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AGU: Geophysical Research Letters

 

Keywords

  • solar cycle variation
  • solar wind acceleration
  • solar wind variations

Index Terms

  • Interplanetary Physics: Solar wind plasma
  • Interplanetary Physics: Solar cycle variations
  • Interplanetary Physics: Interplanetary magnetic fields
  • Interplanetary Physics: Heliopause and solar wind termination
  • Interplanetary Physics: Solar wind sources

Abstract

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

D. J. McComas

Space Science and Engineering Division, Southwest Research Institute, San Antonio, Texas, USA

Department of Physics and Astronomy, University of Texas at San Antonio, San Antonio, Texas, USA

R. W. Ebert

Space Science and Engineering Division, Southwest Research Institute, San Antonio, Texas, USA

Department of Physics and Astronomy, University of Texas at San Antonio, San Antonio, Texas, USA

H. A. Elliott

Space Science and Engineering Division, Southwest Research Institute, San Antonio, Texas, USA

B. E. Goldstein

Jet Propulsion Laboratory, Pasadena, California, USA

J. T. Gosling

Space Science and Engineering Division, Southwest Research Institute, San Antonio, Texas, USA

Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado, USA

N. A. Schwadron

Department of Astronomy, Boston University, Boston, Massachusetts, USA

R. M. Skoug

Los Alamos National Laboratory, Los Alamos, New Mexico, USA

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.

Received 11 June 2008; accepted 14 August 2008; published 18 September 2008.

Citation: McComas, D. J., R. W. Ebert, H. A. Elliott, B. E. Goldstein, J. T. Gosling, N. A. Schwadron, and R. M. Skoug (2008), Weaker solar wind from the polar coronal holes and the whole Sun, Geophys. Res. Lett., 35, L18103, doi:10.1029/2008GL034896.

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