The core is modelled as a Rankine combined vortex: solid-body rotation inside the core radius R, irrotational swirl outside it.
v(r) = v_max·(r/R) r ≤ R
v(r) = v_max·(R/r) r > R
Tangential wind is fed by low-level shear and by the updraft parcel theory predicts from CAPE (wmax ≈ √(2·CAPE)), stretching ambient rotation into a tight column. Cyclostrophic balance (dp/dr = ρv²/r) integrates to a closed-form pressure field, giving a central deficit of ΔP = ρ·v_max² and a solid-body vorticity of ζ = 2v_max/R.
The visible funnel is where that pressure drop is large enough to cool air below its dew point — lower humidity needs a bigger drop, so the funnel shrinks and lifts as the humidity slider falls. Debris near the surface is lofted once local wind speed crosses a fixed threshold, spiralling inward and up before being flung out at the core edge.
- Dashed ring — core radius R (solid-body / irrotational boundary).
- Grey disc — condensation funnel, sized from the pressure field and humidity.
- Amber flecks — debris lofted where surface wind exceeds ~25 m/s.