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[Michaelangelica]

Originally Posted by carlton-temple

re above note : The article was on the BBC...15/6/09 entitled "Grey sky research"

Thank you

Grey sky research

Richard Hollingham
Presenter, Frontiers


On the edge of an east London rooftop stands an increasingly bedraggled man. Arms outstretched, the rain lashes at his face and cascades down his beard onto sopping clothes.

In each hand he holds out a dish containing tiny metal crucibles; he grins as the raindrops ping against the containers.

Just another day at the office for University of East London scientist Bruce Moffett and the perfect weather to investigate the biological properties of rain.

The idea that bacteria in the clouds cause rain might, at first, rank as one of the more bizarre scientific theories.
Raindrop
It takes a quarter of a million of these to make one litre

However, over the past 25 years a small group of scientists has been studying the role bacteria in the clouds might play in our weather and, with papers published in leading scientific journals, the evidence that they're right is beginning to stack up.

"It takes something like a quarter of a million rain drops to make one litre," Moffett shouts to me through the wind.

Fortunately we don't need a litre. "I've got to make sure I have a raindrop in each." And then it's back to the lab to see what's in there.

Ice makers

Before rain can fall - at least in temperate climates - the water in clouds has to freeze.

But - and you may not believe this - sometimes, water doesn't freeze at 0C. Pure water will not freeze until -40C, and clouds rarely get that cold.

So to get water to freeze you need some help. A catalyst such as soot or dust will do the trick but if you want water to freeze at relatively warm temperatures, say around -5C or -6C, bacteria turn out to be the best "ice nucleators".

Cindy Morris, a plant pathologist at the French National Research Institute for Agriculture in Avignon, has identified a particular bacterium, Pseudomonas syringae, which is extremely effective at making water freeze.

In her lab she takes a tube of water, cooled to -6C (and not frozen), and puts in a single drop of bacterial culture. Within about two seconds, the water has turned to ice.
Rainclouds and cropfields
Bacteria found in crops may make the best "ice nucleators"

It's an impressive demonstration. "There's nothing magic about it," laughs Morris. "You can't break the laws of physics."

Pseudomonas syringae is found on the leaves of plants. By forming ice, the bacteria damages cell walls, releasing nutrients that it can then feed on.

But these organisms can easily get carried off by the wind and, once airborne in the clouds, pull off the same trick and persuade water droplets to freeze. At least that's the theory.

BBC NEWS | Science & Environment | Grey sky research

Fond this, from NASA, while trying to find BBC site

Impact of Polluted Skies on Clouds and Climate
Few parts of Earth’s climate system have such chameleon-like effects as the tiny airborne particles known as aerosols.
The effect of aerosols on clouds has seemed especially paradoxical. Some observations have shown cloud cover increasing as aerosols increased, while other observations showed cloud cover decreasing as aerosols increased.
New research from NASA scientists has finally zeroed in on when aerosols increase clouds and when they decrease clouds.
Regardless of location or weather conditions,

• aerosols that absorb sunlight decrease cloud formation,
• while aerosols that don’t absorb much sunlight increase clouds.

Impact of Polluted Skies on Clouds and Climate : Image of the Day
And
this
on Night shinning clouds. I wonder if this is like the phosphorescence in the sea at night? Phosphorescence is said to be due to bacteria.
Photo in the News: Mysterious "Night-Shining Clouds" Sighted