~ Pergamon www.elsevier.com/loeate/asr Adv. Space Res. Vol. 30, No. 12, pp. 2719-2724, 2002 © 2002 COSPAR. Published by Elsevier Science Ltd. All rights reserved Printed in Great Britain 0273-1177/02 $22,00 + 0.00 PII: S0273-1177(02)00762-7 MORPHOLOGY OF HIGH LATITUDE AURORAL ELECTRON PRECIPITATIONS OBTAINED BY THE AUREOL-3 SATELLITE M. Stepanova l, O. Luizar ~'2, E. E. Antonova 3, J. M. Bosqued 4, and R. A. Kovrazhkin 5 t Departamento de Fisica, USACH, Casilla 307, Santiago, Chile. 2Departamento de Fisica, Universidad Nacional San Antonio Abad del Cusco, Peru. 3Skobeltsyn Institute of Nuclear Physics, MSU, Moscow 119899, Vorobievi GorL Russia. 4CESK CNRS/UPS, BP 4346, 31028 Toulouse, France. 5Space Research Institute, RAS, Profsoyuznaya 84/32, Moscow 117810, Russia. • ABSTRACT Latitudinal distribution of auroral electron precipitations was studied using the Aureol-3 satellite data. Analysis of 148 events in the morning, night, and evening sectors showed that structures of all types have a wide MLT distribution. However, during low geomagnetic activity the distribution of latitudinally asymmetric events is close to Iijima and Potemra's Region 1 and 2 current picture: the equatorward events prevail in the morning and postmidnight sectors, and the polarward ones - in the evening and premidnight. An increase in geomagnetic activity makes the MLT distribution of different types of events more uniform. This fact may indicate existence of the multi-layer structure of currents and consequently medium scale electric fields, in which the maximum currents considerably exceed the average values observed in the Region 1 and 2. © 2002 COSPAR. Published by Elsevier Science Ltd. All rights reserved. INTRODUCTION Numerous researches of the auroral particle precipitations made it possible to establish the relationship between auroral precipitation structures and different magnetospheric domains (Galperin and Feldstein, 1996; Feldstein and Galperin, 1985; NeweU and Meng, 1992). However, the limited efforts have been concentrated in the study of morphology of the medium-scale auroral precipitation events. During a long time it was considered that one of the most pronounced kinds of electron precipitations are the inverted- V or lambda structures (Frank and Ackerson, 1971; Hekkila, 1970). Lin and Hoffman (1992) established that such events occur predominately in the dusk-to-midnight sector, and that the distribution of scale-lengths follows an exponential law. However they did not study in details the morphology of electron precipitations. Newell (2000) showed that large-scale acceleration events come in a variety of shapes of which the "classic" inverted-Vs are only a small minority comparing to another types of events, predominately: events in which spectral flux peak energy increases (or decreases) monotonically with latitude or maintains constant, and large-scale suprathermal bursts. The latitudinal distribution of the large-scale electron precipitations along the auroral oval has still not been analyzed too. Antonova et al,. (1998) and Luizar et al., (2000) studied the latitudinal variation of the upward field-aligned current associated with the large-scale electron accelerated precipitations. In was shown that the number of maximums in the current distribution and the characteristic length of currelR variation coincide with the prediction of the hot stratification theory, based on the gradient mechanism of the field-aligned current generation (Tverskoy 1982a, b). However, these predictions were 2719