Modeling the Global Coronal Field with Simulated Synoptic Magnetograms from Earth and the Lagrange Points L 3 $L_{3}$ , L 4 $L_{4}$ , and L 5 $L_{5}$

Abstract

The solar photospheric magnetic flux distribution is key to structuring the global solar corona and heliosphere. Regular full-disk photospheric magnetogram data are therefore essential to our ability to model and forecast heliospheric phenomena such as space weather. However, our spatio-temporal coverage of the photospheric field is currently limited by our single vantage point at/near Earth. In particular, the polar fields play a leading role in structuring the large-scale corona and heliosphere, but each pole is unobservable for ${>}\,6$ months per year. Here we model the possible effect of full-disk magnetogram data from the Lagrange points $L_{4}$ and $L_{5}$ , each extending longitude coverage by $60^{\circ}$ . Adding data also from the more distant point $L_{3}$ extends the longitudinal coverage much further. The additional vantage points also improve the visibility of the globally influential polar fields. Using a flux-transport model for the solar photospheric field, we model full-disk observations from Earth/ $L_{1}$ , $L_{3}$ , $L_{4}$ , and $L_{5}$ over a solar cycle, construct synoptic maps using a novel weighting scheme adapted for merging magnetogram data from multiple viewpoints, and compute potential-field models for the global coronal field. Each additional viewpoint brings the maps and models into closer agreement with the reference field from the flux-transport simulation, with particular improvement at polar latitudes, the main source of the fast solar wind.