Localized reconnection and substorm onset on Dec. 22, 1996

This study uses observations from the Wind, Geotail and Interball spacecraf t together with global MHD simulation to investigate the onset of a substor m on Dec. 22, 1996. At 1240 UT, during the growth phase, a small localized neutral line formed in the dawn sector at x similar to -10 R-E and initiall y extended less than 3 R-E in azimuth. The formation of this neutral line w as associated with the total Poynting flux being focused in the region clos e 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 forme d in the dusk magnetotail at similar to 1256 UT. Lobe reconnection at this neutral line corresponded to a second intensification of the substorm at si milar to 1316 UT.