Calculated upper stratospheric effects of solar UV flux and NOy variations during the 11-year solar cycle

Model derived sensitivities of O3 near 40 km to solar UV flux changes (11-year and 27-day) fall within the range 0.36–0.55 with S11y ≈ S27d. These sensitivities derived from observations have been reported to be 0.91 and 0.39–0.46, respectively. This discrepancy appears to be due to long-term (2–10 years) fluctuations in stratospheric NO2 in the 1980s. Such fluctuations, if not taken into account in the analysis of the data, could lead to high values of the sensitivity for the 11-year activity cycle but not for the 27-day solar rotation period. Simulations accounting for such effects suggest a consistency between theoretical values of S11y and those derived from data if NO2 effects are included. The appropriate values are approximately 0.48, a value similar to published model calculations and results from the analysis of data from the 27-day solar rotation period. Verification of this suggestion awaits an NO2 data base of sufficient quality and length to permit solar-cycle trend calculations to be made.