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.

*Physics o f Auroral Phenomena”, Proc. XL Annual Seminar, Apatity, pp. 82-85, 2017 © Polar Geophysical Institute, 2017 Polar Geophysical Institute PROPERTIES OF THE MAGNETOSHEATH PLASMA TURBULENCE UPSTREAM AND DOWNSTREAM INTERPLANETARY SHOCKS L. Rakhmanova, M. Riazantseva, N. Borodkova, O. Sapunova, G. Zastenker Space Research Institute o f Russian Academy o f Sciences, Moscow, Russia Abstract. We present a case study o f small-scale plasma fluctuations affected by the interplanetary shock in the Earth's magnetosheath. The study concentrates the kinetic scales - scales of the order o f ion gyroradius. Features of the ion flux fluctuation spectra are considered upstream and downstream the interplanetary shock registered on board the Spektr-R spacecraft in the flank magnetosheath. Present analysis indicates differences between plasma turbulence influenced by interplanetary shocks in the solar wind and in the magnetosheath. Moreover, interplanetary shocks are shown not to change the level of the ion flow intermittency in the magnetosheath. 1. Introduction Magnetosheath plasma is known о be turbulent (e.g. Lacombe et al., 2006; Mangeney et al., 2006; Alexandrova et al., 2008). To date magnetosheath turbulence is well discussed from MHD to electron scales with the help of magnetic field data (see e.g. Alexandrova et al., 2008, Huang et al., 2014 and references therein). Recently statistical studies of the kinetic-scale (scales around ion giroradius) turbulence features in the magnetosheath with the help o f plasma measurements was presented also (Riazantseva et al., 2016; Rakhmanova et al., 2016). Developed turbulent cascade in the near-Earth plasma is believed to have several scales including injection range exhibiting power law with spectral slope —1, inertial range exhibiting power law with spectral slope -5/3 and the range of dissipation with steeper spectra (see review by Bruno and Carbone, 2013). Large-scale plasma structures such as interplanetary shocks may contribute to the cascade formation and provide an interesting examples of turbulence dynamics. Plasma turbulence in the solar wind affected by the interplanetary (IP) shocks was studied by (Pitha et al., 2016). Authors considered several tens of IP shocks in the solar wind and found out follows: 1) power spectral density of the ion flux fluctuations increased by a factor of 10 downstream fast forward IP shocks; 2) spectral indices downstream the IP shocks are proportional to those upstream the IP shocks; 3) in half of the cases kinetic- scale part o f the spectra turned to have exponential cut-off instead o f power law spectra downstream the IP shocks. Present study deals with magnetosheath plasma turbulence affected by the IP shocks. We consider several case studies o f the IP shock propagation through the magnetosheath and compare Fourier spectra upstream and downstream the shock. Also we present an analysis of ion flow intermittency level upstream and downstream the shock front. 2. Observations We use BMSW (Fast Solar Wind Monitor) instrument ( Zastenker et al., 2013; Safrankova et al., 2013) data on board Russian Spektr-R spacecraft. The instrument measures ion flux value and direction and, in some cases, proton density, bulk and thermal velocity with a time resolution 31 ms. This time resolution is enough to study turbulent cascade at scales of transition between inertial and dissipation ranges. In the current study we use ion flux value measurements for this data is continually available from Spektr-R. The ion flux variations represent mostly the fluctuations o f ion density (see e.g. Pitha et al., 2016). Fig. 1 shows the example of IP shock registered in the magnetosheath on December 19, 2015 at 16:26. Panels a-c present ion flux value, number density and bulk velocity respectively from Spektr-R (black lines). Grey lines presents solar wind data from Themis-C spacecraft, shifted to match the shock fronts. Spektr-R is located at {-41; -25; 13} Re in GSE coordinate system; Themis-C is located at {-16; 54; -1} Re in the solar wind. The IP shock speed is Vjp = 525 km/s, the angle between magnetic field direction and the shock normal is Obn^SS0. The IP shock characteristics were calculated using multispacecraft technique in the solar wind (Song and Russel, 1999). In order to study influence of the IP shock on the kinetic-scale plasma turbulence we consider Fourier spectra calculated on -17 min time intervals. This time intervals corresponds to~0.01-10 Hz in frequency domain. Typically, ion flux spectra in the magnetosheath in this frequency range are described by two power laws with break between them. Rakhmanova et al., (2016) showed spectral indices to be Si=l .8±0.2, S2=2.9±0.3 and Fbreak=0.8±0.5 Hz, where Si and S 2 are the slopes of the first and the second power law parts respectively, and F break is the frequency at which the break between two power law parts is observed. Shadowed areas in Fig. 1 show time intervals used for spectra calculations foe the analyzed case. These intervals are shifted from the front by several minutes to avoid an influence o f wave phenomena associated with the shock front. Fig. 2 presents the frequency spectra upstream (black line) and downstream (grey line) the IP shock on December 19, 2015. Spectra are approximated with two power laws and break. The spectral indices are shown in the figure. One can see that spectral power increases by the factor of 40 downstream the IP shock. This value is comparable by the order of magnitude with the results of (Pitha et al., 2016) in the solar wind. Spectral slope Si is close to 82