Clouds dissipate quickly during solar eclipses as the land surface cools

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Feb 14, 2024, 7:32:02 AM2/14/24

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https://www.nature.com/articles/s43247-024-01213-0

Authors

12 February 2024

Citations: Trees, V.J.H., de Roode, S.R., Wiltink, J.I. et al. Clouds dissipate quickly during solar eclipses as the land surface cools. Commun Earth Environ 5, 71 (2024). https://doi.org/10.1038/s43247-024-01213-0

Abstract

Clouds affected by solar eclipses could influence the reflection of sunlight back into space and might change local precipitation patterns. Satellite cloud retrievals have so far not taken into account the lunar shadow, hindering a reliable spaceborne assessment of the eclipse-induced cloud evolution. Here we use satellite cloud measurements during three solar eclipses between 2005 and 2016 that have been corrected for the partial lunar shadow together with large-eddy simulations to analyze the eclipse-induced cloud evolution. Our corrected data reveal that, over cooling land surfaces, shallow cumulus clouds start to disappear at very small solar obscurations (~15%). Our simulations explain that the cloud response was delayed and was initiated at even smaller solar obscurations. We demonstrate that neglecting the disappearance of clouds during a solar eclipse could lead to a considerable overestimation of the eclipse-related reduction of net incoming solar radiation. These findings should spur cloud model simulations of the direct consequences of sunlight-intercepting geoengineering proposals, for which our results serve as a unique benchmark.

Conceptual model of shallow cumulus cloud evolution during a solar eclipse.

The time progresses in the horizontal direction to the right. Background color shading indicates the virtual potential temperature of the atmosphere and land surface in our simulation. The red and blue arrows are the sensible and latent heat fluxes, respectively, which depend strongly on the temperature difference between the surface and the atmosphere just above the surface. The yellow arrows represent the amount of incoming solar radiation, which is largest around noon but is reduced during a solar eclipse as illustrated by the lunar disk covering the solar disk. When the growing atmospheric boundary layer height (dotted line) intersects with the lifting condensation level (dashed line), clouds are formed, but they are diminished when the updrafts are slowed down during a solar eclipse, as indicated by the smaller inclination of the black arrow.