Tornadoes in Los Angeles, devastating California rains, and the great February East Coast snowstorm all seem to be connected to atmospheric events half a world away and up to a year ago in time.
These events include widespread warming of Pacific waters. This, in turn, can be traced to changes in wind and air pressure patterns in the western Pacific that began about a year ago, according to research recently reported by the US National Oceanic and Atmospheric Administration (NOAA).
Thus, for meteorologists, the extreme weather buffeting much of North America is further evidence of what they call teleconnections between the equatorial Pacific and the rest of the world. Large-scale weather changes in the equatorial Pacific can influence (teleconnect with) weather patterns many thousands of miles away.
According to scientists with the Marine Life Research Group at Scripps Institution of Oceanography, about a third of Pacific surface waters are several degrees F. warmer than usual. The area extends from southern Chile to the Gulf of Alaska and westward along the equator to the international date line. Group director Joseph L. Reid says the area of this massive warming has been growing for 10 months. It reached the Gulf of Alaska in January.
Off western South America, such warming is called El Nino, the child. It is so named because it is a recurring event that usually sets in around Christmastime. It generally is accompanied by a sharp decline in anchovy fishing.
This time, however, early signs of El Nino appeared last May. Ned A. Ostenso, an assistant administrator of NOAA, reported Feb. 23 that the El Nino warming has reached 6 to 8 degrees F. above normal this time. It appears to be the strongest warming so far this century.
Dr. Ostenso explained that NOAA research suggests that the warming off Chile and Ecuador diverted the jet stream southward along the North American West Coast, across the Gulf of Mexico, and back up the East Coast. This has led to warmer and wetter weather in the US South and East. The February East Coast snowstorm occurred when moisture flowing up from the gulf combined with colder northern air.
Meanwhile, off California, the ocean warming has brought sardines, swimming red crabs (on which tuna feed), and some other animals 300 to 500 miles north of their usual habitat, according to Professor Reid. The warming has also been accompanied by a rise in sea level along the California coast. Reid notes, for example, that sea level off San Diego was 6 inches above average in September. That's the highest monthly reading since recording began in 1925.
El Nino and other events in the equatorial Pacific which seem to lie behind all this unusual weather are part of what meteorologists call the southern oscillation. This is an intermittent, yet distinctive, shift in cloudiness, rain , sea surface temperatures, winds, and air pressure patterns that occurs irregularly at roughly two- to four-year intervals. It can be traced even into the Indian Ocean.
Meteorologists generally agree that its influences (teleconnections) are global. Ostenso has linked it to drought in Australia and floods in Ecuador, as well as to this winter's extreme weather in North America.
In 1976-77, teleconnections with the southern oscillation diverted North Pacific air flows northward to bring record warmth to Alaska. Then the flow turned southeastward to bring severe winter weather to the Eastern US. This time , the effect has been to bring abnormal winter rains to California.
Ostenso said that meteorologists are only beginning to understand the southern oscillation's global effects. But he explained that, for the first time , the Pacific warming has been widely monitored as it developed. Observations have been made from ships, by instrumented buoys and balloons, and by weather satellites. Thus meteorologists have an unprecedented opportunity to learn firsthand what may be involved.