Estimating the Open Solar Flux from In-Situ Measurements

Abstract A fraction of the magnetic flux threading solar photosphere extends to sufficient heliocentric distances that it is dragged out by wind. Understanding this open (OSF) central space weather, as OSF forms heliosphere, magnetically connects Sun planets, and dominates motion energetic particles. Quantification also a key means verifying global coronal models. However, estimates derived from extrapolating field photospheric observations are consistently smaller than those based on heliospheric (HMF) measurements, around factor two. It therefore important understand uncertainties in estimating in-situ HMF measurements. This requires both an assumption latitudinal invariance radial component structures without immediate connection Sun, such local inversions (or ‘switchbacks’), can be correctly accounted for. In study, we investigate second assumption. Following established methodology, use electron data determine topology correct for would otherwise lead overestimation OSF. The estimation applied interval 1994 – 2021 combines measurements Wind ACE spacecraft. time range over which methodology has previously been 13 years (1998 2011) 27 years. We find cannot fully explain discrepancy between estimations, with best estimate still, average, 1.6 higher values extrapolated observations.