Speaker: Xiaoli Zhou (NOAA CSL/CIRES)
Topic: Shallow warm cloud mesoscale organization and its interaction with aerosols

Marine boundary layer clouds tend to organize into mesoscale cellular convection (MCC). However, how these MCCs develop and interact with aerosols remains unaddressed and has major implications for future climate projection. In this talk, I will present the fundamental mechanism of thermally direct mesoscale cellular circulation that supports the development and cell broadening of MCC. For non-precipitating MCC, cell broadening is induced by longwave radiative cooling of air sinking down sloping cloud tops. For precipitating MCC, cell broadening is induced by moisture stratification which increases updraft buoyancy. We find that the spatial variability of sub-cloud moist cold pools tends to respond to, rather than determine, the mesoscale variability, which may distinguish them from dry cold pools associated with deeper convection. I will introduce a two-dimensional wavelet analysis approach that allows statistical characteristics of MCC of various scales. Using this approach, we quantify the impact of MCC of various scales on aerosol-induced cloud water adjustment and brightness. We find that MCC cell scale can play a nontrivial role in regulating aerosol-induced brightness via cloud water adjustment. In cells that are primarily non-precipitating, the adjustment in small-scale MCCs can be seven times more negative than in large-scale MCCs, owing to stronger evaporation via cloud-top entrainment. The impact of MCC cell scale needs to be taken into consideration for improving projections of future MCC and climate change.