Abstract
Abstract. Interball-1 observations of a substorm development in the mid-tail on 16 December 1998 are compared with the auroral dynamics obtained from the Polar UV imager. Using these data, the relationship between plasma flow directions in the tail and the location of the auroral activation is examined. Main attention is given to tailward and earth-ward plasma flows, interpreted as signatures of a Near Earth Neutral Line (NENL). It is unambiguously shown that in the mid-plasma sheet the flows were directed tailward when the auroral bulge developed equatorward of the spacecraft ionospheric footprint. On the contrary, when active auroras moved poleward of the Interball-1 projection, earthward fast flow bursts were observed. This confirms the concept that the NENL (or flow reversal region) is the source of auroras forming the poleward edge of the auroral bulge. The observed earthward flow bursts have all typical signatures of Bursty Bulk Flows (BBFs), described by Angelopolous et al. (1992). These BBFs are related to substorm activations starting at the poleward edge of the expanded auroral bulge. We interpret the BBFs as a result of reconnection pulses occurring tail-ward of Interball-1. In addition, some non-typically observed phenomena were detected in the plasma sheet during this substorm: (i) tailward/earthward flows were superimposed on a very strong duskward flow, and (ii) wavy structures of both magnetic field and plasma density were registered. The latter observation is probably linked to the filamentary structure of the current sheet.Key words. Magnetospheric physics (auroral phenomena; plasma sheet; storms and substorms)
Highlights
Magnetospheric substorms represent one of the basic forms of interaction between the solar wind and magnetosphere, and as such are intensively studied
The main conclusion of this study is that the direction of impulsive plasma flows detected in the mid-tail correlates with the location of aurora forming the auroral bulge relative to the satellite footprint
This is in agreement with the concept that the Near Earth Neutral Line (NENL) maps into the poleward edge of the auroral bulge (e.g. Pudovkin et al, 1991)
Summary
Magnetospheric substorms represent one of the basic forms of interaction between the solar wind and magnetosphere, and as such are intensively studied. The fast tailward retreat of the NENL is associated with the poleward shift of auroras forming the auroral bulge (Hones, 1992). Angelopolous et al (1992) described a phenomenon called Bursty Bulk Flows (BBFs) occurring in the central plasma sheet, and related to earthward plasma transport. It has been suggested (Henderson et al, 1998; Sergeev et al, 1999, 2000; Solovyev et al, 1999) that BBFs relate to the northsouth auroral forms, which often occur within the auroral bulge during expansion and recovery phases of substorm The results will be interpreted on the basis of the NENL model
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