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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 34, issue 11
Ann. Geophys., 34, 985–998, 2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 34, 985–998, 2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Regular paper 14 Nov 2016

Regular paper | 14 Nov 2016

Multipoint spacecraft observations of long-lasting poloidal Pc4 pulsations in the dayside magnetosphere on 1–2 May 2014

Galina Korotova1,2, David Sibeck3, Mark Engebretson4, John Wygant5, Scott Thaller5, Harlan Spence6, Craig Kletzing7, Vassilis Angelopoulos8, and Robert Redmon9 Galina Korotova et al.
  • 1IPST, University of Maryland, College Park, MD, USA
  • 2IZMIRAN, Russian Academy of Sciences, Moscow, Troitsk, Russia
  • 3Code 674, NASA/GSFC, Greenbelt, MD, USA
  • 4Department of Physics, Augsburg College, Minneapolis, MN, USA
  • 5College of Science and Engineering, University of Minnesota, Minneapolis, MN, USA
  • 6EOS, University of New Hampshire, Durham, NH, USA
  • 7Department of Physics and Astronomy, Iowa University, Iowa City, IA, USA
  • 8Department of Earth, Planetary and Space sciences, UCLA, Los Angeles, CA, USA
  • 9Solar and Terrestrial Physics division, NGDC/NOAA, Boulder, CO, USA

Abstract. We use magnetic field and plasma observations from the Van Allen Probes, Time History of Events and Macroscale Interactions during Substorms (THEMIS) and Geostationary Operational Environmental Satellite system (GOES) spacecraft to study the spatial and temporal characteristics of long-lasting poloidal Pc4 pulsations in the dayside magnetosphere. The pulsations were observed after the main phase of a moderate storm during low geomagnetic activity. The pulsations occurred during various interplanetary conditions and the solar wind parameters do not seem to control the occurrence of the pulsations. The most striking feature of the Pc4 magnetic field pulsations was their occurrence at similar locations during three of four successive orbits. We used this information to study the latitudinal nodal structure of the pulsations and demonstrated that the latitudinal extent of the magnetic field pulsations did not exceed 2 Earth radii (RE). A phase shift between the azimuthal and radial components of the electric and magnetic fields was observed from ZSM  =  0.30 RE to ZSM  =  −0.16 RE. We used magnetic and electric field data from Van Allen Probes to determine the structure of ULF waves. We showed that the Pc4 magnetic field pulsations were radially polarized and are the second-mode harmonic waves. We suggest that the spacecraft were near a magnetic field null during the second orbit when they failed to observe the magnetic field pulsations at the local times where pulsations were observed on previous and successive orbits. We investigated the spectral structure of the Pc4 pulsations. Each spacecraft observed a decrease of the dominant period as it moved to a smaller L shell (stronger magnetic field strength). We demonstrated that higher frequencies occurred at times and locations where Alfvén velocities were greater, i.e., on Orbit 1. There is some evidence that the periods of the pulsations increased during the plasmasphere refilling following the storm.

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