ROLE OF THE FIELD-ALIGNED DENSITY DISTRIBUTION FOR EFFICIENCY OF ELECTRON SCATTERING BY HISS WAVES A.V. Artemyev, G.A. Kotova, M.I. Verigin (Space Research Institute, RAS, Moscow) Abstract. In this paper we consider peculiarities of electron density distribution along field lines in the plasmasphere and corresponding effects of these peculiarities on relativistic electron interaction with whistler waves. We describe the approximation of field-aligned density distribution based on Interball-1 measurements. This approximation allows considering the shift of the plasma density minimum relative to the magnetic equator. We use this approximation to recalculate the diffusion rates related to the relativistic electron interaction with hiss waves. The shift of the plasma density minimum results in the two times increase of the pitch-angle diffusion rate for -IMeV electrons. “Physics o f Auroral Phenomena", Proc. XXXVII A nnual Sem inar, Apatity, pp. 55-58, 2014 © Kola Science Centre, Russian Academy of Science, 2014 Polar Geophysical Institute Introduction Energetic electron scattering and acceleration in the inner magnetosphere are mostly provided by the electron resonant interaction with whistler waves ( Lyons and Williams, 1984; Trakhtengerts and Rycroft, 2008). The most intense whistler wave emission in the radiation belts corresponds to the lower band chorus waves (see Agapitov et al., 2013 and references therein). However, being intense in the outer radiation belt, chorus waves are almost absent in the plasmasphere L< 4 where hiss waves play the major role in electron scattering ( Meredith et al., 2007). Modem models of resonant interaction of hiss waves with relativistic electrons include many effects: multifrequency distributions of hiss ( Meredith et al., 2007, Meredith et al., 2009), oblique propagation of hiss ( Artemyev et al., 2013; Ni et al., 2013), variation of hiss amplitudes with the geomagnetic latitude ( Mourenas, et al., 2014), variation of the background plasma density along the field lines ( Orlova et al., 2014). The latter effect is very important because the resonant conditions for hiss interaction with electrons are quite sensitive to the local plasma density. To calculate diffusion rates and estimate the time-scale of electron scattering and acceleration several plasma density models are often considered: the global core plasma model (< Gallagher et al., 2000), models based on CRESS observation ( Sheeley et al., 2001; Meredith et al., 2003), the empirical models based on IMAGE RPI active sounding ( Denton et al., 2006, Ozhogin et al, 2012). Only last models give approximations of a plasma density variation along field lines. However, these models are purely empirical and their parameters have no physical meaning. In this paper we use measurements of the plasma density by the ALPHA-3 experiment onboard the INTERBALL-1 spacecraft ( Bezrukikh et al., 1998) to reproduce the fine distribution of the plasma density along the field lines by physical equations and test possible effects of this distribution on relativistic electron scattering by hiss waves. 1. Plasma density model The ALPHA-3 experiment onboard the Interaball-1 spacecraft measured ion spectra with the period varying from 18 s up to 2 min ( Bezrukikh et al., 1998). Under assumptions of the Maxwell energy distribution and with taking into account effects of satellite potential, plasma corotation, and spacecraft motion an ion density amplitude can be restored ( Kotova et al., 2002; Kotova, 2007). Due to the quasi neutrality condition the derived ion density can be supposed to be equal to the electron density. Thus, the empirical plasma density distribution can be obtained. Following Verigin et al. (2012) approach we use the approximation for plasma density along the field lines: N(A,AA) = Neqe rje - 179 /( 1 - 17 ) ( 1 ) 1- 0 - « w ) V 1~ ;7e9e~W ( b % ,) where Neq is an equatorial amplitude o f the plasma density (in this study we derive it from ( Sheeley et al., 2001) approximation), q(A,AA) = ™PgR E 2TpL 1 1 1 cos A0 cos (А - АA) 3 \ L r A^ ^/l + 3 s in 2( / l - АЛ.) co s6 ^ T]{A,AA) — 1 ---------- -— 6 yj l + 3 sin 2 ^ cos ( A - AA ) (co s6 A q - cos6 (A - АД) j ( 2 ) 55

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