Articles | Volume 24, issue 9
Ann. Geophys., 24, 2363–2374, 2006

Special issue: Twelfth EISCAT International Workshop

Ann. Geophys., 24, 2363–2374, 2006

  20 Sep 2006

20 Sep 2006

EISCAT observations of plasma patches at sub-auroral cusp latitudes

J. Moen1,*, H. C. Carlson2, K. Oksavik3, C. P. Nielsen4, S. E. Pryse5, H. R. Middleton5, I. W. McCrea6, and P. Gallop6 J. Moen et al.
  • 1Department of Physics, University of Oslo, Norway
  • 2Air Force Research Laboratory, Air Force Office of Scientific Research, Arlington, Virginia, USA
  • 3The Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, USA
  • 4Norwegian Polar Institute, Ny-Aalesund, Norway
  • 5Institute of Mathematical and Physical Sciences, University of Wales, Aberystwyth, SY23 3BZ, UK
  • 6Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0QX, UK
  • *also at: Arctic Geophysics, The University Centre in Svalbard, Longyearbyen, Norway

Abstract. A sequence of 3 patches of high-density (1012 m−3) cold plasma on a horizontal scale-size of 300–700 km was observed near magnetic noon by the EISCAT VHF radar above Svalbard on 17 December 2001. The patches followed a trajectory towards the cusp inflow region. The combination of radar and all-sky observations demonstrates that the patches must have been segmented equatorward of the cusp/cleft auroral display, and hence their properties had not yet been influenced by cusp particle showers and electrodynamics on open flux tubes. The last patch in the sequence was intersected by radio tomography observations, and was found to be located adjacent to a broader region of the same high electron density further south. The patches occurred under moderately active conditions (Kp=3) and the total electron content (TEC) of the high-density plasma was 45 TEC units. The train of patches appeared as a segmentation of the tongue of ionization. The sequence of patches occurred in association with a sequence of flow bursts in the dusk cell return flow. It is proposed that reconnection driven pulsed convection is able to create sub-auroral patches in the region where high density mid-latitude plasma is diverted poleward toward the cusp. It is the downward Birkeland current sheet located at the equatorward boundary of the flow disturbance that represents the actual cutting mechanism.