Long-term response of stratospheric ozone and temperature to solar variability

I Bordi,F Berrilli,E Pietropaolo

doi:10.5194/angeo-33-267-2015

Abstract

Abstract. The long-term variability in stratospheric ozone mass mixing ratio (O3) and temperature (T) from 1979 to 2013 is investigated using the latest reanalysis product delivered by the European Centre for Medium-Range Weather Forecasts (ECMWF), i.e., ERA-Interim. Moreover, using the Mg II index time series for the same time period, the response of the stratosphere to the 11-year Schwabe solar cycle is investigated. Results reveal the following features: (i) upward (downward) trends characterize zonally averaged O3 anomalies in the upper (middle to lower stratosphere) stratosphere, while prevailing downward trends affect the T field. Mg II index data exhibit a weaker 24th solar cycle (though not complete) when compared with the previous two; (ii) correlations between O3 and Mg II, T and Mg II, and O3 and T are consistent with photochemical reactions occurring in the stratosphere and large-scale transport; and (iii) wavelet cross-spectra between O3 and Mg II index show common power for the 11-year period, particularly in tropical regions around 30–50 hPa, and different relative phase in the upper and lower stratosphere. A comprehensive insight into the actual processes accounting for the observed correlation between ozone and solar UV variability would be gained from an improved bias correction of ozone measurements provided by different satellite instruments, and from the observations of the time behavior of the solar spectral irradiance.

Highlights

Variations in the solar irradiance represent one of the possible natural causes of climate change that is still poorly understood
In the present work we investigate the connection between long-term variability of stratospheric ozone and temperature, at different latitudes and altitudes, in response to the UV solar variability associated with the 11-year cycle
The tendency towards an increasing ozone concentration in the upper stratosphere instead remains questionable because it is likely affected by the mentioned problem concerning the O3 data assimilation

Summary

Introduction

Variations in the solar irradiance represent one of the possible natural causes of climate change that is still poorly understood (see Gray et al, 2010, for a review). The Sun is the main source of energy for the Earth’s system, and its variations may potentially influence the atmospheric dynamics Such an effect is controversial and tricky to prove, especially at tropospheric levels where the atmospheric variability is high. A way by which solar activity may influence the atmospheric circulation is through the stratosphere, in a topdown perspective (e.g., Gray et al, 2010; NRC, 2012) This occurs mainly through the absorption of UV solar radiation by ozone in the stratosphere (i.e., at midlatitudes, the altitudes between about 10–12 and 50 km) at wavelengths between 200 and 300 nm, leading to the radiative heating observed at those levels, to positive temperature vertical gradients, and to increased static stability. Solar UV photons have sufficient energy to give rise to chemical reac-

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Conclusion