Stormy weather blues

Researchers discover how human activities are responsible for good or bad weather at the weekend

Published: Thursday 15 October 1998

-- (Credit: Rajat Baran)THERE are few things as unpredictable as the weather, right? If there is one field where Murphy's Law is proved correct time and again, it is climatology. Writer Jerome K Jerome's well known book Three Men In A Boat has a witty observation on how, almost always, Mother Nature tends to discredit the weather forecasters. But things work differently now. Climatologists now have sophisticated equipment - satellite data, computer-assisted calculations and lots more - that help them predict the weather. So, despite all the digs made at the daily weather forecasts carried by newspapers, climatology is a precision-driven science, and scientists are doing all they can to understand the weather better. In the past few decades, they have pointed out how human activities have interfered consistently with global climate patterns - global warming being the most evident and also one of the most debated issues in recent times.

In a recent development, climatologists have discovered an intriguing pattern in rainfall statistics. If the drudgery of the working week gets you down, you are not alone, they inform. Even the weather can get stuck in a seven-day cycle. In some regions, rainfall and tropical storms behave differently at weekends, climatologists have reported.

"There are so many myths about weather being bad or good at the weekend," says Randail Cerveny of State University of Arizona in Tempe, USA. "It turns out some may even be grounded in truth." Cerveny and his colleague Robert Balling say their results are a strong indicator of how dramatically human activity is changing the world's climate.

The researchers examined rainfall in the Atlantic Ocean between 1979 and 1995 by analysing data from the global microwave satellite network. As might be expected, the ocean as a whole was unaffected by which day of the week it was. But the region just off the east coast of the us got a drenched weekend: on Saturdays there was about 22 per cent more rain than on Mondays.

They also studied data on five decades of hurricanes and tropical storms in the Atlantic. Here, too, the effects of human activities was clear. Wind speeds in storms were weaker at weekends than during the week, by as much as 18 km per hour.

"This is an amazing finding," says Chris Landsea, a meteorologist at Miami's National Oceanic and Atmospheric Administration in Florida, USA. "If what people are doing can alter hurricanes, we need to understand the process much better," he says.

Cerveny suspects that the link between people, precipitation and pulverising storms is pollution. In records from monitoring stations, the duo discovered how carbon dioxide and ozone levels shoot up as the weekend approaches. This so-called "Sunday effect" had previously been noticed in large metropolises and is often believed to be caused by differences in daily driving patterns and industrial activity.

The researchers speculate that particulate pollution seeds cloud formation offshore, which could perhaps explain why rainfall increases. The same process would steal vapour away from the centre of storms, robbing them of some power. Cerveny and Balling hope other researchers will test these ideas in computer-generated models.

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