Four-Way Satellite Convergence — SKT/STF Boundary Diagnosis

Swarm FACField-Aligned Current measurements from ESA's Swarm satellite constellation. FACs flow along magnetic field lines between the magnetosphere and ionosphere. Swarm measures them via the curl of the magnetic field perturbation. + RBSP HOPEHelium, Oxygen, Proton, and Electron detector on NASA's Van Allen Probes (formerly RBSP). Measures the energy and composition of magnetospheric plasma. Key for identifying the plasmapause — the boundary between cold, dense plasmasphere and hot, tenuous plasma sheet. + Swarm EFIElectric Field Instrument on ESA's Swarm satellites. Measures ionospheric plasma density and drift velocity. Reveals the sharp density gradients at the boundary between different magnetospheric current systems. + Swarm AOBAuroral Oval Boundary detection from Swarm data. Maps the poleward and equatorward edges of the auroral zone using particle precipitation signatures. The equatorward boundary is a key marker of the open-closed field line boundary. — 2015 Mar 12-14, St. Patrick's Day Storm

Thesis: SKT (65.4°N, L≈5.6) sits at the boundary between two magnetospheric current systems. Four independent satellite measurements converge on the same explanation: FAC sign reversal, plasmapauseThe sharp outer boundary of the plasmasphere — the region of cold, dense plasma co-rotating with Earth. Beyond the plasmapause, plasma is hot and tenuous. Its location (~L=3-5 depending on activity) marks a fundamental boundary in magnetospheric structure. crossing, identical ionospheric density, and auroral oval edge. The LISA spatial anomaly is a current system boundary effect, not ionospheric or crustal.

1. Swarm FAC Latitude Profile (dual-satellite, Greenland sector)

SKT at R1/R2 sign reversal — local FAC minimum. STF in R1 core.

Mean |FAC| ±1σ SKT (65.5°) STF (67.5°)

2. RBSP HOPE Ion Density vs L-shell

Plasmapause crossing between SKT (L=5.6) and STF (L=6.3): 2:1 density drop

Orbit 1 (pre-storm) Orbit 2 (storm) SKT L=5.6 STF L=6.3

3. Swarm EFI Ionospheric Electron Density

N_elec at SKT ≈ N_elec at STF — ratio 1.02 ± 0.18. Conductivity NOT the cause.

Mean N_elec ±1σ SKT STF

4. Swarm Auroral Oval Boundaries (polar MLT/QDLat)

SKT at equatorward edge — straddles boundary in 15% of passes (7/47)

Equatorward Poleward — SKT ring — STF ring Straddle pass

Convergence Summary

1. FAC Structure

SKT sits at the R1/R2 FAC reversal — a local minimum in |FAC| where the current changes sign. The spatial gradient is maximized here: ground magnetometers see perturbation amplitudes that differ systematically from neighbors. Per-pass ratio: 0.34–2.48, matching ground LISA MLT dependence.

2. Plasmapause

RBSP HOPE shows a 2:1 density drop between L=5.6 (SKT) and L=6.3 (STF). SKT maps to inside the plasmasphere (cold, dense); STF maps to the plasma sheet (hot, tenuous). Temperature jumps 2012→8609 eV. The plasmapause IS the R1/R2 boundary at this L-shell range.

3. Ionospheric Density

Swarm EFI Langmuir probe: N_elec ratio = 1.02. The ionosphere above SKT and STF has identical electron density. Therefore ionospheric conductivity differences do NOT explain the ground perturbation anomaly. The cause is in the magnetospheric current input, not the ionospheric closure path.

4. Oval Boundary

AOB equatorward boundary median = 65.1° QDLat ≈ SKT. Evening-midnight boundary 64.5° is equatorward of SKT. SKT is inside the oval 74% of passes, sub-auroral 23%. Straddling (SKT out, STF in) in 15% — exactly when the ground LISA signature would be strongest.

Conclusion: All persistent LISA hot outliers localize magnetospheric current system boundaries. SKT/STF mark the R1/R2 FAC boundary = plasmapause = equatorward auroral oval edge.