On the contribution of quiet-sun magnetism to solar irradiance variations: Constraints on quiet-sun variability and grand-minimum scenarios

We investigate the potential effect of quiet-Sun magnetism on spectral solar irradiance through a series of small-scale dynamo simulations with zero vertical flux imbalance ( = 0) and varying levels of small-scale magnetic field strength, and one weak network case with an additional flux imbalance corresponding to a flux density of = 100 G. From these setups, we compute the dependence of the outgoing radiative energy flux on the mean vertical magnetic field strength in the photosphere at a continuum optical depth tau = 1 ( (tau=1)).

We find that a quiet-Sun setup with a mean vertical field strength of (tau=1) = 69 G is about 0.6% brighter than a non-magnetic reference case. We find a linear dependence of the outgoing radiative energy flux on the mean field strength (tau=1) with a relative slope of 1.4 x 10(-4) G(-1). With this sensitivity, only a moderate change of the quiet-Sun field strength by 10% would lead to a total solar irradiance variation comparable to the observed solar cycle variation.