Localized reconnection and substorm onset on Dec. 22, 1996

This study uses observations from the Wind, Geotail and Interball spacecraft together with global MHD simulation to investigate the onset of a substorm on Dec. 22, 1996. At 1240 UT, during the growth phase, a small localized neutral line formed in the dawn sector at x ∼ −10 R E and initially extended less than 3 R E in azimuth. The formation of this neutral line was associated with the total Poynting flux being focused in the region close to the neutral line. During the growth phase the neutral line expanded in azimuth and moved tailward. At the onset of the expansion phase lobe field lines began to reconnect, and a second small, localized neutral line formed in the dusk magnetotail at ∼1256 UT. Lobe reconnection at this neutral line corresponded to a second intensification of the substorm at ∼1316 UT.