On the Origin of Otho-Gardenhose Heliospheric Flux

TL;DR

This study investigates the occurrence, structure, and origins of orthogardenhose flux in the heliospheric magnetic field, revealing its dependence on solar activity, scale sizes, and contributions from different mechanisms, with implications for Parker Solar Probe observations.

Contribution

It provides a detailed analysis of orthogardenhose flux at various scales and distances, highlighting the mechanisms and solar conditions influencing its occurrence, which extends understanding beyond Parker spiral theory.

Findings

OGH flux is more common at sunspot minimum.

Small-scale HMF structures cause OGH flux, with different scale sizes for different mechanisms.

Half of the HMF deflection occurs below 0.3AU.

Abstract

Parker spiral theory predicts the heliospheric magnetic field (HMF) will have components of opposite polarity radially toward the Sun and tangentially antiparallel to the solar rotation (i.e. in GSE coordinates, with Bx/By<0). This theory explains the average orientation of the HMF very well but does not predict orthogardenhose (OGH) flux with BX/BY>0 that is often observed. We here study the occurrence and structure of OGH flux, as seen in near-Earth space (r=1AU) and by the Helios spacecraft at 0.29<r<1AU, in order to evaluate the contributions to OGH flux generation of the various mechanisms and factors that are not accounted for in Parker spiral theory. We study the loss of OGH flux with increasing averaging timescale between 16 seconds and 100 hours and so determine its spectrum of scale sizes. OGH flux at sunspot minimum is shown to be more common than at sunspot maximum and caused by smaller-scale structure in the HMF, with a mode temporal scale at a fixed point of 10hrs compared to 40hrs. OGH generated by rotating the HMF through the radial direction is also shown to differ in its spectrum of scale sizes from that generated by rotating the HMF through the tangential direction: the former does not contribute to the excess open heliospheric flux at a given r but the latter does. We show that roughly half of the HMF deflection from the ideal Parker spiral giving OGH at Earth occurs at r below 0.3AU. We highlight some questions which can be addressed by the Parker Solar Probe mission which will study the HMF down to r=0.046AU.