Multi-spacecraft Study of the Solar Wind at Solar Minimum: Dependence on Latitude and Transient Outflows

Abstract

Context. The recent launches of Parker Solar Probe (PSP), Solar Orbiter (SO) and BepiColombo, along with several older spacecraft, have provided the opportunity to study the solar wind at multiple latitudes and distances from the Sun simultaneously. Aims. We take advantage of this unique spacecraft constellation, along with low solar activity across two solar rotations between May and July 2020, to investigate how the Heliospheric Current Sheet (HCS) structure varies with latitude. Methods. We visualise the sector structure of the inner heliosphere by ballistically mapping the polarity and solar wind speed from several spacecraft onto the Sun's source surface. We compare this observed sector structure, and the local orientations of the boundaries, to a predicted HCS. Results. We show that fine scale ripples in the HCS can be resolved down to several degrees in longitude, with solar wind speed being a useful indicator of when a spacecraft is near the HCS without changing magnetic polarity. We found that the local orientation of sector boundaries were broadly consistent with the shape of the HCS but were steepened due to compression from stream interaction regions. We identified several transient magnetic clouds associated with HCS crossings, and have shown that these could disrupt the local HCS orientation up to five days after their passage, but did not significantly affect the position of the HCS. Conclusions. This spacecraft constellation, along with ballistic mapping, can reveal the structure of the HCS on scales of a few degrees in longitude and latitude, while discerning between co-rotating and transient structures. This also provides an accurate representation of the solar wind within ±10 • latitude, which could be used as a more rigorous constraint on solar wind models and future space weather predictions. In the future, this range of latitudes will increase as SO's orbit becomes more inclined.

Plasma Properties, Switchback Patches and Low $α$-Particle Abundance in Slow Alfvénic Coronal Hole Wind at 0.13 au

“…The two solar wind streams are ballistically mapped to the source surface before a potential field source surface (PFSS) model (Altschuler & Newkirk 1969;Schatten et al 1969) is applied, using the pfsspy library (Stansby et al 2020a), to determine solar origins of the wind (For other studies that use PFSS mapping see e.g. Badman et al 2020;Laker et al 2021;O'Kane et al 2021). Both streams originate at the boundaries of the Southern polar coronal hole, separated by ∼30 • in longitude, according to the model (See Fig.…”