We present a new, multicomponent magnetic proxy for solar activity
derived from full disk magnetograms that can be used in the
specification and forecasting of the Sun’s radiative output. To compute
this proxy we project Carrington maps, such as the synchronic Carrington
maps computed with the Advective Flux Transport (AFT) surface flux
transport model, to heliographic cartesian coordinates and determine the
total unsigned flux as a function of absolute magnetic flux density.
Performing this calculation for each day produces an array of time
series, one for each flux density interval. Since many of these time
series are strongly correlated, we use principal component analysis to
reduce them to a smaller number of uncorrelated time series. We show
that the first few principal components accurately reproduce widely used
proxies for solar activity, such the the 10.7\,cm radio
flux and the Mg core-to-wing ratio. This suggests that these magnetic
time series can be used as a proxy for irradiance variability for
emission formed over a wide range of temperatures.