ICS-9 Substorm discussion : M-I coupling studies Substorm auroral onset develops slowly for few min prior to time generally referred to as auroral breakup Thus onset processes develop gradually during this few min period? If so, what is occurring and why? Much auroral structure associated with developing onset aurora How does this relate to the onset process? No signature at TH D, E at or before onset, when aurora shows within onset MLT region – several events, no counterexample shown These classical Akasofu onsets must be inside-out? Substorm onset occurs near equatorward edge of plasma sheet electron precipitation Why? How does this relate to onset processes? Substorm growth and expansion electrodynamics: related to SAPS, Harang reversal, and Region 2 electric field and current evolution Thus R2 electrodynamics (pressure gradients, E-fields, currents, energy-dependent magnetic drift) critical aspect of onset process?