Embedded current sheets in the Earth’s magnetotail

Abstract

[1] In this investigation we introduce and discuss quantitative parameters of a thin current sheet embedded in the background plasma sheet. We use Cluster statistics and empirical models, as well as self-consistent simulations, to understand the formation and development of embedded current sheets, in particular in the course of substorms. Data and theory show that the embedded sheet thickness is of the order of a proton larmor radius, a constraint equivalent to magnetic flux conservation. The embedded sheet can be essentially described by two dimensionless parameters B 0 /B ext and F 0 /F ext . B 0 is the magnetic field at the embedded sheet boundary, B ext is the field at the boundary of the background plasma sheet, and F 0 and F ext are magnetic flux values. During the growth phase current density in embedded sheet and B 0 increase, while thickness decreases. Sheets with the most intense currents (large B 0 ) are observed after onset. The self-consistent anisotropic sheet model, including both electron and proton currents and combined with the Harris-type background shows that when the proton-scale embedded sheet becomes sufficiently thin, an electron-scale current sheet can appear inside it due to enhanced electron curvature drift.

Cluster as current sheet surveyor in the magnetotail

“…Large variation in the thickness distribution agrees with the recent statistical study by Rong et al (2011). The applicability of multiple Gaussian fitting supports the notion of embedded current sheet structure as proposed by Petrukovich et al (2011).…”

X lines in the magnetotail for southward and northward IMF conditions

“…The energy stored for the triggering of the X lines and the substorm in the tail under northward IMF is just the remnant energy in the period of preexiting southward IMF [Li et al, 2008;Du et al, 2011;Miyashita et al, 2011]. Due to the weaker convection electric field for northward than southward IMF [Maezawa, 1976;Usadi et al, 1993;Borovsky et al, 1998;Petrukovich et al, 2003;Wang et al, 2006], it is prone to conjecture that not enough energy and/or magnetic flux can be deposited in the tail to form a thin current sheet and generate an X line under northward IMF condition [Min et al, 1985;Ma et al, 1995;Pritchett and Coroniti, 1994;Petrukovich et al, 2011].…”

Drift modes of a quasi-two-dimensional current sheet

“…The normal compo nent of the magnetic field is also present in the sys tem. In this study, we use the combined TCS and BCS model proposed in [3,51]. This model represents a superposition of the two dimensional BCS [47] and one dimensional TCS [36] consideration), and are the scalar potential and the y component of the vector potential, is the BCS ion temperature, and is the drift velocity.…”

“…The gradient in the "EarthSun" direction allows drift modes to develop in the BCS even at ~ 0 [50]. In [51], a combined model of the TCS embedded into the BCS was constructed based on the models [47] and [36]. This model includes the effects associ ated with the anisotropy of electron and transient ion pressures and the particle pressure gradient in the "Earth-Sun" direction.…”