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.

Role o f thefield-aligned density distributionfo r efficiency o f electron scattering by hiss waves In Eq. (6) the index s denotes the inputs from different wave populations with corresponding mean frequency ow and frequency dispersions 5cos. In this paper we consider three wave populations with parameters and normalizations As given by Artemyev et al. (2013). The distribution of wave normal angles в is assumed to be the same for all three wave populations with the mean Xm=Xm(X) and the dispersion SX~SXm(X) provided by Cluster observations (see Artemyev et al, 2013). The diffusion time is much larger than the electron bounce oscillation period. Thus, we need average Eq. (4) over the bounce oscillations (Lyons, 1974): (7, T 0J cos cceq where aeq is an electron equatorial pitch-angle, T=T(aeq) is the period of bounce oscillations, A,mx is the latitude of the electron mirror point, the local pitch-angle a can be defined form the conservation of the magnetic moment: sin2(a)=sin2(a e9)5(A)/Beqand 5(A) is the background dipole magnetic field with the equatorial value Beq. We consider electron scattering by whistler waves at 1=2.5 where the plasma model gives C 0 pe/Qc= 3.1 at the equator (Sheeley et al., 2001). The distribution of cope along the field lines is taken from the model presented in section I. Fig. 2 shows <Daa> as functions of acq for four energies of electrons and three sets o f parameters of the density model. For different energies the effect of the symmetry of the plasma density distribution is more important at different pitch-angle ranges. The most pronounced effect can be observed for ~1 Mev electrons: in the vicinity of loss-cone (a e,<H°) pitch-angle rates increase two times for AA=I5° in comparison with the symmetric distribution (AA=0). For very large energies (~5 MeV) the effect is opposite: the asymmetry of the density distribution results in the 30% decrease of the diffusion rates. 1E-005 * ^ 1E-007 О 1E-008 Figure °d 0 04,0 a 00 a 00 2. Pitch-angle diffusion rates (Daa is normalized on p with p=mec ( / - l ) m) for three sets of parameters and four energy values. Iii. Discussion&conclusions The shift of the plasma density minimum relative to the geomagnetic equator results in the increase of the diffusion rate in the vicinity of the loss-cone for ~1 MeV electrons. Although this increase seems to be small (only factor ~2) it can potentially play an important role for electron scattering in the plasmasphere. Lifetimes of IMeV electrons in this region is less than 10 days (Meredith et al., 2009), while numerical calculations give 10-20 days (Meredith et al., 2007). Thus, the decrease of lifetime due to peculiarities of the density distribution along the field lines can help to overcome this discrepancy. It is also interesting to note that observed effect of the density distribution on pitch- angle diffusion rate depends on the particle energy. For small energy electrons (0.5-2 MeV) we obtain the pronounce increase of the diffusion rate, while for high-energy electrons (~5MeV) we found the decrease of the diffusion rate for the system with the shift of the density minimum. One additional possible effect of peculiarities of the density distribution along the field lines corresponds to the electron scattering (and\or acceleration) by magnetosonic waves. This wave emission is very important for electron scattering in plasmasphere where magnetosonic waves can effectively interact with electrons. The electron scattering by magnetosonic waves can help to fill the gap in the profile of the diffusion rate versus pitch-angle (.Meredith et a l, 2009). The electron lifetime strongly depends on the minimum value of the diffusion rate and, thus, an additional increase of <Daa> around the local minimum can substantially influence the final electron lifetime (see discussion in Mourenas et a l, 2013). Amplitude of diffusion rates provided by electron resonant interaction with magnetosonic waves is very sensitive to the equatorial amplitude of the plasma density (Shprits et al., 2013, 57