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Last Updated: Monday, 8 December, 2003, 13:08 GMT
Rain mission seeks flood forecast
By Carolyn Fry

ARA, BAESystems
The "rainmen" chase down their quarry
An international team of scientists is flying into the heart of clouds so forecasters can predict more accurately where and how much rain will fall.

Two overlapping projects will use state-of-the-art technology to track storms as they evolve and to photograph the ice crystals that lead to rain. Understanding more about what causes downpours will enable civil agencies to prepare better for flash flooding.

The research team is drawn from six UK universities, and the Met Office.

The German Aerospace Centre and the University of Karlsruhe; Meteo France; and the US National Center for Atmospheric Research are also involved.

Fall to Earth

"We've had some pretty severe floods lately and the main uncertainty in forecasting these is knowing where the storms start," explains Dr Alan Blyth, a cloud expert at the University of Leeds.

"The forecasters can say there will be showers but they can't tell exactly where they'll form, how heavy they'll be and whether they'll develop into severe storms."

Ice, Spec Inc
Ice: Scientists want a better understanding of the rainmaking process
The scientists will study cumulous clouds which form by convection. Rising, water-laden air expands and cools, forming first cloud droplets then ice crystals high in the atmosphere.

The crystals grow by colliding with cloud droplets to become "graupel particles" a kind of low-density hail.

When these reach such a size that they fall to Earth, we often experience rain. Many flash floods are associated with convective clouds.

The team will use new technology to seek out embryonic clouds. Instruments including radar and wind profilers will help the researchers track thermals and monitor air movements between 50 metres and 4 kilometres from the ground.

The information gathered will help improve forecasting models.

Follow the clouds

While the Convective Storms Initiation Project gets under way, a separate collaboration will look closely at the processes producing rain.

In particular, the team will use an airborne imaging system to photograph tiny particles inside clouds.

Acrobat, UFAM
Instruments including radar track phenomena from the ground (Image by UFAM)
Scientists know that ice crystals are seeded by nuclei such as dust particles but they do not fully understand why there are many more ice crystals than nuclei.

Finding this out may help forecasters differentiate between light showers and major deluges.

"Although we conceptually know the rain process we're not sure of the quantities; how many ice crystals are produced, when they're produced, at what temperature and under what conditions," explains Dr Blyth.

"We'd like to watch for when clouds are forming and then follow them as they ascend.

"We'll particularly be looking at the temperature of minus five degrees Celsius in the cloud because at that level there's a process where ice splinters are produced.

"The cloud particle imager will get close to where that is thought to happen and will be able to capture those splinters."

If the work is successful, TV images of rowing-boat rescues and sodden carpets may not be so frequent. And the days of carrying an umbrella around "in case it rains", may finally end.

Marseille declared disaster area
03 Dec 03  |  Europe
Earth Simulator delights scientists
01 Oct 03  |  Science/Nature
University wins rainmaking grant
02 Dec 02  |  Technology

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