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.
"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.
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."
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.