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Solar and Space Physics: A Science for a Technological Society
38
2
Solar and Space Physics: Recent
Discoveries, Future Frontiers
SCOPE AND RELEVANCE OF THE DISCIPLINE
To appreciate the complex structure and evolution of Earth’s home in space, one need only look at the
striking image of the extended solar atmosphere, the corona, taken during the July 11, 2010, solar eclipse
(Figure 2.1, left panel). Turbulent convection below the Sun’s visible surface is the engine that drives the
extreme ultraviolet (EUV) and X-ray radiation and the solar wind. The solar magnetic field is churned and
twisted by this subsurface convection and in turn produces the fine-scale structure of the solar corona. The
right panel of Figure 2.1 shows magnetic lines of force from a physics-based prediction of coronal structure
based on solar surface magnetic field measurements for the same event. The correspondence between the
imaged corona and the simulated magnetic field structure is striking.
The corona is the source of both EUV radiation and the solar wind, an outward flowing plasma and
entrained magnetic field with speeds in the range of 400 to 800 kilometers per second, or around a million
miles per hour. Solar ultraviolet and X-ray radiation, for example from solar flares, reaches Earth directly
in 8 minutes, where it is absorbed in the thermosphere, the uppermost portion of Earth’s atmosphere. This
photon energy heats the thermosphere and produces the electrically conductive ionosphere within the
thermosphere. The ionosphere is linked both with the neutral atmosphere below through waves generated
in the troposphere near Earth’s surface that propagate upward through the atmosphere and with the magnetosphere above via electric currents and the flow of charged particles. In contrast with the EUV radiation,
the solar wind does not impact Earth directly but instead encounters Earth’s dipolar magnetic field, which
deflects the solar wind and channels electric currents and energetic particles to the polar regions, shielding
the middle and equatorial atmosphere.
Earth is therefore best understood not as orbiting the Sun in isolation through a vacuum, but as a physical system intimately linked to the highly variable solar atmosphere that engulfs the entire solar system.
The magnetized solar atmosphere, solar wind, and Earth’s magnetosphere, ionosphere, and atmosphere
are connected through a chain of interactions that govern the state of our space environment. Furthermore,
the Sun occasionally sends out powerful mass ejections, which are accompanied by shock waves that
accelerate charged particles to very high speeds, up to nearly the speed of light. These disturbances in the
Solar and Space Physics: A Science for a Technological Society
38
2
Solar and Space Physics: Recent
Discoveries, Future Frontiers
SCOPE AND RELEVANCE OF THE DISCIPLINE
To appreciate the complex structure and evolution of Earth’s home in space, one need only look at the
striking image of the extended solar atmosphere, the corona, taken during the July 11, 2010, solar eclipse
(Figure 2.1, left panel). Turbulent convection below the Sun’s visible surface is the engine that drives the
extreme ultraviolet (EUV) and X-ray radiation and the solar wind. The solar magnetic field is churned and
twisted by this subsurface convection and in turn produces the fine-scale structure of the solar corona. The
right panel of Figure 2.1 shows magnetic lines of force from a physics-based prediction of coronal structure
based on solar surface magnetic field measurements for the same event. The correspondence between the
imaged corona and the simulated magnetic field structure is striking.
The corona is the source of both EUV radiation and the solar wind, an outward flowing plasma and
entrained magnetic field with speeds in the range of 400 to 800 kilometers per second, or around a million
miles per hour. Solar ultraviolet and X-ray radiation, for example from solar flares, reaches Earth directly
in 8 minutes, where it is absorbed in the thermosphere, the uppermost portion of Earth’s atmosphere. This
photon energy heats the thermosphere and produces the electrically conductive ionosphere within the
thermosphere. The ionosphere is linked both with the neutral atmosphere below through waves generated
in the troposphere near Earth’s surface that propagate upward through the atmosphere and with the magnetosphere above via electric currents and the flow of charged particles. In contrast with the EUV radiation,
the solar wind does not impact Earth directly but instead encounters Earth’s dipolar magnetic field, which
deflects the solar wind and channels electric currents and energetic particles to the polar regions, shielding
the middle and equatorial atmosphere.
Earth is therefore best understood not as orbiting the Sun in isolation through a vacuum, but as a physical system intimately linked to the highly variable solar atmosphere that engulfs the entire solar system.
The magnetized solar atmosphere, solar wind, and Earth’s magnetosphere, ionosphere, and atmosphere
are connected through a chain of interactions that govern the state of our space environment. Furthermore,
the Sun occasionally sends out powerful mass ejections, which are accompanied by shock waves that
accelerate charged particles to very high speeds, up to nearly the speed of light. These disturbances in the