Physics of auroral phenomena : proceedings of the 37th Annual seminar, Apatity, 25 - 28 February, 2014 / [ed. board: A. G. Yahnin, N. V. Semenova]. - Апатиты : Изд-во Кольского научного центра РАН, 2014. - 125 с. : ил., табл.

PROBLEM OF ELECTRON DISAPPEARANCE DURING THE MAGNETIC STORM MAIN PHASE: RELATION TO THE DOWN- DUSK ASYMMETRY OF ENERGETIC ELECTRON RADIATION BELT L.L. Lazutin (SINP MSU, Moscow, e-mail: lll@srd.sinp.msu.ru) Problem of energetic electron - magnetic storm dynamics is a subject of wide discussion by scientific community. Several types of particle losses and accelerations, adiabatic and nonadiabatic results in a radiation belt transformations. Fig. 1 present typical electron radial profiles measured by low-altitude (1000 km) polar orbiter SERVIS-1 before, during and after magnetic storm. At the end of the main phase electron flux at L=3.5-8 decreased to the background level and toward the end of the recovery phase emerged with resulting changes in different radiation belt regions. We will try to approach the problem regarding main phase down - dusk asymmetry of the outer radiation belt. 1. Observations During the main phase of the magnetic storms a down-dusk asymmetry was observed in magnetic field configuration [Shi et al, 2006, Tsyganenko, 2002] and in energetic electron population of the outer radiation belt [Onsager et al., 2002, Lazutin, 2012]. Asymmetry registered as the magnetic field and particle decrease at the evening sector was presumably caused by partial ring current. Fig. 2 presents particle radial profiles measured by low-altitude satellite SERVIS-1, all profiles measured during several hours. Satellite was sun- oriented. Profiles marked by broken lines were measured at the evening sector, while morning ones are shown by solid lines. Similar features were registered during several magnetic storms, where evening profiles were shifted toward lower L as compared to the morning ones. “Physics o f Auroral Phenomena”, Proc. XXXVII A nnual Seminar, Apatity, pp. 26-28, 2014 © Kola Science Centre, Russian Academy of Science, 2014 There are three possible explanations of such asymmetry. 1. side and new ones were accelerated at the midnight-morning sector. Popular losses mechanisms o f outer belt energetic electrons include electron precipitation to the atmosphere caused by increased pitch-angle diffusion [Fridel et al., 2002, Millan and Thorne, 2007, Shprits et al, 2008, Drew et al., 2012] and magnetopause shadowing [for example Ukhorskiy, et al., 2006]. Shadowing occurs when magnetic field decrease in the inner magnetosphere cause electrons with previously closed magnetic drift orbits transit to the open orbits and became lost at the magnetopause If we agree that electrons became lost at the evening part of the magnetic drift orbit, we must suppose that each time electron flux became recovered by new acceleration at the midnight-morning part of the orbit. Only that can explain while every time when satellite arrived at the morning sector it encountered recovered particle flux. Particle fast enhancement in the midnight=moming sector of the auroral zone are caused by substorm acceleration during fast activation - dipolarization processes [Lazutin. 1986 and referenced therein]. Usual energy of the accelerating electrons are restricted by several hundreds keV, increase of the 1.7 MeV electrons is rather rear occasion It is impossible to register acceleration of electron flux of MeV electrons so often as shown at Fig. 2 Therefore suggestion that energetic electrons became lost at the evening sector must be ruled out 29.08 30.08 31.08 01.09 02.09 Figure 1. Transformation of the outer belt electron L-profiles during moderate magnetic storm, measured by SERVIS-1 satellite Polar Geophysical Institute 26