Abstract With the advent of Ulysses measurements during the solar minima of Solar Cycles 23 and 24, the heliospheric magnetic field and the solar wind were observed to behave much differently than expected. In particular, previous studies showed that the magnetic open flux of the Sun, calculated as the product of the radial component of the Sun’s magnetic field and the squared radial distance from the Sun, was observed to have decreased along with observed changes in solar-wind streams, such as solar wind proton density. This was in contrast to the standing theory, prior to the measurements made by Ulysses, that the “baseline” of the magnetic open flux should remain constant across the minima. Studies conducted after these measurements accounted for the discrepancies by showing that the Total Open Magnetic Flux (TOMF), the total amount of open flux outside the streamer belt, is a conserved “baseline” quantity from solar minimum to minimum. In this work, we examine a range of solar-wind parameters across five solar minima in Cycles 21, 22, 23, 24, and 25. Using measurements of the heliospheric magnetic field, dynamic solar wind, and heavy ion composition from multiple spacecraft, we investigate the width of the Heliospheric Current Sheet (HCS) streamer belt in the recent Solar Cycle 25 solar minimum using Advanced Composition Explorer (ACE) Solar Wind Ion Composition Spectrometer (SWICS) (1.1 and 2.0) and Solar Wind Electron, Proton and Alpha Monitor (SWEPAM) data. We also investigate the width of the HCS-streamer belt for the Solar Cycle 22 minimum using a newly proposed entropy methodology. With this analysis, we show continued validation of the conservation theory for the TOMF at solar minimum for Solar Cycles 22 and 25.
MacTaggart et al. (Fri,) studied this question.