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Aerosol invigoration of atmospheric convection through increases in humidity

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Science  01 Jan 2021:
Vol. 371, Issue 6524, pp. 83-85
DOI: 10.1126/science.abc5181

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Aerosols give clouds a lift

It has been observed that atmospheric aerosols can strengthen updrafts in deep convective clouds such as those that form in thunderstorms. Past work has linked such invigoration with the latent heat released by water condensation or freezing in chains of processes that depend on aerosol concentrations. Abbott and Cronin suggest a third possibility in which updrafts intensify because high aerosol concentrations increase environmental humidity by mixing more condensed water into the surrounding air, which in turn favors stronger updrafts.

Science, this issue p. 83

Abstract

Cloud-aerosol interactions remain a major obstacle to understanding climate and severe weather. Observations suggest that aerosols enhance tropical thunderstorm activity; past research, motivated by the importance of understanding aerosol impacts on clouds, has proposed several mechanisms that could explain that observed link. We find that high-resolution atmospheric simulations can reproduce the observed link between aerosols and convection. However, we also show that previously proposed mechanisms are unable to explain the invigoration. Examining underlying processes reveals that, in our simulations, high aerosol concentrations increase environmental humidity by producing clouds that mix more condensed water into the surrounding air. In turn, higher humidity favors large-scale ascent and stronger convection. Our results provide a physical reason to expect invigorated thunderstorms in high-aerosol regions of the tropics.

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