Coupling of perturbations in the solar wind density to global Pi3 pulsations: A case study

Abstract

A typical Pi3 pulsation is examined by magnetic field measurements from multiple satellites and ground stations. Low‐latitude ground observations with a wide longitudinal span indicate that the amplitude of the Pi3 pulsation peaks on the dayside and is gradually decreasing toward the nightside. This effect and the fact that the wave phase on the dayside leads that on the nightside, imply that the source of the Pi3 lies on the dayside. Variations in solar wind dynamic pressure observed by the GEOTAIL satellite (just outside of the magnetosphere) are highly correlated with these ground magnetic field variations. We argue in this case that the global Pi3 pulsation is directly driven by impulsive variations in the solar wind dynamic pressure. The Pi3 pulsation observed along the latitudinal magnetometer chain at 0930LT shows significant equatorial enhancement and additional observations along a latitudinal chain at 1630LT show that the phase of the Pi3 pulsation at high latitudes lags behind that at low latitudes. The low‐altitude polar orbiting satellite Oersted also observed this pulsation in the dayside inner magnetosphere. The B∥ (northward) component at Oersted is strictly out of phase with the X component observed at the dip equator below the spacecraft path, which indicates that the Pi3 pulsation at the dip equator is caused by oscillation of an ionospheric current. We propose that the Pi3 pulsations at different latitudes are generated by different mechanisms.