Articles | Volume 34, issue 4
Ann. Geophys., 34, 379–392, 2016
Ann. Geophys., 34, 379–392, 2016

Regular paper 07 Apr 2016

Regular paper | 07 Apr 2016

Equivalent currents associated with morning-sector geomagnetic Pc5 pulsations during auroral substorms

K. Kauristie1, M. V. Uspensky1, N. G. Kleimenova2, O. V. Kozyreva2, M. M. J. L. Van De Kamp1, S. V. Dubyagin1, and S. Massetti3 K. Kauristie et al.
  • 1Finnish Meteorological Institute, Helsinki, Finland
  • 2Institute of Physics of the Earth, Russian Academy of Sciences, Moscow, Russia
  • 3Institute for Space Astrophysics and Planetology, National Institute of Astrophysics, Rome, Italy

Abstract. Space and time variations of equivalent currents during morning-sector Pc5 pulsations (T  ∼  2–8 min) on 2 days (18 January and 19 February 2008) are studied in the context of substorm activity with THEMIS and MIRACLE ground-based instruments and THEMIS P3, P5, and P2 probes. These instruments covered the 22:00–07:00 magnetic local time during the analyzed events. In these cases abrupt changes in the Pc5 amplitudes, intensifications and/or weakenings, were recorded some minutes after auroral breakups in the midnight sector. We analyze three examples of Pc5 changes with the goal to resolve whether substorm activity can have an effect on Pc5 amplitude or not. In two cases (on 19 February) the most likely explanation for Pc5 amplitude changes comes from the solar wind (changes in the sign of interplanetary magnetic field Bz). In the third case (on 18 January) equivalent current patterns in the morning sector show an antisunward-propagating vortex which replaced the Pc5-related smaller vortices and consequently the pulsations weakened. We associate the large vortex with a field-aligned current system due to a sudden, although small, drop in solar wind pressure (from 1 to 0.2 nPa). However, the potential impact of midnight substorm activity cannot be totally excluded in this case, because enhanced fluxes of electrons with high enough energies (∼  280 keV) to reach the region of Pc5 within the observed delay were observed by THEMIS P2 at longitudes between the midnight and morning-sector instrumentation.

Short summary
This study presents some example events in which sudden changes in the auroral activity at midnight sector seem to have an impact on the intensity of morning-sector magnetic pulsations. Mechanisms which could link these two separate regions are discussed in the paper. Sudden changes in the solar wind properties and fast westward-propagating electrons are suggested to explain the coupling between midnight-sector and morning-sector phenomena.