Exploring causal relationships and adjustment timescales of
cloud-aerosol interactions in geostationary satellite observations and
CAM6 using wavelet phase coherence analysis
Abstract
We present for the first time within the cloud physics context, the
application of wavelet phase coherence analysis to disentangle
counteracting physical processes associated with the lead-lag phase
difference between liquid water path (LWP) and cloud droplet number
concentration (Nd) in an Eulerian framework using satellite-based
observations and climate model outputs. This approach allows us to
identify the causality and typical adjustment timescales governing the
correlation between LWP and Nd. Satellite observations indicate a more
prevalent positive correlation between daytime LWP and Nd regardless of
whether LWP leads or lags Nd. The positive cloud water response,
associated with precipitation processes, typically occurs within 1 hour,
while the negative response resulting from entrainment drying, usually
takes 2-4 hours. CAM6 displays excessively rapid negative responses
along with overly strong negative cloud water response and insufficient
positive response, leading to a more negative correlation between LWP
and Nd compared to observations.