Current sheet flapping in the near-Earth magnetotail: peculiarities of propagation and parallel currents

Abstract

Abstract. We consider series of tilted current sheet crossings, corresponding to flapping waves in the near-Earth magnetotail. We analyse Cluster observations from 2005 to 2009, when spacecraft visited the magnetotail neutral plane near X ∈ [−17, −8], Y ∈ [−16, −2] R E (in the GSM system). Large separation of spacecraft allows us to estimate both local and global properties of flapping current sheets. We find significant variation in flapping wave direction of propagation between the middle tail and flanks. Th series of tilted current sheets represent the system of periodic, almost parallel currents with typical thickness of current filaments about L = 0.4 R E . The earthward gradients of B z magnetic field are reduced within this current system in comparison with the gradients in the quiet near-Earth magnetotail. The wavelength (i.e. a distance between two crossings of current sheets with the same orientations) of the flapping waves is larger than 2π L for most of observations. The velocity of flapping wave propagation is about ion bulk velocity and is significantly lower than the velocity of ion drift relative to electrons. We discuss possible drivers of flapping and estimate the amplitude of the total parallel current generated by flapping waves.

Observations of Short‐Period Ion‐Scale Current Sheet Flapping

“…This is consistent with the statistical surveys by Yushkov et al. (2016) and Gao et al. (2018), who found that flapping motions far in the flank propagate toward the sun.…”

“…Taking advantage of the abundance of the flapping events in the magnetotail, the statistical surveys carried out by Yushkov et al. (2016) and Gao et al. (2018) showed that the wave‐like magnetotail current sheet observed in the flanks propagates away from the midnight sector.…”

The Distribution of Two Flapping Types of Magnetotail Current Sheet: Implication for the Flapping Mechanism

“…Thus, the flapping type described by Sun et al () as propagating toward midnight is probably the steady flapping we found in this study. Yushkov et al () indeed found that the CS normal near midnight tends to be along the Z axis within −6 < Y < 0 R E , and CS is significantly tilted away from the Z axis beyond Y < −6R E (see their Figure 2), but they interpreted it as a significant variation of the direction of flapping wave propagation. In other words, our study not only supports previous findings on the distribution of the CS normal on the Y coordinates but also further enhances knowledge of flapping dynamics in terms of the distribution of flapping types.…”

“…It has been noticed in previous studies that the source of flapping motion is located around the midnight region, suggesting such possible sources as fast plasma flow or magnetic reconnection (Sergeev et al, , ). Some studies indeed extended the surveyed region to cover midnight in order to explore features of the sources, but they have remained focused on the normal orientation of each encountered CS rather than on the two flapping types we have described here (e.g., Runov et al, ; Sun et al, ; Yushkov et al, ). For example, with the statistical analysis of each encountered CS normal by Cluster, Sun et al () argued that magnetotail CS could have two types of flapping motions, kink‐like flapping motion propagating toward both flanks and kink‐like flapping propagating toward midnight within | Y | < 8R E .…”

Magnetotail Configuration During a Steady Convection Event as Observed by Low‐Altitude and Magnetospheric Spacecraft

“…Such a shift implies sunward propagation of plasma structures from ThE to ThD (separated mainly in X by ~1.3 R E ) with a velocity of ~40 km/s, which is consistent with the measured average proton bulk flow. A plausible interpretation of this fluctuating By appearance is that the azimuthal CS signatures are modulated by localized sunward convected structures, possibly either the remnants of BBFs produced by time‐varying reconnection, or the flapping wave (flapping waves were also observed in the dawnside plasma sheet; Yushkov et al, ). We recall that these observations were made in the region of return convection near the dawn terminator at 10 to 12 R E .…”