Latitude-Aware Calibration
The same solar wind conditions don't mean the same thing for everyone. A Bz of −10 nT and 500 km/s solar wind might give you a 40% probability in Adelaide but 55% in Hobart. Lumina's latitude calibration is what makes that happen — it adjusts the odds based on where you are relative to the auroral oval.
Why latitude matters for probability
The auroral oval is a ring centred on the magnetic pole. The further you are from the pole (lower magnetic latitude), the further the oval has to expand before it becomes visible from your location. That expansion doesn't happen linearly — it takes progressively more energy to push the oval each degree further equatorward.
Lumina models this by adjusting the odds (not raw probability) based on your magnetic latitude relative to a baseline location (Adelaide, ~49.8°S magnetic).
How the adjustment works
The calibration works in log-odds space. For each degree your magnetic latitude is further poleward than the baseline, your odds multiplier increases by about 6%. The adjustment is clamped to a reasonable range to prevent extreme values for very high or low latitudes.
In practice:
- Adelaide (~50°S magnetic) — baseline, multiplier = 1.0. No adjustment.
- Hobart (~58°S magnetic) — ~8° further poleward, multiplier ≈
1.06⁸ ≈ 1.6. Same conditions give ~60% higher odds. - Invercargill (~57°S magnetic) — ~7° further poleward, multiplier ≈
1.5. Similar to Hobart. - Christchurch (~53°S magnetic) — ~3° further poleward, multiplier ≈
1.2. Modest boost. - Auckland (~45°S magnetic) — ~5° further equatorward, multiplier ≈
0.75. Reduced odds compared to the baseline.
Why Adelaide is the baseline
Adelaide sits at about 49.8°S magnetic latitude — roughly the midpoint of the AU/NZ aurora-watching range. It's far enough south that aurora is realistically visible a few times a year, but far enough north that you need genuine activity, not just background noise. That makes it a natural reference point.
But mostly because I live in Adelaide 😁