The interaction of finite‐width reconnection exhaust jets with a dipolar magnetic field configuration

Abstract

The structure and properties of earthward propagating exhaust jets produced by a magnetic reconnection source region localized in the out‐of‐plane direction are investigated with 3‐D particle‐in‐cell simulations that incorporate a realistic plasma sheet configuration in which a dipole magnetic field region is connected to an asymptotic tail equilibrium with finite Bz. The jet is found to separate initially into two segments of width ∼10–15di each (di is the ion inertia length). The dawnward segment moves ahead of the duskward one and continues to intensify, while the latter is buffeted by the return flows generated by the former and stagnates. The leading front develops the characteristic structure of a sharp Bz increase and density drop on a 1–2di scale. The current associated with this Bz increase is carried mainly by the electrons, and the jet front is the site of a Region 1 sense field‐aligned current system. The ions develop a moderate temperature anisotropy with Ti||>Ti⊥ ahead of the front, while the electron temperature remains isotropic. The ion heating behind the front is quasi‐adiabatic, while the nonthermal electron tail is enhanced out to the limit of the simulation spectrum (∼15Eth). The ion velocity distribution function behind the front exhibits a strong parallel phase space enhancement at speeds ∼0.5VA associated with the earthward flow, while closer to the dipole region there is a drop out in parallel phase space at speeds of ∼1.5–2.5VA. The electron distribution is isotropic with an enhanced central plateau extending out to ∼4VA.

Externally Driven Onset of Localized Magnetic Reconnection and Disruption in a Magnetotail Configuration

“…The duskward extension has now become disconnected, but the main reversal region remains about 10 d i in extent. This dimension is quite similar to that found by Pritchett and Runov () in a 3‐D simulation in which reconnection was forced in a localized region by an effective anomalous resistivity (current blocking). The bulk tailward exhaust flow is now somewhat larger, ∼0.25 V A , and there is also an earthward flow of magnitude ∼0.1 V A emerging from the dawnward edge of the reversed B z region.…”

“…The wavelength is on the order of 1–2 d i . This structuring is strongly reminiscent of that produced by the BICI acting at an interchange head produced by a tailward gradient in the B z profile (Pritchett et al, ) or at a dipolarization front that develops from a reconnection exhaust (Pritchett & Runov, ). A similar modulation is present off the equatorial plane as is illustrated in Figure that presents y , z plane cuts at x / d i =9 for numerous field quantities.…”

“…The initial near‐Earth magnetotail configuration is constructed in a manner similar to that described in Pritchett and Runov (). The initial magnetic fields are obtained by superposing an asymptotic magnetotail vector potential A 0 y , t ( x , z ) of the type given by Schindler (), Birn et al (), and Lembège and Pellat (), with the vacuum field of a line (2‐D) dipole field, …”

Near‐Earth Reconnection Ejecta at Lunar Distances

“…Moreover, electrons, bouncing between equatorial plane and the dipole magnetic field on the earthward side may gain more energy from multiple entries in the DFB Birn et al (). The observed asymmetry in electron heating requires further investigation with particle‐in cell and test particle simulations that include the dipole field in the initial equilibrium (e.g., Pritchett & Ronuv ).…”

Effects of Cross‐Sheet Density and Temperature Inhomogeneities on Magnetotail Reconnection

“…Most previous PIC simulations have focused on the effects of magnetic field configuration, such as the presence of a normal component of magnetic field (e.g., Lu, Wang, et al, 2018;Pritchett, 2005, and references therein), the presence of a magnetic flux enhancement (see, e.g., Sitnov et al, 2014), the strength of the dipole geomagnetic field (see, e.g., Pritchett & Runov, 2017), and the spatial and temporal localization of external drivers (see, e.g., Liu et al, 2014;. Most previous PIC simulations have focused on the effects of magnetic field configuration, such as the presence of a normal component of magnetic field (e.g., Lu, Wang, et al, 2018;Pritchett, 2005, and references therein), the presence of a magnetic flux enhancement (see, e.g., Sitnov et al, 2014), the strength of the dipole geomagnetic field (see, e.g., Pritchett & Runov, 2017), and the spatial and temporal localization of external drivers (see, e.g., Liu et al, 2014;.…”