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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 21, issue 12
Ann. Geophys., 21, 2233–2258, 2003
https://doi.org/10.5194/angeo-21-2233-2003
© Author(s) 2003. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 21, 2233–2258, 2003
https://doi.org/10.5194/angeo-21-2233-2003
© Author(s) 2003. This work is distributed under
the Creative Commons Attribution 3.0 License.

  31 Dec 2003

31 Dec 2003

Polar, Cluster and SuperDARN evidence for high-latitude merging during southward IMF: temporal/spatial evolution

N. C. Maynard1, D. M. Ober1, W. J. Burke2, J. D. Scudder3, M. Lester4, M. Dunlop5, J. A. Wild4, A. Grocott4, C. J. Farrugia6, E. J. Lund6, C. T. Russell7, D. R. Weimer1, K. D. Siebert1, A. Balogh8, M. Andre9, and H. Rème10 N. C. Maynard et al.
  • 1Mission Research Corporation, Nashua, New Hampshire, USA
  • 2Air Force Research Laboratory, Hanscom Air Force Base, Massachusetts, USA
  • 3Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa, USA
  • 4University of Leicester, Leicester, UK
  • 5Rutherford-Appleton Laboratory, Didcot, UK
  • 6EOS, University of New Hampshire, Durham, New Hampshire, USA
  • 7IGPP, UCLA, Los Angeles, California, USA
  • 8Imperial College, London, UK
  • 9Uppsala University, Upsalla, Sweden, USA
  • 10CESR, Toulouse, France

Abstract. Magnetic merging on the dayside magnetopause often occurs at high latitudes. Polar measured fluxes of accelerated ions and wave Poynting vectors while skimming the subsolar magnetopause. The measurements indicate that their source was located to the north of the spacecraft, well removed from expected component merging sites. This represents the first use of wave Poynting flux as a merging discriminator at the magnetopause. We argue that wave Poynting vectors, like accelerated particle fluxes and the Walén tests, are necessary, but not sufficient, conditions for identifying merging events. The Polar data are complemented with nearly simultaneous measurements from Cluster in the northern cusp, with correlated observations from the Super-DARN radar, to show that the locations and rates of merging vary. Magnetohydrodynamic (MHD) simulations are used to place the measurements into a global context. The MHD simulations confirm the existence of a high-latitude merging site and suggest that Polar and SuperDARN observed effects are attributable to both exhaust regions of a temporally varying X-line. A survey of 13 merging events places the location at high latitudes whenever the interplanetary magnetic field (IMF) clock angle is less than ~150°. While inferred high-latitude merging sites favor the antiparallel merging hypothesis, our data alone cannot exclude the possible existence of a guide field. Merging can even move away from equatorial latitudes when the IMF has a strong southward component. MHD simulations suggest that this happens when the dipole ilt angle increases or when IMF BX increases the effective dipole tilt.

Key words. Magnetospheric physics (magnetopause, cusp and boundary layers; magnetospheric configuration and dynamics; solar wind-magnetosphere interactions)

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