Physics of auroral phenomena : proceedings of the 40th annual seminar, Apatity, 13-17 March, 2017 / [ed. board: N. V. Semenova, A. G. Yahnin]. - Апатиты : Издательство Кольского научного центра РАН, 2017. - 143 с. : ил., табл.

E.A. Shirokov et al. the entire emitter—receiver line, we will choose r 0 in the interval r 0 < r 0max = A , where Л corresponds to the geomagnetic latitude change of 0.1° along the geomagnetic field line at given Am and Mcllwain parameter L . The minimum estimate is obviously determined by the source half-size: r 0min= 0.5/lr. V , receiving antenna i 'a 1 “о)? ^ 4 7 A /-resonance direction i/ for the group velocity Figure 1. Geometry o f the problem. ictitious source У Calculation Results In this section, we apply the general formulas obtained above to some measurements o f chorus wave electric fields onboard THEMIS spacecraft [Burch and Angelopoulos, 2009]. Each THEMIS spacecraft is equipped with the Electric Field Instrument (EFI) that consists of the three dipole orthogonal antennas. These antennas have a half-length o f 24.8 m, 20.2 m, and 3.47 m. We will refer to them as dipoles A, B, and C, respectively. Dipoles A and В consist of 2 small spheres (see (9)), and dipole С consists of 2 straight thin rods (see (7)). Since the dipoles are orthogonal to each other, they allow one to measure three components of the incident wave electric field and can be treated independently from each other. The electric field value should be calculated from these three components, and each o f them should be obtained according to (1). The antennas orientation angles a and ft have been found from the Flux Gate Magnetometer (FGM) data that provide the results of geomagnetic field measurements. For our analysis we chose some of the events which were previously considered by [Agapitov et al., 2014] in relation to electron energization. The two chorus events that we have analyzed in depth are described in Table 1. Angle 0obs that corresponds to the observed spectrum maximum was found using a singular value decomposition method [Santolik et al., 2003] from the Search Coil Magnetometer (SCM) data only. Table 1. The analyzed chorus events detected by THEMIS Event 1 2 THEMIS С A Date (yyyy-mm-dd) 2007-08-28 2008-11-26 UT (hh:mm:ss) 15:51:48 03:18:23 An (deg) 15 0 L 5.4 5.0 ®o ( s '1) 9425 15708 (deg) 78.0 64.7 9obs (deg) 75.0 58.0 ltr (km) 13 7.6 a (deg)[a] 78.6, 110, 23.7 62.1,116, 40.1 P (deg)И 62.5, 148, 180 51.0, 126, 180 k s (*o = r0nHX) 2.7, 2.7, 0.4 13, 12, 0.8 /—N I 'w' ’л’ J to 9.0, 9.0,1.9 50, 49, 5.8 w The three values correspond to dipoles A, B, and C, respectively. The results of calculations, performed for these events, are presented in the last two lines o f Table 1. One can see that in case r 0 = r 0min the receiver effective length is several times larger as compared to case г0 = г0[ШХ. However, 60