Every gauge on this desk runs published physics — the same families of equations forecasters and modelers use. You control the solar wind: how fast it blows, how much plasma it carries, how strong its magnetic field is, and — the part that decides everything — which way that field points. Earth answers. First run is guided; after that, the desk is yours.
The picture is a side view of near-Earth space: the sun is off-screen to the left, the dotted ring is geosynchronous orbit at 6.6 Earth radii — where the big communications satellites live — and the blue curve is the magnetopause, the boundary where Earth's magnetic field stops the solar wind. Its shape is the Shue et al. (1998) model3, recomputed live from your dials. Squeeze the wind hard enough and the nose of the shield gets pushed inside the satellite ring — it really happens; the model you are driving was built from an event that did exactly that in January 19973, and May 2024 did it again.
The thin blue curves are magnetic field lines — schematic, but pinned to the physics: the outermost closed dayside line noses in exactly at the Shue standoff, and the footprints of the open lines track the modeled oval. Turn Bz south and watch them work: dayside lines peel open at the reconnection ✕ and sweep back over the poles into the tail — Dungey's circuit, drawn in 19618 — while a bright trickle of particles funnels in along them and sparks the nightside oval. Then hold a storm and watch the tail itself: it stretches as it stores energy, snaps earthward, and the oval erupts — a substorm, the loading–unloading cycle Akasofu mapped in 196412, run here about 200× faster than nature so you can see whole cycles. The small disc at lower right is the same auroral oval seen from above the pole — the observatory's home view, in miniature: it slides equatorward, thickens, reddens at its outer edge, and bulges at midnight when the tail lets go.
The gauges are the desk instruments. Polar-cap voltage is the electrical potential the solar wind drives across Earth's polar ionosphere — the EMF of the aurora engine, from the Boyle et al. (1997) empirical formula1, soft-capped near ~250 kV where real storms saturate6,7. The Kp estimate inverts the same paper's climatology (Φ ≈ 16.5 + 15.5·Kp)1. The merging rate is the Newell et al. (2007) coupling function2 — the best single predictor of how strongly the magnetosphere is being driven. Storm size asks the O'Brien & McPherron (2000) ring-current model4 a simple question: if this exact wind blew steadily for a few hours, where would the ring current settle? And the city ladder places the auroral oval's midnight equatorward edge with the Carbary (2005) Kp fit5.
Why "north or south" decides everything: Earth's field points north at the nose of the magnetosphere. A southward interplanetary field is anti-parallel to it — the geometry lets the two fields merge and reconnect, the circuit Dungey drew in 19618. Northward field, no merging, no storm — no matter how fast the wind.
Color is the sky telling you the electron energy. Slow electrons (under ~1 keV) stop above 200 km, where the air is thin enough for oxygen's forbidden 630 nm transition to survive its 110-second wait — pure red, and only ever at the top. The 1–10 keV workhorses stop at 100–150 km and light oxygen green — most of the light in most displays. The hardest electrons (>10 keV) punch below 100 km into molecular nitrogen: a pink-magenta fringe on the bottom edge of violent curtains. The red-to-green ratio is a real diagnostic, falling monotonically as the electrons harden13,14 — and the ladder never reorders: red, green, pink, top to bottom. Distance reshuffles what you see: the high red carries ~2,200 km past the horizon while green sets at ~1,150 km, which is why far aurora is red aurora. The field guide's color chapter is the full story — and the Painter's Exam above is where you prove you can use it.
This lab is honest about being a teaching model. Each formula is real and cited, and each runs unmodified — but they are stitched together as a steady-state snapshot: you hold a wind condition, the desk shows where the system would settle. Real storms are time histories — sheaths, magnetic clouds, substorm cycles — which is exactly what the observatory's measured storm replays are for. The differences that matter:
| Gauge | Model | Source |
|---|---|---|
| Polar-cap voltage | Φ = 10⁻⁴·v² + 11.7·B·sin³(θ/2) kV, θ = clock angle; soft cap 250·tanh(Φ/250) | Boyle et al. 19971; saturation6,7 |
| Kp estimate | Kp = (Φ − 16.5) / 15.5, clamped 0–9 | Boyle et al. 19971 |
| Merging rate | dΦ/dt = v⁴ᐟ³·B²ᐟ³·sin⁸ᐟ³(θ/2) | Newell et al. 20072 |
| Magnetopause | r₀ = (10.22 + 1.29·tanh(0.184(Bz+8.14)))·Pd⁻¹ᐟ⁶·⁶, flaring α(Bz, Pd) | Shue et al. 19983 |
| Storm size | injection −4.0·(VBs−0.5) nT/h, decay τ = 2.40·e^(9.74/(4.69+VBs)) h, +7.26·√Pd − 11 | O'Brien & McPherron 20004 |
| Oval's equatorward edge | Λ = 67.22 − 1.89·Kp (midnight) | Carbary 20055 |
Wind pressure: Pd = 1.6726×10⁻⁶·n·v² nPa. Storm-size classes follow the usual Dst conventions (−50 moderate, −100 intense, below −250 superstorm) — the same scale used across the field guide.
Entries marked runs in this page execute as code in this lab, unmodified.
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