Global ozone long‐term trends from satellite measurements and the response to solar activity variations

Solar ultraviolet induced perturbations of the middle atmosphere occurring on the solar cycle time scale have received the most theoretical attention in the past because of the need for comparison with predicted anthropogenic trends or for evaluation of possible climatological consequences. However, short‐term perturbations occurring on time scales comparable to the solar rotation period are more readily observable at present. Studies of these perturbations allow basic tests of our understanding of the relevant physics and chemistry that are needed for more accurate long‐term model predictions. Detection of short‐term solar UV induced ozone and/or temperature responses is hindered even at low latitudes by endogenic dynamical forcing which results in an inverse phase relationship (for either ozone or temperature) with higher‐latitude variations for many events. Nevertheless, consistent correlative evidence for contributions of solar UV variability to ozone temporal behavior in the upper stratosphere and lower mesosphere has been obtained in recent years. The mean amplitude of the ozone response at low latitudes reaches a maximum near the 3‐mbar level of approximately 0.5% for a 1% change in the solar flux at 205 nm. The phase lag of the ozone response relative to the 205‐nm flux increases with decreasing altitude and is positive below 3 mbar. Above 3 mbar, increasingly negative lags are measured (i.e., the ozone maximum leads the UV maximum). The increasingly negative lags imply the existence of a positive temperature perturbation following the UV maximum that acts to reduce the amplitude of the ozone response during the latter part of the ozone response cycle. Weak correlative evidence for the presence of the inferred temperature perturbations has been obtained in some studies. It is shown that these temperature perturbations have approximately the correct amplitudes and phase lags needed to explain the negative ozone lags. The derived positive temperature phase lags are approximately twice as large as would be predicted by one‐dimensional models that consider only radiative‐photochemical coupling. The importance of dynamical coupling in producing these temperature perturbations is therefore indicated. A possible major source of dynamical coupling is alteration of the reflection‐transmission properties of planetary waves, a process for which some observational evidence exists on the solar rotation time scale. Finally, in regions where transport effects on ozone concentration may be neglected, simultaneous measurements of ozone, temperature, and solar UV flux can be combined to calculate parameters that are directly relatable to photochemical theory. These are the odd oxygen photochemical relaxation time (approximately half of the conventional odd oxygen lifetime) and the chemical sensitivity of odd oxygen to local temperature changes. It is therefore possible that observed upper stratospheric and lower mesospheric responses to measured solar irradiance changes will be useful to constraining photochemical theory.

Section: Solar Ultravioletmentioning

confidence: 99%

Solar ultraviolet radiation induced variations in the stratosphere and mesosphere

Hood¹

1987

“…Paper number 4D0896 0148-0227/84/004D-0896505.00 Keating et al [1981] presented an analysis of globally averaged total ozone as derived from nearly 6 years of Nimbus 4 backscattered ultraviolet (BUV) measurements in which a correlation with the 10.7-cm solar activity index was obtained after filtering of the ozone averages to remove semiannual, annual, and quasibiennial variations. Further correcting for instrument drift as determined from comparisons with ground-based measurements yielded an estimate of 2-3% for the global mean total ozone variation between solar maximum in 1970 and solar minimum in late 1975.…”

confidence: 99%

The temporal behavior of upper stratospheric ozone at low latitudes: Evidence from Nimbus 4 BUV data for short‐term responses to solar ultraviolet variability

Hood¹

1984

Ozone mixing ratios at pressure levels near 2 mbar, derived from Nimbus 4 backscattered ultraviolet (BUV) profile data and averaged within 13 latitude zones between 65°N and 65°S, are studied for the period November 1970 to April 1972. In agreement with previous analyses the largest temporal variations are negatively correlated with changes in zonally averaged equivalent temperature measured simultaneously with the Nimbus 4 selective chopper radiometer. After approximately removing this component using a first‐order photochemical model, residual mixing ratios for latitudes ≲30° contain short‐term variations (periods ≲35 days; rms amplitude ∼1%) that are positively correlated with variations in the solar 10.7‐cm flux and in the 185–190 nm solar ultraviolet flux model of Lean et al. (1982). The correlation coefficients (R = 0.2–0.5; p> 0.95) are larger for each latitude zone when computed versus the ultraviolet flux model than when computed versus the 10.7‐cm flux, suggesting that photochemical responses of upper stratospheric ozone to solar ultraviolet variability at wavelengths near 200 nm are primarily responsible. At latitudes ≳40°, larger‐amplitude wintertime ozone fluctuations associated with planetary‐scale pressure waves become dominant and reduce the computed correlation coefficients to statistically insignificant levels. Linear regression analyses are performed to obtain estimates for the average percent change of ozone at low latitudes and on the considered time scale for given changes in 10.7‐cm flux and in the UV flux model.

“…The possibility of a link between ozone and solar variability was raised early in this century by Humphreys [1910] and has been extensively discussed in the past (see, for example, Willett [1962]; London and Oltmans [1973]; Korshover [1973, 1976]; Keating et al [1981]; Keating [1981]). The understanding of such a relationship is indeed a prerequisite for detecting possible changes in the atmospheric composition due to anthropogenic effects.…”

Section: Introductionmentioning

confidence: 99%

Response of middle atmosphere to short‐term solar ultraviolet variations: 2. Theory

Brasseur¹,

Rudder²,

Keating³

et al. 1987

Self Cite

Ozone and temperature responses to solar variability, based on satellite data, have been reported in a companion paper (Keating et al., this issue). The present paper is intended to present a theoretical interpretation of this analysis with the purpose of better understanding the chemical behavior of the stratosphere and the coupling between temperature and ozone concentration, when a periodic forcing is applied to the solar ultraviolet (UV) flux. The response of the temperature and of the trace species concentrations, including ozone, to short‐term variations in the solar UV irradiance is calculated by a one‐dimensional chemical‐radiative time‐dependent model. The applied solar variability is assumed to be sinusoidal with a period of 27 days (in accordance with the rotation period of the sun) or 13.5 days (when two active regions are on opposite sides of the sun). The amplitude varies with wavelength, which is consistent with observations made by the Nimbus 7 solar backscattered ultraviolet (SBUV) experiment. The maximum ozone sensitivity in the stratosphere appears to be located near 3 mbar. The calculated amplitude and phase of the ozone response are significantly modified when the feedback between ozone and temperature is taken into account. The ozone/temperature coupling tends to modify the ozone phase lag such that, in the upper stratosphere and in the mesosphere, the ozone peak occurs a few days before the UV peak. Comparison of the model results with the observed ozone and temperature responses, based on satellite data, shows that the theory is consistent in many respects with observations. The calculated time lag of the temperature response, however, is approximately a factor of 2–4 smaller than the time lags derived from the measurements, suggesting evidence for some additional process not included in the model calculation. Large negative ozone sensitivities and positive temperature responses are predicted in the mesosphere as a result of the absorption by O2 of the solar irradiance at the Lyman α wavelength. The model also shows that the expected variation in the stratospheric nitric acid mixing ratio is a factor 2 larger than the corresponding opposite variation in the ozone concentration.