1INAF, Osservatorio Astronomico di Roma, Monte Porzio Catone, Italy
2Helmholtz-Zentrum für Ozeanforschung Kiel (GEOMAR), Kiel, Germany
3LPC2E, CNRS and University of Orléans, Orléans, France
4Max-Planck-Institut für Sonnensystemforschung, 37191 Katlenburg-Lindau, Germany
5Laboratory of Atmospheric Physics, Aristotle University of Thessaloniki, Greece
6Institut für Umweltphysik, Universität Bremen FB1, Bremen, Germany
7Astrophysics Group, Blackett Laboratory, Imperial Collede London, SW7 2AZ, UK
8Centre for Atmospheric Sciences, Dept. of Atmospheric, Oceanic and Planetary Physics, University of Oxford, UK
9Institut für Meteorologie, Freie Universität Berlin, Berlin, Germany
10University of Colorado, Laboratory for Atmospheric and Space Physics, Boulder, CO, USA
11Physikalisch-Meteorologisches Observatorium, World Radiation Center, Davos Dorf, Switzerland
12IAC ETH, Zurich, Switzerland
13School of Space Research, Kyung Hee University, Yongin, Gyeonggi 46-701, Republic of Korea
14LATMOS-IPSL, CNRS and University of Versailles-Saint-Quentin, Guyancourt, France
Abstract. During periods of high solar activity, the Earth receives ≈ 0.1% higher total solar irradiance (TSI) than during low activity periods. Variations of the solar spectral irradiance (SSI) however, can be larger, with relative changes of 1 to 20% observed in the ultraviolet (UV) band, and in excess of 100% in the soft X-ray range. SSI changes influence the Earth's atmosphere, both directly, through changes in shortwave (SW) heating and therefore, temperature and ozone distributions in the stratosphere, and indirectly, through dynamical feedbacks. Lack of long and reliable time series of SSI measurements makes the accurate quantification of solar contributions to recent climate change difficult. In particular, the most recent SSI measurements show a larger variability in the UV spectral range and anomalous changes in the visible and near-infrared (NIR) bands with respect to those from earlier observations and from models. A number of recent studies based on chemistry-climate model (CCM) simulations discuss the effects and implications of these new SSI measurements on the Earth's atmosphere, which may depart from current expectations.
This paper summarises our current knowledge of SSI variability and its impact on Earth's climate. An interdisciplinary analysis of the topic is given. New comparisons and discussions are presented on the SSI measurements and models available to date, and on the response of the Earth's atmosphere and climate to SSI changes in CCM simulations. In particular, the solar induced differences in atmospheric radiative heating, temperature, ozone, mean zonal winds, and surface signals are investigated in recent simulations using atmospheric models forced with the current lower and upper boundaries of SSI solar cycle estimated variations from the NRLSSI model data and from SORCE/SIM measurements, respectively. Additionally, the reliability of available data is discussed and additional coordinated CCM experiments are proposed.