Coupled stratospheric ozone and temperature responses to short‐term changes in solar ultraviolet flux: An analysis of Nimbus 7 SBUV and SAMS data

Abstract

The nature of stratospheric ozone and temperature responses to changes in solar ultraviolet flux occurring at low latitudes on the time scale of the solar rotation period is investigated using 22 months of Nimbus 7 solar backscattered ultraviolet (SBUV) ozone and stratosphere and mesophere sounder (SAMS) temperature data. After filtering to remove periods ≳35 days, average cross‐correlation functions for low‐latitude residual ozone versus SBUV measurements of the solar irradiance at 205 nm are largest (R = 0.3–0.6) at phase lags ranging from −3.6 ± 0.6 days at 0.7 mbar to 3.2 ± 0.5 days at 10 mbar. Maximum correlation coefficients for residual temperature variations (R = 0.2–0.35) are obtained versus the 205‐nm flux at lags ranging from 3.6 ± 0.9 days at 0.3 mbar to 13.0 ± 0.7 days at 10 mbar. In both cases, correlations generally increase when the 205‐nm flux is used as the solar ultraviolet variable rather than proxy indicators such as the 10.7‐cm flux. The consistency between response estimates calculated for separate latitude bands and the tendency for correlation coefficients to be larger during time periods of relatively strong 27‐day solar ultraviolet flux variations supports a causal relationship. Linear regression analyses are therefore performed to determine mean ozone and temperature response amplitudes for given changes in the 205‐nm flux at low latitudes as a function of pressure level in the upper stratosphere. Peak‐to‐peak variations in the 205‐nm flux were as large as 6% on the solar rotation time scale during the study period, yielding maximum ozone responses of 3% (∼0.37 μg g−1) near 3 mbar and maximum temperature responses of 0.36% (∼1 K) near the stratopause. The observed ozone and temperature responses and their phase lags are interpreted, using a model that accounts to first order for the coupled behavior of solar‐induced ozone and temperature perturbations in the upper stratosphere and lower mesosphere. The model appears capable of accounting for gross features of the observed ozone and temperature responses, including the negative ozone phase lags relative to the 205‐nm flux found above 3 mbar. Using the measured response amplitudes and phase lags, the model is applied to estimate the change in O2 photolysis rate in the upper stratosphere produced by a given change in the 205‐nm flux on the considered time scale. The mean temperature dependence of perturbation‐order ozone concentration changes is also constrained by the data.