Abstract
Abstract. Solar spectral fluxes (or irradiance) measured by the SOlar Radiation and Climate Experiment (SORCE) show different variability at ultraviolet (UV) wavelengths compared to other irradiance measurements and models (e.g. NRL-SSI, SATIRE-S). Some modelling studies have suggested that stratospheric/lower mesospheric O3 changes during solar cycle 23 (1996–2008) can only be reproduced if SORCE solar fluxes are used. We have used a 3-D chemical transport model (CTM), forced by meteorology from the European Centre for Medium-Range Weather Forecasts (ECMWF), to simulate middle atmospheric O3 using three different solar flux data sets (SORCE, NRL-SSI and SATIRE-S). Simulated O3 changes are compared with Microwave Limb Sounder (MLS) and Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) satellite data. Modelled O3 anomalies from all solar flux data sets show good agreement with the observations, despite the different flux variations. The off-line CTM reproduces these changes through dynamical information contained in the analyses. A notable feature during this period is a robust positive solar signal in the tropical middle stratosphere, which is due to realistic dynamical changes in our simulations. Ozone changes in the lower mesosphere cannot be used to discriminate between solar flux data sets due to large uncertainties and the short time span of the observations. Overall this study suggests that, in a CTM, the UV variations detected by SORCE are not necessary to reproduce observed stratospheric O3 changes during 2001–2010.
Highlights
The Sun is the primary source of energy to the Earth’s atmosphere, so it is essential to understand the influence that solar flux variations may have on the climate system
Using different solar flux data sets and dynamical conditions, we examine whether the model can reproduce these past O3 changes, and whether the model comparisons can help to establish the accuracy of the solar fluxes used
The model is able to reproduce changes over the recent 2004–2007 time period, which has previously been used to support the different solar flux variability measured by SOlar Radiation and Climate Experiment (SORCE)
Summary
The Sun is the primary source of energy to the Earth’s atmosphere, so it is essential to understand the influence that solar flux variations may have on the climate system. Some coupled 2-D and 3-D Chemistry Climate Models (CCMs) are able to simulate a “double-peak”structured solar signal in tropical O3, the simulated upper stratospheric peak is at lower altitudes than SBUV and SAGE observations (e.g. see Fig. 4 in Austin et al, 2008) in almost all cases These differences in the middle atmospheric solar signal have gathered renewed interest with the availability of solar spectral data from the Solar Radiation and Climate Experiment (SORCE), launched in 2003. Using the Whole Atmosphere Community Climate Model (WACCM) with SORCE solar fluxes and comparing it with Sounding the Atmosphere using Broadband Emission Radiometry (SABER) data, Merkel et al (2011) showed an out-of-phase (larger than −2 %) daytime O3 solar signal in the mesosphere and upper stratosphere (above 40 km) during the recent solar maximum.
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