Asian brown cloud casts shadow on U.S. weather.

Byline: James P. Miller

TRINIDAD, Calif. _ There are storms you can see here on California's far northern coast, and storms you can't.

When a big gale comes ashore at Trinidad, Calif., it's hard to miss. The heaving gray waters of the Pacific Ocean crash against the house-size boulders that litter the coastline, then shatter into white spray. A buoy lurches in the waves, its bell tolling a mournful warning, and a curtain of rain sweeps in from the sea.

But when a plume of pollution, known as the Asian brown cloud, blows in from China, nobody in Trinidad even knows it's happening. Add one more item to the long list of things Asia exports to the United States: air pollution.

The contaminated air that rides the jet stream to Trinidad is laced with the sulfates and soot from Asia's industrial smokestacks, and nitrogen oxides that emerge from tailpipes of Asia's rapidly growing fleet of automobiles. It contains particles from fires set to clear jungles for farming, and from the millions of households that burn coal, wood or animal dung for heating and cooking.

Scientists identified the phenomenon only five years ago. The Asian brown cloud, researchers now know, routinely climbs high enough into the atmosphere to hitch a ride on the fast-moving jet stream heading east to North America. In April and May, when seasonal winds are ...