Variety of shapes of solar wind ion flux spectra: Spektr-R measurements

Abstract

The paper is devoted to the shapes of the solar wind ion flux fluctuation spectrum at the transition between the inertial and the kinetic range using in situ high-resolution measurements of the Russian mission Spektr-R. We analyse the variability of the transition region and select five typical types of spectral shapes: (i) spectra with two slopes and one break, (ii) spectra characterized by a nonlinear steepening in the kinetic range, (iii) spectra with flattening in the vicinity of the break, (iv) spectra with a bump in the vicinity of the break and (v) spectra without any steepening in the kinetic range. The most popular is the well-known type (i) observed in approximately half of the cases. The second most popular type of spectra is type (iii) occurring in approximately one third of the cases. The other three types are observed less often: type (ii) – in approximately 6 %; type (iv) in 3 % and type (v) in 6 % of cases. An analysis of typical plasma conditions for different types of spectra revealed that the last two type of spectra (iv) and (v) are generally observed in a very slow solar wind with a low proton density, (i) and (iii) are observed in the solar wind with rather typical conditions and (ii) is usually observed in high-speed streams. The effect of nonlinear steepening of the spectra in the kinetic range increases with the solar wind speed. We present also the analysis of statistical properties of the observed events and compare them with the predictions of several statistical turbulence models. We show that intermittency is always observed in the solar wind flow despite the presence of one or another shape of spectra. The log-Poisson model with a dominant contribution of filament-like structures shows the best parameterization of the experimentally observed scaling.

Kinetic‐Scale Ion Flux Fluctuations Behind the Quasi‐Parallel and Quasi‐Perpendicular Bow Shock

“…Riazantseva et al () presented statistical study of spectral shapes of the ion flux fluctuations in the SW. Spectra with two slopes and break was shown to occur at ~50% of cases. This result is similar to what we show in the present study.…”

“…This result is similar to what we show in the present study. However, statistics of Riazantseva et al () included various ambient plasma conditions. According to Šafránková et al (), in the undisturbed SW flow spectra of density fluctuations usually have the plateau prior to the transition from the MHD to kinetic scales.…”

“…Spectra of this type are believed to be common in the SW and MSH. However, Riazantseva et al () and Rakhmanova, Riazantseva, Zastenker, and Yermolaev () showed variability of shapes of the ion flux fluctuation spectra. In the current study the spectra of different shapes are analyzed separately.…”

“…Three main types of spectral shape are distinguished: with two slopes separated with break (52%), with bump at the transition frequencies (19%), and with plateau at the transition frequencies (21%). Riazantseva et al (2017) presented statistical study of spectral shapes of the ion flux fluctuations in the SW. Spectra with two slopes and break was shown to occur at~50% of cases. This result is similar to what we show in the present study.…”

“…Kinetic‐scale plasma fluctuations have been explored systematically since 2011 with the help of the BMSW (Fast Solar Wind Monitor, Šafránková, Němeček, Přech, Zastenker, Cěrmák, et al, ; Zastenker et al, ) instrument on board Spektr‐R spacecraft. Parameters of plasma turbulence based on BMSW measurements were considered in the SW (Chen et al, ; Riazantseva et al, , , ; Šafránková, Němeček, Přech, & Zastenker, ; Šafránková et al, , ) as well as in the flank MSH (Rakhmanova et al, ; Rakhmanova, Riazantseva, Zastenker & Yermolaev, ; Riazantseva et al, , ). The BMSW data set covers 6 years of continuous plasma measurements in the SW and MSH that allow for statistical study of plasma fluctuations for various ambient conditions and upstream SW parameters.…”