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June 18, 2003 |
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THE NATION
La Niña May Be Bearer of Gloom
Scientists say cooling in the Pacific suggests the return of a
weak system that would mean more fog and droughts in Southern California.
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Government forecasters are detecting the possible return of
La Niña, the weather pattern associated with the gloomy June fog in Southern
California and persistent droughts throughout the area.
La Niña, which means "The Little Girl" in Spanish, is an abnormal
cooling of water temperatures in the equatorial Pacific.
Vernon Kousky, a research meteorologist with the National Oceanic and
Atmospheric Administration, said that over the last few months the Pacific has
cooled by 2 to 5 degrees just off the western coast of South America,
suggesting the emergence of a weak La Niña.
This possible La Niña follows last year's weak El Niño, the ocean condition
typified by warmer than normal temperatures in the equatorial Pacific.
Bill Patzert, a satellite oceanographer at the Jet Propulsion Laboratory in
Pasadena, said this La Niña is expected to be mild, although it is already
proving temperamental.
The current ocean cooling is bringing drier, cooler, foggier weather to coastal
California, suggesting that the gray June gloom that Los Angeles has been
experiencing probably won't lift anytime soon.
In the spring, cooler ocean temperatures contrast with warmer urban coastal
areas, resulting in gray fog being drawn inland. Patzert said if La Niña
conditions persist, the tendency for "gloom" may last into August.
Evidence of cooler ocean temperatures comes from special buoys scattered
throughout the equatorial Pacific. Satellites also precisely measure the height
of the ocean's surface. Differences in the sea height indicate changes in
temperature because colder water takes up less space. Lower sea surface heights
are an indication of cooler ocean surface temperatures.
The cooling of the Pacific causes the jet stream, responsible for weather
patterns across North America, to enter the United States from the Northwest, dive
down into the Midwest and then head back up the East Coast. This pattern causes
storms throughout the Midwest and East, but bypasses the Southwest, resulting
in drought conditions in California.
Kousky said the current weather system will cause more thunderstorms in Ohio
and Tennessee and, if conditions persist, possibly increased hurricane activity
for the East Coast. Wetter than normal conditions may also develop over
northern Australia, Indonesia and southeastern Africa later this year.
Lately, the Southwest has been stuck in a dry spell, the result of the 1998 La
Niña, which persisted until last year when a moderate El Niño temporarily
returned conditions to normal.
This drought and the recent attack of June gloom may be part of a bigger
weather transition, Patzert said. A 50-year cycle know as the Pacific Decadal
Oscillation seems to be entering a cooler phase last seen a half-century ago.
In the 1980s and 1990s, Los Angeles International Airport reported an average
of 20 fog days each year. In the 1950s and 1960s, 40 fog days a year was the
norm.
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