Substorm active phase as a series of two types of reconnection occurred in the closed plasma sheet and in the open tail lobes
The maps of field-aligned current (FAC) density in the ionosphere, obtained for 27.08.2007 substorm with the time increments 1 to 5 minutes were used together with Cluster, WIND and Polar data. The downward and upward FACs of the substorm current wedge (SCW) were detected in each FAC maps, and their intensity <i>J </i>was also measured. The substorm onsets were divided into two groups, denoted by PSR (initial plasma sheet reconnection/pseudobreakups) and TLR (tail lobe reconnection/full expansion onsets). A fast tailward propagation of the initial PSR region was described as transition from PSR to TLR regime, associated with the northward turn of the IMF. Thus, actually, the TLR/full expansion onset is the total PSR+TLR regime. The source region of PSR and TLR was assumed to be the two-dimensional (∂/∂z=0) thin current sheet in the equatorial plane that was given as the rectangular area with its <i>X</i>- and <i>Y</i>-sizes. The second basic assumption used was that <i>J </i>is the intensity of the FAC flowing from (or into) the edge region of the cross-tail current disruption region. From here, using electrodynamics, the estimates of some disruption region parameters have been calculated. The disrupted magnetic field is ~5 % of the un-disrupted magnetic field during initial PSR, and ~95 % for the time interval of amplified PSR+TLR. The same ratio of <i>Q </i>values was calculated for PSR and PSR+TLR. Dramatic growth of the power <i>Q </i>for PSR+TLR time interval was observed in all area of SCW from near till medium and distant tail. It was associated with the northward turn of the IMF, as usually for substorms.