Most people have heard of the Jet Stream -- those high-speed "rivers of air" several miles up in the sky. True, our exposure to it amounts largely to seeing a long wavy arrow on the newspaper’s weather map or hearing it blamed by the lady on the Six O'clock News for extended wet or dry spells. Frequent airplane travelers might hold responsible the Jet Stream for taking longer to fly from New York to San Francisco than from San Francisco to New York.
Knowledge of the Jet Stream actually goes back about 150 years. This is curious because then no airplanes or high altitude balloons existed, so any knowledge of the thing must have been gathered by people on the ground looking up. For sure, science types had attempted to measure cloud speeds for centuries before, but the patterns of wind versus altitude remained fuzzy.
A clarifying moment came in August 1883 with the eruption of Krakatoa volcano in Indonesia. Aside from several so-so Hollywood movies, the 1883 eruption is famous for many things. For one, it belched the loudest sound heard on Earth. Too, its explosion-generated water wave rates high on the list of deadly tsunami events. Less well appreciated is that Krakatoa's eruption lead to the first solid observations of the Jet Stream. Of course, prior to today’s 'jet era' the phenomenon carried a quainter name - The Smoke Stream.
Krakatoa blasted tons of ash and aerosol into the atmosphere. Because the eruption happened at a known place and time, observations of the spreading material constrained the direction and speed of high altitude winds. Certainly, some notations were more definitive than others. "Ash began to fall here at 2PM." is pretty cut and dried. Conversely, "The first week of November witnessed many red sunsets." carries equivocal weight. Still, armed with hundreds of wide-spread sightings, scientists learned enough to conclude that well defined wind currents existed in the higher levels of the atmosphere and that the currents had sufficient velocity to circle the entire globe in six or eight days.
Take a look at this movie that I made to get more of the story.
The Jet Stream might be more relevant to you and me than wavy map arrows or that extra thirty minutes in seat 34c. Any day, the Jet Stream could carry pollutants from a far away nuclear power plant leak or a coal-fired industrial accident to our doorstep in less than a week. The Jet Stream once even served as weapon of war. Japanese military tried to waft incendiary balloons on it to the west coast of United States in World War II. The “Smoke Stream” name might hold best for that application.
Steven N. Ward Santa Cruz
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John Rundle is a Distinguished Professor of Physics and Geology at UC Davis and the Executive Director of the APEC Collaboration for Earthquake Simulations. He chaired the Board of Advisors for the Southern California Earthquake Center from 1994 to 1996. Read John's blog.