Wisps of clouds form a honeycomb-like structure (center) over the Peruvian coast (file photo).
Such open-cell marine clouds "communicate" with each other so that they constantly oscillate, or rearrange themselves, in a synchronized pattern, according to a new study from the U.S. National Oceanic and Atmospheric Administration (NOAA).
Inside the thick clouds of the cell walls, water droplets grow, then fall as rain, and the walls dissipate. The raindrops evaporate as they fall, cooling the air, which generates downward air currents.
When the downdrafts hit the ocean surface, they flow outward and collide with each other and "force the air to move upward again" and "form new open cell walls at a different location," explained study co-author Hailong Wang, a cloud physicist at the Pacific Northwest National Laboratory in Richland, Washington.
The new clouds eventually rain in unison, too, part of a reorganization cycle that can persist for days, according to the study.
Hexagonal clouds—a "closed cell" system common on overcast days—shade a swath of the South Atlantic Ocean (file photo).
The new NOAA cloud study helps clarify the role of rain in determining cloud patterns, which in turn govern how much sunlight reaches Earth's surface.
Whereas open-cell cloud patterns (as in the previous picture) are driven by rain, the droplets in closed-cell clouds are too small to easily grow into raindrops, said study co-author Wang.
"Those two different patterns have very different reflectivity to the solar radiation," he said. "The open cells, they reflect much less solar radiation back to space, so they allow more solar radiation going down to the ocean surface ... and in that way heat the ocean."
Open-cell clouds hover over the Bahamas (file photo). The team behind the new cloud study had noticed that honeycomb-like clouds reorganize themselves in a synchronized cycle.
After simulating the oscillating clouds in a computer model, the researchers zeroed in on rain as the probable catalyst for each rearrangement event. Shipborne scanning lasers, which returned precise measurements of marine clouds, confirmed the findings, according to NOAA.
The "communicating" cloud system is an example of self-organization in nature, the seemingly purposeful formation of structure without outside intervention from humans. The process is also seen in crystal growth, planet formation, and insect swarms.
Open-cell and closed-cell cloud systems obscure the Pacific Ocean just off California (file photo).
Covering vast areas of the ocean at any given time, such systems play a major role in regulating the amount of sunlight that reaches the planet. And since little is understood about clouds' effects on temperatures worldwide, cloud cover remains something of a wild card in global warming predictions.
The new study, though, could shed some light on what causes overcast, "cooling" cloud systems vs. open-cell, "warming" systems to form. According to the study, computer simulations show that cloud patterns are greatly influenced by the amount of aerosols in the atmosphere.
Aerosols are tiny, floating particles, such as the soot generated by burning fossil fuels. Water in the atmosphere tends to condense around aerosols, so more aerosols mean more water droplets and thus denser, closed-cell clouds, which are less prone to raining.
And because rain appears to be the trigger for open-cell clouds to form and reorganize, Wang said, "less rain may keep the clouds in a closed-cell pattern."
Open- and closed-cell cloud systems swirl over Peruvian coastal waters (file photo).
Current climate models lack the resolution to precisely re-create oscillating, open-cell cloud systems. As a result, the models are of little use in predicting how much solar energy clouds will reflect away from Earth—a cooling ability called albedo.
Wang said that if scientists can determine exactly how the different patterns are formed, as the new study helps to do, "then the climate models can better calculate the overall albedo and energy budget of the Earth"—allowing for better climate forecasts.
The oscillating-cloud findings were published online August 12 by the journalNature.