FIRST comes the ZAPPING WHITE FLASH!! followed by the crashing KABLOOOM!! Big dogs cower. Grown men wince. Trees are split like match sticks. And forest fires start in the Pacific northwest and California, causing millions of dollars of damage.
This is summer's lightning-and-thunder road show, a long-running hit that has lightning striking the earth an astonishing 8.6 million times a day with up to a billion volts of electricity generated. And equally as astonishing, after centuries of modest lightning research, no one knows exactly how and why lightning starts in clouds.
``We really don't understand in any detailed way how lightning is initiated in clouds,'' says Martin Uman, director of the Lightning Research Laboratory at the University of Florida in Gainesville and author of several books about lightning.
``We know there is a region of negative electric charge at the bottom of the cloud,'' he says, ``and positive at the top, and out of one of those regions the lightning starts and comes down. But we don't know why.''
With dry conditions now in eight Western states in the US, lightning has contributed to 39 major fires there covering almost 400,000 acres, according to the National Inter-agency Fire Center in Boise, Idaho. About 14,000 firefighters are at work trying to control the fires.
Mr. Uman says that lightning research is modest at best. The Apollo 12 rocket launch in 1969 was confirmed to have triggered a lightning bolt, which served as an impetus for serious but limited lightning research.
``Funding for lightning research is very sparse because nobody has really cared,'' he says. ``There has been research about what happens on the ground with power lines and forest fires, but not much at the cloud end. If we know the conditions under which lightning starts, we might be able to detect that condition, and have more advanced warning, or maybe even alter the conditions.''
Because society is increasingly dependent on electricity to power everything from chips in computers to carving knifes, experts insist more should be known about lightning and electricity. Asked if he thinks it is possible to determine how lightning begins, Uman says, ``Absolutely. I would say several million dollars a year for a program of five to 10 years of research would shed a lot of light on the problem.''
The experts may not know what triggers lightning, but thunder is no mystery. When lightning flashes it heats the air around it to searing temperatures, which expands so suddenly and powerfully that the air booms.
``There are several theories about how lightning starts,'' says Marx Brook, a retired physicist in New Mexico, ``and there is a growing conviction that it is a collision process in the clouds when hail falls through snow crystals, and this produces an electric charge. But Mother Nature would be in a bind if she had only one method to do something, and we don't have much evidence yet for any method.''
While the destructive nature of lightning is well-known - some 150 people are struck and killed by lightning each year - it is possibly one of earth's underrated elixirs responsible for plenty of good, the experts say.
``The first is that the lightning charge enhances the precipitation growth,'' says Mr. Brook, who is doing lightning research for NASA. ``In other words, it brings rain.''
Some experts suggest that lightning may have created the first molecules on earth from which life evolved. ``Whether or not it did, nobody knows,'' Uman says. ``But it was certainly the source of fire for primitive man, and we wouldn't be here today without fire.''
In forests, lightning is a leavener. ``All forests are balances of things that grow in ash and fire,'' Uman says, ``and lightning helps clear the forest floor so many living things can be there.''
``Also,'' says Lynette Flan, a geologist at Wichita State University in Wichita, Kan., ``lightning is good for vegetation because when it comes, it frees up nitrogen in the air, and the rain washes it into a kind of nitrogen fertilizer.''
Although ``streak'' lightning - the well-known flashing bolt - is the most common form of lightning, there are other varieties. Forked lightning has multiple leaders reaching to earth. With ribbon lightning, multiple flashes appear parallel to each other. Bead, or ``chain,'' lightning stays longer in the air, and resembles a beaded necklace. The rarest form is ball lightning, about the size of a baseball. In a fiery clump, it hovers in the air and disappears with a bang.
The National Lightning Detection Network (NLDN), located in Tucson, Ariz., keeps track of lightning flashes in the US. A host of customers, like utility companies and airlines, want to keep an eye on the path of storms, and the frequency of lightning. A little more than 100 sensors are located throughout the US and linked to a satellite.
``So far this year,'' says Lynn Shoemaker, an NLDN spokeswoman, ``we have detected 16,457,154 flashes. The previous year for the same six months there were almost 15 million flashes. But there is no technology yet to tell us exactly where lightning will strike next.'' About 20 percent of lightning flashes hit the ground.