Resolving a long-standing model-observation discrepancy on ozone solar cycle response

To have the capability for long-term prediction of stratospheric ozone (O₃), chemistry-climate models have often been tested against observations on decadal timescales. A model-observation discrepancy in the tropical O₃ response to the 11 year solar cycle, first noted in 1993, persists for more than 20 years: While standard photochemical models predict a single-peak response in the stratosphere, satellite observations show an unexpected double-peak structure. Such discrepancy has led to the question of whether the current standard O₃ photochemistry is deficient. Various studies have explored uncertainties in photochemistry and dynamics but there has not been compelling evidence of model biases. Here we suggest that decadal satellite orbital drifts relative to the diurnal cycle could be the primary cause of the discrepancy. We show that the double-peak structure can be reproduced by adding the A.M./P.M. diurnal difference to the single-peak response predicted by the standard photochemistry. Thus we argue that the standard photochemistry is consistent with the observed solar cycle modulation in stratospheric O₃.