Devils in the sky

It is possible to identify non-productive clouds through satellite-transmitted pictures, say Israeli scientists

Published: Thursday 30 September 1999

-- sky covered with dark nimbus clouds, followed by a torrential downpour -- are these becoming things of the past? Believe it, or not, this might happen in the near future if pollution levels continue to soar.

However, in between these ominous predictions, as they say, every cloud has a silver lining. Scientists at the Hebrew University in Israel have declared that it is possible to identify "non-productive" clouds with the help of satellite-transmitted pictures. The rain producing ability, of these clouds get affected due to air pollution. Once identified, it would be easier to address the problem.

This amazing discovery was disclosed by Daniel Rosenfield of the department of atmospheric sciences at Hebrew University and Itamar Lensky, a graduate student.

According to Rosenfield and Lensky microstructure analyses clearly show those areas that suffer from high levels of air pollution adversely affect concentrations of small particles within the clouds. These particles, in turn, make up the nuclei, around which droplets of water form in the clouds.

The problem begins when these particles form tiny droplets that are too small to bond together and become actual raindrops. However, in cleaner areas, the droplets are around 30-50 micrometres and can easily coalesce into fully-fledged raindrops.

The researchers discovered this phenomenon when they started examining Israel's cloud cover. Israel this year is suffering from a serious lack of rainfall. Rosenfield and Lensky discovered that clouds coming from the Mediterranean area were often adversely affected by pollution. They found that the clouds, that were laden with these particles, originated in air masses over Europe. This problem increased when the clouds passed over Israel picking up more particles.

The connection between air pollution and the ability of the clouds to form rain is tricky. Experts feel the problem is at par with global warming, but unfortunately has not received sufficient attention because of the lack of a means, until now, of scientifically measuring the phenomenon.

Unfortunately, this rain-inhibiting factor is often most serious in areas which are underdeveloped and are dependent on rain-fed agriculture. The cause of pollution, that inhibit the formation of rain clouds, can either be urban or industrial or the result of burning fields to clear dry vegetation. The latter is a widespread practice in under-developed regions of the world. The ability to pinpoint such "non-productive" clouds will make it possible for scientists to take steps to reverse the situation. This can not only be done by taking preventive measures but also by seeding clouds with larger, non-polluting particles that will cause formation of larger droplets that can bring rain.

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