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Friday, November 29, 2013
How pollution makes bigger THUNDERSTORMS: Poor air quality creates bigger, longer-lasting clouds
Pollution causes taller and bigger anvil-shaped clouds, say experts
Lingering big clouds also warm the Earth by trapping heat
Pollution makes thunderstorms worse
by creating bigger, longer lasting clouds and cooling temperatures with
their shadows, say scientists. Computer
simulations of cloud data from the western Pacific, south eastern China
and Oklahoma showed pollution increased their size, thickness and
a closer look at the properties of water droplets and ice crystals
within, the researchers found pollution resulted in smaller droplets and
ice crystals regardless of location.
Billow talk: pollution increases clouds' size, thickness and duration, say experts
In clean skies ice
particles were heavier and fell faster causing the clouds to dissipate.
But in polluted skies they were smaller and too light to drop leading to
the larger clouds.
Dr Jiwen Fan, of Pacific
Northwest National Laboratory in Washington, said: ‘This study
reconciles what we see in real life to what computer models show us. ‘Observations consistently show taller and bigger anvil-shaped clouds in storm systems with pollution.’ A polluted sky has many more aerosols - natural and manmade particles - making more but smaller cloud droplets.
Lingering: The study found that pollution makes afternoon thunderstorms last further into the night
Researchers have long believed smaller droplets start a chain reaction that leads to bigger, longer-lasting clouds. Instead
of raining down, the lighter droplets carry their water higher, where
they freeze. The freezing squeezes out the heat the droplets carry with
them and causes the thunder cloud to become draftier. Dr
Fan said: ‘Modelling the details of cloud microphysical properties is
very computationally intensive so models don't usually include them.’ Polluted
clouds have an effect on temperatures, with afternoon thunderstorms
lasting long into the night rather than dissipating and trapping heat
like a blanket. In the day the clouds’ shadows diminish sunlight penetration and so keep the Earth cooler. Accounting
for pollution effects on storm clouds could affect the ultimate amount
of warming predicted for the earth in the next few decades Accurately representing clouds in climate models is key to improving the accuracy of predicted changes to the climate.