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.

“Physics o f Auroral Phenom ena”, Proc. XXXIX Annual Sem inar, A patity, pp. 66-69, 2 0 1 6 © Polar Geophysical Institute, 2016 G eophysical Institute EVOLUTION OF RAPID FLUCTUATIONS OF THE PLASMA PARAMETERS DURING THE CROSSING OF THE EARTH’S MAGNETOSHEATH L. Rakhmanova, M . R iazantseva, G. Zastenker Space Research Institute o f Russian A cadem y o f Sciences, 84/32 P rofsoyuznaya Street, M o scow , R u ssian Federation, 117997 Abstract. We present a case study of a flank magnetosheath crossing by the Spectr-R satellite. Rapid measurements of the ion flux value and its direction with 31 ms time resolution provided by the BMSW instrument are examined at different distances from the magnetosheath boundaries - the bow shock and the magnetopause. The magnetosheath behind the quasi-perpendicular bow shock is analyzed. Time resolution of data is sufficient for observation of frequency spectra of plasma fluctuations either in MHD and ion kinetic scales. We examine evolution of spectral parameters such as power density, slopes and break frequency together with evolution of properties of a probability distribution function. We find out that (i) power spectral density rises toward the MSH boundaries, (ii) spectra slopes do not change significantly across the magnetosheath, (iii) break frequency of the fluctuations grows toward the magnetopause. We demonstrate that plasma can be less intermittent in the middle MSH comparing to its boundaries. 1. Introduction Near-Earth space plasma is known to be turbulent for decades (e.g. Tu and Marsch, 1995). Nowadays the solar wind (SW) turbulence is well discussed from MHD to electron kinetic scales (see review by Alexandrova et al. (2013) and references therein). The Earth’s magnetosheath (MSH) turbulence is less studied despite its crucial role in the solar wind- magnetosphere interaction. Basing on in-situ measurements the turbulent cascade in the MSH was studied at MHD scales both for plasma and magnetic field (e.g. Shevyrev et al. 2003; Shevyrev and Zastenker, 2005). At MHD scales (f<fci,.fcj is ion gyro-frequency) fluctuations were shown to follow Kolmogorov spectra ~ f 5/3 at the MSH flanks ( Alexandrova et al., 2008) and ~ f 1just behind the bow shock in the subsolar MSH ( Czaykowska et al., 2001). At kinetic scales (f>fci) only magnetic field fluctuations are generally considered (e.g. Rezeau et al., 1999; Mangeney et al., 2006; Alexandrova et al., 2008; Huang et al., 2014). In this frequency range the steepening of the spectra is observed: spectra follow ~f ~slaw with 5 ranging from 2 to 3. Plasma fluctuations in the MSH at the kinetic scales were considered only with the help of indirect measurements (e.g. Lacombe et al„ 1995) for the lack of plasma data with a sufficient time resolution. Studies of turbulence in the SW as well as in the MSH based on direct plasma measurements were presented only recently. Such investigation became possible after Spectr-R satellite launching in 2011. The BMSW instrument on board the Spektr-R satellite provides measurements o f the plasma parameters with a time resolution 31 ms. Investigations of the density fluctuations measured by the BMSW in the SW were reported by ( Safrdnkova et al„ 2013a, 2015; Chen et al„ 2014). Velocity fluctuations spectra and their comparison with the density ones are discussed in (Safrdnkova et al., 2013a, 2016). Statistical study of the MSH turbulent cascades based on ion flux measurements from BMSW was presented by Riazantseva et al. (2016). The authors conducted a statistical comparison between the turbulent spectra and features of a probability distribution function in the MSH and SW without respect to the different regions inside the MSH. A dynamic of the turbulence features during plasma transfer through the MSH was not addressed in that paper. In the present paper we study an evolution of small-scale plasma fluctuations and their properties of turbulence with the change of distance to the MSH boundaries with the help of the BMSW measurements. We analyze the power density of plasma fluctuations, shape of fluctuations spectra and change o f structure functions properties while the satellite moves from the magnetopause to the bow shock. 2. Observations The BMSW (Fast Solar Wind Monitor) instrument ( Zastenker et al., 2013, Safrdnkova et al., 2013b) provides measurements of the plasma parameters - ion flux value and its direction, proton density, bulk and thermal velocity - with a time resolution 31 ms. The ion flux direction is characterized by the polar angle 0 - a deviation of a flux vector from the Sun-Earth line. The ion flux value fluctuations are supposed to represent mostly fluctuations of ion density variations (see e.g. Pitna et al., (2016) for a comparison between ion flux and density spectra). We conjecture that polar angle fluctuations represent fluctuations of plasma bulk velocity. BMSW measurements in the MSH are reliable for 0<25° due to the increasing errors of ion flux value determination for larger angles (see Gagua et al., 2009). The flank MSH crossing under study takes place on February 9, 2012. Spektr-R crosses the magnetopause at 09:43 at {6; 2; 10}GSE R e and enters the SW at 12:24 at {4; 4; 13}Gse R e - The ion flux and polar angle measurements 66