★★ Intermediate

🌞 Solar Wind & Magnetosphere

The Sun constantly blasts charged particles outward at 400–800 km/s. Earth's magnetic dipole deflects this stream, carving out a cavity called the magnetosphere — complete with a bow shock, magnetopause, magnetosheath, and magnetotail. When the interplanetary magnetic field (IMF) turns southward, magnetic reconnection allows particles to funnel down field lines, lighting up auroras at the poles.

Solar wind speed (v_sw) = 400 km/s IMF B_z = 0 Particle density = 1.0×

r_mp = — R_E r_bs = — R_E Magnetosheath: — Aurora: off

Solar Wind–Magnetosphere Coupling

Bow shock: where the supersonic solar wind abruptly decelerates to sub-Alfvénic speeds. Standoff distance ≈ 14 R_E upstream. Visualised in orange.

Magnetopause: the pressure-balance boundary between the magnetosheath (compressed solar wind plasma) and the inner magnetosphere. Described by the Shue (1997) model: r = r₀ (2/(1+cos φ))^α, r₀ ≈ 10–12 R_E, α ≈ 0.58. Visualised in blue.

IMF B_z: when the interplanetary magnetic field points southward (B_z < 0), it anti-parallels Earth's dayside field — enabling magnetic reconnection. Particles enter the polar cusps and precipitate toward the poles, producing auroras. Drag the B_z slider below −2 nT to see this.