EFFECT OF SUDDEN IMPULSES ON CURRENTS IN THE AURORAL IONOSPHERE UNDER NORTHWARD INTERPLANETARY MAGNETIC-FIELD CONDITIONS - A CASE-STUDY

We examine the response of amoral magnetic records to the passage of an interplanetary shock at a time when the interplanetary magnetic field was northward. We restrict our attention solely to the sector within 3 hours of local magnetic midnight for a single case selected when a bursty bulk flow event was recorded in the near tail by ISEE 2. Over most of the nightside at high latitudes only a weak disturbance if any is seen. At lower latitudes a plateau is seen in the H component, coincident with the bursty bulk flow event. At 65 degrees latitude from about midnight to 3:00 LT a weak pair of negative bays is observed, also coincident with the bursty bulk flow event. We conclude that the tail and the auroral ionosphere were closely coupled during this sudden impulse, but the auroral zone disturbance appears to be mainly the brief activation of a section of the auroral electrojet rather than a classic substorm. No expansion or motion of the electrojet was observed, and the activation was no longer than that of the bursty bulk flow in the tail.