Johnstone evaluated the data from airports along the northern California coast and found two airports Arcata and Monterey that had consistent fog records going back to 1951. With these data, he was able to show that frequent coastal fog is almost always associated with a large temperature difference between the coast and inland areas.
Using a network of 114 temperature stations along the Pacific Coast, Johnstone and Dawson demonstrated that the coast-inland contrast has decreased substantially, not just in Northern California, but along the entire U.S. coastline from Seattle to San Diego. This change is particularly noticeable in the difference between Ukiah, a warm Coast Range site in Northern California, and Berkeley on San Francisco Bay. At the beginning of the 20th century, the daytime temperature difference between the two sites was 17 degrees Fahrenheit; today, it is just 11 degrees Fahrenheit.
The relationship between temperature gradient and fog frequency implies a 33 percent drop in fog along the coast during this time.
Greater fog frequency is connected to cooler than normal ocean waters from Alaska to Mexico and warm water from the central North Pacific to Japan. This temperature flip-flop is a well-known phenomenon called Pacific Decadal Oscillation an El Nio-like pattern of the north Pacific that affects salmon populations along the US West Coast. The new results show that this pattern may also have substantial effects on the coastal forest landscape.
In addition, the data show that the coast gets foggier when winds blow from the north along the coast, which fits with observations that northerly winds push surface waters offshore and allow the upwelling of deep, cold, nutrient-rich water.
"This is the first data actually illustrating that upwelling along the Pacific co
|Contact: Robert Sanders|
University of California - Berkeley