Solar irradiance at top of atmosphere

For solar irradiance at top of atmosphere, choose either a constant grey solar constant:

solaire = 1365

(for example) and:

ok_suntime_rrtm = n

in config.def. Or choose a spectrally and time varying solar irradiance:

ok_suntime_rrtm = y

in config.def. Means we read from a NetCDF file solar irradiance at top of atmosphere as a function of day of the year and spectral band. If ok_suntime_rrtm = y then gcm needs solarforcing.nc, containing variables tsi, which is the solar constant, and ssi_frac, which is the fraction in each of the nsw bands, daily, for 1 year (solarforcing.nc has to be prepared with the right number of days).