Evidence for cloud variations of climatic importance due to natural and
man-induced aerosol variability is visible in satellite images of marine
boundary layer clouds. Ship tracks are cloud features caused by increased
aerosols from ship effluents and illustrate how increases in aerosols can
increase cloud reflectivity. In contrast, naturally occurring
featuresbdefined as a cloud riftsbare characterized by large persistent
areas of broken, low reflectivity stratocumulus clouds usually surrounded by
solid stratocumulus clouds. The rifts are sometimes associated with
distinctly cellular conditions, have lifetimes of days, and move with the
boundary layer winds.  Observations indicate that the air associated with
the rifts is super clean air with cloud condensation nuclei (CCN)
concentrations approaching zero and broken cloud fields that have a strong
propensity for drizzle. In this talk, in situ and remote observations in
ship tracks and rifts will be used to illuminate cloud-aerosol indirect
effects and highlight new observing techniques for studying
cloud-aerosol-drizzle interactions and addressing critical questions on the
observed variability in clouds important for climate change issues.