During wind and rain

When the wind velocity is constant, expect rains and storms

Published: Friday 15 January 2010

Scientists  around the world have been confused by the role of wind and pollutants on rainfall. But now they have a model. It shows that wind shear—a change in wind speed and direction between different altitudes—plays a crucial role in the whole process.

A research team from Pacific Northwest National Laboratory of the Department of Energy in the US created a computer model using atmospheric data from northern Australia and eastern China.

The team simulated the development of eight clouds by varying the concentration of pollutants such as aerosols, wind shear and humidity.

The model found that when wind shear is more or when the wind keeps changing its speed and direction, the pollutants it carries along do not allow clouds to form. When the wind is relatively stable, one can expect rains and even storms because it means the wind shear is weak and clouds can be formed. The model also explains that wind shear plays a bigger role than humidity on cloud formation.

“This finding may provide some guidelines on how pollutants affect the local climate and precipitation, especially for the places where ‘afternoon showers’ happen frequently and affect the weather system and hydrological cycle,” said atmospheric scientist Jiwen Fan of the US Department of Energy. The results were presented at the December 17 meeting of the American Geophysical Union.

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