Global evolution of a substorm-associated DP2 current system observed by superDARN and magnetometers

This paper deals with an evolution of the electric field in the dayside auroral and equatorial ionosphere during asubstorm on July 16, 1995. A southward turning of the IMF detected by WIND (171 Re) caused enhancements in the auroral electrojet intensity in the 7–10 MLT and 15.5–18.5 MLT sectors as observed by the IMAGE (74-56 cgmlat) and CANOPUS (70-58 cgmlat) magnetometer chains. SuperDARN detected an equatorward motion of the radar scattering region at speeds of several −10 degs/hour in the dayside (05–17 MLT), suggesting an increase in the flux of the open magnetic field in the polar cap. Furthermore, coherent magnetic variations are observed at subauroral to equatorial latitudes simultaneously with the auroral magnetic variations within a temporal resolution of 10 s. This suggests that the electric field increase during the growth phase is established instantaneously around the convection reversal in the 15.5–18.5 MLT sector, and furthermore penetrates instantaneously to mid and low latitudes. SuperDARN detected a continuous equatorward motion of the auroral oval during the expansion phase around the cusp, which implies a continuous magnetic merging at the day-side magnetopause during the expansion phase. A rapid decrease in the electric field is inferred from coherent auroral and equatorial magnetic field decreases during the recovery phase, which may have been caused by northward turning of the IMF. This magnetic field decrease resembles the change in magnetic field of the counter-electrojet at the dip equator in the afternoon sector.

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