X. Cao

Outward expansion of the lunar wake: ARTEMIS observations

Magnetohydrodynamics (MHD) predicts that lunar wake expands outward at magnetosonic velocities in all directions perpendicular to background solar wind; however, fluid theories emphasize that lunar wake expands outward at sound speeds mainly along the interplanetary magnetic field (IMF). Early observations supported the MHD predictions in the near-moon region despite lack of solar wind and IMF observations. Thanks to the special orbit design of the ARTEMIS mission, the solar wind conditions are well determined at the time of concurrent observations in the lunar wake. 164 wake crossings made by ARTEMIS are statistically studied in this paper. Observations indicated that, in either distant or near-Moon regions, the lunar wake expands outward at the fast MHD wave velocities. This simple model provides a powerful way to determine wake boundaries, particularly at large distances where the boundary signatures are indistinct, thus allowing further studies on the Moon-solar wind/crustal field-solar wind interactions. Citation: Zhang, H., et al. (2012), Outward expansion of the lunar wake: ARTEMIS observations, Geophys. Res. Lett., 39, L18104, doi: 10.1029/2012GL052839.

Active phase of a substorm as a chain of two types of reconnection: In the closed plasma sheet and in the open tail lobes

The maps of the field-aligned current (FAC) density distribution in the ionosphere obtained by the TIM-2 magnetogram inversion technique are used to investigate the August 27, 2001 substorm. The open magnetic flux Ψ and intensity J of the substorm current wedge (SCW) have been determined with a step of 1–5 min. The substorm onsets are divided into two types, PSR (plasma sheet reconnection) and TLR (tail lobe reconnection). The fast expansion tailward of the PSR region is described as the transition from PSR to PSR+TLR. Assuming that the SCW FACs flow down into the ionosphere from the edges of the disruption region of the cross-tail dawn-dusk current, several parameters of the disruption region have been estimated. The disrupted magnetic field has been found to be ∼5% of the undisrupted one for PSR and ∼95% for PSR+TLR. The disturbance power Q for PSR is an order of magnitude lower than that for PSR+TLR. The abrupt growth of Q during the transition from PSR to PSR+TLR is observed over the entire SCW area from its near-Earth part to the midtail and distant tail.

Continuous lobe reconnection in the mid-tail and its relationship to substorms: Cluster observations of continuous lobe reconnection in the mid-magneto tail

When the IMF turns southward, a great amount of magnetic energy is stored in the magnetotail, and the electric field across the magnetotail substantially enhances. As long as magnetic reconnection (MR) in the magnetotail initiates and continues, the magnetic field and plasma in the central plasma sheet are carried away to the near-Earth and down to the tail, the magnetic field and plasma in the lobe region enter the CPS and are involved in MR. We call this process“Continuous Lobe Reconnection (CLR)”. In this paper a detailed analysis of Cluster observation of MR through 2001–2003 is made. Plenty of CLR events are found that led to considerable changes of tail configuration, appearance of BBF, as well as large-scale bubbles in which both plasma temperature and number density substantially decrease. It is shown that in general CLR events last for dozens of minutes and have good correspondence to substorm initiation under the condition of continuous southward IMF.