On the Northward Shift of the Heliospheric Current Sheet at the End of Solar Cycle 24

TL;DR

This study investigates the unusual northward shift of the heliospheric current sheet at the end of solar cycle 24, using coronal modeling and in-situ data, revealing a stable shift established in 2018 influenced by the quadrupole magnetic term.

Contribution

It provides the first detailed analysis of the HCS shift at the end of solar cycle 24 using combined coronal models and in-situ measurements, highlighting the influence of the quadrupole term.

Findings

The HCS shift was established in early 2018 and remained stable for two years.

In-situ data show increased southern polarity T occurrences from 2018-2020.

Model results indicate the shift originates in the corona and propagates outward.

Abstract

Since solar cycle 16, the { heliospheric} current sheet (HCS) has been found to be shifted southward during the late declining to minimum phase. However, this trend is broken at the end of solar cycle 24. In this paper, we analyze the shift of the HCS by using information obtained from coronal model and insitu data provide by the near-Earth OMNI database and the Parker Solar Probe (PSP). Coronal potential field source surface (PFSS) modeling results show that the northward shift is established at the beginning of 2018 and remains stable for about two years. Interplanetary magnetic field data obtained from and within 1 au also support the northward shift, as the southern polarity T appears more frequently than the northern polarity A between 2018-2020. Both model results and insitu observation obtained by PSP imply that the HCS shift is established in the corona, and then propagates into the heliosphere. The quadrupole term still has a significant influence on the formation of the HCS shift.