Earth magnetic field effects on Swarm electric field instrument

Earth magnetic field effects on the particle sensors carried by the Swarm satellites are investigated using particle in cell (PIC) and test-particle modelling. In the reference frame of the spacecraft in which plasma flows at relative velocity v → , Earth magnetic field leads to an ambient electric field E → = − v → × B → , which affects the shape of particle distribution functions at the particle sensors. This in turn impacts the distribution of particle fluxes on the microchannel plate (MCP) in the ram face mounted thermal ion imagers (TIIs). Shifts in the centroid of these distributions depend on the direction and magnitude of the local magnetic field and, as such, are expected to vary periodically along the spacecraft orbit. The magnitude of these shifts is estimated quantitatively, and the effect of their variation on the calibration and interpretation of the electric field instrument (EFI) are also discussed.