Differential rotation shears the magnetic field above a sunspot active region, storing magnetic free energy in increasingly twisted field loops. When oppositely-directed field lines are forced together, they snap and reconnect into a lower-energy state — magnetic reconnection — dumping that stored energy into particle acceleration and X-ray emission within seconds:
dW/dt = k · shear_rate (buildup)
F(t) = F0 + ΔF·(1-e^(-t/τr))·e^(-t/τd) (Neupert-style light curve)
F0 ≈ 10⁻⁸ W/m² is the quiet-Sun background; τr is a fast rise (~1 s here, compressed for viewing) and τd is the decay constant you control — physically set by how quickly the flare loops cool and drain.
Flares are classified by peak flux in the GOES 1–8 Å X-ray band, a logarithmic letter scale where each step is ×10 and the trailing number is a linear multiplier within that decade:
A 10⁻⁸ – 10⁻⁷ W/m² background
B 10⁻⁷ – 10⁻⁶
C 10⁻⁶ – 10⁻⁵ minor
M 10⁻⁵ – 10⁻⁴ radio blackouts possible
X 10⁻⁴ and above major (record ≈X28, 2003)
- Shear buildup rate — how fast the active region accumulates stored magnetic free energy; a full store (100%) is enough to power an X-class flare.
- Decay time constant τ — how long the released loops take to cool and drain, stretching or compressing the light curve's tail.
- Trigger reconnection now — forces an immediate release of whatever energy is currently stored, so you can compare a small, partially-charged flare to a fully-charged one.
- Launch CME — when enabled, reconnection also ejects a bubble of magnetised plasma outward, visualising the (separate, slower) coronal mass ejection that a large flare often accompanies.
Real-world relevance: this is the same energy-storage-then-release picture (and the same GOES classification table) space-weather forecasters use to read live X-ray flux from NOAA's GOES satellites and issue radio-blackout warnings within minutes of an eruption.