NRL Scientists Study the Changing Sun

3/17/2003 - 20-03r
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NRL scientists study variations in the Sun and how this variability affects the Earth's global climate and space weather. Changes observed in the Sun over time impact us today and have implications for policy-making on global change, the economics of space-based technologies, and national defense.

In 1610, Galileo determined from observations of dark spots on its surface that the Sun was changing. In 1854, amateur astronomer, Heinrich Schwabe, reported that sunspots undergo an 11-year cycle of activity. In the 20th century, a far broader perspective of the changing Sun emerged.

Sunspots are but one of numerous phenomena linked to the Sun's magnetic field, whose changes during the activity cycle are driven by a sub-surface dynamo. Knowledge of the changing Sun exploded with access to space-enabled, continuous observations unobstructed by the Earth's atmosphere - at short wavelengths, and with accuracy and precision unattainable from the ground.

Space-based radiometric measurements established that even the solar "constant" - the total electromagnetic energy from the Sun and the primary source of Earth's energy - changes, increasing by one-tenth percent during recent cycle maxima. The entire electromagnetic spectrum contributes to these changes in different ways, depending on wavelength, with short-wavelength, extreme ultraviolet (EUV) and X-ray radiation changing by factors of two to ten during the activity cycle.

EUV and X-ray images of the Sun revealed large-scale brightness distributions in the outer solar atmosphere - the corona - traceable to magnetic fields at the surface. The organization, outward extension and expansion of magnetic fields are now known to structure the entire solar atmosphere and generate solar change. Depending on the magnetic field configuration, the Sun's outer atmosphere can extend into the heliosphere, the region of space produced by the solar wind.

Magnetic flux and plasma flowing through open fields comprise the solar wind, whose speed and density also change during the activity cycle. Magnetic fields in the Sun's atmosphere at times reconfigure and reconnect dramatically on very short time scales, releasing large fluxes of electromagnetic and particle radiation - flares - and plasma - coronal mass ejections. Such short-term events are superimposed on the more slowly evolving changes arising from the varying amount and strength of magnetic flux during the activity cycle.

Proxy records of solar activity produced by heliospheric modulation of galactic cosmic rays suggest that 11-year activity cycles may themselves be superimposed on larger changes on time scales of centuries to millennia. Knowing how and why the Sun's energy changed in the past -- and how it may change in the future --is important for reliable climate change attribution and for improved utilization of technologies in space.

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The U.S. Naval Research Laboratory provides the advanced scientific capabilities required to bolster our country's position of global naval leadership. The Laboratory, with a total complement of approximately 2,500 personnel, is located in southwest Washington, D.C., with other major sites at the Stennis Space Center, Miss., and Monterey, Calif. NRL has served the Navy and the nation for over 90 years and continues to advance research further than you can imagine. For more information, visit the NRL website or join the conversation on Twitter, Facebook, and YouTube.

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