CISK: Tropical Cyclone Intensification
Conditional Instability of Second Kind — positive convective feedback
Intensity I(t) & Radius R(t)
Storm structure & Phase space
I=0 | R=0 | Phase: developing
CISK (Charney & Eliassen 1964): convective heating drives inflow which moistens the boundary layer,
enabling more convection — a positive feedback. Above SST threshold (~26°C), growth rate exceeds dissipation.
Environmental wind shear disrupts the warm core, suppressing intensification.
Simple model: dI/dt = α(SST)*I*(1−I/I_max) − D(shear)*I, dR/dt = β*I − γ*R.
Rapid intensification defined as ≥30 knots/24h (Category jump).