Motion of reconnection region in the Earth's magnetotail

Abstract

We obtain the X‐line velocity in the Earth's magnetotail for 24 reconnection events observed by the Cluster spacecraft between 2001 and 2005. The data set consists of 10 single X‐lines and 14 X‐lines from the time intervals of multiple reconnection. Except for two X‐lines from multiple reconnection, all the X‐lines move tailward (radial outward) along the current sheet, which is consistent with the direction of the pressure gradient. The X‐lines also propagate outward from the midnight sector in the dawn‐dusk direction. The X‐line speed in the Earth‐tail direction is comparable and proportional to the reconnection inflow speed and approximately 0.1 of the reconnection outflow speed. These results suggest that both the global pressure distribution and the local reconnection physics may affect the motion of the X‐line.

Spatial dimensions of the electron diffusion region in anti-parallel magnetic reconnection

“…A recent statistical study using the Cluster spacecraft showed that the reconnection X-line in the magnetotail tends to move tailward (∼ x direction in this paper) at about 70 km s −1 on average (Alexandrova et al, 2015). This tendency is consistent with past event studies (e.g., Baker et al, 2002;, in which the tailward X-line speed was estimated as the order of 100 km s −1 .…”

“…The statistical study of the X-line motion using Cluster (Alexandrova et al, 2015), which analyzed reconnection events following current sheet crossings, showed that the X-line tends to move in the north-south (∼ z) direction correlated with the motion of the current sheet, and its motion speed is about 30 km s −1 on average and varies up to 100-200 km s −1 (corresponding to t z = 0.2-5 s when 0.01 < n ∞ < 0.1 and β e ∼ 0.1). Since the averaged speed in the x direction in Alexandrova et al (2015) is 70 km s −1 , these X-line motion speeds indicate that the case with τ < 1 (U rz /U rx > 0.1) would not be uncommon at least for reconnection events with current sheet crossings.…”

“…The statistical study of the X-line motion using Cluster (Alexandrova et al, 2015), which analyzed reconnection events following current sheet crossings, showed that the X-line tends to move in the north-south (∼ z) direction correlated with the motion of the current sheet, and its motion speed is about 30 km s −1 on average and varies up to 100-200 km s −1 (corresponding to t z = 0.2-5 s when 0.01 < n ∞ < 0.1 and β e ∼ 0.1). Since the averaged speed in the x direction in Alexandrova et al (2015) is 70 km s −1 , these X-line motion speeds indicate that the case with τ < 1 (U rz /U rx > 0.1) would not be uncommon at least for reconnection events with current sheet crossings. Since the expected observation duration of the electron diffusion region for such events (0.2-5 s) is comparable to or less than typical spin periods (i.e., the time resolution) of spacecraft such as Geotail, Cluster or THEMIS, the detailed structure of the electron diffusion region is expected to be realized for the first time by further comparison with the MMS mission which measures particles with millisecond resolution.…”

Magnetotail Fast Flow Occurrence Rate and Dawn‐Dusk Asymmetry at XGSM ∼ −60 RE

“…We see three possibilities for the X-line source of earthward and tailward flows observed near lunar orbit (see Figure 10): (a) the classical dual near-Earth neutral line (NENL) and distant neutral line (DNL) concept 10.1002/2017JA024776 (Baker et al, 1996;Hones, 1977;McPherron, 1970); (b) patchy reconnection over a broad range in the magnetotail, as suggested by recent simulations (e.g., Wiltberger et al, 2015); (c) a tailward moving near-Earth X-line (Alexandrova et al, 2015;Maezawa & Hori, 1998;Oka et al, 2011;Russell & McPherron, 1973), which is responsible for both, earthward and tailward flows, depending on its dynamic location relative to ARTEMIS' orbit.…”

Multi‐instrument Investigation of the Location of Saturn's Magnetotail X‐Line

“…Arridge et al () observed an interval during which Cassini passed through a tailward moving reconnection site, and therefore, this is perhaps a common occurrence. X‐lines that retreat tailward are often observed at the Earth (e.g., Alexandrova et al, ; Eastwood et al, ) and also at Jupiter (Kasahara et al, ; Kronberg et al, ). Therefore, the second example likely shows an interval during which a reconnection site, or a series of reconnection sites, can be inferred to move down the magnetotail, farther from the spacecraft.…”