SAPS intensification during substorm recovery:

A multi-instrument case study

Roman A. MakarevichUniversity of Alaska Fairbanks, USA

A. C. Kellerman, J. C. Devlin, H. YeLa Trobe University, Australia

L. R. Lyons and Y. NishimuraUniversity of California Los Angeles, USA

Subauroral Polarization Stream

Den

sity

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

-------------

++++++

++++

Magnetospheric Voltage Generator

Southwood and Wolf (1978):

V = Ed

Charge separation d

(Voltage = Ed = const)

Electric Field E

Evidence for Generator Scenarios

Voltage Generator Current 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 Generator Current Generator

Radial separation occurs within 10 min of substorm onset, i.e. during the expansion phase

MI feedback becomes effective 10-20 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

Fig01.ps

TIG beam 4

UNWbeam 0

SAID

SAPS and Substorm Phases

IMAGE

Ground

UNW

Recovery

SAPS intensification during recovery phase

arb

un

its

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 Generator Current 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 10-20 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

Fig01.ps

Some evidence of equatorward motion

SAPS and PBI

PBI appears and propagates equatorward