Two graphs from the paper.
The activation of cloud droplets on soluble particulate matter (cloud condensation nuclei) scavenges and grows the largest particles, to create a bimodal particulate distribution. The particle-depleted size range is known as the Hopper Minimum. Using measurements of this minimum the investigators are able to use two methods to make broadly consistent inferences as to the maximum cloud base supersaturation. Credit: Gong et al. [2023], Figure 3 (a, d)
Editors’ Highlights are summaries of recent papers by AGU’s journal editors.
Source: AGU Advances

Water supersaturation mediates the interactions between clouds and particulate matter, between the physical and chemical realms of the atmosphere. Supersaturation determines the minimum size of the soluble aerosol particles on which cloud-droplets grow. Larger supersaturations, as would be expected from stronger updrafts, can grow clouds from smaller particles, leading to more but smaller cloud droplets. At the same time, for a given updraft, the effect of fewer particles can be buffered by a larger supersaturation activating more of them.

Gong et al. [2023] make the first long-term measurements of supersaturation in boundary-layer clouds. By shining new light on this crucial link, they show how, when clouds form in aerosol poor air, the buffering effect of greater supersaturations is often enhanced by stronger updrafts. Their work provides a new tool for studying aerosol cloud interactions, and raises an intriguing question: is the depleted aerosol itself a consequence of the stronger updrafts?

Citation: Gong, X., Wang, Y., Xie, H., Zhang, J., Lu, Z., Wood, R., et al. (2023). Maximum supersaturation in the marine boundary layer clouds over the North Atlantic. AGU Advances, 4, e2022AV000855. https://doi.org/10.1029/2022AV000855

—Bjorn Stevens, Editor, AGU Advances

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