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

Abstract

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

Absorption of Solar Radiation by Noctilucent Clouds in a Changing Climate

“…We realize that temperature changes are considered to be more important for NLC in other models, which, however, do not include microphysical processes (see, e.g., Hervig et al, 2015). In previous studies we have presented various comparisons of results from LIMA and MIMAS with ground based and satellite borne observations and found excellent agreement (see, e.g., Lübken et al, 2021;Vellalassery et al, 2023;Schmidt et al, 2018, and references therein). In Figure 1 we show the temporal behavior of methane concentration in the troposphere used in MIMAS.…”

Long-Term Evolution in Noctilucent Clouds’ Response to the Solar Cycle: A Model-Based Study

“…Studies have shown a clear anti-correlation between the solar cycle Lyα and ice water content (IWC) during solar cycles 22 and 23, but it decreases during the recent solar cycle 24 [13,17]. Our previous study [17] found a clear anti-correlation between Lyα flux and IWC in the model and satellite observations for solar cycles 22 and 23, which becomes weaker in solar cycle 24. Moreover, the magnitude of the solar cycle-induced IWC variations in Solar Backscatter Ultraviolet (SBUV) and Halogen Occultation Experiment (HALOE) satellite observations is the same as the IWC variations in the MIMAS model.…”

“…A positive correlation exists between the solar Lyman-alpha (Lyα) flux and the background temperature at NLC altitudes. Depending on the altitude, the correlation can be positive or negative for water vapour [17]. Studies have shown a clear anti-correlation between the solar cycle Lyα and ice water content (IWC) during solar cycles 22 and 23, but it decreases during the recent solar cycle 24 [13,17].…”

“…Depending on the altitude, the correlation can be positive or negative for water vapour [17]. Studies have shown a clear anti-correlation between the solar cycle Lyα and ice water content (IWC) during solar cycles 22 and 23, but it decreases during the recent solar cycle 24 [13,17]. Our previous study [17] found a clear anti-correlation between Lyα flux and IWC in the model and satellite observations for solar cycles 22 and 23, which becomes weaker in solar cycle 24.…”

Dominant role of charged meteoric smoke particles in the polar mesospheric clouds

“…However, the 27-day solar cycle in PMCs is typically ambiguous, unless the superposed epoch analysis method is applied to remove background noise, and the lag time is only about 0-3 days (Dalin et al, 2018;Robert et al, 2010;Thurairajah et al, 2017), shorter than the at least five days required for the photodissociation (Shapiro et al, 2012). The 11-year solar cycle in PMCs is evident prior to 2002, but has disappeared over the past two decades, for reasons that remain unknown (Hervig et al, 2019;Vellalassery et al, 2023).…”