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Space and time variations of equivalent currents during morning-sector Pc5pulsations (T  ∼  2–8 min) on 2 days (18 January and 19 February 2008) are studied in the context of substorm activity with THEMIS andMIRACLE ground-based instruments and THEMIS P3, P5, and P2 probes. Theseinstruments covered the 22:00–07:00 magnetic local time during theanalyzed events. In these cases abrupt changes in the Pc5 amplitudes,intensifications and/or weakenings, were recorded some minutes after auroralbreakups in the midnight sector. We analyze three examples of Pc5 changeswith the goal to resolve whether substorm activity can have an effect on Pc5amplitude or not. In two cases (on 19 February) the most likely explanation forPc5 amplitude changes comes from the solar wind (changes in the sign ofinterplanetary 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 andconsequently the pulsations weakened. We associate the large vortex with afield-aligned current system due to a sudden, although small, drop in solarwind pressure (from 1 to 0.2 nPa). However, the potential impact of midnightsubstorm activity cannot be totally excluded in this case, because enhancedfluxes of electrons with high enough energies (∼  280 keV) toreach the region of Pc5 within the observed delay were observed by THEMIS P2at longitudes between the midnight and morning-sector instrumentation

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