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The Solar Atmosphere

Earth is shown as a relatively small dot within the teardrop-shaped cavity of the magnetosphere in this illustration. The flow of particles from the Sun known as the solar wind gives the magnetosphere its shape. The Sun's turbulent atmosphere, at more than a million degrees C, is a place of constant churning and frequent explosions. Loops of magnetic fields arc above the surface, filled with clouds of electrified gas. Known as plasma, the electrified gas forms when temperatures become so hot that atoms break apart into charged particles. The charged plasma particles are blown away from the Sun in every direction, moving millions of miles per hour—which is enough speed to escape the gravitational pull of the Sun. This vast flow is known as the solar wind, and it extends beyond the far reaches of our solar system.

The Sun’s outer atmosphere, or corona is visible from the ground only during a total solar eclipse (or an artificial eclipse created by a specialized telescope called a coronagraph), when it appears as a pale cloud encircling the Sun. But whether or not an eclipse is in progress, observers should never look directly at the Sun. Even after traveling 93 million miles, the energy we call sunlight can damage the eye. NCAR's Advanced Coronal Observing System observes the corona in several different wavelengths daily.

NCAR researchers are working on an instrument, known as a multichannel polarimeter, designed to examine the Sun’s magnetic fields by focusing on wavelengths emitted by a type of iron that is a common and easily visible solar element. The polarimeter will give researchers insights into the forces that twist and ultimately tear apart magnetic loops.

When the solar wind leaves the corona, it flows around obstacles such as planets. Those planets—each with its own magnetic field—respond in particular ways. The shape of Earth's magnetic field resembles the pattern formed when iron filings align around a bar magnet. Under the influence of the solar wind, Earth's magnetic field lines are compressed in the direction of the Sun and stretched out downwind. This creates the magnetosphere, a complex, teardrop-shaped cavity around Earth.

The solar wind also has profound impacts on Earth’s upper atmosphere, a region known as the mesosphere and lower thermosphere/ionosphere. This zone, 40–110 miles (60–180 km) above Earth’s surface, is difficult to probe. Ground-based instruments can detect only a small portion of it, and sounding rockets provide just a brief picture of the region before falling back into the lower atmosphere. Scientists want to know more about the upper atmosphere, partly to bolster communications networks and help keep satellites on course, and partly to learn how it influences temperature and energy in the lower atmosphere.

Researchers capture data on the mesosphere and lower thermosphere/ionosphere in a variety of ways. One of the most important research tools is a NASA satellite named TIMED (Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics). The four instruments on board measure winds, temperatures pressure, energy from auroras, information on the chemistry of important gases, and other features. NCAR scientists developed and run TIDI (TIMED's Doppler Interferometer), which measures the speed and direction of high-atmosphere winds across the globe. Researchers expect measurements from TIDI to shed light on other related phenomena at the edge of Earth's atmosphere.

NCAR scientists are incorporating TIMED data into computer models being developed to better represent the complex physical and chemical processes in the upper atmosphere.