Weather wise

THE 14 people who perished in a tornado in Hall County, Georgia, last weekend were victims of an often deadly and impressively powerful meteorological phenomenon. Those experiencing the hurricanes common a few hundred miles to the south are witnesses to even more awesome forces. But just how much energy is there in the weather?

In 1975, the meteorologist Gyorgy Koppny calculated the kinetic energy of a number of weather phenomena, and a comparison can be made with the energy of various human activities.

An average tornado such as the one in Georgia releases about a billion kilojoules of energy in a few minutes, about the same as all the street lights in London consume in a whole night. A single stroke of lightning, lasting a fraction of a second, liberates as much energy as a London bus running for 24 hours. A Jumbo jet flying for a day and a night burns enough fuel to power a light April shower. A summer thunderstorm lasting an hour, with several dozen lightning strokes, torrential rain and all the upward convection of a large cumulus cloud, equals the energy output of the Nagasaki atomic bomb. Larger phenomena release even more formidable amounts of energy; jet streams, the high-level, high-speed winds that govern the tracks of depressions and help airliners on their eastward journey across the Atlantic, are equivalent in energy terms to a full-scale nuclear war.

t Thanks to improved computers scientists may be able to provide much better long-term weather forecasts. Seasonal forecasts of up to six months ahead are at present far less reliable than the daily forecasts issued to the public. This is because the circulation systems governing the weather are by nature chaotic and unpredictable.

But writing in the science journal Nature this week, Tim Stockdale at the European Centre for Medium Range Weather Forecasts in Reading, Berkshire, describes how his team has used super-fast computers to successfully predict the weather several months ahead.

The new machines were able to predict the wet summer in southern Europe last year, and, according to Mr Stockdale, have forecast a warm summer ahead for us. Accurate long-range forecasts will have a profound effect. Farmers would pay dearly to know just when the ideal time will be to collect the harvest, and the railway companies might just be able to cope with the wrong kind of snow, if they knew it was coming.