Waves in high-speed plasmoids in the magnetosheath and at the magnetopause
- 1Belgian Institute for Space Aeronomy, Avenue Circulaire 3, 1180 Brussels, Belgium
- 2Swedish Institute of Space Physics (IRF), P.O. Box 812, 981 28 Kiruna, Sweden
- 3Swedish Institute of Space Physics (IRF), Box 537, 751 21 Uppsala, Sweden
- 4Department of Physics, Umeå University, 901 87 Umeå, Sweden
- 5Space and Plasma Physics, Royal Institute of Technology (KTH), 100 44 Stockholm, Sweden
- 6Institut de Recherche en Astrophysique et Planétologie, UPS-CNRS, 31028 Toulouse, France
Abstract. Plasmoids, defined here as plasma entities with a higher anti-sunward velocity component than the surrounding plasma, have been observed in the magnetosheath in recent years. During the month of March 2007 the Cluster spacecraft crossed the magnetopause near the subsolar point 13 times. Plasmoids with larger velocities than the surrounding magnetosheath were found on seven of these 13 occasions. The plasmoids approach the magnetopause and interact with it. Both whistler mode waves and waves in the lower hybrid frequency range appear in these plasmoids, and the energy density of the waves inside the plasmoids is higher than the average wave energy density in the magnetosheath. When the spacecraft are in the magnetosphere, Alfvénic waves are observed. Cold ions of ionospheric origin are seen in connection with these waves, when the wave electric and magnetic fields combine with the Earth's dc magnetic field to yield an E × B/B2 drift speed that is large enough to give the ions energies above the detection threshold.