EarthCARE sees rain build up hours before ocean cloud decks break apart
Satellite data from EarthCARE show cloud water and rainwater rising as much as 25 hours before tightly packed marine clouds break into open fields over the southeast Pacific. Cloud cover fell from nearly complete to about 60 percent around the transition. The peer-reviewed study is observational: it traces a sequence, does not measure the role of sea temperature, winds or stability, and cannot yet be applied to every ocean.
Science··Midday
Rain builds up in the hours before a cloud deck breaks apart
A peer-reviewed study of new satellite observations links rain with the breakup of vast decks of low marine cloud. Marine stratocumulus forms low layers over the sea. In a closed-cell pattern, tightly packed clouds cover nearly all the sky; in an open-cell pattern the cloud is broken up and more sunlight reaches the ocean.[1], [2]
Liquid cloud water and rainwater began to rise as much as 25 hours before breakup. Droplet numbers then fell, the droplets grew larger and precipitation intensified. Over the southeast Pacific, cloud cover dropped from nearly complete to roughly 60 percent around the transition.[1]
EarthCARE's radar, lidar and imager followed 803 air parcels
Johanna Mayer and colleagues combined the radar, lidar and multispectral imager aboard the EarthCARE satellite, launched in May 2024. They used one consistent processing version of data from August 2024 to November 2025 and compared four regions: the northeast and southeast Pacific and the northeast and southeast Atlantic. The detailed timeline of transitions covers only the southeast Pacific.[1]
The sample covered single-layer ocean clouds with tops below 3 kilometres, sorted by organisation in scenes of 128 by 128 kilometres. It compared roughly 5,000 closed-cell scenes with 2,500 open-cell scenes, and about 60 percent of the closed-cell scenes contained drizzle. Researchers followed 803 air-parcel trajectories: 330 started as closed cloud that later opened, and 473 were already open and were traced backwards. Around 60 percent of the transitions happened at night.[1]
Moisture, aerosol removal and cold pools form the proposed sequence
The authors propose that extra moisture in the boundary layer starts the rain, that the rain scavenges aerosol particles from the air, and that evaporation beneath the clouds creates cold pools. Those links are proposals; the measurements themselves are observational.[1]
The study did not quantify the contributions of sea temperature, winds or atmospheric stability. Some droplet measurements exist only in daylight, and classification errors, trajectory timing and still-maturing satellite products add uncertainty. The regional results cannot be applied directly to every ocean.[1]
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