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.

A partial correlation analysis of the stratospheric ozone response to 27‐day solar UV variations with temperature effect removed

“…In particular, the time lag becomes negative (ozone leads solar UV) at 1 and 2 hPa in S21 period 2. The difference in time lag is consistent with the theoretical interpretation that temperature effect can shift the maximum ozone response to earlier times [Hood, 1987]. In both the periods the total correlation coefficients peak at 5 hPa, while the partial correlation coefficients have similar values at 2 and 5 hPa.…”

“…In some studies, ozone sensitivity was calculated by linear regressions in which only one independent variable (solar UV flux) was considered [Hood and Cantrell, 1988 are shown in Figure 9 (solid lines). In all of the periods, there is a peak at or near the 27-day period, with a confidence level of at least 95%.…”

“…To examine the effect of temperature, correlations of temperature and solar UV variations have been separately analyzed and incorporated into a physical model in some studies [Hood, 1986;Keating et al, 1985]. With such a model the negative time lag of ozone relative to solar UV flux (ozone leading solar UV) found in the upper stratosphere could be explained as the result of interactions of ozone, temperature and solar UV flux [Hood, 1986;Hood and Jirikowic, 1991]. In some other studies, solar UV flux and temperature have been put together in a multiple regression model for ozone [Chandra, 1986].…”

“…The response of stratospheric ozone to solar UV flux changes occurring on the timescale of the 27-day solar rotation period has been extensively studied since satellite data became available [Gille et al, 1984;Hood, 1984;Keating et al, 1985;Chandra, 1986;Hood, 1986;Lean, 1987;Hood and Zhou, 1998]. Statistical and spectral analyses, including cross-correlation analyses, are useful mathematical tools for such studies.…”

Signature of the 27-day solar rotation cycle in mesospheric OH and H<sub>2</sub>O observed by the Aura Microwave Limb Sounder

“…The sensitivity analysis of the mesospheric OH concentrations to the short-term solar variability is based on crosscorrelation functions, which we calculate according to Chatfield (1982), and on the linear regression technique proposed by Hood (1986).…”