude responds positively to the solar cycle, mainly due to temperature changes caused by the solar cycle. The response of NLC properties to the solar cycle varies with latitude, with most NLC properties showing larger and similar responses at higher latitudes (69°N and 78°N) than at mid-latitudes (58°N). We will also present results from our recent simulations projecting into the future up to 2070, based on RCP 8.5 scenarios for increasing greenhouse gases.