Short time-scale evolution of aerosol-cloud interactions

The difficulty in establishing causality between stratocumulus cloud droplet number concentration (Nd) and liquid water path (LWP) is well established. Recent studies on the satellite observations of the development of clouds over short time scales to examine the role of Nd perturbations in LWP variations demonstrated that LWP evolved differently depending on the initial Nd. This highlighted the need to consider the temporal development rather than the instantaneous measurements.

Here we characterise the dependence of this short timescale behaviour on the local meteorological environment, with aerosol production, entrainment from the free troposphere and wet scavenging all acting to modify the Nd. Many of these effects act to further steepen the Nd–LWP relationship and obscure the causal Nd impact on LWP. The multi-dimensional process space to represent stratocumulus is reduced to the two-dimensional Nd-LWP state space. The role of different physical processes is investigated and process-level fingerprints are extracted in this space.