Solar ultraviolet radiation induced variations in the stratosphere and mesosphere

Abstract

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.

Long-term Variation of Upper Stratospheric Circulation in the Northern Hemisphere in December

“…Of course, the period of the present analysis is too short to obtain conclusive results. It is, however, noted that for short-term variations of solar UV such as are related to the solar rotation, there exists increasing evidence of ozone and temperature response in the upper stratosphere (Chandra, 1985;Hood, 1987;Keating et al, 1987). Another problem is how to explain the large amplitude of the variation of mean zonal winds to the assumed solar forcing (Fig.…”

On forced and free atmospheric oscillations near the 27-day periodicity

“…In this context, further hints of short-term solar influences on dynamics involve the high efficiencies of observed waves by UV flux variability (Hood and Jirikowic 1991;Krivolutsky et al 2003). In pure photochemical calculations, the heating rate efficiency accounts for the 0.1 K per per cent increase of the 205-nm flux, which is two times less than that observed (Hood 1987). The apparent discrepancy has been related to a possible dynamical effect of short-term solar variability.…”

Solar Influences on Global Change

“…Changes in ozone and temperature resulting from the 27-day solar irradiance rotation cycle are better understood (Hood, 1987;Hood and Douglass, 1988;Chandra, 1991;Brasseur, 1993) and have confirmed the response of the middle atmosphere to changes in solar UV energy inputs. Ozone changes related to the 11-year irradiance cycle are expected to be larger than those detected over solar rotation time scales (Chandra, 1991) because the UV irradiance variation is larger (Lean, 1991) and the sensitivity of ozone to longer period forcing is greater (Brasseur, 1993).…”