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Thursday, August 6, 1998 Published at 09:35 GMT 10:35 UK


Weekends are wetter: official

Forecasting the weather may become easier

The feeling that it always rains at weekends may be more than just a myth about the weather.

New research shows weekends are wetter. The cause, scientists suspect, is the build up of pollution during the week, resulting in rain at the weekend.

Dr Randall Cerveny explains what the findings mean
"We knew that cities have an effect on local weather with urban heat islands and so forth, and people are pretty sure that we're having a general global effect with carbon dioxide," said Dr Randall Cerveny of Arizona State University.

"But nobody had ever looked at the in-between area of large-scale regional weather. We appear to be affecting global weather on a scale that is comparable to El Nino."

Together with Robert Balling, Dr Cerveny examined rainfall in the Atlantic Ocean between 1979 and 1995 by analysing global satellite data.

As expected the ocean as a whole was unaffected by which day of the week it was.

But they found that the results were very different closer to the shore.

The region just off the heavily populated east coast of the US was soaked at weekends.

[ image: Does it always rains at music festivals?]
Does it always rains at music festivals?
On Saturdays there was about 22% more rain than on Mondays.

An examination of five decades of data on hurricanes and tropical storms in the Atlantic showed a similar cyclical pattern.

The scientists at Arizona State University suspect that the link between human activity and the weather is pollution.

Writing in Nature they said: "Although our statistical findings limit the identification of cause-effect relationships, we advance the hypothesis that the thermal influence of pollution-derived aerosols on storms may drive these weekly climate cycles."

The BBC's Karl Newman: 'Levels of the gases build up during the week'
Records from monitoring stations showed that levels of two urban pollutants, ozone and carbon monoxide, rose as the weekend approached.

This so-called Sunday effect had previously been noted in large cities.

Pollutant-derived droplets were thought to seed offshore cloud formation and also steal vapour from the centre of storms, robbing them of power.

The findings are published in the science journal Nature and also reported in New Scientist.

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