Cooling Summer Daytime Temperatures in Coastal California During 1948-2005: Observations, Modeling, and Implications
This page finalized July 22, 2008
Chair’s Air Pollution Seminar
Tuesday, August 19, 2008
Cooling Summer Daytime
Robert Bornstein, Ph.D.
study evaluated long-term (1948-2005) air temperatures in California
during summer (June-August). The aggregate results showed
asymmetric warming, as daily minimum temperatures increased faster than
daily maximum temperatures. However, the spatial
distributions of daily maximum temperatures in the South Coast
(Southern California) and San Francisco Bay Area air basins exhibited a
complex pattern, with cooling at low-elevation coastal areas and
warming at inland areas.
Previous studies have suggested that cooling summertime maximum temperatures in coastal California were due to increased irrigation, coastal upwelling, or cloud cover. However, a current hypothesis is that this temperature pattern arises from a “reverse-reaction” to green house gas (GHG) induced global warming. In this hypothesis, the global warming of inland areas results in increased sea breeze activity in coastal areas. Average temperatures from global circulation models (GCM) show warming that decreases from inland areas of California to its coastal areas.
However, such large scale models cannot resolve these smaller scale topographic and coastal effects. Meso-scale modelling on a 4 km grid is thus being carried out to evaluate the contributions from GHG global warming and land use changes (including urban heat island development) to the observed trends. Significant societal impacts may result from this observed reverse reaction to GHG warming, and possible beneficial effects include decreased: maximum O3 levels, human thermal-stress, and energy requirements for cooling.
While Professor Bornstein will make the presentation, the study collaborators, Drs. Taha, Gonzalez, and Lebassi will also be available to respond to questions and comments.
Robert Bornstein, Ph.D., has
served at the Department of Meteorology at San Jose State University
since 1969. Professor Bornstein’s research has included modeling
and observation of how urbanization creates new urban climates and how
these new climates control the spread of air pollution within urban
environments. Professor Bornstein was elected American
Meteorological Society Fellow in 2004 and was editor of "Atmospheric
Environment." Professor Bornstein is currently on the Bay Area
Air Quality Management District Technical Advisory Committee and on the
World Meteorological Organization’s Committee on Urban Climate.
Professor Bornstein's 3-D urban modeling efforts include MM5
simulations of meteorological conditions during the maximum SCOS97
ozone episode, as well as similar studies for Houston, New York City,
Atlanta, and Israel.
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