Observations of solar wind directly driven auroral electrojets and gravity waves

We present simultaneous observations of the IMF, auroral electrojets, and gravity waves on December 7, 1994. It is found that when the IMF Bz component turned southward, auroral electrojet currents appeared after a time delay of about 9 min. The Saskatoon I-IF radar observed quasi-periodic gravity waves after each burst of the auroral electrojet with a time delay of about 60-70 min. The IMF southward turnings, the auroral electrojets, and the gravity waves had a recurrence period of about 40 min. These observations show clearly the cause and effect relationship between the IMF southward turnings, the auroral electrojets, and the gravity waves. Another important phenomenon observed in this event is that the quasi-periodic occurrence of the gravity wave pulses in far-field points was determined by the repetitive energy input in the source region rather than by the wave dispersion. It seems that each burst of the auroral electrojet generated a single gravity wave pulse. (Author)