Solar Physics

, Volume 281, Issue 1, pp 423-447

First online:

Open Access This content is freely available online to anyone, anywhere at any time.

The Heliospheric Plasma Sheet Observed in situ by Three Spacecraft over Four Solar Rotations

  • K. D. C. SimunacAffiliated withUniversity of New Hampshire Email author 
  • , A. B. GalvinAffiliated withUniversity of New Hampshire
  • , C. J. FarrugiaAffiliated withUniversity of New Hampshire
  • , L. M. KistlerAffiliated withUniversity of New Hampshire
  • , H. KucharekAffiliated withUniversity of New Hampshire
  • , B. LavraudAffiliated withIRAP (CNRS-UPS), University of Toulouse
  • , Y. C.-M. LiuAffiliated withUniversity of New HampshireState Key Laboratory of Space Weather, Center for Space Science and Applied Research, Chinese Academy of Sciences
  • , J. G. LuhmannAffiliated withUniversity of California
  • , K. W. OgilvieAffiliated withNASA Goddard Space Flight Center
    • , A. OpitzAffiliated withIRAP (CNRS-UPS), University of Toulouse
    • , M. A. PopeckiAffiliated withUniversity of New Hampshire
    • , J.-A. SauvaudAffiliated withIRAP (CNRS-UPS), University of Toulouse
    • , S. WangAffiliated withUniversity of New Hampshire


In this paper we present in situ observations of the heliospheric plasma sheet (HPS) from STEREO-A, Wind, and STEREO-B over four solar rotations in the declining phase of Solar Cycle 23, covering late March through late June 2007. During this time period the three spacecraft were located in the ecliptic plane, and were gradually separating in heliographic longitude from about 3 degrees to 14 degrees. Crossings of the HPS were identified using the following criteria: reversal of the interplanetary magnetic field sector, enhanced proton density, and local minima in both the proton specific entropy argument and in the alpha particle-to-proton number density ratio (N a/N p). Two interplanetary coronal mass ejections (ICMEs) were observed during the third solar rotation of our study period, which disrupted the HPS from its quasi-stationary state. We find differences in the in situ proton parameters at the HPS between the three spacecraft despite temporal separations of less than one day. We attribute these differences to both small separations in heliographic latitude and radial evolution of the solar wind leading to the development of compression regions associated with stream interaction regions (SIRs). We also observed a modest enhancement in the density of iron ions at the HPS.