Sensitivity of the evolution of an idealized tropical cyclone to small perturbations in initial input fields

Previous studies have shown that varying the dust concentration from the Saharan Air Layer (SAL) affects the temporal evolution of tropical cyclones (TCs) through its role as cloud condensation nuclei (CCN). Further, such sensitivity studies have shown that an increase in CCN concentration from only 100 cm^-3 to 101 cm^-3 produces changes in TC evolution comparable to those observed with larger increases in CCN concentration.

A series of idealized simulations with the Regional Atmospheric Modeling System (RAMS) version 6.0 that investigate the sensitivity of tropical cyclone evolution to small perturbations in initial fields are described here. Three nested domains with horizontal resolution of 24-km, 6-km, and 2-km and 40 unevenly spaced vertical levels with spacing of 1-km at higher levels and 300-m near the surface are used. Each simulation allows the initial vortex to evolve for 4 days. The control simulation uses a CCN concentration of 1000-cm^-3, initializes convection with a bubble 0.1 K warmer than the environment, and applies the Jordan sounding, which is a 1946-1955 mean composite sounding for stations in the West Indies area. Effects of small perturbations in CCN concentration, temperature, relative humidity, mid-level easterly jet intensity, trade wind inversion strength, and warm bubble temperature on TC evolution are examined. The test results will also assist in reevaluating how models can be used to attribute changes in TC evolution to variations in initial conditions.