Comment on "Tail Reconnection Triggering Substorm Onset"
A. T. Y. Lui
The Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723–6099, USA.
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Fig. 1. (A) Alignment of five THEMIS satellites in the magnetotail during the substorm event on 26 February 2008 using the Geocentric Solar Magnetospheric (GSM) coordinate system: P1, XGSM = –21.5 RE; P2, XGSM = –17.2 RE; P3, XGSM = –10.9 RE; P4, XGSM = –10.2 RE; P5, XGSM = –5.5 RE. (B to D) The X component of convective plasma flows at P1, P3, and P4 satellites around event onset time. The red dashed lines mark the onset of substorm activity at the satellite. (E to G) The magnetic field elevation angle at P1, P3, and P4 satellites around event onset time. (H and I) The temporal variations of the Z components of the convective plasma flow and the magnetic field at P1 around the event onset time, showing the variations of Vz and Bz for the outer satellite P1 over a longer time interval encompassing the reconnection onset signature identified in (1) as marked by the label MR (magnetic reconnection). The red vertical dashed lines mark the three onsets of Vz > 0 and Bz < 0.
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Fig. 2. (A and B) Time evolution of the total plasma flow and the magnetic field for P1 [adapted from figure 4, A and B, in (1)]. (C and D) Time evolution of the total plasma flow and the magnetic field for P2 [adapted from figure 4, F and G, in (1)]. (E to H) The X component of convective plasma flows observed by four THEMIS satellites during a 3-hour time interval encompassing the substorm interval examined in (1). (I) The corresponding official auroral indices from the Kyoto University World Data Center. Dashed line marks the onset of a substorm intensification after a substorm onset at ~04:02 UT. (J) The magnetic perturbations at the Leirvogur magnetic station: H, D, and Z components are the horizontal, declination, and vertical components, respectively. (K) A sketch to show a possible time sequence of substorm activity observed in this event and the positions of four THEMIS satellites relative to these disturbance sites. The green arrows show the convective plasma flows. Current disruption onset in the near-Earth region precedes the AETH onset on the ground by 95 s. This initial disturbance instigates current disruption in multiple sites that develop at progressively further downstream distances. Reconnection occurs in one of the current disruption sites in the midtail, preceding the AETH onset by 17 s.
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