Two substorms occurred at ～04:05 and ～04:55 UT on February 26,2008 are studied with the in-situ observations of THEMIS satellites and ground-based aurora and magnetic field measurements.Angelopoulos et al.have made a comprehensive study of the 04:55 UT event.We showed detailed features of the two substorms with much attention to the first event and to the rela-tionship between mid-tail magnetic reconnection(MR) and substorm activities.It was found that in the earlier stage of each substorm,a first auroral intensification occurred 2-3 min soon after the start of mid-tail MR,followed by a slow and very lim-ited expansion.The auroral arcs were weak,short-lived,and localized,characterizing all features of a pseudobreakup.We re-garded the first auroral brightening as the initial onset of the substorms.A few minutes later,a second stronger auroral intensification appeared,followed by quick and extensive expansions.It was interesting to note that the second brightening and related poleward expansion happened almost simultaneously(within a couple of minutes) with the onset of earthward flow and dipolarization in the near-Earth tail and other phenomenon of the substorm expansion phase.We thus regarded the second auroral brightening as the major onset of the substorms.Furthermore,it was seen that during the growth phase of the two substorms,the polar cap open flux Ψ kept increasing,while it quickly reduced during the substorm expansion and recovery phase.These variations of Ψ implied that the evolution of the two substorm expansion phases were closely related to MR of tail lobe open field lines.Analysis of substorm activities revealed that the two events studied were small substorms;while estimate of MR rate indicated that the MR processes in the two substorms were weak.The aforementioned observations suggested that mid-tail MR initiated the pseudobreakup first;the earthward flow generated by MR transported magnetic flux and energy to the near-Earth tail to cause the formation of SCW and CD,which induced near-Earth dipolarization and major auroral brightening,and eventually led to the onset of the substorm expansion phase.These results were clearly consistent with the picture of NENL and RCS models and supported the two step initiation scenario of substorms. Two substorms occurred at ~ 04:05 and ~ 04:55 UT on February 26, 2008 are studied with the in situ observations of THEMIS satellites and ground-based aurora and magnetic field measurements. Angelopoulos et al. Made a comprehensive study of the 04:55 UT event.We showed detailed features of the two substorms with much attention to the first event and to the rela-tionship between mid-tail magnetic reconnection (MR) and substorm activities. It was found that in the earlier stage of each substorm, a first auroral intensification occurred 2-3 min soon after the start of mid-tail MR, followed by a slow and very lim-ited expansion. auroral arcs were weak, short-lived, and localized, characterizing all features of a pseudobreakup.We re-garded the first auroral brightening as the initial onset of the substorms .A few minutes later, a second stronger auroral intensificationPrevious, followed by quick and extensive expansions.It was interesting to note that the second brightening and related polewar d expansion happened almost simultaneously (within a couple of minutes) with the onset of earthward flow and dipolarization in the near-Earth tail and other phenomenon of the substorm expansion phase. We thus think the second auroral brightening as the major onset of the substorms. Moreover, it was seen that during the growth phase of the two substorms, the polar cap open flux Ψ kept increasing, while it quickly reduced during the substorm expansion and recovery phase. The variations of Ψ implied that the evolution of the two substorm expansion phases were closely related to MR of tail lobe open field lines. Analysis of substorm activities revealed that the two events studied were small substorms; while estimate of MR rate indicated that the MR processes in the two substorms were weak. These figures indicate that that mid- tail MR initiated the pseudobreakup first; the earthward flow generated by MR flux magnetic flux and energy to the near-Earth tail to cause the fo rmation of SCW and CD, which induced near-Earth dipolarization and major auroral brightening, and led led to the onset of the substorm expansion phase. These results were clearly consistent with the picture of NENL and RCS models and supported the two step initiation scenario of substorms.