Low-frequency magnetic variations at the high-<i>β</i> Earth bow shock

Abstract

Abstract. Observations of Earth's bow shock during high-β (ratio of thermal to magnetic pressure) solar wind streams are rare. However, such shocks are ubiquitous in astrophysical plasmas. Typical solar wind parameters related to high β (here β>10) are as follows: low speed, high density, and a very low interplanetary magnetic field of 1–2 nT. These conditions are usually quite transient and need to be verified immediately upstream of the observed shock crossings. In this report, three characteristic crossings by the Cluster project (from the 22 found) are studied using multipoint analysis, allowing us to determine spatial scales. The main magnetic field and density spatial scale of about a couple of hundred of kilometers generally corresponds to the increased proton convective gyroradius. Observed magnetic variations are different from those for supercritical shocks, with β∼1. Dominant magnetic variations in the shock transition have amplitudes much larger than the background field and have a frequency of ∼ 0.3–0.5 Hz (in some events – 1–2 Hz). The wave polarization has no stable phase and is closer to linear, which complicates the determination of the wave propagation direction. Spatial scales (wavelengths) of variations are within several tens to a couple of hundred of kilometers.

On the Role of the Ion Weibel Instability in the Formation of the Earth Bow Shock Front

“…На участках фронта головной ударной волны Земли со слабым (порядка 1 нТ) межпланетного поля могут наблюдаться сильные колебания магнитного поля и плотности [1][2][3][4]. При этом временной ряд, измеряемый спутником, создаёт иллюзию пересечения протяжённого фронта ударной волны с быстрыми осцилляциями магнитного поля и плотности плазмы от значений перед фронтом до значений за фронтом (рис.…”

Detailed Structure of Very High‐β Earth Bow Shock

“…In our previous investigation (Petrukovich et al., 2019) (hereafter cited as PCS19), we conducted a thorough analysis of occurrence in solar wind and of shocks in such conditions. A data set of 22 shock crossings, observed by Cluster multispacecraft mission with the minimal spacecraft separation from several tens to couple hundred km, was presented.…”