Greenhouse gas effects on the solar cycle response of water vapour and noctilucent clouds

Abstract. The responses of water vapour (H2O) and noctilucent clouds (NLCs) to the solar cycle are studied using Leibniz Institute for Middle Atmosphere (LIMA) model Mesospheric Ice Microphysics And tranSport (MIMAS) model. NLCs sensitive because their formation depends on background temperature H2O concentration. affects concentration in upper mesosphere mainly two ways: directly through photolysis and, at time place NLC formation, indirectly changes. We found that correlates positively with changes due altitudes above about 82 km, where form. effect leads an anti-correlation Lyman-α radiation, which gets even more pronounced below ∼ 83 km when present. response variability period 1992 2018, including most recent cycles. amplitude variation decreased by 40 % 2005 2018 compared preceding cycle, resulting a lower late period. investigated increasing greenhouse gases (GHGs) throughout performing runs without increases carbon dioxide (CO2) methane (CH4). increase amplifies variability. Applying geometry satellite observations, we find missing averaging over 80 85 has positive negative (depending altitude), largely cancel each other out. One main finding is that, during NLCs, strongly altitude.