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
Received: 23 Jul 2016 – Revised: 19 Oct 2016 – Accepted: 20 Oct 2016 – Published: 14 Nov 2016
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.
Korotova, G., Sibeck, D., Engebretson, M., Wygant, J., Thaller, S., Spence, H., Kletzing, C., Angelopoulos, V., and Redmon, R.: Multipoint spacecraft observations of long-lasting poloidal Pc4 pulsations in the dayside magnetosphere on 1–2 May 2014, Ann. Geophys., 34, 985-998, doi:10.5194/angeo-34-985-2016, 2016.