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Solar and Space Physics: A Science for a Technological Society
286
SOLAR AND SPACE PHYSICS: A SCIENCE FOR A TECHNOLOGICAL SOCIETY
The chromosphere is another key region of our home in space that has yet to be understood. Major
goals for the upcoming decade are to measure the structure and dynamics of the chromosphere accurately
and to understand their role in the origin of the heat and mass fluxes into the corona and wind (motivation
M1). Attacking those problems requires simultaneous observation of emission from the photosphere to the
corona at high spatial, temporal, and spectral resolution. That is the motivating strategy for Solar-C and for
the IRIS Explorer mission. IRIS will deliver pioneering observations of chromospheric dynamics in preparation for Solar-C, which will observe the full, coupled solar atmosphere, including all detailed plasma and
magnetic measures, with spatial resolution never before achieved—about 0.1 arc-seconds. With its vast
improvement in resolution and coverage, Solar-C, like SPP, will be a discovery mission.
The defining feature of the photosphere-corona system is its magnetic coupling; understanding this
coupling requires accurate measurement of the magnetic field in the corona, especially the full vector
field so that the free energy can be measured. Measurement of the coronal field has challenged solar and
heliospheric physics for decades, but with the recent advances in both ground-based and space-based
instrumentation, researchers are finally poised to meet this challenge. Solar-C will determine the vector
field in the chromosphere with high resolution and over extended duration, thereby permitting reliable
extrapolation of the field into the corona. At the same time, ATST, FASR, and COSMO would measure the
coronal magnetic field directly from the ground. With those revolutionary capabilities, it will be possible
to follow the buildup and release of magnetic energy in the corona and address many of the most fundamental questions in solar and heliospheric science and space weather, such as the physical processes that
produce flares and CMEs.
One of the fundamental questions is the origin of the thermal structure of the closed-field corona.
Researchers have long observed coronal loops but have never definitively seen the heating process, which
is expected to occur at scales well below that provided in present images. The heating process is expected
to have clear signatures in the internal structure of coronal loops. Solar-C is designed specifically to have
the spatial, temporal, and spectral resolution required to reveal this internal structure and dynamics. Those
observations will be pioneering. Simultaneously with observing the plasma structure, Solar-C, ATST, and
FASR would constrain the properties of electric currents in the corona and thereby probe the heating
mechanism itself. With those missions and projects in the coming decade, enormous progress will be
made toward achieving one of the central goals in solar and heliospheric science: understanding how the
Sun produces the hot closed corona.
10.4.3 Determine How Magnetic Energy Is Stored and Explosively Released
Solar cycle 23 was the best-observed cycle of the space era, 5 and scientists now have greatly improved
understanding of basic processes in large solar eruptions as well as more sophisticated models of these
events. However, key questions remain. Expected progress toward SHP science goal 3 is outlined below
for associated SHP actions 3a-d:
• Determine how the sudden release of magnetic energy enables both flares and CMEs to accelerate
particles to high energies efficiently. There are rather complete models of particle acceleration and transport
5 Since the last solar maximum, Hinode, STEREO, Fermi, and SDO have joined SOHO and RHESSI to provide solar imaging
over 360° with much greater spatial, temporal, and spectral resolution. In addition, in situ instruments now encircle the Sun. These
unprecedented observatories promise exciting new observations of CME and flare eruptions as solar activity increases. Expected to
come on line in the coming decade or shortly are ATST, which will measure coronal magnetic fields; SPP and Solar Orbiter, which
explore SEP, CME, and interplanetary properties near the Sun; and IMAP, a spacecraft to be placed at L1 to observe ENAs from the
heliospheric boundary region that also requires background measurements of the solar wind.
Solar and Space Physics: A Science for a Technological Society
286
SOLAR AND SPACE PHYSICS: A SCIENCE FOR A TECHNOLOGICAL SOCIETY
The chromosphere is another key region of our home in space that has yet to be understood. Major
goals for the upcoming decade are to measure the structure and dynamics of the chromosphere accurately
and to understand their role in the origin of the heat and mass fluxes into the corona and wind (motivation
M1). Attacking those problems requires simultaneous observation of emission from the photosphere to the
corona at high spatial, temporal, and spectral resolution. That is the motivating strategy for Solar-C and for
the IRIS Explorer mission. IRIS will deliver pioneering observations of chromospheric dynamics in preparation for Solar-C, which will observe the full, coupled solar atmosphere, including all detailed plasma and
magnetic measures, with spatial resolution never before achieved—about 0.1 arc-seconds. With its vast
improvement in resolution and coverage, Solar-C, like SPP, will be a discovery mission.
The defining feature of the photosphere-corona system is its magnetic coupling; understanding this
coupling requires accurate measurement of the magnetic field in the corona, especially the full vector
field so that the free energy can be measured. Measurement of the coronal field has challenged solar and
heliospheric physics for decades, but with the recent advances in both ground-based and space-based
instrumentation, researchers are finally poised to meet this challenge. Solar-C will determine the vector
field in the chromosphere with high resolution and over extended duration, thereby permitting reliable
extrapolation of the field into the corona. At the same time, ATST, FASR, and COSMO would measure the
coronal magnetic field directly from the ground. With those revolutionary capabilities, it will be possible
to follow the buildup and release of magnetic energy in the corona and address many of the most fundamental questions in solar and heliospheric science and space weather, such as the physical processes that
produce flares and CMEs.
One of the fundamental questions is the origin of the thermal structure of the closed-field corona.
Researchers have long observed coronal loops but have never definitively seen the heating process, which
is expected to occur at scales well below that provided in present images. The heating process is expected
to have clear signatures in the internal structure of coronal loops. Solar-C is designed specifically to have
the spatial, temporal, and spectral resolution required to reveal this internal structure and dynamics. Those
observations will be pioneering. Simultaneously with observing the plasma structure, Solar-C, ATST, and
FASR would constrain the properties of electric currents in the corona and thereby probe the heating
mechanism itself. With those missions and projects in the coming decade, enormous progress will be
made toward achieving one of the central goals in solar and heliospheric science: understanding how the
Sun produces the hot closed corona.
10.4.3 Determine How Magnetic Energy Is Stored and Explosively Released
Solar cycle 23 was the best-observed cycle of the space era, 5 and scientists now have greatly improved
understanding of basic processes in large solar eruptions as well as more sophisticated models of these
events. However, key questions remain. Expected progress toward SHP science goal 3 is outlined below
for associated SHP actions 3a-d:
• Determine how the sudden release of magnetic energy enables both flares and CMEs to accelerate
particles to high energies efficiently. There are rather complete models of particle acceleration and transport
5 Since the last solar maximum, Hinode, STEREO, Fermi, and SDO have joined SOHO and RHESSI to provide solar imaging
over 360° with much greater spatial, temporal, and spectral resolution. In addition, in situ instruments now encircle the Sun. These
unprecedented observatories promise exciting new observations of CME and flare eruptions as solar activity increases. Expected to
come on line in the coming decade or shortly are ATST, which will measure coronal magnetic fields; SPP and Solar Orbiter, which
explore SEP, CME, and interplanetary properties near the Sun; and IMAP, a spacecraft to be placed at L1 to observe ENAs from the
heliospheric boundary region that also requires background measurements of the solar wind.