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MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109 TELEPHONE (818) 354-5011
http://www.jpl.nasa.gov http://www.jpl.nasa.gov/

Charli Schuler 818-354-3965
Jet Propulsion Laboratory, Pasadena, Calif.

News Release: 2003-016                                               =20
       February 12, 2003

NASA Scientist Clears The Fog on Gloomy Summers
===============================================

The word California invokes many images: miles of sunny beaches,
streets lined with swaying palm trees, mountains that touch the great
blue sky and cold nights filled with thick, dense fog.  What was that?
Cold? Fog?

Since the "beachgoer's dream" summers that preceded 1998, California
has experienced consistently cooler and foggier summers than usual -
not exactly grade-A performance for the coast that's supposed to have
the most.  The question many sun worshipers may be asking is, "Why?"

"History seems to be repeating itself every 50 years," said Dr.
William Patzert, an oceanographer at NASA's Jet Propulsion Laboratory
in Pasadena, Calif. "The weather switches from warmer temperatures,
wetter winters and less fog to cooler temperatures, drier winters and
more fog, and back and forth."

Patzert and colleagues Dr. Steve LaDochy and Jeff Brown from
California State University, Los Angeles, studied the factors
responsible for variable coastal temperatures and fog frequencies
along the southern California coast from 1948 to 2001. They are
presenting their findings at the 83rd Annual Meeting of the American
Meteorological Society, being held through February 13 in Long Beach,
Calif.

From the mid-1940s to the 1970s, temperatures (as measured at Los
Angeles International Airport and Los Angeles Civic Center, among
other locations) were generally cooler, winters were drier and fog
levels were fairly high. In the 1980s and 1990s, temperatures warmed
up, winters were wetter and the number of foggy days each year was
halved.  Now, it seems that since the 1997-98 El Ni=F1o, we've 
returned to the previous prolonged "June Gloom" pattern.=20

"'June Gloom,' when unusually heavy coastal fog and cooler
temperatures hug the coast, occurs in the early stage of summer,"
Patzert said. "The dismal weather results from an extreme contrast
between warming land and cool ocean temperatures, when the temperature
of the land rises quickly, but the temperature of the Pacific Ocean,
which covers about one third of the earth's surface, takes longer to
heat up.  Fog, or vapor condensed into fine particles of water, is
basically a set of clouds on the ground produced by this land-sea
interaction. During some decades, the large-scale climate shifts in
the Pacific Ocean keep the California current ocean temperatures
cooler. This gives southern California more heavy fog days. The switch
to a warmer pattern results in fewer foggy days."

Patzert said studies have shown relationships between sea-surface
temperatures in the tropics and weather in the United States, but
several other oceanic measurements show even stronger connections to
Southern California temperatures. The Pacific Ocean appears to be the
most obvious factor affecting coastal temperatures and moisture. By
comparing various studies and indexed measurements of Pacific Ocean
sea surface temperature variability, Patzert and his colleagues found
strong correlations between north Pacific Ocean climate cycles and
coastal temperatures and heavy fog frequencies. Warmer eastern
tropical Pacific Ocean temperatures, for example, give us less fog.
They therefore deduced that large-scale, long-term temperature
patterns in the northern and tropical regions of the Pacific Ocean are
useful in predicting year-to-year fog conditions.

The researchers also found that while fog has been more noticeable
during the past four years, heavy fog has declined significantly since
1950, in part because of urban influences. For instance, downtown Los
Angeles temperatures have increased by approximately 2 degrees
Fahrenheit (1 degree Celsius) since 1950, and particulate air
pollution has declined by about 50 percent. This increase between the
land in the Los Angeles basin and Pacific Ocean temperatures could
explain the long-term trend in decreasing fog. This also suggests that
future urban growth, global climate change and continuing Pacific
Ocean cycles may significantly affect future coastal weather in
Southern California.

Although Patzert forecasts a prolonged "June Gloom" for this summer,
he says, "There's no need to escape to the tropics just yet. As with
any cloud, there is usually a silver lining. While the past has held a
record of long-term gloomy periods, uncharacteristic mood swings have
been known to occur on a sporadic basis. Case in point: last month, in
the middle of winter, it was warm and clear enough outside for a beach
barbecue."

The California Institute of Technology in Pasadena manages JPL for
NASA.

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