“…These SSI measurement-model differences have been proven to affect the HO x photochemistry (Haigh et al, 2010;Merkel et al, 2011;Ermolli et al, 2013); more UV irradiance leads to an enhancement of O 3 photolysis as well as H 2 O photodissociation, which leads to more HO x production through Reactions (R4)-(R8). Further, Wang et al (2013) showed that using a solar forcing derived from these SSI measurements the modelled OH variability agrees much better with observations. Lastly, (3) these discrepancies might be related to the WACCM representation of the mean meridional circulation which has been shown to have some deficiencies (Smith et al, 2011;Smith, 2012), suggesting that the gravity wave parametrization needs to be modified.…”