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AGU: Geophysical Research Letters

 

Keywords

  • heliospheric magnetic field
  • coronal mass ejections
  • solar cycle

Index Terms

  • Solar Physics, Astrophysics, and Astronomy: Solar activity cycle
  • Solar Physics, Astrophysics, and Astronomy: Coronal mass ejections
  • Solar Physics, Astrophysics, and Astronomy: Solar and stellar variability
  • Interplanetary Physics: Ejecta, driver gases, and magnetic clouds
  • Interplanetary Physics: Interplanetary magnetic fields

Abstract

GEOPHYSICAL RESEARCH LETTERS, VOL. 35, L20108, 5 PP., 2008
doi:10.1029/2008GL035813

Conservation of open solar magnetic flux and the floor in the heliospheric magnetic field

M. J. Owens

Space and Atmospheric Physics, The Blackett Laboratory, Imperial College London, London, UK

N. U. Crooker

Center for Space Physics, Boston University, Boston, Massachusetts, USA

N. A. Schwadron

Center for Space Physics, Boston University, Boston, Massachusetts, USA

T. S. Horbury

Space and Atmospheric Physics, The Blackett Laboratory, Imperial College London, London, UK

S. Yashiro

Department of Physics, Catholic University of America, Washington, D.C., USA

H. Xie

Department of Physics, Catholic University of America, Washington, D.C., USA

O. C. St. Cyr

NASA Goddard Space Flight Center, Greenbelt, Maryland, USA

N. Gopalswamy

NASA Goddard Space Flight Center, Greenbelt, Maryland, USA

The near-Earth heliospheric magnetic field intensity, |B|, exhibits a strong solar cycle variation, but returns to the same “floor” value each solar minimum. The current minimum, however, has seen |B| drop below previous minima, bringing in to question the existence of a floor, or at the very least requiring a re-assessment of its value. In this study we assume heliospheric flux consists of a constant open flux component and a time-varying contribution from CMEs. In this scenario, the true floor is |B| with zero CME contribution. Using observed CME rates over the solar cycle, we estimate the “no-CME” |B| floor at ∼4.0 ± 0.3 nT, lower than previous floor estimates and below |B| observed this solar minimum. We speculate that the drop in |B| observed this minimum may be due to a persistently lower CME rate than the previous minimum, though there are large uncertainties in the supporting observational data.

Received 26 August 2008; accepted 29 September 2008; published 30 October 2008.

Citation: Owens, M. J., N. U. Crooker, N. A. Schwadron, T. S. Horbury, S. Yashiro, H. Xie, O. C. St. Cyr, and N. Gopalswamy (2008), Conservation of open solar magnetic flux and the floor in the heliospheric magnetic field, Geophys. Res. Lett., 35, L20108, doi:10.1029/2008GL035813.

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