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Solar Research

At NCAR, solar researchers focus on the physical processes that govern the Sun, the interplanetary environment, and the Earth's upper atmosphere to better understand Earth's space environment and our all-important star.

One of NCAR's most specialized tasks is to measure the flow of energy--both charged-particle and electromagnetic radiation--emanating from the Sun. The High Altitude Observatory (which joined NCAR shortly after the center's formation) collected pioneering data on the Sun's outer atmosphere, or corona, in the 1940s and 1950s.

Today, NCAR remains a leader in solar observing. The corona, still a key area of interest, is now recognized as the launching pad for what's called space weather. Streams of energized particles embedded in the solar magnetic field--the solar wind--blow outward from the corona to fill the whole solar system. When variations in the solar wind reach Earth's outer atmosphere, they can trigger geomagnetic storms that have a major impact on satellites, power grids, and radio signals.

Special cameras called coronagraphs use internal and external "occulters" to block the solar disk so that the fainter signal from the Sun's corona can be observed. NCAR has deployed telescopes at solar eclipses for decades but added portable coronagraphs to provide a longer observing period, since the moon only obscures the bulk of the Sun for a few minutes. The center has also sent coronal measuring tools into space. A coronagraph built for and operated by the crew aboard the Skylab space station in 1973 collected some of the first images of coronal mass ejections, the source of some of our most severe space weather.

Perched atop one of Hawaii 's two highest mountains, the Mauna Loa Solar Observatory is is a major center of solar scrutiny. The observatory, operated by NCAR since 1965, produces data-rich images of the Sun's activity on a daily basis, weather permitting.

MLSO's Advanced Coronal Observing System includes the chromospheric helium imaging photometer (CHIP) that measures changes in the chromosphere every three minutes and indirectly tracks the evolution of coronal mass ejections, as well as the Mark-IV K coronameter (Mk4), which captures the corona's behavior in the visible-light spectrum.

A key goal of solar observations is to measure the total luminosity of the Sun and the portion of that energy that reaches Earth, as well as how both of these vary over time. Toward this goal, NCAR trains instruments on the Sun's surface and its lower atmosphere, called the photosphere. At Mauna Loa, the Precision Solar Photometric Telescope (PSPT) produces images of the solar disk at three different wavelengths every five minutes. The images reveal features that affect the amount of radiation given off by the Sun. These range from dark elements, primarily sunspots, to bright features such as faculae and plages.

Solar magnetism is another area of keen interest for NCAR and its collaborators. The Sun's magnetic field, generated by rotating forces in the Sun's interior, drives solar activity and shapes the solar atmosphere. NCAR scientists observe and model conditions inside the Sun by measuring wave motions with instruments such as the Experiment for Coordinated Helioseismic Observations (ECHO).

Near the Sun's surface, magnetism has been traced for over a decade by ground- and space-based instruments, such as NCAR's Advanced Stokes Polarimeter . These devices infer the magnetic field by measuring several components of visible radiation.

Sensing radiation from the corona is much more difficult, because of its comparatively weak signal. In 2004, NCAR scientists tested their new coronal multichannel polarimeter (CoMP). It promises to provide the first-ever measurements of magnetic field across the entire solar limb (the slice of the Sun's corona perpendicular to Earth).

Major effort goes into observing and modeling the effects the Sun has on the Earth's environment. NCAR researchers operate instruments at the Polar Cap Observatory and on satellites such as TIMED to measure the influence of solar radiation on the Earth's upper atmospheric winds. Powerful computer models are then used to predict how the upper winds vary and interact with the middle and lower atmosphere.

NCAR's solar researchers have also produced instruments whose vision extends far beyond the solar system. In the late 1990s, NCAR scientist Timothy Brown took a hand-built device to rural Colorado , where he made the first observations of an extrasolar planet crossing in front of its star. NCAR is now part of a group of collaborators at work analyzing the ever-increasing amounts of data on extrasolar planets.

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