AN IONOSPHERIC TRAVELING 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 A pril 21, 1986 around 8:40 MLT. Simultaneously, the near-conjugate sate llite VIKING observed strong magnetic and electric field variations on closed magnetic field lines. The signatures seen by the spacecraft ar e consistent with a passage through two oppositely directed field-alig ned current tubes. The total upward and downward currents turned out t o be matched within a region of approximately 1000 km in the ionospher e. Because of the close spatial and temporal proximity of both observa tions we interpret the field-aligned currents as being associated with the ITCV. This is the first time that in-situ measurements of the cur rents connecting the ITCV to the source region close to the magnetopau se have been published. Both the current density and the dimensions of the current tubes could be estimated here.