Super fast plasma streams as drivers of transient and anomalous magnetospheric dynamics

Abstract

Abstract. We present multi spacecraft measurements in the magnetosheath (MSH) and in the solar wind (SW) by Interball, Cluster and Polar, demonstrating that coherent structures with magnetosonic Mach number up to 3 -Supermagnetosonic Plasma Streams (SPS) -generate transient and anomalous boundary dynamics, which may cause substantial displacements of the magnetospheric boundaries and the riddling of peripheral boundary layers. In this regard, for the first time, we describe a direct plasma penetration into the flank boundary layers, which is a candidate for being the dominant transport mechanism for disturbed MSH periods.Typically SPS's have a ram pressure exceeding by several times that of the SW and lead to long-range correlations between processes at the bow shock (BS) and at the magnetopause (MP) on one side and between MSH and MP boundary layers on the other side. We demonstrate that SPS's can be observed both near the BS and near the MP and argue that they are often triggered by hot flow anomalies (HFA), which represent local obstacles to the SW flow and can induce the SPS generation as a means for achieving a local flow balance. Finally, we also discuss other causes of SPS's, both SW-induced and intrinsic to the MSH.SPS's appear to be universal means for establishing a new equilibrium between flowing plasmas and may also prove to be important for astrophysical and fusion applications.

Anti-sunward high-speed jets in the subsolar magnetosheath

“…7). As a result, the interaction of prominent rotational discontinuities with the bow shock (see Lin et al, 1996a, b) or the existence of hot flow anomalies (Savin et al, 2012) cannot be responsible for the typical HSJs in our database. However, our criteria for HSJ selection are also expected to exclude jets generated by interaction of rotational discontinuities with the bow shock, as they produce dynamic pressure pulses with enhancements in the boundary tangential velocity components perpendicular to v x in the subsolar magnetosheath (Lin et al, 1996a, b).…”

“…They provide "long-range correlations between processes at the bow shock and at the magnetopause" (Savin et al, 2012), possibly enabling foreshock waves and structures to affect the inner magnetosphere. In summary, high-speed jets are a key element in the coupling of processes upstream of the magnetopause with the magnetosphere-ionosphere system.…”

“…Savin et al (2012) presented a study of the relationship between magnetosheath plasma jets and hot flow anomalies upstream of the bow shock (e.g., Schwartz et al, 2000). The authors argue that hot flow anomalies (obstacles to the solar wind flow) trigger high-speed jets (HSJs) locally to restore solar wind flux balance (see also, Savin et al, 2004Savin et al, , 2008.…”

“…The authors argue that hot flow anomalies (obstacles to the solar wind flow) trigger high-speed jets (HSJs) locally to restore solar wind flux balance (see also, Savin et al, 2004Savin et al, , 2008. Because interactions of current sheets in the solar wind with the bow shock are required for hot flow anomaly occurrence (e.g., Schwartz et al, 2000;Omidi and Sibeck, 2007), the work of Savin et al (2012) again relates the appearance of magnetosheath plasma jets to discontinuities in the IMF.…”

Plasma flow patterns in and around magnetosheath jets

“…At inclined shock surfaces, the solar wind plasma is compressed, but less decelerated and thermalized, leading to entities of dense and fast plasma inside the magnetosheath (Hietala et al, 2009(Hietala et al, , 2012. Other generation mechanisms are related to IMF discontinuities, discontinuity-related hot flow anomalies (HFAs), and spontaneous HFAs originating from foreshock cavitons (Lin et al, 1996a, b;Savin et al, 2012;Zhang et al, 2013;Kajdič et al, 2013;Omidi et al, 2013;Archer et al, 2014;Chu et al, 2017).…”