How large is the sun's total magnetic flux?

Variations in the radiative output of the Sun axe directly allied to changes in the amount and distribution of solar surface magnetic field. The variability of solar irradiance on time-scales significantly shorter than a solar cycle can be produced by the spatial and temporal evolution of active regions, whereas its secular variations ensue from changes of the quiet-Sun magnetic flux on longer time-scales. The relative amounts of the magnetic flux in active regions and in the quiet Sun as well as their cyclic evolution have been studied by Harvey (1994) on the basis of the NSO/Kitt Peak synoptic maps. Since a single pixel of such a map is much bigger than individual small-scale magnetic elements and opposite polarities may be present within the same pixel, some magnetic flux went uncounted, so that the flux obtained by Harvey (1994) represents a lower limit to the true amount of magnetic flux present on the Sun. We use MDI full-disc and high-resolution magnetograms to estimate the total magnetic flux of the Sun.