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Jet Stream Drives Oregon Coast Fishing Success

The position of the jet stream off the Oregon coast determines how lucky your day of fishing will be when you go to sea. If the jet stream is to the north, fishing will be good; to the south, not as good.

Scientists have known for many years that the relative north-south position of the jet stream has an effect on the wind direction along the shores of Oregon, as well as Washington and California. However, recently they have discovered a direct correlation between the jet stream and the amount of plankton productivity along the shore. Since plankton are at the base of the oceanic food web, they directly affect the well-being of other species that consume them, such as larger plankton, fish, birds, and even whales.

This research was done as a follow-up to the discovery of variations in wind during a summer 2001 Oregon coastal study. While scientists were studying the movement of sea water across the continental shelf, they discovered repeatable variations in the winds along the coast. "We know so little about variation in time and space,” says Yvette Spitz of Oregon State University (OSU). Spitz utilized a computer model to confirm the group's discoveries about these re-occurring wind oscillations.

The principal investigator for this research, funded by the National Science Foundation, is John Bane, an oceanographic scientist at the University of North Carolina, Chapel Hill. Also involved in the work was Ricardo Letelier from OSU, and William Peterson with the National Marine Fisheries Service. The results were published in the August 14 issue of the Proceedings of the National Academy of Sciences.

During the project, the group discovered repeating, fairly consistent, intraseasonal oscillations in the wind. The lengths of the oscillations were 15 to 40 days, more typically 20 days. These summer time oscillations were determined to be caused by the shift in the jet stream's position as it crossed the coast.

In the Northern Hemisphere, the jet stream moves from west to east across the upper atmosphere. It tends to oscillate, snake-like, as it circles the earth. Along the southern side of the jet stream are high pressure systems, such as the East Pacific high. The winds around a high pressure system rotate clockwise around the system. If the jet stream crosses the coast to the north, as it typically does during the summer, there is a high pressure system just off the coast which causes an ongoing north to south wind.

As the winds blow along the coast, they drive the sea slightly offshore. When this happens, it creates a deficit of water along the coast that must be replaced. This replacement is accomplished by the sea bringing water up from the deep ocean. Oceanographers call this sea water movement upwelling.

Since nutrients preferred by the plankton are lying on the ocean floor or suspended in the deeper water of the ocean, this upwelling brings the nutrients up and the plankton respond by increasing their numbers, or "blooming.” Their increased numbers increase the numbers of larger plankton, small fish, and other animals, with effects throughout the food web. If the jet stream crosses the coast to the south, the winds blow south to north, no upwelling occurs, and the oceanic food web responds accordingly.

The data from the 2001 study, combined with data gathered by sea buoys, ships, and a small aircraft, and historical information were examined to uncover the correlation between jet stream position and plankton productivity. The plots of the two data streams are almost identical in shape with the increased plankton productivity coming a few days after the wind changes direction.

There is also some indication of a longer term, possibly 18- to 20-year, variation in these cycles, although this variation was not explored during the research. Another issue not explored during this work was the impact of El Nino on these short-term oscillations.

Dan Helman is a physical oceanography student at the University of Washington.

Image:

Green phytoplankton "bloom” off Oregon coast as shown from a SEAWIFFS Satellite image. Photo: NASA


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