Plasma penetration of the dayside magnetopause

Abstract

Data from the Cluster spacecraft during their magnetopause crossing on 25 January 2002 are presented. The magnetopause was in a state of slow non-oscillatory motion during the observational period. Coherent structures of magnetosheath plasma, here typified as plasmoids, were seen on closed magnetic field lines on the inside of the magnetopause. Using simultaneous measurements on two spacecraft the inward motion of the plasmoids is followed from one spacecraft to the next, and it is found to be in agreement with the measured ion velocity. The plasma characteristics and the direction of motion of the plasmoids show that they have penetrated the magnetopause, and the observations are consistent with the concept of impulsive penetration, as it is known from theory, simulations, and laboratory experiments. The mean flux across the magnetopause observed was 0.2-0.5% of the solar wind flux at the time, and the peak values of the flux inside the plasmoids reached approximately 20% of the solar wind flux.

Jets Downstream of Collisionless Shocks

“…Dmitriev and Suvorova (2012) give a flow-parallel scale size of 4.7 R E , based on a life time of 140 s for a single event, while Hietala et al (2009Hietala et al ( , 2012 reported on perpendicular scale sizes of at least 1 R E . Finally Gunell et al (2012) estimated the dimension of a small number of plasmoids-using the definition of -perpendicular to both their velocity and the magnetic field to be 0.2 R E .…”

“…The velocity of magnetosheath jets is not only higher than that of the surrounding magnetosheath plasma, it also often differs in direction, being generally oriented more along the Sun-Earth line (Gunell et al 2012;Hietala et al 2012;). reported that the increasing deviation from the surrounding magnetosheath flow with increasing dynamic pressure ratio, and the depth in the sheath, is consistent with a tendency for the jets to continue 'straight' along the Sun-Earth line as compared to the background magnetosheath flow.…”

“…Observations from radially-aligned spacecraft have been used to show that the jets can be associated with density enhancements that propagate Earthward through the magnetopause boundary layers (Gunell et al 2012;Karlsson et al 2015b). On occasion, spacecraft closer to the Earth observe densities greater than those further away, suggesting either very large boundary distortions or perhaps 'impulsive penetration' of magnetosheath plasma (e.g., Lemaire 1977;Gunell et al 2012), a laboratory-derived concept which is discussed in more detail in Sect.…”

Recent highlights from Cluster, the first 3-D magnetospheric mission

“…) topause and bow shock. Subsequently, Gunell et al (2012) showed that plasma could penetrate the magnetopause and its motion could be followed by two spacecraft separated by 100 km (number 5 in Fig. 2) on closed field lines.…”

Crescent-shaped electron velocity distribution functions formed at the edges of plasma jets interacting with a tangential discontinuity

“…The terrestrial magnetosheath is often populated by high-speed plasma jets (also called plasmoids or plasma irregularities) streaming towards the frontside magnetopause (e.g., Dmitriev andSuvorova, 2012, 2015;Karlsson et al, 2012;Gunell et al, 2014) and impact it several times per hour (Plaschke et al, 2016). These finite-size plasma structures have an excess of antisunward dynamic pressure with respect to the ambient magnetosheath (e.g., Hietala et al, 2012;Savin 20 et al, 2012;Archer and Horbury, 2013;Plaschke et al, 2013Plaschke et al, , 2017Karlsson et al, 2018) and their interaction with the magnetopause can trigger local and global magnetospheric and geophysical effects (e.g., Plaschke et al, 2009;Hietala et al, 2012Hietala et al, , 2018.…”