Ade. Spoor Sea. Vol.5, No.4, pp.135—138, 1985 0273—1177/85 $0.00 + .50 Printed in Great Britain. All rights reserved. Copyright © COSPAR STATISTICAL STUDY OF INVERTED-V EVENTS: A COMPARISON BETWEEN EXPERIMENT AND THEORY J. M. Bosqued,° C. Maurel, 5 H. Rème,5 J. A. Sauvaud,5 R. A. Kovrazhkin55 and Yu. I. Ga1perin~ 5CESRICNRS, Toulouse University, 31029 Toulouse, France * Space Research Institute, U.S.S.R. Academy of Sciences, Moscow, U.S.S.R. ABSTRACT We present a detailed study of the distribution and of the interaal structure of the inver- ted—V electron precipitation commonly detected in the 500 — 2000 km altitude range aboard the AUREOL—3 satellite. These structured precipitations are statistically observed inside the auroral oval with a maximum occurence in the nightside sector. They correspond to primary electron fluxes peaked at energies generally below 10 key. it is shown that, as predicted by kinetic theories, most inverted—V structures present a clear relationship between the field— aligned current density carried by the 1 — 20 keV primary electrons and the potential drop inferred from particle distribution functions. Furthermore the study demonstrates the existence of strong electron heating, relat~d to the energy gain, when the current density exceeds some threshold of about 1 — 5 rA(m) INTRODUCTIJN Inverted—V events, discrete structures in precipitating electrons, have been studied inten- sively by polar orbiting satellites since their discovery a decade ago /1/. These structures correspond to the precipitation of 1 — 10 keV electrons from the plasma sheet, with energy spectra displaying a peak whfch is often attributed to a field—aligned potential difference at an altitude around 1 R~,. Several mechanisms capable of maintaining these aligned electric fields have been identif/ed anomalous resistivity, collisionless thermoelectric effects, electric double layers, etc. , and a general overview of them has appeared in the monograph of Akasofu and Ran /2/. This paper presents some new observations of auroral electron accelera- tion carried Out by the SPECTRO charged particle analyzers aboard the Franco—Soviet AIJREOL—3 satellite; this spacecraft was launched into a quasi—polar orbit (apogee 2000 km, perigee 400 km, inclination 82.5°) on 21 September 1981. The data presented here were taken in 1982 by the ROBE experiment, in which electrons and protons are selected in E/q by an electrostatic quadrispherical analyzer, then detected by a set of 18 channel electron multipliers. As the satellite was 3—axis stabilized, the particles were then analyzed in 9 pitch angles between 00 and 1100. The 0.2 — 22 keV energy range is analyzed in 16 logarithmically spaced steps, in 1.6 or 3.6 seconds, depending upon the mode of operation. The complete experiment has been described elsewhere /3/. 1. THE DATA The velocity space electron distribu~ions f(v) were constructed from the differential fluxes 0 using the simple relation f(v) = m Ø/2E, and then used to infer the accelerating potential difference using the energy peak. All the functions were integrated in order to calculate the current density .J~, carried by the hot electrons as well as the energy fluxE.. In this integration only pl~imary electrons were taken into account, and secondary or primary degraded electrons trapped between the magnetic mirror point and the parallel electric field were eliminated in velocity space /4/. Finally, all the electron distributions were fitted by Maxwellian distributions in order to obtain the electron density 0e and temperature E. Inverted—V structures were defined by the presence of three successive energy spectra with a peak; for the data acquisition duration here, this corresponds to shout 5 seconds. Figure 1 shows the probability of occurrence of inverted—V events in a MAT—A diagram. About 250 structures are shown here in 1 hour MLT bins and 2° latitude bins. Note °that these structures are detected at all MLT’s (except on the dayside between 10 and 16h) in the classical auroral oval, and also over the polar caps; the maximum probability is located between 20 and 01 MLT, where the widest and most energetic structures are detected (~1° in latitude) while the narrowest are located in the morning sector, at high latitudes (~75°). This diagram is very similar to that of inverted—V structures constructed using AE—C satellite data /5/ and to that of the statistics of ion conical distributions and electrostatic shocks from the S3—3 satellite /6,7/. 1 35