Earth's field lines follow the dipole geometry r = L·cos²λ (L = equatorial shell radius, λ = magnetic latitude). The solar wind's dynamic pressure P ≈ n·m·v² pushes the dayside boundary inward until it balances the field's magnetic pressure — the classic Chapman–Ferraro balance — while the same flow drags the nightside field lines out into a long magnetotail:
standoff Rₘₚ ≈ R0 + k1·Bfield − k2·Pwind
tail stretch ≈ 1 + k3·wind − k4·field + k5·storm
Charged particles trapped on the inner shells (L ≈ 1.3–2.2) bounce back and forth between magnetic mirror points near the poles — the same mechanism that populates the Van Allen belts and feeds the aurora. A storm impulse spikes the wind pressure, compresses the dayside, and briefly floods the belts, which is why the aurora reading jumps right after you press it.
- Blue arc — compressed dayside field lines (sunward, left).
- Violet arc — stretched nightside magnetotail (right).
- Amber dots — solar wind particles deflected around the magnetopause.
- Green glow — trapped particles / aurora feed near the poles.