The Interstellar H Flow: Updated Analysis of SOHO/SWAN Data

TL;DR

This study updates the analysis of interstellar hydrogen flow and solar wind ionization using SOHO/SWAN data, revealing a consistent interstellar magnetic field influence and a broader slow solar wind belt during the current solar minimum.

Contribution

The paper provides an updated analysis of interstellar hydrogen flow direction and solar wind ionization evolution, highlighting differences in solar minimum conditions compared to previous cycles.

Findings

Interstellar hydrogen flow direction is consistent with previous results, confirming magnetic field influence.

The slow solar wind belt is wider during the current minimum, persisting until at least 2008.

High-speed solar wind acceleration occurs at higher altitudes during this minimum.

Abstract

We update two kinds of results obtained with the SWAN instrument on board SOHO. First, we use H cell data recorded in 2001 and derive the H flow direction in the same way we performed the study at solar minimum. We compare with the Helium flow and doing so we correct for the coordinate system change between the Ulysses and SOHO mission. The deflection plane we obtain is compatible with the previous result within error bars, confirming the predominant role of the interstellar magnetic field. Secondly, we extend the derivation of solar wind ionization temporal evolution as a function of heliolatitude. The pattern for the present solar minimum is strikingly different from the previous minimum, with a much wider slow solar wind equatorial belt which persists until at least 2008. Comparing with synoptic LASCO/C2 electron densities we infer from a preliminary study that the acceleration of the high speed solar wind occurs at a higher altitude during this minimum, a change expansion models should be able to explain.