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March 1998

Science Briefing

From AAAS: The van Loon-Labitzke correlations pass muster down under

The sun's 11-year solar cycle may be driving periodic changes in the earth's lower stratosphere from pole to pole, according to a new analysis by NCAR's Harry van Loon and Karin Labitzke of the Free University of Berlin (FUB). The findings were presented on 14 February at the annual meeting of the American Association for the Advancement of Science (AAAS) in Philadelphia.

Harry van Loon

The two scientists had previously related a 10- to 12-year oscillation in the stratosphere of the Northern Hemisphere to four 11-year solar cycles, beginning in 1958. Now, with the help of the vast data reanalysis conducted by NCAR and the National Centers for Environmental Prediction, Harry and Labitzke have revealed a mirror image of the solar-stratosphere correlations in the Southern Hemisphere, spanning three solar cycles from 1968 to 1996.

Harry and Labitzke used the flux in the 10.7-centimeter radio waveband, an objectively observed quantity highly correlated with the 11-year cycle. They compared these radio data with FUB's daily analyses of the stratosphere. The results show a strong correlation between the solar cycle and the 10- to 12-year oscillation of two quantities in the lower stratosphere: mean temperatures (particularly during each hemisphere's summer) and constant pressure heights above sea level.

The new findings, say Harry, "increase our confidence that the solar-stratospheric relationship is more than a statistical coincidence." For many years scientists have tried to find an earthly link to the sun's 11-year cycle. Previous attempts have turned up humorous correspondences to the number of Republicans in the House of Representatives and the length of women's skirts. Until Harry and Labitzke's work, even serious scientific stabs at the problem eventually proved false. A solid link takes on added significance now as scientists search for a clear sun-earth connection for computer models used to predict climate change.

"The role of the sun in climate change is still an unsolved problem," says Harry. "Any relationship between changes in solar output and what happens here on earth is important for understanding long-term climate." The sun's output has varied about 0.1% over one solar cycle during the past several decades. Over centuries, however, larger variations may occur.

Also from AAAS: New insight on the sun's output

Until now, there's been a lot of uncertainty about the way the sun's radiation varies over time. HAO scientist Peter Fox and colleagues are using precise observations, theoretical atomic physics, and computer modeling to get the best representation so far of the total radiative output of the sun (including the ultraviolet, visible light, and infrared wavelengths that reach the earth).
Peter Fox

"This is a step towards quantifying what the entire sun is doing, which will give us a better understanding of the sun's influence on earth's climate," says Peter. He presented the findings of his research (with HAO's Oran White, HAO consultant Juan Fontenla of US West, and Eugene Avrett of the Smithsonian Astrophysical Observatory) on 14 February at AAAS.

To represent more accurately the physical processes of the entire surface of the sun, the NCAR team is taking a detailed look at how individual features, like sunspots, change the amounts of radiation in several different wavelengths. The team uses observations from the precision solar photometric telescope (PSPT), combined with computer modeling that incorporates prior observations and solar physics theory. The PSPT is operated by HAO at its Mauna Loa Solar Observatory in Hawaii as part of NSF's Radiative Input from the Sun to the Earth (SunRISE) program.

"Tree rings and ice cores tell us a little about variations in the sun over centuries. But we have only the 11-year sunspot record for the last 300 years to link directly to today's sun, and we don't have direct measurements of the radiation before the 1970s," Peter explains. The new information will

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Edited by Bob Henson, bhenson@ucar.edu

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