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Topic Name: Nasa satellite shows regional variation in warming from sun during solar cycle

Category: STAR (Space, Telecommunications & Radioscience)

Research persons: Tom Woods, Judith Lean

Location: Laboratory for Atmospheric and Space Physics, University of Colorado, United States

Details

A NASA satellite designed, built and controlled by the University of Colorado at Boulder is expected to help scientists resolve wide-ranging predictions about the coming solar cycle peak in 2012 and its influence on Earth's warming climate, according to the chief scientist on the project.

Senior Research Associate Tom Woods of CU-Boulder's Laboratory for Atmospheric and Space Physics said the brightening of the sun as it approaches its next solar cycle maximum will have regional climatic impacts on Earth. While some scientists predict the next solar cycle -- expected to start in 2008 -- will be significantly weaker than the present one, others are forecasting an increase of up to 40 percent in the sun's activity, said Woods.

Woods is the principal investigator on NASA's $88 million Solar Radiation and Climate Experiment, or SORCE, mission, launched in 2003 to study how and why variations in the sun affect Earth's atmosphere and climate. In August, NASA extended the SORCE mission through 2012. The extension provides roughly $18 million to LASP, which controls SORCE from campus by uploading commands and downloading data three times daily to the Space Technology Building in the CU Research Park.

Solar cycles, which span an average of 11 years, are driven by the amount and size of sunspots present on the sun's surface, which modulate brightness from the X-ray to infrared portion of the electromagnetic spectrum. The current solar cycle peaked in 2002.

Solar activity alters interactions between Earth's surface and its atmosphere, which drive global circulation patterns, said Woods. While warming on Earth from increased solar brightness is modest compared to the natural effects of volcanic eruptions, cyclical weather patterns like El Nino or human emissions of greenhouse gases, regional temperature changes can vary by a factor of eight.

During the most recent solar maximum, for example, the global mean temperature rise on Earth due to solar-brightness increases was only about 0.2 degrees Fahrenheit, said Woods. But parts of the central United States warmed by 0.7 degrees F, and a region off the coast of California even cooled slightly. A paper on the coming decade of solar activity by Woods and Judith Lean of the Naval Research Laboratory in Washington, D.C., was published online Oct. 30 in the scientific newsletter, Eos.

"It was very important to the climate change community that SORCE was extended, because it allows us to continue charting the solar irradiance record in a number of wavelengths without interruption," Woods said. "Even relatively small changes in solar output can significantly affect Earth because of the amplifying affect in how the atmosphere responds to solar changes."

With mounting concern over the alteration of Earth's surface and atmosphere by humans, it is increasingly important to understand natural "forcings" on the sun-Earth system that impact both climate and space weather, said Woods. Such natural forcing includes heat from the sun's radiation that causes saltwater and freshwater evaporation and drives Earth's water cycle.

Increases in UV radiation from the sun also heat up the stratosphere -- located from 10 miles to 30 miles above Earth -- which can cause significant changes in atmospheric circulation patterns over the planet, affecting Earth's weather and climate, he said. "We will never fully understand the human impact on Earth and its atmosphere unless we first establish the natural effects of solar variability."

SORCE also is helping scientists better understand violent space weather episodes triggered by solar flares and coronal mass ejections that affect the upper atmosphere and are more prevalent in solar maximum and declining solar cycle phases, said Woods. The severe "Halloween Storms" in October and November 2003 disrupted GPS navigation and communications, causing extensive and costly rerouting of commercial "over-the-poles" jet flights to lower latitudes, he said.

Woods also is the principal investigator on a $30 million instrument known as the Extreme Ultraviolet Variability Experiment, or EVE, one of three solar instruments slated for launch on NASA's Solar Dynamic Observatory in December 2008. Designed and built at LASP and delivered to NASA's Goddard Space Flight Center in Maryland last September, EVE will measure precise changes in the sun's UV brightness, providing space weather forecasters with early warnings of potential communications and navigation outages.

About one-third of the annual SORCE budget goes for commanding and controlling the satellite, roughly one-third for producing public data sets and one-third for analyzing how and why the sun is changing, he said. "CU-Boulder students are our lifeblood," said Woods. "They are involved in all aspects of the SORCE mission, from uploading commands to the spacecraft to analyzing data."

Note for Climate change

Climate change refers to the variation in the Earth's global climate or in regional climates over time. It describes changes in the variability or average state of the atmosphere over time scales ranging from decades to millions of years. These changes can be caused by processes internal to the Earth, external forces (e.g. variations in sunlight intensity) or, more recently, human activities.

In recent usage, especially in the context of environmental policy, the term "climate change" often refers to changes in modern climate which according to the IPCC are 90-95% likely to have been in part caused by human action. Consequently the term anthropogenic climate change is frequently adopted; this phenomenon is also referred to in the mainstream media as global warming. In some cases, the term is also used with a presumption of human causation, as in the United Nations Framework Convention on Climate Change (UNFCCC). The UNFCCC uses "climate variability" for non-human caused variations.

For information on temperature measurements over various periods, and the data sources available, see temperature record. For attribution of climate change over the past century, see attribution of recent climate change.

Note for solar cycle

The solar cycle, or the solar magnetic activity cycle, is the dynamical engine and energy source behind all solar phenomena driving space weather. Powered by a hydromagnetic dynamo process relying on the inductive action of internal solar flows, the solar cycle

• structures the sun's atmosphere, corona and wind;
• modulates the solar irradiance;
• modulates the flux of short-wavelength solar radiation, from ultraviolet to X-Ray;
• modulates the occurrence frequency of flares, coronal mass ejections, and other geoeffective solar eruptive phenomena;
• indirectly modulates the flux of high-energy galactic cosmic rays entering the solar system.

About Solar Radiation and Climate Experiment

The Solar Radiation and Climate Experiment (SORCE) is a NASA-sponsored satellite mission that provides state-of-the-art measurements of incoming x-ray, ultraviolet, visible, near-infrared, and total solar radiation. The measurements provided by SORCE specifically address long-term climate change, natural variability and enhanced climate prediction, and atmospheric ozone and UV-B radiation. These measurements are critical to studies of the Sun; its effect on our Earth system; and its influence on humankind.

SORCE measures the Sun's output with the use of state-of-the-art radiometers, spectrometers, photodiodes, detectors, and bolometers engineered into instruments mounted on a satellite observatory. The SORCE satellite orbits around the Earth accumulating solar data. Spectral measurements identify the irradiance of the Sun by characterizing the Sun's energy and emissions in the form of color that can then be translated into quantities and elements of matter. Data obtained by the SORCE experiment can be used to model the Sun's output and to explain and predict the effect of the Sun's radiation on the Earth's atmosphere and climate.

About Researcher:

Dr. Judith Lean

Dr. Judith Lean is a solar physicist at U.S. Naval Research Laboratory in Washington, D.C., who specializes in the study of the variability of solar radiation. She chaired a recent study on solar influences on global change for the National Research Council. E-mail: lean@ demeter.nrl.navy.mil Dr. David Rind is a physicist at the NASA Goddard Institute for Space Studies in New York City, whose interests are in modeling the sensitivity of the atmosphere and climate to different forcings.

E-mail: cddhr@giss.nasa.gov