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Effects of irrigation on regional climate
Laboratory scientists Celine Bonfils and David Lobell have found that the rapid expansion of irrigated land in the 20th century has had a cooling effect on California’s Central Valley. Although irrigation affects a worldwide land area comparable to urbanization, its regional climatic effects have been much less studied. Scientists have lacked adequate information to incorporate irrigation into regional climate change projections and to help explain historical trends. “Globally, we derive 40 percent of our food from irrigated regions, so we’d like to be able to model future climate changes in these regions,” says Bonfils.

Using data from observations of temperature and irrigation trends throughout the state, the authors demonstrated a clear irrigation-induced cooling in agricultural areas and showed that this effect has recently slowed down. In the San Joaquin Valley (the southern portion of the Central Valley), a cooling of 1.8 to 3.2°C has occurred since irrigation was introduced in 1887. The results of the study, which appeared in the August 21, 2007, edition of the Proceedings of the National Academy of Sciences, suggest that this pattern applies to major irrigated regions worldwide.

According to Bonfils and Lobell, the amount of irrigated land in California has stabilized in recent decades, so the suppression of greenhouse warming will gradually lessen in the future. A potential decrease in irrigation may even contribute to a more rapid warming. Changes in irrigation alone are not expected to influence broad-scale temperature patterns, but they may introduce major uncertainties into climate projections in agricultural regions using irrigation.

Contact: Celine Bonfils (925) 423-9923 (bonfils2@llnl.gov).


Successful Phoenix pulsed-power shot in Nevada
On August 4, 2007, at the Laboratory’s Big Explosive Experimental Facility at the Nevada Test Site, a team successfully executed helical hydrodynamic test one, or HHT-1. A hydrodynamic test is a nonnuclear scientific experiment that shows how materials react to high-explosives detonation. Hydrodynamic refers to the fluidlike flow of solids under the influence of such an explosion. The shot was the first in a series of tests as part of the Phoenix Project, which will use a pulsed-power system to drive Livermore’s isentropic compression experiments.

The Phoenix research is intended to examine the properties of materials at extreme pressures. The focus of HHT-1 was to test a new helical generator system that will be used in future experiments. Program Manager Scott McAllister says, “All of the test data were successfully recorded, and the helical generator performed exactly as predicted.”

Livermore participants included McAllister, David Reisman, Fred Ellsworth, David Goerz, and Leon Berzins. In addition, major contributions from other organizations in the Department of Energy complex and the Department of Defense were important components of the test’s success.

Contact: Scott McAllister (925) 422-3807 (mcallister1@llnl.gov).


Most energetic laser bay commissioned
In late July, at the National Ignition Facility (NIF), control room operators fired a series of laser shots using a group of eight beams known as bundle 44. The infrared energy output of each beam was approximately 22 kilojoules. This achievement successfully brought to a close the sequential testing of all 96 beams in Laser Bay 2, one of NIF’s two laser bays. “With the success of this test, NIF is the world’s highest energy laser,” says Thomas D’Agostino, head of the National Nuclear Security Administration (NNSA). “The day is coming soon when we will be able to simulate the conditions of extreme temperature and pressure approaching those existing in nuclear explosions.”

The next step will be to repeat the process in NIF’s other laser bay now that the installation of optics and other components in that laser bay is about 90 percent complete. Overall commissioning is scheduled for June 2009, according to NIF’s commissioning manager, Bruno Van Wonterghem. A series of experiments called “Eos” will use the first set of beams from the completed laser bay to validate the performance of NIF’s targets.

NIF will convert the infrared energy from its 192 laser beams to 1.8 megajoules of ultraviolet energy. When delivered to millimeter-size targets at the center of NIF’s target chamber, this energy will create conditions similar to those in the core of stars and inside exploding nuclear weapons. In addition to supporting NNSA’s stockpile stewardship program, NIF will provide opportunities to conduct fusion energy research and to explore regimes of high-energy-density physics in the laboratory.

Contact: Chris Haynam (925) 423-2085 (haynam1@llnl.gov) or Bruno Van Wonterghem (925) 423-9494 (vanwonterghem1@llnl.gov).

 

 


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