Aerosol Interactions with Cloud Dynamics

Simulations in our group of aerosol influences on stratocumulus clouds, thunderstorms over Florida, and thunderstorms over and downwind of St. Louis, MO have revealed complex dynamical responses to variations in CCN, GCCN, and/or IN concentrations. This is a result of changes in precipitation rates from these clouds systems. It is shown that once the precipitation cycle is augmented in clouds, they are no longer subject to simple linear thinking as in the Twomey hypothesis or Abrecht's extension of it to drizzling clouds. Once the precipitation process is modified clouds may become optically thicker or thinner, they may rain more or they may rain less, they may become more vigorous or less so depending on the nature of the nonlinear response of clouds to changes in precipitation. Thus the climate response to changing aerosol populations becomes less predictable once those changes alter the precipitation cycle of many cloud systems.