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

Abstract

[1] 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. Citation: McComas, D.

Solar Magnetism in the Polar Regions

“…The solar wind parameters also showed different behavior during the third orbit compared to the first (McComas et al, 2008). The fast solar wind was about 3% slower, about 17% less dense, about 14% cooler and had about 20% less mass flux.…”

“…The contrast between solar wind structure during solar minimum and maximum has been emphasized by in situ measurements from outside the confines of the ecliptic plane by the Ulysses spacecraft. Ulysses observations of the solar wind from both polar coronal holes have shown clear long-term variations in the solar wind parameters (McComas et al, 2008) and in the interplanetary magnetic field (Smith and Balogh, 2008). Ulysses completed orbits over both poles roughly every six years between 1992 and 2008, nearly three full orbits.…”

Energy Spectrum of the Recurrent Variation of Galactic Cosmic Rays During the Solar Minimum of Cycles 23/24

“…All of the phenomena and processes mentioned caused diminishing of the solar-modulation influence on GCR intensity and its variations. McComas et al (2008) recognized a shrinkage of the size of the heliosphere (caused by the drop of the solar-wind dynamic pressure), which should result in an increase in the GCR intensity at 1 AU (Mewaldt et al, 2010). Indeed, the GCR intensity values measured by neutron monitors were the highest ever recorded (e.g.…”

“…We have explained (Gil and Alania, 2011) the hardening of the rigidity spectrum of the recurrent variation of the GCR intensity in the maximum epochs of SA by the larger average zone of the co-rotating interaction regions (causing the recurrent variation of the GCR intensity) in comparison with the minimum epochs of SA. Hence, a shrinkage of the size of the heliosphere caused by the drop of the solar-wind dynamic pressure during the last Solar Minimum 23/24 (McComas et al, 2008), together with the enhancement of the second and the third harmonics of the recurrent variability effect, could be a significant reason for the exceptional softening of the rigidity spectrum of the second and third harmonics of this recurrence of the GCR intensity during the last Solar Minimum 23/24. Also, the peculiar temporal changes of the coronal-hole structure during SC 23/24 could affect the rigidity spectrum of the recurrent variation.…”

“…Dikpati, 2013). McComas et al (2008) indicated a huge drop (≈ 36 %) in the average strength of the HMF. The lowest monthly value of HMF strength during the last minimum was 3.5 nT in April 2009.…”