Effects of Aerosols on the Brightness of Marine Low Clouds: From Observations, Simulations, to Data-Driven Approaches

Dear Colleagues,

Bright, warm marine clouds occur ubiquitously over global oceans, reflecting a good fraction of the incoming solar radiation that would otherwise (in the absence of these clouds) be largely absorbed by the dark ocean (∼94%), thereby effectively cooling the Earth. The brightness of these clouds, and thereby their ability to cool the Earth, is highly sensitive to the aerosol loading in the marine boundary layer. At short time scales (~10 mins), where warm clouds exhibit constant macrophysical properties (e.g., liquid water path and cloud cover), increasing aerosol loading leads to more reflective clouds (cloud brightening), owing to increased cloud droplet number and reduced drop sizes (the Twomey effect). However, processes that modulate cloud macrophysical properties, e.g., entrainment, evaporation, and precipitation, are also affected by microphysical changes in droplet number and size, leading to cloud macrophysical adjustments that can either enhance or offset the microphysical brightening depending on the meteorological conditions. Observations and idealized simulations of cloud adjustments following anthropogenic aerosol perturbations confirm the bidirectional macrophysical responses, while the aggregated response remains uncertain, owing to the less understood/quantified conditionality of these responses.

The aim of this Special Issue is to provide recent advances in understanding and quantifying aerosol-warm-cloud interactions, their conditionality on meteorology and spatiotemporal scales, and their aggregated impact on the regional and global climate. Original research studies, reviews, and perspective articles on the broad topic of aerosol-cloud interactions are all encouraged. We invite and welcome studies at all scales, from laboratory to field work and from regional investigations to global assessments, using all kinds of approaches, from in situ and remote sensing observations to modelling and machine learning approaches.

Dr. Jianhao Zhang
Dr. Hendrik Andersen
Dr. Tom Goren
Guest Editors

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• aerosol-cloud interactions
• aerosol indirect effects
• twomey effect
• cloud macrophysical adjustments
• marine boundary layer clouds
• satellite remote sensing
• cloud modeling
• marine cloud brightening
• geoengineering
• climate intervention