In situ measurements of the variable slow solar wind near sector boundaries

TL;DR

This study combines remote sensing and in situ measurements to analyze the formation of density structures and flux ropes in the slow solar wind near sector boundaries, revealing recurrent emission processes during solar maximum.

Contribution

It provides a comprehensive interpretation linking remote observations and in situ data to a model of dense blob and flux rope formation in the slow solar wind.

Findings

In situ signatures match the production of dense blobs and flux ropes by helmet streamers.

Recurrent emission of dense structures occurs during solar maximum.

Properties are consistent across measurements near the Sun and farther out.

Abstract

The release of density structures at the tip of the coronal helmet streamers, likely as a consequence of magnetic reconnection, contributes to the mass flux of the slow solar wind. In situ measurements in the vicinity of the heliospheric plasma sheet of the magnetic field, protons and suprathermal electrons reveal details of the processes at play during the formation of density structures near the Sun. In a previous article, we exploited remote-sensing observations to derive a 3-D picture of the dynamic evolution of a streamer. We found evidence of the recurrent and continual release of dense blobs from the tip of the streamers. In the present paper, we interpret in situ measurements of the slow solar wind during solar maximum. Through both case and statistical analysis, we show that in situ signatures (magnetic field magnitude, smoothness and rotation, proton density and suprathermal electrons, in the first place) are consistent with the helmet streamers producing, in alternation, high-density regions (mostly disconnected) separated by magnetic flux ropes (mostly connected to the Sun). This sequence of emission of dense blobs and flux ropes also seems repeated at smaller scales inside each of the high-density regions. These properties are further confirmed with in situ measurements much closer to the Sun using Helios observations. We conclude on a model for the formation of dense blobs and flux ropes that explains both the in situ measurements and the remote-sensing observations presented in our previous studies.