Energetic particle bursts and substorm activity observed by GEOTAIL at X =-32 R-E

On February 9, 1995, the EPIC instrument on board the Japanese spacecraft G EOTAIL observed energetic electron and ion bursts in the near-magnetotail ( X = -32 R-E) The observations occurred during a period where the B-Z compon ent of IMF was turned southward 90 minutes prior to the bursts (WIND data l ocated at X = 193 R-E) The two bursts, were observed shortly after 0430 UT. and were separated by a short time interval (similar to 10 minutes). The e nergetic bursts were followed by intense substorm activity, which was recor ded by GEOTAIL, as well as by ground magnetometers and geosynchronous satel lites. The first interval of substorm activity started almost immediately w ith the first energetic electron burst and the second some 40 minutes after the second burst. During the first substorm GEOTAIL observed a strong tail ward flow of ions, which lasted for almost 10 minutes and a flow reversal w asn't recorded by GEOTAIL. During the second activity, the B-Z component of KIF turned positive 30 minutes before the onset (60-min time delay is alre ady calculated), GEOTAIL, observed a continuous tailward-dawnward flow foll owed bq a short simultaneous earthward-tailward flow which was followed by a final flow reversal and earthward flow for the subsequent 10 minutes. Following Hones' model of substorms, we would expect the formation of a neu tral line in the plasma sheet. Minutes after the substorm onset a structure of closed loops develops from reconnected plasma sheet field lines and flo ws tailward over GEOTAIL. At the beginning of the recovery phase at Earth. the substorm neutral line should have moved past GEOTAIL to a more tailward location, accounting for the northward turning of the field and the revers al of plasma flow at that time. The observations are especially interesting in view of the fact that although the northward turning was recorded by GE OTAIL, the plasma reversal was recorded more than an hour after the tailwar d flow of ions. During the interval between the tailward and earthward flow s, the satellite recorded a new intensification in ion flow together with g round signatures of the intensification of the current wedge which indicate s a second substorm activity. (C) 1998 Elsevier Science Ltd. All rights res erved.