An abrupt increase in pressure associated with interplanetary shocks will compress the Earth's magnetic field. This leads to a sudden impulse also observed in low-latitude magnetometer records. These events are followed by heavily damped oscillations of approximately 5 min periods, depending on plasma conditions. The general features are explained by a simple model. Our results are supported by satellite and ground-based observations. The results are also important for space–weather predictions.

Currents due to slow bulk electron motion along vertical magnetic fields are studied for plasmas subject to a gravitational force. A general feature of this problem is a singularity in the plasma pressure force that develops at some finite altitude when a plasma that is initially in static equilibrium is set into slow motion. Classical fluid models thus do not allow general steady-state solutions for field-aligned currents. The alternative is that only time-varying solutions exist.