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Krishna Ramanujan					For Release:
Goddard Space Flight Center, Greenbelt, Md.		March 6, 2003
(Phone: 301/286-3026)
Kramanuj{at}pop900.gsfc.nasa.gov

Release No: 03- 24

NASA-FUNDED RESEARCH LOOKING AT EL NINO EVENTS TO FORECAST WESTERN
U.S. SNOWFALL

A NASA-funded study uses a computer model to understand an observed
link between winter and spring snowfall in the Western U.S. and El
Nino Southern Oscillation. Almost 75 to 85 percent of water resources
in the Western U.S comes from snow that accumulates in the winter and
early spring and melts as runoff in spring and summer. Understanding
this connection and using it to predict future snowfall rates would
greatly help both citizens and policy makers.

One of the missions of NASA's Earth Science Enterprise (ESE), which
funded this research, is to better understand how the Earth system is
changing. Within this framework, NASA is committed to studying
variability in the water cycle, how well we can predict future changes 
in the Earth system and the consequences of change in the Earth system 
for human civilization.

Lead authors Jiming Jin and Norman Miller of the U.S. Department of
Energy's Lawrence Berkeley National Laboratory, Berkeley, Calif., in
collaboration with Soroosh Sorooshian and Xiaojang Gao at the
University of Arizona, Tucson, find that higher and lower tropical
Pacific sea surface temperatures (SSTs) that characterize El Nino and
La Nina change atmospheric wind patterns in the mid-latitudes in
winter and spring, shift the way moist air gets transported in the
atmosphere, and directly affect Western U.S. precipitation and snow
accumulation.

El Nino / Southern Oscillation (ENSO) marks a see-saw shift in surface 
air pressure between Darwin, Australia and the South Pacific Island of 
Tahiti. When the pressure is high at Darwin it is low at Tahiti and 
vice versa. El Nino, and its sister event La Nina, are the extreme 
phases of this southern oscillation, with El Nino referring to a 
warming of the eastern tropical Pacific, and La Nina a cooling.

By better understanding the connections between these processes,
scientists can update their computer climate models to improve their
ability to forecast future snowfall and water availability in the
west.

"If the computer climate models can accurately describe the processes
that connect ENSO and snowpack in the Western U.S., then the model can 
be used to predict the impact of ENSO on snowfall in those areas," 
said Jin. "In addition, the model can give us more detailed
information than observations, which can lead to a further
understanding of those observed processes."

The researchers entered over 45 years of data from 1949 to 1995 into
their computer climate model. They included observed global sea
surface temperatures, wind data, the amount of water contained in
snowpack for the beginning of the first four months of each year from
over 300 western U.S. field sites, and precipitation and surface air
temperature observations.

They also used NASA-derived Normalized Difference Vegetation Index
(NDVI) data for improved model predictions. NDVI measures the amount
of solar energy reflected and absorbed by vegetation. NDVI was created 
by Compton Tucker of NASA Goddard, using data from the National 
Oceanic and Atmospheric Administration=92s (NOAA) Geostationary 
Environmental Orbiting Satellite (GOES) Advanced Very High Resolution 
Radiometer (AVHRR) instrument. The data used in this research also 
comes from the Moderate Imaging Spectroradiometer (MODIS) instrument 
aboard NASA's Terra satellite.

During the weak ENSO episodes, Washington, Oregon, Idaho, and Montana
experienced decreased precipitation during weak El Ninos, and
increased precipitation during the opposite La Nina phase. During the
strong El Nino episodes, stronger winter and spring precipitation was
found south of Sacramento, including parts of California, Nevada,
Utah, Colorado and all of Arizona and New Mexico. However, during
strong La Nina events, the researchers did not find any changes to
precipitation patterns in the western U.S.

The model matched well with actual observations except when it came to 
weak ENSO episodes, including both El Nino and La Nina. During those 
events, the mid-latitude atmosphere in the model reacted too strongly 
to the shifts in tropical Pacific SSTs, and moist air masses from that 
region moved incorrectly. Still, it shows that different intensities 
of ENSO episodes have differing affects on western U.S.  snowfall. The 
researchers hope to fine-tune the model's responses in the future.

This research may yield a forecast tool that greatly benefits citizens 
and water resource managers in the Western U.S. Jin and Miller are 
currently developing new snow assimilation techniques that show 
improved forecast skill, which they hope will make water allocation 
decisions more accurate and cost efficient.

These findings were presented at the 83rd Annual Meeting of the
American Meteorological Society in Long Beach, Calif.

This research was funded by NASA's ESE Interdisciplinary Science and
Applications Programs. The Applications Division applies the results
of the nation's investment in ESE to issues of national concern, such
as environmental quality, resource management, community growth, and
disaster management to support policy makers at the state and local
levels.

For more information, please see:
http://www.gsfc.nasa.gov/topstory/2003/0210snowpack.html

Normalized Difference Vegetation Index (NDVI)
http://daac.gsfc.nasa.gov/CAMPAIGN_DOCS/LAND_BIO/ndvi..html

NASA's Terra Satellite
http://terra.nasa.gov/

The Advanced Very High Resolution Radiometer
http://www.ngdc.noaa.gov/seg/globsys/avhrr.shtml

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