Multisatellite observations of the magnetosphere response to changes in the solar wind and interplanetary magnetic field

Abstract

Abstract. We employ multipoint observations of the Van Allen Probes, THEMIS, GOES and Cluster to present case and statistical studies of the electromagnetic field, plasma and particle response to interplanetary (IP) shocks observed by the Wind satellite. On 27 February 2014 the initial encounter of an IP shock with the magnetopause occurred on the postnoon magnetosphere, consistent with the observed alignment of the shock with the spiral IMF. The dayside equatorial magnetosphere exhibited a dusk–dawn oscillatory electrical field with a period of ∼330 s and peak-to-peak amplitudes of ∼15 mV m−1 for a period of 30 min. The intensity of electrons in the energy range from 31.5 to 342 KeV responded with periods corresponding to the shock-induced ULF (ultralow frequency) electric field waves. We then perform a statistical study of Ey variations of the electric field and associated plasma drift flow velocities for 60 magnetospheric events during the passage of interplanetary shocks. The Ey perturbations are negative (dusk-to-dawn) in the dayside magnetosphere (followed by positive or oscillatory perturbations) and dominantly positive (dawn-to-dusk direction) in the nightside magnetosphere, particularly near the Sun–Earth line within an L-shell range from 2.5 to 5. The typical observed amplitudes range from 0.2 to 6 mV m−1 but can reach 12 mV during strong magnetic storms. We show that electric field perturbations increase with solar wind pressure, and the changes are especially marked in the dayside magnetosphere. The direction of the Vx component of plasma flow is in agreement with the direction of the Ey component and is antisunward at all local times except the nightside magnetosphere, where it is sunward near the Sun–Earth line. The flow velocities Vx range from 0. 2 to 40 km s−1 and are a factor of 5 to 10 times stronger near noon as they correspond to greater variations of the electric field in this region. We demonstrate that the shock-induced electric field signatures can be classified into four different groups according to the initial Ey electric field response and these signatures are dependent on local time. Negative and bipolar pulses predominate on the dayside while positive pulses occur on the nightside. The ULF electric field pulsations of Pc and Pi types produced by IP shocks are observed at all local times and in the range of periods from several tens of seconds to several minutes. We believe that most electric field pulsations of the Pc5 type in the dayside magnetosphere at L<6 are produced by field line resonances. We show that the direction of the shock normal determines the direction of the propagation of the shock-induced magnetic and plasma disturbances. The observed directions of velocity Vy predominately agree with those expected for the given spiral or orthospiral shock normal orientation.