Comparison of Two Solar Minima: Narrower Streamer Stalk Region and Conserved Open Magnetic Flux in the Region Outside of Streamer Stalk

TL;DR

This study compares two recent solar minima, revealing a narrower streamer stalk region and conserved open magnetic flux outside it, with implications for solar magnetic field models.

Contribution

It provides a detailed analysis of solar wind source regions and demonstrates the conservation of open magnetic flux across two solar minima.

Findings

Narrower streamer stalk region in the recent solar minimum.

Conservation of open magnetic flux outside the streamer stalk.

Lower magnetic field strength outside the streamer stalk region.

Abstract

To explore the difference between the most two recent solar minima, we analyze the in-situ ACE and ULYSSES observations and examine the distributions of the three types of solar wind (streamer-stalk-associated wind, wind from outside the streamer stalk that can be associated, in part, with coronal holes, and interplanetary coronal mass ejections). We use the taxonomy provided by Zhao et al. (2009) to identify the three types of solar wind. We then map the in-situ observations to the 2.5 solar radii surface. With the aid of the potential-field-source surface model (PFSS), we calculate the normal distance from the solar wind "foot point" to the local helisopheric current sheet on that surface. We find that the source region of the streamer stalk wind is narrower compared to the previous minimum. The area outside the streamer stalk is accordingly larger, but the magnetic field strength is observed to be lower, with the result that the total amount of the magnetic open flux from the outside of streamer stalk region is conserved in the two successive solar minima. The implications of the conservation of open magnetic flux for models of the behavior of the solar magnetic field are discussed.