From at least the early 1940s to the end of the 20th century, it always rained more in the state of Jalisco, in central Mexico, than in its neighbor Aguascalientes. But in 2000, on a patch of parched pasture in Aguascalientes, workers from Mexico City-based Electrificación Local de la Atmósfera Terrestre SA (ELAT) erected a peculiar field of interconnected metal poles and wires somewhat resembling the skeleton of a carnival tent. Since then, about as much rain has fallen on the plains of Aguascalientes as on its more lush neighbor.

The brainchild of a fractious group of Russian émigrés, the poles and wires are in fact a network of conductors meant to ionize the air. If the technique is done properly, the thinking goes, the natural current between the earth and the ionosphere is amplified, leading—through a mechanism that is not fully understood—to rainfall. There are now 17 such installations in six states in Mexico, and in January, federal government agencies decided to back construction and operation of 19 more by 2006, potentially altering the weather in much of parched north and central Mexico. Meanwhile, by May, ELAT's competitor Earthwise Technologies Inc., of Mexico City and Dallas, could win the right to establish ionization stations in southwest Texas's water-starved Webb County, which would make it the first such installation in the United States.

But some atmospheric scientists aren't so sure the Russians aren't selling snake oil. "[Ionization] is highly unconventional and in my realm of experience, I have seen no concrete evidence published in a refereed journal, nor have I seen sufficient credible eyewitness verification that the technology works as touted," says George Bomar, the meteorologist charged by the Texas government with licensing the state's weather modification projects [see photograph, "Storm Clouds Gather"].

Ionization technology, called alternatively IOLA (ionization of the local atmosphere) by Earthwise and ELAT (electrification of the atmosphere) by the company ELAT, washed ashore in the New World with a group of Russian scientists, who left for Mexico after the Soviet Union's collapse. The scientists had already formed a company called ELAT in Moscow, but soon "a less than amicable split" occurred, according to Earthwise CEO Steven C. Howard. The last Soviet ambassador to Mexico, Oleg Darusenkov, now a businessman and adviser to Earthwise, put the contingent led by Serguei Komarov in touch with that company's executives. Meanwhile, Komarov's former colleague Lev Pokhmelnykh formed ELAT by joining with another Darusenkov associate, the Mexican astronomer and scientific establishment insider Gianfranco Bissiachi. Each company believes it holds key patents.

IOLA and ELAT compete with conventional cloud seeding, which—though it also remains scientifically unproven—is used in more than 24 countries and 10 U.S. states. Cloud seeding usually involves dispersing a chemical agent such as silver iodide into cloud formations, which helps ice crystals form, leading, it is thought, to bigger clouds and more precipitation than without seeding. The ionization approach, according to Bissiachi, now ELAT's vice president of R and D and operations, does a similar job but twice over. Ions attract water in the atmosphere, creating the aerosol that produces clouds, and they also charge the dust already in the air, making particles become more attractive nuclei for water droplets, which coalesce and fall to the ground as rain.

The ion technology's backers think their idea beats cloud seeding for a number of reasons. It produces more rainfall, and it doesn't need clouds to be in the area to work. Also, it should be less expensive, because it doesn't require aircraft to spread chemicals, the usual method. Further, they believe that changing the polarity and quantity of the ions could reduce rainfall where it's too plentiful, prevent hail, and even break up fog at airports. To these claims, Earthwise adds that its technology reduced air pollution in trials in Mexico City and Salamanca, because the condensation it caused warmed the air, creating an updraft that carried away pollution.

Earthwise's installations are structures about 7 meters high, shaped like short open-topped air-traffic control towers, that house proprietary ion generators and blowers to lift the ions. Separate antennas amplify the ionization by manipulating the local electric and electromagnetic fields. ELAT's installations work in the same manner but are more primitive in appearance, consisting of a 37-meter high central tower surrounded by 8-meter posts arranged hexagonally at a distance of 150 meters. The tower and posts are interconnected by wires, which when set to a high dc voltage by a 2-kilowatt generator, ionize air molecules such as nitrogen and oxygen. According to Bissiachi, as the ions waft upward, they produce about 1 milliampere of current. This current swamps the Earth's natural current—about 1 picoampere—and can affect the weather up to 200 kilometers from the station, he says.

Summing up all its tests from 2000 to 2002, ELAT and its U.S. and Canadian counterpart Ionogenics, in Marblehead, Mass., claim that ionization led to about double the average historical precipitation—stimulating, among other things, a 61 percent increase in bean production in Mexico's central basin in the last three years. Cloud seeding, in comparison, typically claims only a 10-15 percent improvement in rainfall.

Despite the claimed successes, ionization has its critics. Atmospheric scientists contacted for this article noted that even the four years of testing was too brief a period to prove that the effects seen were not due to some sort of extraordinary variability in the local weather. Bissiachi claims that the criticism goes to a deeper prejudice. "Meteorologists are not used to thinking that electrical phenomena could be important to the normal hydrodynamic model," he says.

Weather modification technology has always had a hard time standing up to rigorous scientific scrutiny. Ross N. Hoffman, a vice president at Atmospheric and Environmental Research Inc. in Lexington, Mass., helped complete a scientific review of cloud seeding, which was released by the U.S. National Research Council, Washington, D.C., in November 2003. It found that even after more than 50 years of use, cloud seeding remained unproven from a scientific standpoint. "[Ionization] faces the same problems cloud seeding does," he says. Among those are uncertainty about the natural variability of precipitation, the inability to accurately measure rainfall, and the need to randomize and replicate experiments. The last is particularly troublesome, since weather modification companies are typically hired to induce rain whenever they can. Randomly turning on or off the system to prove a point is not in the customer's interest, Hoffman notes.

Ionization also suffers doubts about its basic plausibility. Brian A. Tinsley, a physicist at the University of Texas, Dallas, and an expert on the effects of ions and current in the atmosphere, points out that the ionosphere is about 250 000 volts positive compared with the ground. But the effect of the resulting current, and changes to it from cosmic rays and other phenomena, on droplet formation and precipitation is "relatively small" and restricted to certain types of clouds in specific locations, he says. Considering the size of the natural voltage and the modesty of its impact on rainfall, effective weather modification using ionization, he believes, would require enormous power input and hundreds of square kilometers of antenna arrays.

But some atmospheric scientists are enthusiastic. Arquimedes Ruiz, a meteorologist who evaluates cloud seeding for the West Texas Weather Modification Association in San Angelo, says he is optimistic about ionization's chances. "In Texas, there are small droplets, so clouds tend to coagulate slowly and dissipate," he notes. He thinks ionization could at least help form the clouds that conventional seeding could then manipulate.

Although ELAT and Ionogenics have the advantage in terms of the amount of data they have collected, it is Earthwise that may end up penetrating the U.S. market first. In November the company signed a US $1.2 million contract to build up to six ionization stations in the region around Webb County and boost rainfall there by 50 percent over the average for the prior 20 years.

However, county commissioners quickly suspended the project following an uproar in the local press, critical of the terms of the contract and the unorthodox technology. Earthwise's Howard is confident that the deal will move forward again in May if he can secure grant money for the project from the Mexican government, which would also be in the affected zone.

"We know how controversial this is," says Howard. "But we've done five projects to date. All were successful. All were outside the United States. We've got to get it here so [U.S.] scientists will evaluate the efficacy of the technology before it can really begin to become commercialized." Howard thinks it could take more than 10 more years of data accumulation to satisfy the technology's critics. But success, he says, is "a question of when, not if."