by Nonny » Wed Sep 07, 2005 1:49 am
Title: Raising a storm. (cover story) <br>Authors: Mullins, Justin <br>Source: New Scientist; 7/27/2002, Vol. 175 Issue 2353, p28, 6p, 1 diagram, 2c <br><br>Born out of chaos, the weather seems a law unto itself. But tweak it at the right time and we can take control, says Justin Mullins<br><br>HURRICANES and typhoons batter the coast leaving hundreds dead. The rains fail and crops wither in the field, or the stuff keeps falling until the rivers burst their banks. There are tornados, blizzards and blinding sunshine. No matter where you live, or how rich you are, you can be sure that the weather will always have the upper hand.<br><br>And no wonder. The atmosphere that drives it is a complex machine powered by colossal amounts of energy from the Sun. And not only that, it's chaotic too. What hope is there of controlling the weather when, in the famous words of Edward Lorenz, the flap of a butterfly's wing in Brazil could set off a tornado in Texas.<br><br>But what if this exquisite sensitivity could be used to our advantage—not merely to predict the weather, but to actually control it. Warm the ocean at a particular spot in the mid-Atlantic, for example, and northern Europe's next depression might stop in its tracks. Cool the air above Santa Barbara and a welcome rainstorm could go rumbling across the Arizona desert.<br><br>Researchers believe they have already glimpsed the soft underbelly of chaos that could put the atmosphere under our command. The new ideas are so potent that these scientists are beginning to think on the grandest scale. Perhaps, they whisper, it will one day be possible to control the weather from pole to pole.<br><br>Set against these grandiose aims, previous attempts at weather modification seem pretty puny. The first came in the late 1940s, when scientists discovered that raindrops form more quickly if ice crystals are present in the clouds. The crystals act as seeds for raindrops by encouraging moisture to condense around them. Perhaps, the scientists reasoned, they could trigger rainfall by seeding clouds with crystals that have a similar structure to ice.<br><br>Experiments followed all around the world. In the late 1960s, during the war in Vietnam, American forces launched a secret programme called Operation Popeye to seed rain clouds over Laos in the hope of flooding enemy supply routes (see “Weather wars”, p 30). The results were inconclusive, but attempts to trigger rain continue to this day in the US, Asia and elsewhere.<br><br>None of these efforts rate as an unqualified success. The biggest problem that has dogged them all is the impossibility of proving that they've worked. After all, when you can't tell in advance how much rain a cloud would have produced unaided, how can you tell whether seeding it really altered its behaviour?<br><br>And how, critics argue, could we ever hope to learn this? The atmosphere is impossibly disordered. Its evolution is governed by a complex set of rules that depend on a multitude of factors including wind speed, temperature and atmospheric pressure. The chaotic nature of this system, first pointed out in the 1960s by Edward Lorenz at the Massachusetts Institute of Technology, means that a small change in any of these factors, perhaps even the proverbial butterfly, is amplified and can end up having a large effect on the state of he weather.<br><br>But Ross Hoffman is undaunted. A student of Lorenz's in the 1970s, and now a meteorologist at consulting firm Atmospheric and Environmental Research in Lexington, Massachusetts, Hoffman sees chaos not as a problem, but as a key to the solution in the quest to control the weather. For the past two years he has been investigating the idea that the chaotic system of the atmosphere can be controlled by “limited resources applied intelligently”: in other words, by injecting small amounts of energy at the right place and time. NASA's Institute for Advanced Concepts is impressed enough to be funding further research.<br><br>In fact, controlling chaos is nothing new. Engineers have already worked out how to control spacecraft following chaotic orbits. And electronics experts have harnessed a circuit that oscillates in a chaotic manner to generate digital radio signals (New Scientist, 8 April 1995, p 36). The weather is far more complex than these systems, but today's forecasting programs and the computers they run on are powerful enough to mimic the behaviour of real weather, for a short while at least. Take this a step further, Hoffman believes, and we could make the shift from forecasting the weather to controlling it.<br><br><!--EZCODE CENTER START--><div style="text-align:center"><!--EZCODE BOLD START--><strong>And now the forecast</strong><!--EZCODE BOLD END--></div><!--EZCODE CENTER END--> <br>Hoffman woke up to the possibility a full quarter of a century ago, in 1977, when he was still under Lorenz's wing at MIT. Casting around for a subject to research, his attention turned to programs called numerical weather prediction models, which are based on mathematical models that encapsulate the laws governing the behaviour of the atmosphere. Feed the current state of the weather into the model, allow it to evolve, update it every few hours with details of real weather conditions, and it will predict the state of the atmosphere at some point in the future. It is programs like these that allow meteorologists to give us our nightly TV weather forecasts.<br><br>Hoffman's idea was to use these programs for more than just forecasting. He figured that by hijacking the model, it ought to be possible to calculate what it would take to nudge the weather in the direction we want it to take. Say, for example, that you want to find out how to intercept a cold front travelling north and send it eastwards instead. His idea was to start out with a model of the weather system based on real data, and let it evolve with time. However, rather than simply watching to see what happened, he wanted to modify the model so that it searches through a wide range of conditions close to but not quite the same as the real weather, looking for those best able to send the cold front to the east. His computer model would then work out the smallest perturbations necessary to achieve this goal. Hoffman even proposed this idea to Lorenz as a potential thesis topic, but Lorenz advised his student against it: it was far too risky a topic. Besides, Hoffman realised, the technology simply wasn't up to it at the time. But since then computers have become more powerful, and weather models more accurate. So a few years ago, Hoffman decided it was worth a second look.<br><br><!--EZCODE BOLD START--><strong>Oddly enough, the ideal test bed for Hoffman's ideas is not a gentle everyday weather system, but a hurricane.</strong><!--EZCODE BOLD END--> That's because hurricanes have been so intensively studied that computer models of these violent weather systems are among the most accurate and advanced. The current state-of-the-art technique for this kind of modelling is known as four dimensional variational data assimilation or 4DVAR, and Hoffman applied a modified version to the path of Hurricane Iniki, which devastated the Hawaiian island of Kauai in September 1992. His plan was to set up a weather simulation based on data from the event, and then try to steer the simulated Iniki away from Kauai by warming the air above an area of ocean to the west of the hurricane. The idea worked perfectly. When he ran the model, he found that in a 6-hour period, he could steer the hurricane over 100 kilometres to the west of Kauai. “It is as if the hurricane is attracted to warmth,” he says in a paper on the work submitted to the journal Geophysical Research Letters this year.<br><br>But his simulation suggested that temperature is not the only variable that must be controlled to move Iniki off-course. Rainfall and the wind speed around the hurricane also needed tweaking. This would be impossible in practice, so the next stage of Hoffman's work is to modify his model to see if the same result can be achieved by changing only one of these factors, and then to calculate exactly how large a change would be needed and where it would have to be applied.<br><br>So how big is this change likely to be? According to Hoffman's current models, steering a hurricane is likely to require altering the temperature of the air by around 1°C or changing the wind speed by several metres per second over areas of several hundred square kilometres. He's planning to repeat the simulations this year to pin down the actual amount needed.<br><br>But even without those results, it's clear that there's no practical way of creating perturbations on this scale to order. For his scheme to stand any chance of success, Hoffman realises he must look for perturbations on a much smaller scale, perhaps over just a few square kilometres.<br><br>One factor that stands in the way of achieving this is the poor resolution of the 4DVAR model. Numerical weather prediction models break up the atmosphere into a grid in which each cell is around 60 kilometres across. But as models improve, and the grids get finer, it should be possible to calculate how even smaller disturbances could do the trick. By 2008, Hoffman expects to be working with a grid just 15 kilometres across. And meteorologists are finding better ways to make the large numbers of accurate measurements of local weather conditions that will have to be plugged into these models. In 2004, for example, NASA's GIFTS satellite will begin to provide detailed maps of temperature and the concentration of water vapour in the atmosphere.<br><br>To make a system that can be used in earnest, the modified weather prediction model will have to be harnessed to control the devices that will pump in the energy at the right time and place. Fed with the latest weather readings, his software will compare the state of the current weather with the model to find the smallest perturbations that can send the weather the way he wants it to go (see Diagram, p 32). And of course Hoffman must be able to come up with a way to create and control these perturbations.<br><br>This is a mighty tall order. One suggestion is to have satellites equipped with steerable minors in low Earth orbit that could reflect sunlight onto the required spots on the planet. Another is to set up arrays of wind turbines that would operate in reverse: driven by an external power source, they would act as giant fans, whipping up an artificial wind. Perhaps cloud seeding techniques, or even a cloud-dispersing gel recently tested by an American company, could do the trick.<br><br>Using aircraft vapour trails to cool parts of the Earth's surface by providing shade from the Sun is another possible way of creating the required temperature differences, Hoffman suggests. But as well as blocking sunlight during the day, these contrails might prevent the escape of infrared radiation. This would have the opposite effect and warm the atmosphere, especially at night. After 11 September, when commercial flights over the US were banned for three days, scientists recorded a 1°C increase in the temperature range at ground level, a significant change. Whether Hoffman could use this effect isn't yet clear.<br><br><!--EZCODE CENTER START--><div style="text-align:center"><!--EZCODE BOLD START--><strong>Steer a hurricane</strong><!--EZCODE BOLD END--></div><!--EZCODE CENTER END--> <br>Despite the difficulties, Hoffman is getting some encouragement for his ideas. “I think it's a promising line of work. It's very plausible,” says Kerry Emanuel, an atmospheric scientist at MIT. Emanuel himself has ideas about how hurricanes can be controlled. The key, he says, is to understand where hurricanes get their energy.<br><br>It turns out that much of their power comes from the evaporation of seawater, which transfers heat energy from the ocean into the atmosphere in the same way that sweat evaporating from skin carries heat away. A typical hurricane extracts energy from the ocean at a rate of up to 1000 watts per square metre. Depriving a hurricane of this source of energy could change its course or weaken it, Emanuel says. It is well known, for example, that hurricanes rapidly lose their energy after reaching land.<br><br>To achieve this, he suggests covering the ocean in the hurricane's path with a film of oil only a few atoms thick. “Thin films strongly curtail evaporation,” he says. Emanuel likens it to creating an artificial landfall for the storm. He is currently testing the idea at MIT's Hurricane Mitigation Lab — motto: “Where hurricanes become a breeze”. His team has built apparatus just a metre across that can create miniature hurricanes and monitor the way they interact with the water they travel over. Using one cylindrical tub set inside another, the device creates a ring of water across which a fan drives air at up to 70 metres per second, whipping the surface into a spray. “It's roughly similar to what you get in a hurricane,” he says.<br><br>Emanuel has already measured how much energy is transferred from the water to the wind in these circumstances, and later this year he plans to see what difference a thin layer of oil makes. “We'll probably start with natural oils such as fish oil or olive oil because they are non-toxic,” he says. Since the layer need only be a single atom thick, a small amount of oil would suffice to cover a large area — a few teaspoons could cover the area of a large lake, says Emanuel. He suggests that a plane fitted with crop-dusting equipment could cover hundreds of square kilometres of ocean in the path of a hurricane.<br><br>There is just one problem. While a thin layer of oil might stop heat being transferred from calm water, Emanuel admits it's unlikely to have much effect when the wind whips the sea into a maelstrom of spray and foam. Most likely the wind will simply mix the oil with the water, allowing evaporation to continue unabated. However, there is a small chance that this will not happen, especially if Emanuel uses synthetic oils such as hexadeconol that have much stronger intermolecular bonds than natural oils. “The potential benefits are so enormous and the cost of this experiment so low that it is worth having a try,” he says. He should find out the results some time later this year.<br><br>Meanwhile Hoffman accepts that the time has not yet come when his ideas can be used to change the weather. But when the technology becomes more sophisticated, in perhaps 20 or 30 years, it may be more realistic to weigh the costs of launching mirrors into space or spraying oil over vast regions of the ocean against the damage that wild weather can do. Emanuel points to one of the most powerful hurricanes ever to make landfall, which devastated Miami in 1926. “If such a hurricane were to hit today it could cause $78 billion worth of damage. That's enough to sink the entire insurance industry.”<br><br>To Hoffman this suggests a rather different way to approach weather modification. “It's not going to be about pointing the hurricane to a particular spot at a particular time,” he says. Instead it may be possible to design models that can calculate the cost of potential damage as a function of wind speed. The computer then calculates a perturbation to the atmosphere that minimises this cost. If this approach is adopted, the exact path of the storm may not matter.<br><br>Neither Emanuel nor Hoffman think it would be right to alter the weather just for the sake of it. The many hurricanes that form in the Pacific and Atlantic each year play an important role in mixing water layers in the upper ocean. Most never threaten populated areas so there is no need to change them. “It would be quite irresponsible,” says Hoffman.<br><br>Yet if this kind of control proves successful for hurricanes, why not use it elsewhere? Smaller weather systems such as rain or snow storms or even tornadoes may not wreak as much havoc, but equally, it would take far less energy to control them. If you can delay the onset of a heavy snowstorm on the Eastern seaboard of the US until after the rush hour, for example, why not do it, says Hoffman.<br><br>But perhaps it isn't quite that simple. Changing the weather to benefit one area could bring unwanted effects elsewhere. Weather over different regions of the globe is tightly coupled, so wherever you alter it there are almost certain to be knock-on effects. Steering a storm system away from New Orleans, for example, might prevent massive loss of life and damage there, but lead to a change in rainfall patterns over Mexico, the Caribbean or South America that might be catastrophic for local farmers. “The nation that controls its own weather will necessarily control the weather of other nations,” says Hoffman. And this could trigger conflict. “Weather wars are conceivable.”<br><br><!--EZCODE BOLD START--><strong>Even more worrying is what could happen if the military get their hands on such a powerful force.</strong><!--EZCODE BOLD END--> Through military eyes, the capability to steer a hurricane this way or that may look temptingly like the ability to point a multi-megaton weapon at a chosen target. In a US Air Force study called AF 2025, which outlines crucial strategic weapons of the future, weather control is singled out as one of the most important. A UN convention signed in the 1970s specifically outlaws the use of weather modification for hostile purposes, and for now, the official US Air Force line is that the weather is of little strategic value. But Arnold Barnes, an atmospheric scientist at the US Air Force Research Lab at Hanscom Air Force Base in Massachusetts, believes that should change. “The position needs to be re-evaluated,” he told an audience at a US Army technology conference last year.<br><br>Who is to say that if weather modification does become a practical possibility, it won't become a weapon of war. It may turn out that one day the temptation to abandon the UN agreement will be too great to resist.<br><br> <p></p><i></i>