SAPS intensification during substorm recovery: A multi-instrument case study Roman A. Makarevich University of Alaska Fairbanks, USA A. C. Kellerman, J. C. Devlin, H. Ye La Trobe University, Australia L. R. Lyons and Y. Nishimura University of California Los Angeles, USA

Subauroral Polarization Stream

Density Latitude Magnetospheric Current Generator Anderson et al. (1991): Electric Field   Recombination   Density   Conductivity   (Current = const) Electric Field   … Trough R2 FAC R1 FAC

Magnetospheric Voltage Generator

Southwood and Wolf (1978): V = Ed Charge separation d   (Voltage = Ed = const) Electric Field E 

Evidence for Generator Scenarios Voltage GeneratorCurrent Generator SAID as a substorm recovery phenomenon (Anderson et al., 1993) Density profiles mimicking E- field profiles (Anderson et al., 1991) SAID narrowing and strengthening in successive satellite passes (Anderson et al., 2001) Statistically similar to trough in MLT and Kp dependence (Karlsson et al., 1998) E-region density decreasing with SAPS intensification (Lyons et al., 2010)

Voltage GeneratorCurrent Generator Radial separation occurs within 10 min of substorm onset, i.e. during the expansion phase MI feedback becomes effective min after the substorm onset Separation decreases as substorm progresses, i.e. during late expansion and recovery FAC and SAPS diminish during recovery Timing of Generator Scenarios Objective: investigate timing and causes of major SAPS intensifications

SAPS Event TIG beam 4 UNW beam 0 SAID

SAPS and Substorm Phases IMAGE Ground UNW Recov ery SAPS intensification during recovery phase arb units

UNW All Beams UNW all beams UNW keogram

TEC Observations SD FIT GPS TEC SD FIT Vorticity (~FAC)

SAPS and Auroral Precipitation SAPS narrows and separation from precipitation increases

SAPS and TEC Trough Strong 2D association between SAPS and TEC trough

Voltage GeneratorCurrent Generator SAPS Characteristics and Evolution: Narrowing and strengthening with time SAPS and TEC trough association No density decrease in line with SAPS strength SAPS Intensification Timing: Should start within 10 min of substorm onset Should start min after substorm onset FAC should diminish during recovery

Magnetospheric and Topside Signatures Magnetosphere (LANL, GOES): No parameter was found to exhibit similar time dependence to the SAPS strength during recovery apart from energetic electron fluxes at 01 and 15 MLT (but not at 00 MLT) Topside ionosphere (DMSP IDM): Significant ion upflows Some topside density enhancement

1.Strong, 2-D association between SAPS and TEC trough was found, but no density decrease during recovery and SAPS intensification 2.Both voltage and current generator scenarios had difficulties explaining observations 3.No parameter was found that exhibited similar time dependence to the SAPS intensity, suggesting that it may be triggered, e.g. by convection and auroral bursts Conclusions

PBI and Convection Burst Some evidence of equatorward motion

SAPS and PBI PBI appears and propagates equatorward