Multi-Point Satellites Observed Dawnside Subauroral Polarization Streams (SAPS) Developed on a Short Timescale Under Weak-Storm and Non-Storm Substorm Conditions

Abstract

We study the development of the magnetosphere-ionosphere (M-I) conjugate dawnside Subauroral Polarization Streams (SAPS) by investigating the newly-formed dawnside SAPS observed soon after dawnside substorm onset. Our topside-ionosphere results show that (a) the eastward dawnside SAPS flow was weaker than the eastward auroral return flow and (b) the equatorward and downward SAPS electric (E) field components were not accompanied by any dawnside upward Region-2 field-aligned currents. These provide observational evidence that (c) the substorm current wedge (SCW) developed on the dawnside and (d) the newly-formed dawnside SAPS observed developed in a voltage generator of magnetospheric origin. Our inner-magnetosphere results show (e) the charge separation at the dawnside plasmapause, where (f) the inward (earthward) SAPS E field developed in (g) a voltage generator, (h) on a short timescale, and (i) during localized particle injections (j) associated with the dawnside SCW. From these (a–j) new results we conclude that the M-I conjugate dawnside SAPS observed developed on a short timescale, in a magnetospheric voltage generator, of which root cause was the fast development of the dawnside SCW. Our conclusion is consistent with the fast-time development of the M-I conjugate duskside SAPS, of which root cause is the fast development of the duskside SCW.