Exploiting Ergodocity, Space-Time Exchange, and the Deborah number in Aerosol-Cloud Interaction Studies

Complex, open, dynamical system are difficult to fully characterize through observations and the cloudy atmospheric boundary layer is no exception.  To study such systems, we would ideally track a parcel of air as it moves in space and time, a view that would yield direct insights into the physical processes taking place in the evolving system. For practical reasons, we instead make frequent use of aircraft measurements along a flightpath at high spatial/temporal resolution (order 10 m/0.1 s) or polar-orbiting satellite-retrievals once or twice a day at spatial scales on the order of 1 km. These data are essentially “snapshots in time” of the state of the cloud system and its environment. Here we ask: what process-level insights can be gleaned about aerosol-cloud processes from these snapshots?  We present examples of collections of observation snapshots that reveal various degrees of process-level understanding. We couch the discussion in terms of the concepts of space-time exchange, ergodicity, and process vs. observation timescales. It is our hope that this work will encourage the atmospheric sciences community to explore the value of these concepts more deeply.