Recommendations for CMIP7 solar forcing data

Historical forcing Version 4.2 available (preliminary data version – use only for tests and model tuning!)

Solar forcing recommendations are based on Funke et al., 2024, Geosci. Model Dev., 17, doi: 10.5194/gmd-17-1217-2024). The CMIP7 historical solar forcing reconstruction covers the period 1/1/1850 - 31/12/2023 and includes the following forcing components with daily resolution for the period:

Irradiance forcing

TSI:     Total solar irradiance in [W m-2]
F10.7: F10.7 cm solar radio flux, in solar flux units [sfu]
SSI:    Spectral solar irradiance for 10-100,000 nm range, in [W m-2 nm-1]

Particle forcing:

Ap:   Daily planetary Ap-index
Kp:   Daily planetary Kp-index
iprp:  Ion-pair production rate by solar protons, in [g-1 cm3]
iprg:  Ion-pair production rate by galactic cosmic rays, in [g-1cm3]
iprm: Ion-pair production rate by medium-energy electrons, in [g-1 cm3]

 A detailed description of how the data were constructed as well as a “technical” documentation of the files’ structures, dimensions, variable names, etc. can be found here.

All data are provided in zipped netcdf (HDF5) files. For those models that do require only a subset of the forcings, these are to be selected from the provided files by the user.

What to prescribe in the CMIP7 pre-industrial control simulation (part of CMIP7 DECK)?

The pre-industrial control forcing (pictrontrol) is constructed from time-averaged historical data (see below) corresponding to 1850-1873 (solar cycle 9+10) mean conditions. See metadata file for more details.

What to prescribe in transient simulations, such as the DECK AMIP Historical and CMIP7 Historical experiments?

"The reference solar forcing dataset (1850-2023) consists of historical reconstructions generated with a preliminary version of the new empirical NASA NOAA LASP (NNL) Solar Spectral Irradiance Version 1 model, NNLSSI1”  (Coddington and Lean, personal communication). See metadata file for more details.

Data access:

Please note that in order to account for solar cycle effects, not only radiative effects but also photochemical effects have to be taken into account. CMIP7 models that do not have interactive chemistry should in addition to adapting the irradiance changes also prescribe the CMIP7 recommended ozone forcing data set (in preparation). A summary figure documenting the main differences with respect to the CMIP6 solar reference historical dataset is provided here:

The main changes with respect to the CMIP6 dataset are 1) the adoption of the new TSIS-1 solar reference spectrum, and the 2) the description of the variability after the NNLSSI model instead of an average of models. Note that particularly the relative change of spectral solar irradiance with respect to CMIP6 (resulting in larger irradiances in the UV and smaller irradiances in the NIR) requires careful evaluation in climate models!

What to prescribe in future simulations (e.g., ScenarioMIP)?

Future solar forcing recommendations are in preparation.

Alternative datasets (for sensitivity studies)

An alternative historical TSI/SSI dataset (1850 – 2023) for sensitivity studies (sen_ssi) was produced with an adapted version of the semi-empirical SATIRE (Spectral And Total Irradiance REconstruction) model (Krivova et al. 2003, 10.1051/0004-6361:20030029 which also uses the new TSIS-1 solar reference spectrum. See metadata file for more details. Note that this alternative SSI dataset is provided only with daily resolution and includes only the TSI and SSI forcing terms.

Data access:

A summary figure documenting the main differences with respect to the CMIP7 solar reference historical dataset is provided here:

Auxiliary software packages

Routine for re-gridding of solar spectral irradiances:

The SSI data recommended on this website for usage in CMIP6 is provided in high spectral resolution (1nm for 10-750nm range, 5nm for 750-5,000nm, 10nm for 5,000-10,000nm, 50nm for 10,000-100,000nm) as spectral irradiance averaged over each bin.

Many (chemistry) climate models require integrated irradiances for each spectral band, while the resolution of their radiation (and/or photolysis) schemes is typically much lower.

This package provides an (hopefully) easy to use routine to convert from one to another.

Given one of the available original input files (netcdf) downloaded from the links above, this routine creates a new netcdf-file containing the integrated SSI for all spectral bands (and all timesteps found in the input file) defined by the user plus the fraction of these bands\' irradiance (SSI_frac) compared to the TSI. As a matter of completeness, TSI is also written to the newly created file, though of course only copied from the original file.

The package can be downloaded here:

Currently, this routine is available for MATLAB only.

NOy upper boundary conditions:

For consideration of Energetic Particle Precipitation (EPP) in chemistry climate models with upper lid in the mesosphere (i.e., below the EPP source region), a NOy Upper Boundary Condition (UBC) is required in order to account for the EPP indirect effect (polar winter descent of EPP-generated odd nitrogen).

The package contains a routine for generation of a flux or density NOy-UBC from geomagnetic Ap data which is included in the solar forcing datasets. Output data is written to a netcdf file as daily resolved NOy zonal mean densities (in units of cm-3) or molecular fluxes (in units of cm-2 s-1) on model-specific pressure levels and bin center latitudes. The routine is available in IDL or MATLAB and can be downloaded here:

This is an updated version (with respect to CMIP6) of the NOy UBC model, based on MIPAS V8 data.

Routine for projection of EPP ionization rates onto geographic coordinates

For consideration of solar proton and mid-energy electron precipitation, as well as galactic cosmic rays in chemistry climate models, particle-induced ion pair production rates (variable iprp, iprm, and iprg) are required. These rates, however, are provided on geomagnetic latitudes and need to be projected onto geographic coordinates.

This package contains a routine for time- and pressure level dependent projection onto geographic coordinates, based on recommended geomagnetic reference field parameters (see metadata file for more details). A slightly outdated version of this package (available for MATLAB only), based on IGRF12, can be downloaded at the SOLARIS-HEPPA CMIP6 page. An updated version (considering IGRF13) will be made available soon.

Release notes

8 July 2024

Dataset version 4.2 available. No data changes, only changes of variable definitions and global attributes:

  • calyear, calmonth_calday now defined as integer variables
  • mip_era =’CMIP6plus’ (will be changed to ‘CMIP7’ with the final version)
  • licence changed to Creative Commons Attribution 4.0 International License.

Alternative TSI/SSI dataset for sensitivity experiments has been added (sen_ssi).

27 May 2024

Dataset version 4.1 available. This is a preliminary data version – use only for tests and model tuning.