Physics of auroral phenomena : proceedings of the 35th Annual seminar, Apatity, 28 Februaru – 02 March, 2012 / [ed. board: A. G. Yahnin, A. A. Mochalov]. - Апатиты : Издательство Кольского научного центра РАН, 2012. - 187 с. : ил., табл.

Magneticfield parameters near the subsolar magnetopause in accordance with THEMIS data A comparatively good linear dependence of the у-component at the magnetopause (see Figure 3) on that in the solar wind is obtained. The correlation coefficient is better and the errors of the parameters of the approximation and standard deviations are lesser for averaged data. For instantaneous values after crossing the approximation with the model ByMP = a+bBySw gives the following values of parameters: a = 1.4 ± 2.1 nT, b = 4.3 ± 0.7, SD = 14.7 nT, correlation coefficient r = 0.67. For the 30s-averaged values: a = -0.3 ± 0.4 nT, b = 5.7 ± 0.1, SD = 4.8 nT, r = 0.78. For the 90s-averaged values: a = -1.3 ± 0.5 nT, b = 5.5 ± 0.2, SD = 4.1 nT, r = 0.75. a) b) c) Fig. 3 The dependence of the у-component of the magnetic field for the considered set of events a) over 3 seconds after crossing the magnetopause, b) averaged over a period of 30 seconds from the moment of crossing c) averaged over a period of 90 seconds - on the By in the solar wind. a) b) c) Fig. 4 The dependence of the z-component of the magnetic field for the considered set of events a) over 3 seconds after crossing the magnetopause, b) averaged over a period of 30 seconds from the moment of crossing c) averaged over a period of 90 seconds -- on the Bz in the solar wind. The results obtained for the z-component of the magnetic field (see Figure 4) are of great interest. There is a vague tendency towards an increase in the value of this component with the increasing of corresponding value in the solar wind. However, almost a half of cases (25 out of 50 for the instantaneous and 30s-averaged values, and 24 out of 50 for the values averaged over a period of 90 seconds) show that the sign of the z-component at the magnetopause changes compared with the sign of Bz in the solar wind. The most common changes are from positive value (in the solar wind) to negative (at the magnetopause): 24 for instantaneous values, 23 for 30s-averaged and 22 for 90-s averaged values, and in a few cases (1 for the instantaneous and 2 for averaged over 30 and 90 seconds values) from negative to positive value. It should be noted that considered set of cases contains the equal number of events with positive and negative Bz in the solar wind. a) b) c) Fig. 5 The dependence of the magnetic field clock angle for the considered set of events a) 3 seconds after crossing the magnetopause, b) averaged over a period of 30 seconds, c) averaged over a period of 90 seconds - on that in the solar wind. The dependencies of clock angle at the magnetopause on that in the solar wind have been obtained and are presented in Figure 5 and Table 1. For clarity, there are a line of equal values of clock angles in solar wind and near the magnetopause in each plot. 47