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Solar and Space Physics: A Science for a Technological Society
REPORT OF THE PANEL ON SOLAR AND HELIOSPHERIC PHYSICS
285
are not easily reached, but a successful investment in this decade in solar-sail technology (§10.5.2.8) will
enable effective long-term use of high-inclination orbits in the 2020s to probe portions of the solar interior
that are important for the solar cycle.
Magnetic fields at the visible surface of the Sun—the photosphere—have been studied for decades.
The well-observed photosphere links the obscured internal sources of activity with the faint corona and
sparsely sampled heliosphere. Conditions measured in this narrow layer provide scientists’ main insights
into the origin of the solar cycle and sources of space weather. One long-standing goal is to understand
how magnetically active regions erupt and disperse at the surface. There are major uncertainties about
the influence of small spatial-scale magnetic fields on the solar cycle and on TSI. Open issues include
how much small-scale fields contribute to the magnetic and TSI budgets of the Sun and how their properties change over the course of a solar cycle (SHP action 1c). Attacking that frontier is a major goal of the
4-meter-aperture Advanced Technology Solar Telescope (ATST).
An important societal goal is to improve the quality of real-time models of the solar magnetic field
to assist in forecasting space weather events and heliospheric conditions (motivation M2). Those models
use observed magnetic boundary conditions as the basis of outward extrapolation of the magnetic field.
Improving the quality and extending the measurements above the surface with optical and radio methods
are goals that will lead to better understanding and improved space weather forecasts. At present, limited
measurements of the solar magnetic field are made by a few ground-based observatories and with the
Hinode and SDO space missions. Augmenting those measurements with ground-based data from the proposed FASR and COSMO facilities, along with the space-based data from the proposed JAXA-led Solar-C
mission, would greatly contribute to meeting the goal.
Great strides in understanding stellar interiors and activity cycles have been made with new highprecision measurements of oscillations and variability. A goal for the next decade is to use such observations to help solve fundamental questions about the dynamo process, internal structure and dynamics,
rotation, and activity cycles of stars similar to the Sun. Information from a broad array of stars will sharpen
understanding of the Sun’s physics (motivation M3).
10.4.2 Determine How the Sun’s Magnetism Creates Its Dynamic Atmosphere
Section 10.3.2 describes a few of the impressive advances of the past decade, but researchers are
still far from understanding how the Sun’s variable magnetic field structures and powers an atmosphere
that extends from the bottom of the chromosphere out to the distant boundaries of the heliosphere. For
example, how the corona couples dynamically to the solar wind is uncertain. The chromosphere clearly
plays an important role in the injection of energy into the corona, but it is observed only in a narrow way
and is poorly understood. The mechanisms that heat the corona and accelerate the wind constitute one
of the central problems in all space science. It is expected that in the coming decade the revolutionary
new observations from the missions and projects discussed in this survey, combined with next-generation
theory and models, will resolve many of these outstanding problems.
To make progress in understanding the solar wind’s dynamics and structure, it is necessary to go as
close to the Sun as possible to measure the properties of the wind at its origin (motivations M1-M3). That
is the goal of Solar Probe Plus and Solar Orbiter, new missions that will each make unique observations
of the structure and evolution of the connection between the corona and interplanetary space. SPP will
measure solar wind characteristics well within the Alfvén radius where the solar magnetic field still controls
the dynamics of the wind. The probe will truly be a discovery mission in that it will explore a region of
the heliosphere that has never been visited before. Solar Orbiter will bring a suite of instruments designed
for coordinated in situ and remote imaging both close to the Sun and out of the ecliptic plane.
Solar and Space Physics: A Science for a Technological Society
REPORT OF THE PANEL ON SOLAR AND HELIOSPHERIC PHYSICS
285
are not easily reached, but a successful investment in this decade in solar-sail technology (§10.5.2.8) will
enable effective long-term use of high-inclination orbits in the 2020s to probe portions of the solar interior
that are important for the solar cycle.
Magnetic fields at the visible surface of the Sun—the photosphere—have been studied for decades.
The well-observed photosphere links the obscured internal sources of activity with the faint corona and
sparsely sampled heliosphere. Conditions measured in this narrow layer provide scientists’ main insights
into the origin of the solar cycle and sources of space weather. One long-standing goal is to understand
how magnetically active regions erupt and disperse at the surface. There are major uncertainties about
the influence of small spatial-scale magnetic fields on the solar cycle and on TSI. Open issues include
how much small-scale fields contribute to the magnetic and TSI budgets of the Sun and how their properties change over the course of a solar cycle (SHP action 1c). Attacking that frontier is a major goal of the
4-meter-aperture Advanced Technology Solar Telescope (ATST).
An important societal goal is to improve the quality of real-time models of the solar magnetic field
to assist in forecasting space weather events and heliospheric conditions (motivation M2). Those models
use observed magnetic boundary conditions as the basis of outward extrapolation of the magnetic field.
Improving the quality and extending the measurements above the surface with optical and radio methods
are goals that will lead to better understanding and improved space weather forecasts. At present, limited
measurements of the solar magnetic field are made by a few ground-based observatories and with the
Hinode and SDO space missions. Augmenting those measurements with ground-based data from the proposed FASR and COSMO facilities, along with the space-based data from the proposed JAXA-led Solar-C
mission, would greatly contribute to meeting the goal.
Great strides in understanding stellar interiors and activity cycles have been made with new highprecision measurements of oscillations and variability. A goal for the next decade is to use such observations to help solve fundamental questions about the dynamo process, internal structure and dynamics,
rotation, and activity cycles of stars similar to the Sun. Information from a broad array of stars will sharpen
understanding of the Sun’s physics (motivation M3).
10.4.2 Determine How the Sun’s Magnetism Creates Its Dynamic Atmosphere
Section 10.3.2 describes a few of the impressive advances of the past decade, but researchers are
still far from understanding how the Sun’s variable magnetic field structures and powers an atmosphere
that extends from the bottom of the chromosphere out to the distant boundaries of the heliosphere. For
example, how the corona couples dynamically to the solar wind is uncertain. The chromosphere clearly
plays an important role in the injection of energy into the corona, but it is observed only in a narrow way
and is poorly understood. The mechanisms that heat the corona and accelerate the wind constitute one
of the central problems in all space science. It is expected that in the coming decade the revolutionary
new observations from the missions and projects discussed in this survey, combined with next-generation
theory and models, will resolve many of these outstanding problems.
To make progress in understanding the solar wind’s dynamics and structure, it is necessary to go as
close to the Sun as possible to measure the properties of the wind at its origin (motivations M1-M3). That
is the goal of Solar Probe Plus and Solar Orbiter, new missions that will each make unique observations
of the structure and evolution of the connection between the corona and interplanetary space. SPP will
measure solar wind characteristics well within the Alfvén radius where the solar magnetic field still controls
the dynamics of the wind. The probe will truly be a discovery mission in that it will explore a region of
the heliosphere that has never been visited before. Solar Orbiter will bring a suite of instruments designed
for coordinated in situ and remote imaging both close to the Sun and out of the ecliptic plane.