Recommendations for CMIP5 solar forcing data
This section provides links solar irradiance data that should be used in CMIP5 simulations. A description of how the data were reconstructed by Judith Lean can be found here, and some guidelines for their use are also provided. For some models, use of the spectrally-resolved data, which accounts for the wavelength dependent changes in solar irradiance, is unwarranted. For these models, the total irradiance time series should be used.
What to prescribe in the pre-industrial control simulation?
Use the TSI and/or spectrally resolved values for a mean representative of 1850 conditions, i.e. cycle average from year 1844 to 1856. Note that 1850 is a year near the peak of the solar cycle.
What to prescribe in the historic simulation (1850-2008)?
The whole time series (monthly values are available only after 1882).
What to prescribe in the future?
Repeat the last cycle (cycle 23), with values from 1996 to 2008 inclusive mapping to 2009-2021, 2022-2034 etc. Please note that cycle 23 starts in 04/1996 and ends in 06/2008. There have been some concerns that cycle 23 was unusually long and repeating this special cycle would give out of phase behavior of a normal 11-year solar cycle around 2050. Cycle 23 is actually only 12.2 years long not 13 years since it goes from 1996.4 to 2008.6. In Lean and Rind (2009, GRL, doi:2009GL038932) the irradiance was projected forward by just repeating cycle 23. Since it is unknown what the sun will do, there is going to be a lot of uncertainty for future solar irradiance projections. Also the two prior cycles (21 and 22) have been shorter than average - the official times of minima are 05/1976, 08/1986.8, 05/1996.4 and now 06/2008.6 so cycle 21 was only 10.3 years and cycle 22 was 9.6 years - which are not 11 years either! Cycles 21 and 22 have been some of the highest and shortest on record and its quite possible that cycle 23 may be more representative of the future - but of course nobody knows.
Spectrally resolved irradiance for CMIP5 models:
For models that can make sensible use of the spectrally-resolved irradiance, the following data should be used:
- annual resolution TSI and spectrally resolved data from 1610 to 2000 and from 2000 to 2008
- monthly resolved TSI and spectrally resolved data from 1882 to 2000 and from 2000 to 2008
Total solar irradiance for CMIP5 models:
For CMIP5 models with a poorly resolved stratosphere and models that are unable to make use of spectrally-resolved data, the following annual mean TSI time series provided by J. Lean should be used: TSI_WLS_ann_1610_2008.txt.
The data files are provided in ascii format and the spectrally resolved data are zipped. Each of the spetrally resolved ascii files is organized as follows:
wavelength grid centers ...
wavelength bands width (1 nm bins from 0 to 750 nm, 5 nm bins from 750 to 5000 nm, 10 nm bins from 5000 to 10000 nm, 50 nm bins from 10000 to 100000 nm) ...
Spectral irradiance (mW/m2/nm) monthly or annually for years indicated in the file name
YEAR MONTH TSI in W/m2
solar flux data ...
YEAR MONTH+1 TSI in W/m2
- It is recommended to scale the total and spectrally resolved data to TIM scale (multiply TSI and/or each spectral band by 0.9965). The Total Irradiance Monitor (TIM) measures the total solar irradiance onboard of the NASA Earth Observing System (EOS) SOlar Radiation and Climate Experiment (SORCE) and continues the climate record, which began in 1978.
- It is recommended to use the TSI time series with varying background (second column in ascii files) for the CMIP5 runs and if desired perform additional sensitivity experiments without the varying background. Here is a picture comparing TSI with and without varying background.