An ionospheric travelling convection vortex event observed by ground-based magnetometers and by Viking

A transient ionospheric travelling convection vortex (ITCV) event was recorded by the EISCAT magnetometer cross in northern Scandinavia on April 21, 1986 around 8:40 MLT. Simultaneously, the near‐conjugate satellite VIKING observed strong magnetic and electric field variations on closed magnetic field lines. The signatures seen by the spacecraft are consistent with a passage through two oppositely directed field‐aligned current tubes. The total upward and downward currents turned out to be matched within a region of ∼ 1000 km in the ionosphere. Because of the close spatial and temporal proximity of both observations we interpret the field‐aligned currents as being associated with the ITCV. This is the first time that in‐situ measurements of the currents connecting the ITCV to the source region close to the magnetopause have been published. Both the current density and the dimensions of the current tubes could be estimated here.