Cisk: A theory for the response of tropical convective complexes to variations in sea surface temperature

A set of balanced and unbalanced slab‐symmetric linear 2‐layer models is analysed. the stability properties depend on a parametrized moisture budget dominated by the value of the underlying sea surface temperature. Convective heating occurs within an inner region characterizing the size of the convective disturbance. the heating is equal to the sum of two terms, representing the mid‐level and lower‐level upward mass‐fluxes. A fast and a slow mode of instability can be distinguished. the slow mode shows finite maximum growth for infinitesimally small disturbances and is the instability traditionally associated with Conditional Instability of the Second Kind (CISK). the fast mode reveals infinitely large positive growth‐rates for finite‐size disturbances. The transition of the model solution from slow to fast mode occurs at a threshold value of sea surface temperature. For the parameters chosen in this study, the threshold occurs at approximately 25.5°C.