[1] We present THEMIS observations of the near-Earth plasma sheet that permit us to assess the geometrical structure of the magnetotail prior to dipolarization. Latitudinal profiles of the magnetic field were obtained by five spacecraft simultaneously around the magnetic equator at a distance of X GSM ∼ −10 R E in the premidnight for two events. It is found that the strength of normal magnetic field B z was increased with a distance from the magnetic equator, which differs considerably from the standard magnetic field model. Instead, the observation can be explained by a magnetic field model that has a minimum in the equatorial field strength (minimum B), as required from the force-balanced magnetotail model with steady earthward convection. Moreover, the analyses showed that the feature of minimum B sustained continuously for ∼20 min before dipolarization onsets.
[1] Pressure anisotropy is a characteristic of space plasmas. Linear magnetohydrodynamic (MHD) theories have shown that the properties of hydromagnetic waves may greatly be modified by the pressure anisotropy. In particular, slow waves may exhibit the anomalous behaviors of positive density-magnetic field correlation, faster propagation speed relative to the intermediate wave and right-handed polarization. This paper examines the formation of anomalous slow shocks by solving the gyrotropic MHD and Hall-MHD equations numerically for the evolution of an initial current sheet that separates two regions of plasma and magnetic field. It is shown that it is possible to have slow shock move ahead the intermediate shock with upstream flow being super-Alfvénic and the downstream being firehose unstable as well as anomalous slow shocks with dBdr > 0 and right-handed polarization.
We report on the observations of spontaneous spin polarized moments in 7.4 nm Pb/PbO nanoparticles, which give rise to re-entrantlike temperature profiles for the magnetic susceptibility and magnetization in the superconducting phase that develops below 6.86 K. Results reveal the existence of a magnetic component below TC and superconductivity remains at low temperatures. A 30-fold increase in the critical magnetic field is also found. Superconductivity mainly arises from the 5 nm Pb core, whereas the 1.2 nm PbO shell contributes to the appearance of a net magnetic moment in the 7.4 nm Pb/PbO core/shell particles.
Space plasma usually exhibits temperature or pressure anisotropy with two distinct components, p∥ and p⊥, denoting the pressure parallel and perpendicular to the magnetic field, respectively. This paper presents the first result of two‐dimensional (∂/∂y = 0) magnetic reconnection with single X‐line in anisotropic plasma based on gyrotropic magnetohydrodynamic (MHD) simulations. The field‐line reconnection is initiated by imposing a localized resistivity on the Harris‐type current sheet with a guide magnetic field By. It is shown that the observational feature of a slow shock (SS) followed by a contact discontinuity (CD) near the central sheet, across which the magnetic field is decreased and the pressure anisotropy is changed from p∥ > p⊥ to p∥ ≈ p⊥, as identified by Hoshino et al. (2000) in the Geotail data, may be reproduced in our simulations. For the initial equilibrium with relatively large pressure anisotropy of p∥ ≫ p⊥, the steady reconnection layer may consist of SS followed by rotational discontinuity (RD) with both upstream and downstream states of SS being super‐Alfvénic which is similar to the anomalous SS‐RD compound structure found in the solar wind and magnetosphere. While for the cases of p⊥ > p∥, the reconnection layer may consist of RD followed by SS and the reconnection rate is larger as compared to the cases of p∥ ≥ p⊥.
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