See:

http://pseudomonas-syringae.org/Outreach/outreach-images/Psyr_72.jpg

What makes it rain?

The short answer may be – bacteria.

For atmospheric water vapour to fall back to Earth as rain it first needs to form ice crystals – that is, it needs to freeze.

The freezing point of water is zero degrees Celsius. The temperature in clouds falls below water's freezing point. So water freezes in clouds, starts falling to Earth, melts on the way down and, bingo, we have rain. There's no mystery, right?

Wrong.

Pure water can remain in liquid form right down to about -40 degrees Celsius. The temperature in most clouds is well above that.

Water that is liquid below 0 degrees Celsius is called "supercooled". To cause supercooled water to form ice crystals you need to add impurities that can act as "nuclei" around which the crystals can form. See what happens when supercooled water is exposed to impurities in a bowl.

http://www.youtube.com/watch?v=fSPzMva9_CE

The most effective "impurity" is actually ice crystals. Add an ice crystal to supercooled water and it will set off a chain reaction of ice crystal formation.

But how do we cause that first ice crystal, the crystal that can start the process, to form in clouds? We need a source of nuclei.

It turns out that the most efficient nuclei may be bacteria, specifically pseudomonas syringae. These bacteria are able to cause ice formation at temperatures as high as -2.2 degrees.

In the 1980s Professor David Sands coined the term bioprecipitation to describe the concept of biological processes causing rain. Evidence for bioprecipitation is mounting. If Professor Sands and his colleagues are correct it may be that micro-organisms are actually the most important source of ice forming nuclei in clouds.

See: Ubiquity of Biological Ice Nucleators in Snowfall

https://www.sciencemag.org/cgi/content/abstract/319/5867/1214

and

http://www.montana.edu/cpa/news/nwview.php?article=5659

Why post this?

Because it's interesting and it illustrates once again the FUNDAMENTAL importance of scientific research. You never know where it will lead. It may even enable you to do something about the weather.

See also this video:

http://www.youtube.com/watch?v=qLbLXXGJe3A

For a video that explains the hydrologic cycle in very simple terms see:

http://www.youtube.com/watch?v=x2jPsfy2iq8

Now isn't this more interesting than endless discussions on whether "God" made the world?

And given the importance of rainfall for this dry, drought stricken land shouldn't we be funding this sort of research?

OH EM GEE.

I'm just floored at the lack of booting the Christians in the bollocks for a change.

You ok?.

Since creating this thread I’ve found it was the topic of a recent BBC Discovery program who, of course, tell the story better than I could.

See: http://www.bbc.co.uk/programmes/p004lf1f

What an interesting post. I used to live in Far North Queensland, and one of the fascinating aspects of weather was what I called its moodiness. If the weather was in the mood, it would rain even from a small cloud, and I saw the same recently as I was driving from Sydney to Melbourne. There was rain, torrential rain, falling from a half clear sky.

It was similar to tropical rain, and has made Australia from Yass south, a blooming desert. The crops look marvelous, for the first time in at least five years. But why?

The Yanks, as part of their war effort in Vietnam found out about weather control and found a way to make it rain bucketloads on that hapless country. The aim was to flood Vietcong Tunnels, and disrupt their anti carpet bombing efforts. They failed. However the technology remained part of their arsenal, and persistent rumours abound that they can still control the weather worldwide.

The supposed technology is HAARP. It is supposed to be microwave technology that can be directed to the upper levels of the atmosphere, with a view to raising the temperature of that particular part, and diverting the jet streams, around a hot spot, so rain does not fall in one place, but falls heavier in another, like over oceans if a drought is required, or over some favoured spot if it is deemed desirable to have a certain area become more productive.

I know of a man who claimed he could install a light tower, and divert the jet streams that carry this water, and someone paid him to install one in drought stricken Quirindi, about two hundred and fifty miles northwest of Sydney. He did and 300 mm of rain fell in the next few weeks. The area benefited was about 20 miles wide or about 300 square miles, and it was claimed he diverted a jet stream of rain from the Gulf of Carpentaria.

The scientists tell us there is more water in the atmosphere than in the oceans. Does anyone know more about this