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Aurora Borealis - Charged Particles in Earth's Dipole

What you are seeing: charged particles trapped in Earth's dipole field. Each one spirals along a field line and bounces between magnetic mirror points, where the converging field reflects it. Particles with a small enough equatorial pitch angle fall into the loss cone: their mirror point sits below the atmosphere, so instead of reflecting they precipitate near the poles and light the auroral oval green. The magnetic-bottle field profile and the precipitation latitude are plotted below. Drag the scene to rotate, wheel to zoom

Figure 1. Charged particles spiraling along Earth's dipole field, exciting the auroral oval. Method: Boris pusher (symplectic Lorentz integration); dipole B⃗∝(3(r^⋅z^)r^−z^)/r3\vec B \propto (3(\hat r \cdot \hat z)\hat r - \hat z)/r^3; atmospheric excitation triggered below 600 km near the poles.
particle count3
dipole strength1.4
pitch angle30 deg
animation speed2

WHAT TO TRY

  • Drop the pitch angle toward a few degrees: more particles fall into the loss cone, the mirror line on the bottle plot rises past the atmosphere, and the precipitation histogram and the auroral oval brighten. Push it toward 90 degrees and the population stays trapped near the equator as the radiation belt, with almost no aurora.
  • Strengthen the dipole: the gyroradius shrinks, so the spirals tighten onto the field lines and the bounce speeds up. The loss-cone geometry depends only on the shell, so the oval latitude holds while the motion sharpens.
  • Raise the particle count and rotate the globe: the trapped blue population traces the doughnut-shaped belts, while the green loss-cone particles funnel down to rings around both magnetic poles.