Seeding clouds to induce rain
Amar Chandel
AFTER much dilly-dallying, Indian states like Karnataka have finally started using the cloud-seeding operations for rains in drought-hit areas. The science behind this very complex process makes fascinating study.

UNDERSTANDING THE UNIVERSE
WITH PROF YASH PAL
Please explain the working of an atom bomb. How does it explode?
I can only talk of the principles of physics and engineering behind the making of the atom bomb. I cannot give you manufacturing details because I have never made any such bomb myself.

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Seeding clouds to induce rain
Amar Chandel

AFTER much dilly-dallying, Indian states like Karnataka have finally started using the cloud-seeding operations for rains in drought-hit areas. The science behind this very complex process makes fascinating study.

Attempts to modify the weather have been conducted for centuries. However, modern cloud seeding dates from the late 1940s, springing from a discovery at the General Electric labs in Schenectady, New York, in 1946. The ability of dry ice shavings to convert supercooled water droplets (those existing as water at temperatures colder than freezing) to ice crystals was observed during the conduct of an unrelated experiment. Later consideration of those observations led to a series of laboratory trials which demonstrated the nucleating properties of various materials in certain cold cloud conditions. Trials in the atmosphere soon followed, and operational cloud seeding programmes began in about 1950.

After more than 55 years of extensive scientific experiments and the application of scientific concepts, the technology has become fairly advanced to provide predictable results if applied under proper supervision. Israeli and American scientists have been particularly successful in inducing rainfall at places of their choice.

As warm air rises from the earth, it begins to cool and forms tiny droplets of water that condense into cloud droplets. Cloud droplets are formed around particles of dust, salt, or soil (called cloud condensation nuclei) that are always present in the atmosphere. These cloud droplets group together into clouds, which can form precipitation in one of two ways. In warm temperatures, the droplets in the clouds merge with many other droplets and become heavy enough to fall to the earth as rain. The cloud droplets are so small it may take a million or more to produce a single raindrop. In colder temperatures, the droplets of water form ice crystals. Other droplets freeze onto these ice crystals, which grow larger and heavier until they fall to the ground as rain, snow, or hail.

Sometimes, this precipitation is inadequate or none at all, because certain required conditions are not present. Factors having a bearing on precipitation include:

A. The vertical and horizontal dimensions of the clouds,

B. The lifetime of the clouds and

C. The sizes and concentrations of cloud droplets and ice particles.

Seeding the cloud with appropriate nuclei can favourably modify one or more of these factors under proper conditions.

There are three types of cloud seeding: static mode, dynamic mode, and hygroscopic seeding.

In the static mode, rainfall is sought to be increased by adding ice crystals (usually in the form of silver iodide or dry ice) to cold clouds. In the dynamic mode, this is done by enhancing "vertical air currents in clouds and thereby vertically process more water through the clouds." Basically, in this method of seeding, a much larger number of ice crystals are added to the cloud than in the static mode.

In hygroscopic seeding, salt crystals are released into a cloud. These particles grow until they are large enough to cause precipitation to form. Clouds can be seeded from above with the help of airplanes that drop pyrotechnics — as is being done in Karnataka — or from the ground by using artillery or ground-to-air rockets. Rainfall starts approximately half an hour after the seeding.

Besides increasing rainfall, cloud seeding has also been used for increasing snowfall, fog dispersal and hail suppression. Results have been fairly encouraging. For precipitation augmentation, the accepted magnitude of increase to be expected from well-designed and properly conducted projects ranges from 5 per cent to 20 per cent for winter precipitation in continental regions and from 5 per cent to 30 per cent for coastal areas. For warm season precipitation increase, single-cloud experiments have indicated increases as large as 100 per cent. Area-wide increases over a project area vary with the frequency of occurrence and spatial coverage of suitable cloud systems, plus the ability to treat all favourable clouds. Hail suppression effectiveness, based upon surface hail data, is estimated to be in the range of a 20-50 per cent reduction.

Cloud seeding is so attractive to many sponsors like water agencies, municipalities, operators of hydroelectric generation companies etc for a variety of reasons. It is a highly portable and flexible technology. It does not require construction of large, permanent and costly structures, such as dams or water conveyance systems. Projects can be mobilised quickly and operations can be regulated as water needs dictate or suspended very quickly if hazardous weather conditions develop.

Further, the benefit/cost ratios associated with most cloud seeding projects are typically very favourable, ranging as high as 25-30:1, depending, in the case of precipitation increase applications, on the value of water.

Seeding has more than its share of controversies. Fears have been expressed that increasing rain in one area decreases it in another. Experts discount this apprehension. According to them, of the total atmospheric moisture passing over any point, the proportion falling as natural precipitation is quite small, typically less than 10-15 per cent. Cloud seeding-induced increases in precipitation of the order of 5-30 per cent still result in a small overall proportion (less than 20 per cent) of the total available moisture reaching the ground. Further, especially when cumuliform clouds are present, and over mountainous terrain where air is forced to rise, the cloud-bearing layer of the atmosphere undergoes nearly continuous moisture replenishment. Analyses of precipitation data from areas downwind of several cloud seeding projects have indicated small percentage precipitation increases extending as far as 180 km downwind of the intended areas of effect on projects that had indications of increases in the intended target area.

They also discount the theory that the commonly used seeding materials pose any direct health or environmental risks. Many detailed studies have been conducted to address these questions. These efforts have ranged from chemistry-focused work to broad-ranging environmental investigations. The bottom line is that no significant environmental effects have been observed.

Seeding materials are applied in very small amounts relative to the size of the geographic areas being affected, so the concentrations of the seeding materials in rainwater or snow are very low. Using silver iodide (the most common seeding material) as an example, the typical concentration of silver in rainwater or snow from seeded cloud systems is less than 0.1 micrograms per litre.

This is much below the U.S. Public Health Service’s stated acceptable concentration of 50 micrograms per litre. As another example, the concentration of iodine in rainwater from seeded clouds is far below the concentration found in common iodised table salt.

In the case of ordinary chemical bombs the requirement 2) above is served by a detonator — a spark would do. The requirement 3) is then automatically ensured because the energy release in a tiny part of the chemical explosive quickly ignites all the other parts. For a nuclear bomb the process of ignition is entirely different. You cannot heat a kilogram of uranium 235 and get a bomb. In fact in uranium some of the nuclei are continuously breaking up, through the entry of stray neutrons from cosmic rays, or an implanted source of neutrons. Entry of a neutron in such a nucleus makes it unstable and break up into smaller nuclei plus some energy. In this process some extra neutrons are also produced, which escape before they have a chance to split other nuclei. Therefore what one does is to have a critical mass of the fissile element deployed together in a relatively sparse manner. If this mass is suddenly compressed together the produced neutrons have good chance of hitting other fissile nuclei and breaking them with production of energy and still more neutrons. Within microseconds or less, the chain reaction takes over and a horrible weapon is exploded. Bombs that demolished Hiroshima and Nagasaki had energy release of about 10,000 tons of TNT each. Later on bombs have been developed that have a more than a thousand times their destructive capacity. Luckily they have not been used so far on populations or people. It is horrible that science should have been used to produce monsters like these. We are clever but not yet humane enough.

An Australian astronomer has claimed to have completed the most accurate calculation ever of how many stars shine in the visible universe — some 70 sextillion, or 70 thousand million million million.

Simon Driver of the Australian National University Research School of Astronomy and Astrophysics said the number was more than every grain of sand on all the beaches and deserts on the earth.

Driver’s team used some of the world’s most powerful telescopes to count the galaxies in one region of the universe close to the earth. They estimated the number of stars in every grouping by measuring how bright each galaxy was, and then extrapolated this number to cover the visible universe. —AFP

Adam and Eve may have put on fig leaves while still in the Garden of Eden but a study that looked at the most intimate of pests — body lice — suggests that humans started wearing clothes 70,000 years ago.

The genetic study of lice strongly suggests they — and clothing — arose soon after modern homo sapiens began moving out of Africa and into the cooler regions of Europe.

Lice provide a unique insight into the development of clothing, according to the researchers, working in Germany. Only humans carry this particular species of louse, which lays its eggs in clothing.

"It seems fairly obvious that the body louse arose when humans made frequent use of clothing," molecular anthropologist Mark Stoneking said in a telephone interview. — Current Biology.

It really is a small world. The idea that there are only six degrees of separation — only a handful of people between you and anyone else in the world — holds true on the Internet, researchers have said.

An experiment in which Internet users were asked to find any one of 18 strangers by using their online connections showed it took, on average, only five to seven steps using friends and acquaintances.

The results, published in the journal Science, illustrate how social networks operate and show they have become truly global, the team at Columbia University yesterday said.

‘’The Internet is just a tool for doing this. It is all about social networks,’’ said Duncan Watts, who led the study.

The findings can shed light on epidemics, cultural fads stock markets and organizations surviving change, he said. ‘’This notion of a small world can explain all sorts of connections,’’ he said. — Reuters

Antidepressants may help stimulate the growth of new brain cells, U.S.-based scientists said after releasing research that may lead to the development of better drugs to fight depression.

Research on rats shows that two different classes of antidepressants can help brain cells regenerate — and not in areas normally thought of as being involved in depression.

‘’This is an important new insight into how antidepressants work,’’ Dr Thomas Insel, director of the National Institute of Mental Health, said in a statement yesterday.

The study fits in with others that suggest depression can shrink the hippocampus, a brain region crucial to learning and memory but only recently found to be involved in depression. Major stress and trauma — both depression triggers — can also cause the shrinkage. — Reuters

With over a million people in the US and several times the number around the globe suffering from allergy to peanuts, American researchers have achieved a breakthrough in evolving an allergy-free variety of the crop. The US Department of Agriculture announced earlier this month that its scientists have discovered a peanut variety lacking one of the major allergens.

By crossbreeding it to popular eating peanuts, the researchers hope to take a first step towards producing an allergy-free supermarket nut.

Peanuts have about six proteins that cause allergies in humans. — PTI