Weaker solar wind from the polar coronal holes and the whole Sun

TLDR

Lower mass and energy supply may stem from reduced open magnetic flux during this period. Observations show that the fast solar wind from polar coronal holes has become slower, less dense, cooler, and carries lower mass and momentum flux, indicating a long‑term global reduction in solar wind output and a shrinking heliosphere.

Abstract

Observations of solar wind from both large polar coronal holes (PCHs) during Ulysses' third orbit showed that the fast solar wind was slightly slower, significantly less dense, cooler, and had less mass and momentum flux than during the previous solar minimum (first) orbit. In addition, while much more variable, measurements in the slower, in‐ecliptic wind match quantitatively with Ulysses and show essentially identical trends. Thus, these combined observations indicate significant, long‐term variations in solar wind output from the entire Sun. The significant, long‐term trend to lower dynamic pressures means that the heliosphere has been shrinking and the heliopause must be moving inward toward the Voyager spacecraft. In addition, our observations suggest a significant and global reduction in the mass and energy fed in below the sonic point in the corona. The lower supply of mass and energy may result naturally from a reduction of open magnetic flux during this period.