Observations of ULF wave related equatorial electrojet and density fluctuations

• The Pc5 ULF waves can penetrate to the ionosphere and modulate equatorial electrodynamics.
• It modulates in the same manner it modulate the auroral currents and thus electric fields.
• The modulation of equatorial electrodynamics can in-turn modulate the vertical drift.
• The corresponding ionospheric density fluctuation that can create a range error of 10.7 cm or more.
• The range error could be higher depending on the ULF wave strength.

We report on Pc5 wave related electric field and vertical drift velocity oscillations at the equator as observed by ground magnetometers for an extended period on 9 August 2008. We show that the magnetometer-estimated equatorial E×B drift oscillates with the same frequency as ULF Pc5 waves, creating significant ionospheric density fluctuations. We also show ionospheric density fluctuations during the period when we observed ULF wave activity. At the same time, we detect the ULF activity on the ground using ground-based magnetometer data from the African Meridian B-field Education and Research (AMBER) and the South American Meridional B-field Array (SAMBA). From space, we use magnetic field observations from the GOES 12 and the Communication/Navigation Outage and Forecast System (C/NOFS) satellites. Upstream solar wind conditions are provided by the ACE spacecraft. We find that the wave power observed on the ground also occurs in the upstream solar wind and in the magnetosphere. All these observations demonstrate that Pc5 waves with a likely driver in the solar wind can penetrate to the equatorial ionosphere and modulate the equatorial electrodynamics. While no direct drift measurements from equatorial radars exist for the 9 August 2008 event, we used JULIA 150 km radar drift velocities observed on 2 May 2010 and found similar fluctuations with the period of 5–8 min, as a means of an independent confirmation of our magnetometer derived drift dynamics.