by Yevgeny DYOMIN, Cand. Sc. (Tech.), consultant, Russian Agency for Automatic Equipment Testing;

Viktor KUSHIN, Dr. Sc. (Tech.), Head of Lab, State Research Center "Institute of Theoretical and Experimental Physics"

The problem of preventing the spread of deserts in many parts of the world is now on the agenda of experts in different countries. An object of special concern is Sahara-a great desert of North Africa, which is the largest in the world. In recent years it has been increasing its southerly extent at the annual rate of 100 m, while storms originating there carry millions of tons of sand over thousands of miles.

Considerable levels of air pollution with fine particles of sand over the south-eastern coast of the United States and the Bermudas were traced by Prof. Joseph Prospero of the School of Marine and Atmospheric Studies of the University of Miami (USA). Ships navigating in the Caribbean and the Indian Ocean are usually covered with fine dust brought there from Sahara, and it was recently discovered that this dust even finds its way to England and Sweden. The area most exposed to this pollution is the southern flank of Europe which is "within the reach" of the hot equatorial wind sirocco. The long period of hot weather (of up to 40°C) in the summer of 2003 in France has also been traced by weathermen to Sahara. Bearing all this in mind, one seems to have all the reasons to denounce the notorious African desert as a scourge of not just that particular continent, but of the whole of our planet.

Looking into the not too distant future, the impact of the global warming will be the strongest in Africa and South America*.

This forecast has been suggested by Acad. Izrael, Director of the RAS Institute of Global Climate and Ecology named after A. Obukhov. He points out that one of the consequences of this change will be a maximum reduction of the levels of natural precipitation in these regions, which suffer from lack of rains even now.

Forecasts of this kind make it quite clear why all of these problems are in the focus of attention of the world scientific community. Back in the 1980s a Japanese construction corporation (Shimizu Kinshotsu) suggested a project ("Aquanet of Desert" at the cost of 18 trill, yen). It provides for building in the African sands of seven artificial lakes, each 30 km in diameter and 20 m deep. The lakes should have concrete banks and bottom and will be interlinked by a network of canals. In other words, the authors of the project suggest a mechanism of artificial water evaporation which should help restore life in Sahara.

Years of studies by Russian specialists, however, have rejected the

* See: Yu. Izrael, "Threat of Climatic Catastrophe?", Science in Russia, No. 4, 2004. - Ed .

Articles in this rubric reflect the opinion of the author. - Ed.

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Diagram of solar emission heating (1) of steam generator (2) with the help of heliostats (3).

Japanese project as unacceptable. They point out that the proximity of the Caspian Sea, for example, does not help improve the conditions of the surrounding arid region. And the ecological crisis in the Aral Sea* region offers one more proof of the fact that natural evaporation of water does not solve the problem of irrigation of the lifeless sands.

The way we see it, Sahara's "thirst" can only be quenched by abundant rains (even hailstorms). A leading Egyptian expert in this field, Prof. Carnal Batanuni, Director of the Cairo Center for Desert Studies, is also in favor of what is called dropping (trickling) irrigation.

It goes without saying that hopes for abundant rainfalls in the aforesaid arid regions are really few and far between because of very low air humidity (3 - 5 g of water per 1 m³ ). But "accumulating" this amount of water in an air layer, of 2 to 3 km over the ground will create conditions in which there will be 6 to 10 kg of moisture per 1 m² of the surface. In other words, there is enough moisture in the troposphere even over the hottest sands. But can we learn to precipitate such rains-learn to "tame" cyclones?

In the opinion of Russian experts, this problem can be solved by what they call a comprehensive approach based on the store of the accumulated knowledge in climate studies and backed by the most advanced domestic and foreign technical achievements. This includes supermeteotrones** - devices which can eject into the atmosphere powerful jets of steam-water mixture, thus activating clouds formation. And clouds can not only pour rains onto deserts, but screen the ground from solar radiation thus preventing sandstorms and devastating tornados.

Incidentally, not long ago Australian researchers put forward an idea of building a solar electric station of an unprecedented size. Such stations can best be located in places of maximum solar exposure, which are deserts. The "power base" of a heliosystem of this kind is a giant glassed "hothouse" 6 km in diameter and 26 m high. Hot air from the unit will stream up into an exhaust pipe one kilometer high and 130 m in diameter. Located there will be turbines with the aggregate capacity of 200 MW The cost of the project is estimated at 400 mln Euros.

From our point of view the "hothouse generator" is of interest as a likely power source for the aforesaid supermeteotrones which can also make it possible to stop using hydrocarbon fuel. In that case we shall have the following "pattern" of energy transformation: solar radiation-ascending air current-electric current-heat of superheated steam. The latter - at pressure of 40 - 50 atm - should be supplied to the gas-turbine section of the supermeteotron and set its driving shaft into motion. The use of steam energy will bring down the operating costs of the aforesaid devices and saturate the steam-air mixture with moisture up to the absolute level. And the main thing is that it will be possible to condense all water present in the air.

* See: R. Timofeev, "Destinies of Two Seas", Science in Russia, No. 6, 2003. - Ed.

** See: Ye. Dyomin, "Invisible Weather Assistant", Science in Russia, No. 1, 2003, Ye. Dyomin et al., "Cyclone Over Sahara", Science in Russia, No. 4, 2003. - Ed.

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To boost the efficiency of the steam generator unit we have developed a diagram of what we call preliminary steam generation. According to the process of water heating and evaporation should be "contained" in a heat-insulated chamber with ceramic-plated walls. From top it should be covered with a plastic roof, transparent for the ultraviolet, which shelters water from the outside air. Heliostats located around focus solar heat and bring water temperature to 100°C. The resulting steam-water mix is supplied into a boiler where its pressure is brought up to 40 atm. Using this arrangement will make it possible to increase the volume of superheated steam and substantially improve its thermodynamic parameters.

And there is yet another possibility of "stimulating" precipitation in desert regions. It has been analyzed by Prof. Igor Yanitsky, Cand. Sc. (Geol. & Mineral.) of the All-Russia Scientific-Research Institute of Mineral Raws. Analyzing weather anomalies, he established the possibility of a cyclone forming in the center of a major anticyclone. This phenomenon was registered in July 1998 when some regions of Buryatia and the Chitinskaya region were flooded by abundant rains. And an even more dramatic "game of nature" of this kind occurred that same year in Northern Caucasus near the extinct Elbrus volcano. Some places in that region were inundated with rains carrying thousand of cubic meters of water per second. And there were similar cases in Sahara itself. Russian geologists prospecting for rare metals in the 1980s in the center of this area-near Ahagar Plato - were nearly drowned during a shower of catastrophic proportions.

Studying the mechanism of the aforesaid phenomena, we come to the following conclusion: they can be triggered by hot current of air saturated with moisture - like those generated by our supermeteotrones. We should be able to "trigger off' cyclones over desert easily-with a wave of one's hand. In doing that we can rely on advanced methods of sounding of the atmosphere. One of them is radar probing to be used for con-tactless investigation of processes in the atmosphere. It has been adopted by experts of the RF Central Aerological Observatory of GOSKOMGIDROMET (State Committee of Hydrometeorology). Its experts can study the patterns of distribution of humidity, temperature and wind velocity in troposphere and the intensity of clouds formation using a home-made laser radar developed at the ERIDAN-1 R&D Center in Obninsk. Using these data one can easily calculate all necessary parameters, regimes and length of operation of supermeteotrones i.e. act in more effective ways.

Experience accumulated in different countries, including republics of Central Asia, demonstrates the tangible economic advantages of desert reclamation. We, on our part, are confident that restoration of the vegetation cover in Sahara will help feed millions of animals and cattle, revive farming and horticulture and, if one looks back into the distant past-even revive fishing.

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