Physics of auroral phenomena : proceedings of the 39th annual seminar, Apatity, 29 February-4 March, 2016 / [ed. board: N. V. Semenova, A. G. Yahnin]. - Апатиты : Издательство Кольского научного центра РАН, 2016. - 167 с. : ил., табл.

L. Rakhmanova el al. et al. (1999) for magnetic field fluctuation spectra -3.4. Just behind the bow shock the obtained slope is somewhat less than the reported previously by Czaykowska et al. [2001] for magnetic field fluctuation spectra - -2.6. The break frequency of fluctuations spectra decreases from 0.4+0.1 Hz in the magnetopause vicinity to 0.13±0.01 Hz in the middle MSH and then grows slightly to 0.25±0.05 Hz at the bow shock for both quantities. Generally a spectra break is supposed to be associated with ion cyclotron frequency (Alexandrova et al., 2008; Czaykowska et al., 2001) or inertial length frequency (Safrankova et al., 2013, 2015). Dotted line in Fig. le shows the inertial length frequency F l, defined as FL= V/2rcL, where L=vA/a>c ( v a is an Alfven speed and coc is the proton gyro-frequency and V is a bulk velocity). A close relation between break frequency o f plasma fluctuations and inertial length frequency in the middle MSH and just behind the bow shock is observed. On the other hand inertial length frequency does not change toward the magnetopause. Upstream IMF (Geotail data, not shown here) and ambient ion flux stay nearly constant. Hence, the break frequency change cannot be explained by the change of any characteristic plasma frequency. We conjecture the specific character of turbulence near the magnetopause leading to the growth of the break frequency. Space plasma turbulence is known to be intermittent, i.e. the probability distribution function (PDF) does not follow the Gaussian distribution (e.g. Bruno et al., 2003; Budaev, 2015). The degree of non-Gaussianity can be characterized by an increase of the flatness coefficient К toward the small scales, where К is defined as the 4-th order moment of PDF А"(т)=&Дт)Л%2(т), where Sp(i)=<(n(t+ t)-n(t))p> (Bruno et al., 2003). K= 3 for Gaussian distribution and K >3 for distributions with heavier tails. Fig. If shows time evolution o f the flatness calculated for the ion flux data at time scales т=0.1, 1, 10, 100 sec. The flatness is calculated on 15 min intervals. According to Fig. If the level of MSH plasma intermittency grows toward the boundaries. In the middle MSH non-intermittent turbulence may be observed. Yordanova et al. (2008) reported more intermittent turbulence at larger distances from the quasi-parallel bow shock. This discrepancy may be caused by considering MSH behind the bow shock o f different types. 3. Summary and discussion Magnetosheath plasma carries energy from the solar wind to the Earth’s magnetosphere. Processes taking place in the MSH should be studied not only at large scales (~ Earth’s radii) but also at small scales (~ion gyroradii). The MSH plasma is turbulent and its turbulence differs from the SW one for the presence o f boundaries. In order to study MSH turbulence not only magnetic field but also plasma data is worth to be examined. We demonstrate an evolution of plasma fluctuations and plasma turbulence properties across the Earth’s magnetosheath at kinetic scales. Our results can be summarized as follows. - Power spectral density of the high frequency fluctuations grows toward the MSH boundaries. At the magnetopause PSD of ion flux value fluctuations is higher than the one of the polar angle fluctuations. - High frequency part of spectra of the ion flux fluctuations are usually slightly steeper in the middle MSH than at its boundaries. Spectra of the polar angle fluctuations are steeper than the ones of the ion flux fluctuations; the slope of the spectra does not change across the MSH. - For both quantities the break frequency of fluctuations spectra decreases from 0.4±0.1 Hz at the magnetopause to 0.13±0.01 Hz in the middle MSH and then grows slightly to 0.25±0.05 Hz at the bow shock. The increase o f the break frequency toward the bow shock can be attributed to the increase of background plasma parameters, i.e. inertial length frequency. However, the break frequency increase toward the magnetopause is not accompanied by changes of ambient plasma or magnetic field. Thus, the specific character of turbulence seems to take place near the magnetopause. - Plasma turbulence is shown to be more intermittent near the boundaries comparing to the middle MSH A c know ledgm en ts. The reported study was funded by RFBR according to the research project No. 16-32-00818. M. Riazantseva and G. Zastenker were funded by RFBR according to the research project No. 16-02-00669 Table 1 Parameter A t the MP Middle MSH At the BS PSD at 2 Hz ion flux value 10 J 10'4 10‘4 polar angle 10'4 105 10-4 s 2 ion flux value -2.6±0.1 -3.0±0.2 -2.6±0.1 polar angle -3.4±0.2 -3.7±0.3 -3.4±0.2 I'bri'ak' Hz ion flux value 0.4±0.1 0.13+0.01 0.25 ±0.05 polar angle 68