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Geoscientific Model Development An interactive open-access journal of the European Geosciences Union
© Author(s) 2016. This work is distributed
under the Creative Commons Attribution 3.0 License.
Development and technical paper
06 Jun 2016
Review status
A revision of this discussion paper was accepted for the journal Geoscientific Model Development (GMD) and is expected to appear here in due course.
Solar Forcing for CMIP6 (v3.1)
Katja Matthes1,2, Bernd Funke3, Monika E. Anderson18, Luke Barnard4, Jürg Beer5, Paul Charbonneau6, Mark A. Clilverd7, Thierry Dudok de Wit8, Margit Haberreiter9, Aaron Hendry14, Charles H. Jackman10, Matthieu Kretschmar8, Tim Kruschke1, Markus Kunze11, Ulrike Langematz11, Daniel R. Marsh19, Amanda Maycock12, Stergios Misios13, Craig J. Rodger14, Adam A. Scaife15, Annika Seppälä18, Ming Shangguan1, Miriam Sinnhuber16, Kleareti Tourpali13, Ilya Usoskin17, Max van de Kamp18, Pekka T. Verronen18, and Stefan Versick16 1GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany
2Christian-Albrechts Universität zu Kiel, Kiel, Germany
3Instituto de Astrofísica de Andalucía (CSIC), Granada, Spain
4University of Reading, Reading, United Kingdom
5EAWAG, Dübendorf, Switzerland
6University of Montreal, Canada
7British Antarctic Survey (NERC), Cambridge, UK
8LPC2E, CNRS and University of Orléans, France
9Physikalisch-Meteorologisches Observatorium Davos/World Radiation Center, Davos, Switzerland
10Emeritus, NASA Goddard Space Flight Center, Greenbelt, MD, USA
11Freie Universität Berlin, Berlin, Germany
12University of Leeds, Leeds, UK
13Laboratory of Atmospheric Physics, Aristotle University of Thessaloniki, Thessaloniki, Greece
14Department of Physics, University of Otago, Dunedin, New Zealand
15Met Office Hadley Centre, Fitz Roy Road, Exeter, Devon, UK
16Karlsruhe Institute of Technology, Karlsruhe, Germany
17ReSoLVE Centre of Excellence and Sodankylä Geophysical Observatory, University of Oulu, Finland
18Finnish Meteorological Institute, Helsinki, Finland
19National Center for Atmospheric Research, Boulder, CO, USA
Abstract. This paper describes the solar forcing dataset for CMIP6 and highlights in particular changes with respect to the CMIP5 recommendation. The solar forcing is provided for radiative properties, i.e., total solar irradiance (TSI) and solar spectral irradiance (SSI), and F10.7 cm radio flux, as well as particle forcing, i.e., geomagnetic indices Ap and Kp, and ionisation rates to account for effects of solar protons, electrons and galactic cosmic rays. This is the first time that a recommendation for solar-driven particle forcing is provided for a CMIP exercise. The solar forcing dataset is provided at daily and monthly resolution separately for the CMIP6 Historical Simulation (1850–2014), for the future (2015–2300), including an additional extreme Maunder Minimum-like sensitivity scenario, as well as for a constant and a time-varying forcing for the preindustrial control simulation. The paper not only describes the forcing dataset, but also provides detailed recommendations for how to implement the different forcing components in climate models.

The TSI and SSI time series are defined as averages of two (semi-) empirical solar irradiance models, namely the NRLTSI2/NRLSSI2 and SATIRE-TS. A new and lower TSI value is recommended: the contemporary solar cycle-average is now 1361.0 W/m2. The slight negative trend in TSI during the last three solar cycles in CMIP6 is statistically indistinguishable from available observations and only leads to a small global radiative forcing of −0.04 W/m2. In the 200–400 nm range, which is also important for ozone photochemistry, CMIP6 shows a larger solar cycle variability contribution to TSI than CMIP5 (50 % as compared to 35 %).

The CMIP6 dataset is tested and compared to its CMIP5 predecessor using timeslice experiments of two chemistry-climate models and a reference radiative transfer model. The changes in the background SSI in the CMIP6 dataset, as compared to CMIP5, impact on climatological stratospheric conditions (lower shortwave heating rates (−0.35 K/day at the stratopause), cooler stratospheric temperatures (−1.5 K in the upper stratosphere), lower ozone abundances in the lower stratosphere (−3 %), and higher ozone abundances (+1.5 % in the upper stratosphere and lower mesosphere). Between the maximum and minimum phases of the 11-year solar cycle, there is an increase in shortwave heating rates (+0.2 K/day at the stratopause), temperatures (~1 K at the stratopause), and ozone (+2.5 % in the upper stratosphere) in the tropical upper stratosphere using the CMIP6 forcing dataset. This solar cycle response is slightly larger, but not statistically significantly different from that for the CMIP5 forcing dataset.

CMIP6 models with a well-resolved shortwave radiation scheme are encouraged to use SSI, as well as solar-induced ozone signals, in order to better represent solar climate variability compared to models that only prescribe TSI and/or exclude the solar-ozone response. Monthly mean solar-induced ozone variations will also be incorporated into the CCMI CMIP6 Ozone Database for climate models that do not calculate ozone interactively. CMIP6 models with interactive chemistry are encouraged to use the particle forcing which will allow the potential long-term effect of particles to be addressed for the first time. The consideration of particle forcing has been shown to significantly improve the representation of reactive nitrogen and ozone variability in the polar middle atmosphere, eventually resulting in further improvements of the representation of solar climate variability.

Citation: Matthes, K., Funke, B., Anderson, M. E., Barnard, L., Beer, J., Charbonneau, P., Clilverd, M. A., Dudok de Wit, T., Haberreiter, M., Hendry, A., Jackman, C. H., Kretschmar, M., Kruschke, T., Kunze, M., Langematz, U., Marsh, D. R., Maycock, A., Misios, S., Rodger, C. J., Scaife, A. A., Seppälä, A., Shangguan, M., Sinnhuber, M., Tourpali, K., Usoskin, I., van de Kamp, M., Verronen, P. T., and Versick, S.: Solar Forcing for CMIP6 (v3.1), Geosci. Model Dev. Discuss., doi:10.5194/gmd-2016-91, in review, 2016.
Katja Matthes et al.
Katja Matthes et al.


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Latest update: 23 May 2017
Publications Copernicus
Short summary
The solar forcing dataset for climate model experiments performed for the upcoming IPCC report is described. This dataset provides the radiative and particle input of solar variability on a daily basis from 1850 through 2300. With this dataset a better representation of natural climate variability with respect to the output of the Sun is provided which provides the most sophisticated and comprehensive respresentation of solar variability that has been used in climate model simulations so far.
The solar forcing dataset for climate model experiments performed for the upcoming IPCC report...