A Salt Lake meteorologist's experiments with cloud seeding to disperse fog may be worth a try at clearing up the fog that periodically closes Spokane International Airport in the late fall and winter, airport officials said.
Spokane usually has about 48 days a year when fog is so dense that visibility is less than one-quarter mile, said Ken Holmes of the National Weather Service.Over the past five years at Spokane International, an average of 181 flights per year were delayed or diverted because of fog. The high was 310 flight interruptions in 1983-84, with a low of 47 the following winter.
Little can be done to get rid of warm fog, which occurs when the air temperature is above 32 degrees. But Spokane's fog is primarily cold fog, which occurs when the air temperature is below the freezing point, and seeding cold fog with dry ice can clear an approach to a runway.
The dry ice - frozen carbon dioxide - attracts water droplets in the fog and causes them to freeze. The frozen particles grow until they become so heavy they fall to the ground.
But Norihiko Fukuta, a University of Utah meteorology professor, has successfully tested a liquid carbon dioxide spray he says can clear fog not just from an airport but from an entire community. During experiments last winter in Salt Lake City, spraying one pound of liquid carbon dioxide from a twin-engine plane cleared a square mile of fog.
Fukuta estimated a single plane with a 400-pound tank of liquid carbon dioxide could clear as much as 400 square miles of fog in less than two hours.