NOAA Scientists Uncover
Oscillating Patterns In Clouds
August 12, 2010 -
Findings has implications for climate change, a new NOAA study has found
that rain clouds form synchronous patterns in which individual clouds in
a large cloud field respond to signals from other clouds, much like
chirping crickets or flashing fireflies on a summer night. The study,
published online in the journal Nature also has significant implications
for our understanding of climate change research.
This research, led
by Graham Feingold of NOAA’s Earth System Research Laboratory in
in distinct patterns that are fingerprints of myriad physical
processes,” Feingold explained. “Precipitation can generate fascinating
honeycomb-like patterns that are clearly visible from satellites. Cloud
fields organize in such a way that their components ‘communicate’ with
one another and produce regular, periodic rainfall events.”
|Satellite image above Peru shows self-organizing honeycomb cloud pattern.|
discovery of synchronized behavior in clouds is one of many recent
findings on self-organization in nature, the study also examines how
suspended particles, or aerosols, in the atmosphere can influence these
patterns and be a factor in climate change.
The team, which
also includes Ilan Koren of the Weizmann Institute, Hailong Wang of
Pacific Northwest National Laboratory, Huiwen Xue of Peking University,
and Alan Brewer of NOAA, used satellite imagery to identify cloud
systems with a “cellular, almost honeycomb-like structure.” In such
systems, thick clouds form the walls of the honeycomb, and cloud-free
zones form the open cells between the walls. The team also observed that
these cellular structures constantly rearrange themselves, with cloud
walls dissolving and open cells forming in their place, while walls form
where open cells once existed.
models, the scientists reproduced this rearrangement or oscillation of
the cloud honeycomb pattern, and identified the driving factor – rain.
Next, they analyzed scanning laser measurements from a ship cruising
under cloud systems to verify their model results.
analyses demonstrated that the rearrangement is a result of
precipitation, and that clouds belonging to this kind of system rain
almost in unison,” Feingold said.
How does this
synchronization come about? Falling rain cools the air as it descends.
This creates downward air currents. These downdrafts hit the surface,
flow outward and collide with each other, forming updrafts. The air
flowing up creates new clouds in previously open sky as older clouds
dissipate. Then the new clouds rain, and the oscillating pattern repeats
precipitation ensues and an open structure has formed, it is difficult
to revert the cloud field to a closed-cell, or overcast state,” Feingold
said. “Rain keeps the oscillating, open honeycomb pattern in motion,
which allows more sun to reach Earth’s surface.”
The scientists say
that their findings point to a significant influence of particulate
matter, or aerosols, on the large-scale structure of clouds and
therefore on climate change. Scientists have long known that aerosols
can influence local rain formation and block solar energy from reaching
the Earth’s surface—for an overall surface cooling effect.
recently, the scientific community has not considered the
self-organization that result from these effects. Computer simulations
for this study indicate that high aerosol concentrations favor the
formation of large, dense cloud fields with less open space and less
rain. This creates a more reflective cloud pattern and cooling of the
surface. Low particulate levels in computer models resulted in rain and
the open honeycomb structure with an oscillating pattern. The open
honeycomb structure in a large cloud field lets more sunlight reach the
surface, and hence results in surface warming.
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