A configuration of field-aligned currents (FACs) that can explain the rapid variation of the geomagnetic field in mid-latitude Europe on 29 October 2003 was recently proposed. Interestingly, this specific system of the FACs might also explain the famous Carrington event on 2 September 1859. By analysing the declination observed in mid-latitude Europe on 29 October 2003, we confirmed an important feature of the proposed current system, the westward movement of one of the FACs.

It is often the case that only magnetic field data are available in in-situ planetary studies using spacecraft. Plasma data are either not available or the amount is highly limited. Nevertheless, the theory of plasma instability tells us how to interpret the magnetic field data (wave frequency) in terms of flow speed and beam velocity generating the instability. We invent an analysis tool for the Mercury upstream waves as example.