10

Report of the Panel on Solar and Heliospheric Physics

To grasp immediately the nature of the field of solar and heliospheric physics, one need only look at the striking image of the 2010 solar eclipse shown in Figure 10.1. The solar atmosphere extends outward from the Sun’s surface, apparently without end. In fact, this extended atmosphere—the heliosphere—does end at roughly 140 AU, where the solar wind runs into the galaxy at the heliopause. Our Earth, its upper atmosphere, and its magnetosphere—and the other planets of the solar system—are all embedded deep inside this extended stellar atmosphere. Hence, the vast physical domain stretching from the center of the Sun out to the heliopause defines our home in space. The heliopause is where our home ends and the rest of the universe begins.

10.1 PHYSICS OF THE SUN AND HELIOSPHERE—MAJOR SCIENCE GOALS

To achieve the key science goals set forth by this decadal survey in Chapter 1, it is necessary to understand the physical processes that create and sustain connections within the heliosphere. Figure 10.1 demonstrates, however, that gaining such an understanding requires overcoming major fundamental physics challenges. The most striking feature of the image is its beautifully intricate structure—obviously due to the Sun’s magnetic field—that has its origins deep below the solar surface. Understanding the processes that produce the solar field is a prerequisite for achieving the goals of the survey, but the recent, unexpected deep solar minimum demonstrates that understanding of the Sun’s dynamo is still rudimentary. Consequently, the Panel on Solar and Heliospheric Physics (SHP) identified as the first of four SHP science goals for the upcoming decade, SHP1, to determine how the Sun generates the quasi-cyclical variable magnetic field that extends throughout the heliosphere.

The extended structure of Figure 10.1 shows that the magnetic field provides a coupling across the solar and heliospheric domain, from the solar interior to the galaxy. In fact, the field not only couples the solar and heliospheric domain but also is essential for its creation. All current theories for heating the corona and accelerating the wind postulate the magnetic field as the central agent. Although this is not immediately obvious from Figure 10.1, because it is only a snapshot, the magnetic coupling of the Sun and heliosphere is always dynamic. The field at the solar surface and low corona is observed to vary dra-



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10 Report of the Panel on Solar and Heliospheric Physics To grasp immediately the nature of the field of solar and heliospheric physics, one need only look at the striking image of the 2010 solar eclipse shown in Figure 10.1. The solar atmosphere extends outward from the Sun’s surface, apparently without end. In fact, this extended atmosphere—the heliosphere—does end at roughly 140 AU, where the solar wind runs into the galaxy at the heliopause. Our Earth, its upper atmosphere, and its magnetosphere—and the other planets of the solar system—are all embedded deep inside this extended stellar atmosphere. Hence, the vast physical domain stretching from the center of the Sun out to the heliopause defines our home in space. The heliopause is where our home ends and the rest of the universe begins. 10.1  PHYSICS OF THE SUN AND HELIOSPHERE—MAJOR SCIENCE GOALS To achieve the key science goals set forth by this decadal survey in Chapter 1, it is necessary to understand the physical processes that create and sustain connections within the heliosphere. Figure 10.1 demonstrates, however, that gaining such an understanding requires overcoming major fundamental physics challenges. The most striking feature of the image is its beautifully intricate structure—obviously due to the Sun’s magnetic field—that has its origins deep below the solar surface. Understanding the processes that produce the solar field is a prerequisite for achieving the goals of the survey, but the recent, unexpected deep solar minimum demonstrates that understanding of the Sun’s dynamo is still rudimentary. Conse- quently, the Panel on Solar and Heliospheric Physics (SHP) identified as the first of four SHP science goals for the upcoming decade, SHP1, to determine how the Sun generates the quasi-cyclical variable magnetic field that extends throughout the heliosphere. The extended structure of Figure 10.1 shows that the magnetic field provides a coupling across the solar and heliospheric domain, from the solar interior to the galaxy. In fact, the field not only couples the solar and heliospheric domain but also is essential for its creation. All current theories for heating the corona and accelerating the wind postulate the magnetic field as the central agent. Although this is not immediately obvious from Figure 10.1, because it is only a snapshot, the magnetic coupling of the Sun and heliosphere is always dynamic. The field at the solar surface and low corona is observed to vary dra- 261

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262 SOLAR AND SPACE PHYSICS: A SCIENCE FOR A TECHNOLOGICAL SOCIETY FIGURE 10.1  White-light image of the solar corona out to 4 solar radii during the solar eclipse of November 7, 2010. SOURCE: Courtesy of M. Druckmüller, Brno University of Technology, M. Dietzel, Graz University of Technology, S. Habbal, Institute for Astronomy, and V. Rušin, Slovak Academy of Sciences. Figure 10-1 matically on temporal scales ranging from seconds to decades. In situ measurements of the heliosphere indicate that that variability creates a broad range of temporal scales, from subseconds for discontinuities produced by explosive events to decades for the solar cycle evolution. Furthermore, the heliosphere is inherently turbulent, and so it produces internal dynamics down to kinetic dissipation scales. All those heliospheric dynamics couple directly to Earth’s magnetosphere and upper atmosphere, again by the mag- netic field, producing the myriad forms of space weather that we must understand and mitigate. The SHP panel therefore identified as its second major science goal for the coming decade, SHP2, to determine how the Sun’s magnetism creates its dynamic atmosphere. In addition to its ceaseless dynamics, a defining feature of our home in space is that it is filled with high- energy radiation, both electromagnetic—ultraviolet (UV) rays, X rays, and gamma rays—and particulate. High-energy particle radiation, especially protons, is the greatest threat to human exploration of the solar system and to deep-space missions. The most dangerous bursts of energetic particles are due to the giant

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REPORT OF THE PANEL ON SOLAR AND HELIOSPHERIC PHYSICS 263 explosions of the solar magnetic field and matter known as coronal mass ejections/eruptive flares. Those events also produce the most destructive space weather at Earth, with damaging consequences ranging from communication and GPS blackouts to the loss of high-orbiting satellites and power transformers on the ground. In recent years, scientists have made substantial progress in understanding the Sun’s magnetic explo- sions. Researchers know where on the Sun they are likely to occur but are far from understanding when and how large the explosions will be and, in particular, how so much of their energy produces particle radiation. It should be emphasized that the processes of magnetic energy storage and release are commonly observed in all laboratory and cosmic plasmas; therefore, understanding them in the Sun and heliosphere will be a fundamental advance for all physics. Thus, the SHP panel’s third major science goal, SHP3, is to determine how magnetic energy is stored and explosively released. As stated above, the heliopause is where the Sun’s extended atmosphere ends and the galactic medium begins. That interface where two regions collide is generally rich in unexplored and unique physics. For example, the dominant energy form in the region is due not to the solar wind plasma or magnetic field but rather to interstellar neutrals that stream freely into the heliosphere and charge exchange with the solar wind ions. The magnetic structure of the region is also unique in that the field is wound into such a tight spiral due to solar rotation that it is almost cylindrical rather than radial. It should also be noted that the structure of the outer heliosphere has important effects close to home: it determines the penetration of high-energy galactic cosmic rays into near-Earth space. In situ measurements by the Voyager spacecraft and new methods to globally image the outer boundary of the heliosphere are spurring a revolution in understanding of this region. During the next decade, the Voyager spacecraft should pass the heliopause and enter interstellar space. Extending their presence robotically, humans will have left their home in space for the first time and entered the universe—a truly historic event. The coming decade will be critical for gaining an understanding not only of how our space environment is created and driven, but also of how it ends. That is the SHP panel’s final major science goal for the decade, SHP4, to discover how the Sun interacts with the local galactic medium and protects Earth. Associated with each of the SHP panel’s four science goals are several SHP actions that, if carried out, promise substantial progress in achieving the goals. Box 10.1 summarizes the SHP panel’s four major science goals and 14 associated actions. 10.2  SOLAR AND HELIOSPHERIC PHYSICS IMPERATIVES To achieve the four major science goals listed in Box 10.1, the SHP panel developed a strategy that consists of a set of imperatives for the federal agencies involved in solar and heliospheric research. The imperatives—actions that are essential for future progress—are listed briefly below according to the relevant agency (or agencies) and discussed in detail below in this chapter. 10.2.1  Prioritized Imperatives for NASA 1. Complete the development and launch of the Interface Region Imaging Spectrograph (IRIS) and Solar Probe Plus (SPP) missions, and deliver U.S. contributions to the European Space Agency–National Aeronautics and Space Administration (ESA–NASA) Solar Orbiter mission. The measurements from those missions are central to the SHP panel’s strategy for addressing SHP science goals 1, 2, and 3 in the next decade (§10.5.3.1). 2. Augment the heliophysics Explorer budget to expand launch opportunities and add new cost- effective mid-size launch vehicles (§10.5.3.2).

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264 SOLAR AND SPACE PHYSICS: A SCIENCE FOR A TECHNOLOGICAL SOCIETY BOX 10.1  SOLAR AND HELIOSPHERIC PHYSICS PANEL’S MAJOR SCIENCE GOALS AND ASSOCIATED ACTIONS SHP1.  Determine how the Sun generates the quasi-cyclical variable magnetic field that extends throughout the heliosphere. a. Measure and model the near-surface polar mass flows and magnetic fields that seed variations in the solar cycle. b. Measure and model the deep mass flows in the convection zone and tachocline that are believed to drive the solar dynamo. c. Determine the role of small-scale magnetic fields in driving global-scale irradiance variability and activity in the solar atmosphere. SHP2.  Determine how the Sun’s magnetism creates its dynamic atmosphere. a. Determine whether chromospheric dynamics is the origin of heat and mass fluxes into the corona and solar wind. b. Determine how magnetic free energy is transmitted from the photosphere to the corona. c. Discover how the thermal structure of the closed-field corona is determined. d. Discover the origin of the solar wind’s dynamics and structure. SHP3.  Determine how magnetic energy is stored and explosively released. a. Determine how the sudden release of magnetic energy enables both flares and coronal mass ejections to accelerate particles to high energies efficiently. b. dentify the locations and mechanisms that operate in impulsive solar energetic-particle sites, and I determine whether particle acceleration plays a role in coronal heating. c. Determine the origin and variability of suprathermal electrons, protons, and heavy ions on timescales of minutes to hours. d. Develop advanced methods for forecasting and nowcasting of solar eruptive events and space weather. SHP4.  Discover how the Sun interacts with the local galactic medium and protects Earth. a. Determine the spatial-temporal evolution of heliospheric boundaries and their interactions. b. Discover where and how anomalous cosmic rays are accelerated. c. Explore the properties of the heliopause and surrounding interstellar medium. 3. Substantially enhance the following key elements of the NASA heliophysics research and analysis programs so that the science community can use the new measurements to attain the SHP science goals outlined above (§10.5.3.4):  • Create new heliophysics science centers composed of teams of theorists, numerical modelers, and data experts to tackle major science problems.  • Implement a graduated increase in individual principal investigator grant programs to 20 percent of Heliophysics Division funding, primarily by increasing the size of individual grants.  • Augment the mission operations and data analysis program to facilitate systems science using the Heliophysics Systems Observatory.  • Ensure that all newly confirmed missions have Phase E budgets adequate to ensure mission suc- cess and that they sponsor a guest-investigator program as part of their success criteria.

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REPORT OF THE PANEL ON SOLAR AND HELIOSPHERIC PHYSICS 265  • Form a consolidated heliophysics instrument and technology development program for innova- tive instrument concepts.  • Provide flight and training opportunities through increased funding of the Low Cost Access to Space program for science-payload development and data analysis. 4. To attack SHP science goals 3 and 4, develop the Interstellar Mapping and Acceleration Probe (IMAP), a mission to observe the interaction of the heliosphere with the interstellar medium, and measure suprathermal ion populations with unprecedented resolution (§10.5.2.2). IMAP is the SHP panel’s highest- priority mid-size mission. 5. To attack SHP science goals 2 and 3, support U.S. participation in the Japanese-led Solar-C mission that will measure the magnetic coupling of the lower atmosphere into the corona (§10.5.2.3). 6. To maximize the science returns on limited resources, extend the Explorer mission development model to mid-size strategic missions (§10.5.3.3). 7. To attack SHP science goal 3, develop the Solar Eruptive Events (SEE) mission to image electron and ion acceleration in SEEs with unprecedented resolution. This is the SHP panel’s highest-priority mission concept for an LWS-class strategic mission (§10.5.2.4). 8. Carry out advanced planning for the Solar Polar Imager and Interstellar Probe missions (§10.5.2.6, §10.5.2.7). 9. To develop solar-sail propulsion for future Heliophysics Division missions, invest about $50 million as “seed money” in a full-scale solar sail demonstration mission by partnering with the Office of the Chief Technologist’s Technology Demonstration Missions program (§10.5.2.8). 10.2.2  Prioritized Imperatives for NSF 1. Provide base funding sufficient for efficient and scientifically productive operation of the Advanced Solar Technology Telescope, which is also central to achieving the SHP panel’s science goals (§10.5.4.1). 2. Establish a midscale projects funding program similar to NASA’s Explorer model (§10.5.4.2). 3. Fund the development and operation of the Frequency-Agile Solar Radiotelescope (FASR) to produce three-dimensional images of the solar atmosphere with high temporal and spatial resolution (§10.5.4.3). 4. Fund the development and operation of the Coronal Solar Magnetism Observatory (COSMO), a large-aperture coronagraph, chromosphere, and prominence magnetometer (§10.5.4.4). 5. Double the size of the National Science Foundation (NSF) small-grants programs to support the effort required for analyzing and modeling the new data sets (§10.5.4.5). 6. Broaden the definition of NSF’s Solar-Terrestrial Research Program to include outer-heliosphere research (§10.5.4.6). 10.2.3  Prioritized Multiagency Imperatives 1. Ensure continued support of current ground-based observations of the Sun, especially the line-of- sight and vector measurements of the solar magnetic field that are being used routinely for space weather operations (§10.5.5.1). 2. Ensure continued support of laboratory facilities for accurate measurement of atomic properties and for instrument calibrations (§10.5.5.2). 3. Develop real-time and near-real-time instrumentation and data streams from future missions and ground-based facilities. In collaboration with other agencies, fly missions devoted to space weather objec- tives. Establish an interagency clearinghouse and archive for space weather data (§10.5.5.3). 4. Ensure continuity of real-time solar wind measurements from L1 (§10.5.5.4).

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266 SOLAR AND SPACE PHYSICS: A SCIENCE FOR A TECHNOLOGICAL SOCIETY 5. Identify key long-term solar and heliospheric data sets and recommend approaches to ensure that they are continued and archived (§10.5.5.5). 6. Continue support of laboratory plasma physics at current or higher levels to complement spacecraft measurements in understanding basic heliophysical processes (§10.5.5.6). 7. NASA, the National Oceanic and Atmospheric Administration (NOAA), and the Department of Defense are encouraged to develop a plan for a mission at the L5 Lagrangian point to conduct high-priority helioseismology studies and develop advanced capabilities to forecast space weather (§10.5.5.7). 10.3  SIGNIFICANT ACCOMPLISHMENTS DURING THE PREVIOUS DECADE There has been considerable progress along with many surprising discoveries in the disciplines that constitute solar and heliospheric physics since publication in 2003 of the National Research Council (NRC) decadal survey, The Sun to the Earth—and Beyond: A Decadal Research Strategy in Solar and Space ­ hysics.1 In the following four subsections, organized by the four SHP science goals outlined in P Section 10.1, the panel describes a small sampling of recent developments. Accomplishments or goals that address the three decadal survey guiding motivations (M1-M3) are also noted.2 10.3.1  Determining How the Sun Generates the Quasi-cyclical Variable Magnetic Field That Extends Throughout the Heliosphere As emphasized in the 2003 decadal survey,3 an enduring major science goal is to determine how the Sun generates its quasi-cyclical variable magnetic field. The practical goal of such research is to learn enough to be able to help to predict the changing space environment and its societal impact (motivation M2). Here the SHP panel sketches four of the many notable accomplishments of the past decade toward meeting these goals. With a wide array of ground- and space-based sensors, solar activity in its many forms was observed to fall in 2008-2009 to low levels not seen for nearly a century. Solar activity is driven by the solar magnetic field, and the recent decline in the polar magnetic field flux is shown in Figure 10.2. The sharp decline was not generally expected. However, researchers noted that before the activity minimum measurements by ground-based instruments and space-based instruments on the Solar and Heliospheric Observatory (SOHO) showed unusually small amounts of magnetic flux near the poles of the Sun. Considered by some to be a useful precursor of the strength of an activity cycle, the low flux levels led to predictions that the current solar cycle maximum would be the lowest since polar flux measurements became available—as appears to be the case. Other venerable solar activity precursors that suggested a high level of activity proved to be spectacularly unreliable. Vital observational work in this research is continuing with ground- based and space-based assets, particularly because there is a chance that the Sun is entering a sustained period of low activity. The effects of record low solar activity were observed throughout the heliosphere. Among the prominent effects with societal consequences were these: cosmic ray fluxes near Earth reached the highest levels on record, and reduced heating of Earth’s upper atmosphere by solar UV radiation led to less drag on satellites. 1  National Research Council (NRC), The Sun to the Earth—and Beyond: A Decadal Research Strategy in Solar and Space Physics, The National Academies Press, Washington, D.C., 2003; and NRC, The Sun to the Earth—and Beyond: Panel Reports, The National Academies Press, Washington, D.C., 2003. 2  The motivations referred to in this section are those outlined in the introduction to Part II of this report: M1, Understand our home in the solar system; M2, Predict the changing space environment and its societal impact; M3, Explore space to reveal universal physical processes. 3  NRC, The Sun to the Earth—and Beyond: Panel Reports, 2003, p. 12.

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REPORT OF THE PANEL ON SOLAR AND HELIOSPHERIC PHYSICS 267 North - S outh S olar P olar fields [mic roT es la] 400 MS O* WS O 300 200 100 0 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 -100 -200 -300 -400 FIGURE 10.2  Average value of the magnetic flux density at the Sun’s polar regions during the last four cycles. The polar flux density peaks at the times of maximum. The recent cycle minimum had the weakest polar flux ever recorded. SOURCE: Courtesy of Leif Svalgaard, Stanford University. Red, data from Wilcox Solar Observatory; blue, data from Mt. Wilson Obser- vatory scaled to match. Figure 10-2 replaced Those surprising events and the rapid development of flux-transport dynamo models have led to intense recent work in solar dynamo modeling. Two key issues that involve the transport of magnetic flux have emerged: the speed with which meridional flows move poloidal magnetic flux to the solar poles and the extent to which this moving flux stays near the surface or diffuses inward on its journey to the poles. Because of the importance of those issues, there is a critical need for measurements of meridional flow and its variability. The measurements are difficult, and a consensus view on how to proceed has yet to emerge. Observational spatial resolution has greatly improved through image-processing techniques applied to ground-based observations made with the 1.6-m New Solar Telescope (NST) at the Big Bear Solar Obser- vatory and other 1-m-class apertures and direct observations made with the 0.5-m Hinode satellite. But it is the combination of these state-of-the-art observations with advanced numerical modeling that has, after 400 years of speculation, revealed the main physical processes at work in sunspot penumbral filaments, bright umbral dots, bright faculae, and small-scale magnetic elements. Figure 10.3 shows a numerical simulation of a sunspot and an actual photograph. Good observational and modeling progress has also been made with respect to the more complicated upper layers of the solar atmosphere. Continuing and improved helioseismic measurements of the solar interior from instruments including those on the SOHO and SDO spacecraft, launched in 1995 and 2010, respectively, and from the GONG ground-based network, have shown cycle-related changes in large-scale internal zonal and meridional flows. The varying flows may play a driving role rather than just being consequences of the solar activity cycle, and they narrow the wide range of realistic solar dynamo models. Helioseismic observations of active regions have shown subsurface helical flows whose strength is closely related to flare activity. In addition, a new analytic method shows surprisingly deep-seated effects of large active regions well before they emerge at the surface (Figure 10.4). Either or both of those findings may develop into useful forecasts of strong solar activity with societal significance.

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268 SOLAR AND SPACE PHYSICS: A SCIENCE FOR A TECHNOLOGICAL SOCIETY FIGURE 10.3  Numerical simulation of a sunspot (left) and a very-high-resolution image (right) from the New Solar Telescope at Big Bear Observatory, which is operated by the New Jersey Institute of Technology. Detailed comparisons have elucidated the physics of such solar features. SOURCE: Left, courtesy of M. Rempel, High Altitude Observatory. Right, courtesy of Big Bear Solar Observatory. For further information on the simulation, see M. Rempel, Numerical sunspot models: Robustness of photospheric velocity and magnetic field structure, Astrophysical Journal 750(1):62, 2012. The Sun sustains life on Earth by its nearly steady output of light. Measurements of total solar irradi- ance (TSI) with different space-based instruments have consistently shown a cycle variation on the order of 0.1 percent but give conflicting results about the absolute value of the TSI. The conflicts have recently been resolved in favor of a lower value that improves agreement with climate research results. The original conflicting results and new results are shown in the two panels of Figure 10.5. The new results indicate that the TSI at the recent cycle minimum was less than at previous minima. It has also been suggested that this level is about as low as can be expected even if a long cessation of solar activity occurs (as during the Maunder minimum). 10.3.2  Determining How the Sun’s Magnetism Creates Its Dynamic Atmosphere Major advances have been made during the past decade in understanding the dynamic and coupled nature of the Sun’s extended atmosphere, which reaches from the chromosphere and corona to the end of the heliosphere (motivations M1-M3). The advances highlight the need for direct sampling of the solar wind in the deep inner heliosphere as close to the Sun as possible, with high-resolution measurements of plasma and electromagnetic fluctuations; high-spatial- and high-temporal-resolution observations of the solar atmosphere from the photosphere into the corona; accurate magnetic field measurements in the low-beta chromosphere and corona; and advanced theoretical models that can couple closely to the upcoming observations.

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REPORT OF THE PANEL ON SOLAR AND HELIOSPHERIC PHYSICS 269 FIGURE 10.4  Upper panel shows the surface magnetic field (grey) with a travel-time perturbation map constructed at a depth of 42-75 million meters (blue) about a day before an active region appeared at the surface as seen in the lower panel. SOURCE: Adapted from S. Ilonidis, J. Zhao, and A. Kosovichev, Detection of emerging sunspot regions in the solar interior, Science 333:993-996, 2011. Reprinted with permission from AAAS.10-4 Figure

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270 SOLAR AND SPACE PHYSICS: A SCIENCE FOR A TECHNOLOGICAL SOCIETY Total Solar Irradiance Observations TSI corrected FIGURE 10.5  Recent improvements in the accuracy and precision of measurements of total solar irradiance have resolved several basic issues. The upper panel shows the original discordant measurements before recalibration. SOURCE: G. Kopp and J. Lean, A new, lower value of total solar irradiance: Evidence and climate significance, Geophysical Research Letters 38(1):L01706, doi:10.1029/2010GL04577, 2011. Copyright 2011 American Geophysical Union. Reproduced by permission of American Geophysical Union. Figure 10-5 In situ measurements of the solar wind plasma velocity distribution functions and electromagnetic fluctuations permit us to identify the dominant kinetic physics responsible for the generation and dissipa- tion of Alfvénic fluctuations and other types of solar wind turbulence (motivations M1 and M3). Progress has been made in measuring and understanding the types of turbulent fluctuations in the solar wind and the likely dissipation mechanisms, but important questions remain. Observations from spacecraft—such as Cluster, Wind, and ACE—and archival data from Helios have been used to probe the power in fluctuations perpendicular and parallel to the local magnetic field as a function of scale and have demonstrated that these fluctuations are highly anisotropic. Higher time-resolution measurements have allowed researchers to trace the evolution of the turbulent cascade and dissipation past ion kinetic scales toward electron scales. More work is needed to determine the relative fraction of fluctuations dissipated by ions and electrons and to distinguish between different mechanisms for dissipation, such as ion-cyclotron resonance, kinetic Alfvén waves, or the formation of small-scale current sheets. It is also unclear where broadband Alfvénic fluctuations and other types of solar wind turbulence, such as 1/f noise, originate, either in the corona or during propagation in the inner heliosphere. Further theoretical work and joint analysis of solar wind plasma and electromagnetic fields will allow a determination of whether nonlinear plasma physics can explain the highly nonadiabatic expansion of the solar wind.

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REPORT OF THE PANEL ON SOLAR AND HELIOSPHERIC PHYSICS 271 In the past decade, substantial progress has also been made in understanding the development of kinetic instabilities in the solar wind due to nonthermal ion and electron distribution functions; in particular, how temperature anisotropies are limited by the mirror, firehose, and cyclotron instabilities (motivations M1 and M3). A surprising result is that the mirror instability appears to play a stronger role than the cyclotron instability in limiting temperature anisotropy. Instabilities have also been proposed to explain the observed restriction of differential ion flow to the local Alfvén speed, but observational confirmation of these theories has remained elusive. In situ measurements of the solar wind are also a powerful diagnostic of the evolving connection between the corona and interplanetary space, and measurements in the past decade have revealed new features in the solar wind and related them to the structure and dynamics of the inner heliosphere and evolving Sun. The anomalously low levels of solar activity in the recent solar minimum were associated with substantial decreases in the density and pressure of the solar wind. Charge state and composition allow changes in the coronal sources of the solar wind to be tracked independently of changes in the solar wind speed due to the evolution of the plasma as it expands into interplanetary space. It is now understood that the three distinct forms of wind—fast, slow, and transient (associated with ICMEs)—can be identified clearly by their ionic charge-state signatures (using O7+/O6+) without assumptions about the dynamic evolution of the wind. Figure 10.6 shows the fractions of the three solar wind components for the decade 1998-2008. The compositions of the three winds provide vital clues to their sources in the Sun and the mechanisms of their formation. The panel notes the particular importance of furthering understanding of the slow wind, as its source and origin have constituted one of the outstanding problems in solar and heliospheric physics. With new insights into the slow wind’s origin and with the upcoming Solar Probe Plus and Solar Orbiter missions, researchers are poised to solve this problem definitively in the coming decade. FIGURE 10.6  Sunspot number (top) and three solar wind components (bottom) during 1998-2008: interplanetary coronal mass ejections (yellow), coronal hole wind (green), and noncoronal hole wind (orange). SOURCE: L. Zhao, T.H. Zurbuchen, and L.A. Fisk, Global distribution of the solar wind during solar cycle 23: ACE observations, Geophysical Research Letters 36:L14104, doi:10.1029/2009GL039181, 2009. Copyright 2009 American Geophysical Union. Reproduced by permission of American Geophysical Union. Figure 10-6

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314 SOLAR AND SPACE PHYSICS: A SCIENCE FOR A TECHNOLOGICAL SOCIETY Adequate MO&DA Budgets and Mission-Related Guest-Investigator Programs The science return from missions depends critically on adequate funding to analyze returned data, to develop relationships of observations across the HSO, and to test theories and models that are required to answer the science questions that motivated these missions quantitatively. Confirmed missions need to have adequate Phase E research budgets that ensure it is possible to achieve mission success. In addition, the budget for all missions needs to include an adequate GI program (typically 3 percent of the total mis- sion cost spread over the prime mission) administered by NASA as part of the mission success criteria. The GI programs enable the community at large to exploit new data further and relate them to other fields of heliophysics research.28 Heliophysics Instrument Development Program Heliophysics is now exploring the boundaries of its domain, performing increasingly complex mea- surements, and preparing for truly predictive capabilities. Progress hinges on growing the capabilities of new instrumentation. High-priority items include the following: • UV-blind ENA detectors that promise breakthroughs in resolution and efficiency; • Detectors for MeV ENAs to open new windows on localized acceleration processes; and • Large-format, high-efficiency array detectors and rapidly switching polarization modulators that can measure heating and acceleration processes in the solar atmosphere. Achieving such capabilities requires increased support for new instrument concepts (recommended in the 2003 decadal survey29). Also needed are opportunities for low-cost rides into space to boost the technology readiness level and means of leveraging technology-development resources in the Office of the Chief Technologist. Therefore, the SHP panel strongly advocates that current funding for instrument development within SR&T, LWS, and the Low Cost Access to Space (LCAS) program be consolidated into a comprehensive heliophysics instrument development program30 that includes funding to cross the “valley of death” gap (technology readiness levels 4-6). If the program grows to about 2 percent of the heliophysics flight pro- gram budget, or about $6 million in current-year funds, comparable savings can be achieved from flight programs. Low-Cost Access to Space Program The NASA Heliophysics Division LCAS program provides opportunities for flying space experiments on sounding rockets (100- to 1,000-km apogee altitude), balloon payloads, and CubeSats to address new science opportunities, develop new instruments and technology, provide complementary science and underflight calibrations for missions, and train the next generation of space scientists and engineers. The SHP panel endorses the NRC’s 2010 recommendation to increase funding support of NASA’s suborbital programs.31 In particular, funding for science-payload development, flight, and data analysis is inadequate and needs to be doubled. 28 A.J. Tylka, Heliophysics System Science and Funding for Extended Missions, white paper submitted to the Decadal Strategy for Solar and Space Physics (Heliophysics), Paper 269; J.G. Luhmann et al., Extended Missions: Engines of Heliophysics System Science, white paper submitted to the Decadal Strategy for Solar and Space Physics (Heliophysics), Paper 167. 29 NRC, The Sun to the Earth—and Beyond: A Decadal Research Strategy in Solar and Space Physics, 2003, p. 11. 30 E.R. Christian, Heliophysics Instrument and Technology Development Program (HITDP), white paper submitted to the Decadal Strategy for Solar and Space Physics (Heliophysics), Paper 34. 31 NRC, Revitalizing NASA’s Suborbital Program: Advancing Science, Driving Innovation, and Developing a Workforce, The National Academies Press, Washington, D.C., 2010.

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REPORT OF THE PANEL ON SOLAR AND HELIOSPHERIC PHYSICS 315 Funding support for NASA’s Wallops Flight Facility (and subcontractors) appears adequate to support 20 or more flights per year, double the current rate. The SHP panel encourages continued development of new capabilities within the NASA LCAS program. High-altitude sounding rockets with three or four vehicles can provide longer observing time and carry heavier payloads. Balloons provide the only practical flight opportunities (because of launch-vehicle issues) for very heavy scientific payloads, such as the Sunrise solar experiment and the GRIPS Gamma-Ray Imager/Polarimeter mentioned above. Ultra-long-duration balloons (the first successful flight was in 2009) promise to provide about 100-day flight times in the near future. CubeSats can provide even longer observing times. Conclusions of the Panel on Solar and Heliospheric Physics Regarding NASA’s Grants Program Achieving the key science goals of this decadal survey requires establishing an effective NASA helio- physics grants program by implementing or augmenting the following key elements: • Creation of new heliophysics science centers composed of teams of theorists, numerical modelers, and data experts to tackle the most compelling science problems; • A graduated increase in individual-PI grants programs to about 20 percent of division funding, pri- marily by increasing the size of individual grants, to realize the science returns from the space missions and develop future ones; • An augmented heliophysics MO&DA program to enable systems science by using the HSO; • Adequate Phase E research budgets for confirmed missions to ensure mission success and appro- priately sized GI programs as part of mission success criteria to ensure mission science productivity; • Formation of a consolidated heliophysics instrument development program to facilitate innovative instrument concepts and make future mission implementation cost-effective; and • Increased funding for science-payload development, flight, and data analysis in the LCAS program to provide urgently needed flight and training opportunities. 10.5.4  NSF-Related Initiatives The following initiatives are based mainly on more than 30 white papers dealing with current or potential NSF-funded facilities and programs (for a list of titles, see Appendix I). 10.5.4.1  Advanced Technology Solar Telescope Operations SHP Imperative: The SHP panel attaches high priority to NSF’s providing base funding sufficient for efficient and scientifically productive operation of the ATST to realize the scientific benefits of the major national investment in it. Justification: Starting in 2017, the world-leading ATST will provide the most detailed and most accu- rate measurements of the Sun’s plasma and magnetic field ever obtained.32 The measurements promise to revolutionize understanding of the Sun and heliosphere. Realizing the abundant scientific payoff from the major national investment in ATST will require adequate sustained funding from NSF for operation, development of advanced instrumentation, and research-grant support for the ATST user community. The National Solar Observatory (NSO) will close all existing facilities except for a synoptic program, but pro- jections indicate that the current NSO base funding will be adequate only to realize a small fraction of 32  Keil et al., Science and Operation of the Advanced Technology Solar Telescope, white paper submitted to the Decadal Strat- S. egy for Solar and Space Physics (Heliophysics), Paper 130; K.P. Reardon et al., Approaches to Optimize Scientific Productivity of Ground-Based Solar Telescopes, white paper submitted to the Decadal Strategy for Solar and Space Physics (Heliophysics), Paper 224.

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316 SOLAR AND SPACE PHYSICS: A SCIENCE FOR A TECHNOLOGICAL SOCIETY the scientific potential of the ATST. Additional annual funding of around 4-5 percent of the capital cost of the ATST will dramatically enhance its science yield. 10.5.4.2  Need for a National Science Foundation Midscale Projects Line SHP Imperative: The SHP panel strongly supports the establishment within NSF of a competed fund- ing program for midscale projects. Justification: NSF does not have a means of funding midscale projects ranging from about $4 mil- lion to $135 million in FY 2010 dollars. Several previous bodies, including the 2010 decadal survey of astronomy and astrophysics (Astro2010),33 have recommended that NSF implement a competed funding program for midscale projects similar to NASA’s Explorer model. A midscale funding program would enable NSF to provide a more balanced and flexible response to scientific opportunities that are currently too large to allow funding by the Major Research Instrumentation program and too small to qualify for fund- ing by the Major Research Equipment and Facilities Construction line. A midscale program would offer excellent return by exploiting new techniques and instrumentation more rapidly, by ensuring a broader scientific portfolio of exciting and timely programs, and by offering additional opportunities for training scientists, engineers, and students. Examples of solar facilities that could be funded by this new line are the Frequency-Agile Solar Radiotelescope (FASR) and the Coronal Solar Magnetism Observatory (COSMO). They are described in more detail below. 10.5.4.3  Frequency-Agile Solar Radiotelescope The SHP panel assigns high priority to NSF’s funding of construction and operation of FASR34 to produce three-dimensional images of the solar atmosphere with high temporal and spatial resolution. Solar radio emission provides uniquely powerful sources of diagnostic information with the potential for transformational insights into solar activity and its terrestrial impacts. That is because a number of distinct emission mechanisms operate at radio wavelengths: thermal free-free emission is relevant to the quiet solar atmosphere, thermal gyroresonance emission is a key mechanism operative in solar active regions, nonthermal gyrosynchrotron emission from electrons with hundreds of kiloelectron volts 10 MeV plays a central role in flares and CMEs, and a variety of coherent emission processes—such as plasma radiation, familiar to aficionados of type II and type III radio bursts—make it possible to trace electron beams and shocks in the solar corona and heliosphere. Radio observations and the diagnostic information that they provide are highly complementary to next-generation observations at optical and infrared wavelengths provided by the ATST and COSMO on the ground, at EUV wavelengths by Solar-C, and at X-ray wave- lengths by SEE in space. FASR is a solar-dedicated radiotelescope that provides a unique combination of superior imaging capa- bility and broad instantaneous frequency coverage and thus exploits the powerful diagnostics available at radio wavelengths. The potential value of such a facility has been recognized in high-priority recommen- dations of FASR in two previous decadal surveys conducted by the National Research Council. The 2003 decadal survey of solar and space physics recommended FASR as its highest-priority “small project”35 in recognition of the unique and transformative role that it will play in addressing basic research questions 33  NRC, New Worlds, New Horizons in Astronomy and Astrophysics, The National Academies Press, Washington, D.C., 2010, p. 28. 34  D.E. Gary et al., The Frequency-Agile Solar Radiotelescope, white paper submitted to the Decadal Strategy for Solar and Space Physics (Heliophysics), Paper 86; D.E. Gary et al., Particle Acceleration and Transport on the Sun: New Perspectives at Radio Wave- lengths, white paper submitted to the Decadal Strategy for Solar and Space Physics (Heliophysics), Paper 87. 35  NRC, The Sun to the Earth—and Beyond: A Decadal Research Strategy in Solar and Space Physics, 2003, p. 54.

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REPORT OF THE PANEL ON SOLAR AND HELIOSPHERIC PHYSICS 317 and its complementary role with respect to other important instruments being developed to address the Sun and heliosphere. The Astro2010 decadal survey characterized FASR as a “compelling” midscale project and recognized it, with ATST, as a core facility in the U.S. ground-based solar portfolio.36 An independent analysis of cost and technical readiness (CATE analysis) described FASR as “doable today.” FASR thus has broad constituencies in solar and space physics and in astronomy and astrophysics. The major advance offered by FASR over previous solar radio instrumentation is its unique combina- tion of ultra-wide-frequency coverage, high spectral resolution, and high image quality. FASR measures the polarized brightness temperature spectrum over a broad frequency range (50 MHz to 21 GHz, or 1.4-600 cm) along every line of sight to the Sun as a function of time. Radiation in this radio wavelength range probes the solar atmosphere from the middle chromosphere to well into the corona. In essence, FASR images the entire solar atmosphere in three dimensions once every second from the chromosphere through the corona while retaining the capability to image a restricted frequency range with time resolution as small as 20 ms. In so doing, FASR enables fundamentally new, unique observables, including: • Quantitative measurements of coronal magnetic fields, both on the disk and above the limb, under quiet conditions and during flares; • Measurements of tracers of energy release and the spatiotemporal evolution of the electron distribu- tion function during flares; • Imaging CMEs and the associated coronal dimming, “EIT waves,”37 and coronal shocks; and • Imaging of thermal emission from the solar atmosphere from chromospheric to coronal heights, including the quiet Sun, coronal holes, active regions, and prominences. FASR’s panoramic view allows the solar atmosphere and physical phenomena therein to be studied as a coupled system. Its powerful and unique capabilities allow it to address such high-priority science questions as these: • The nature and evolution of coronal magnetic fields —What is the quantitative distribution of coronal magnetic fields? —How do coronal magnetic fields evolve in time and space? —How is magnetic energy stored? • The physics of flares —What is the physics of magnetic energy release? —How and where are electrons accelerated? —What are the relevant particle transport processes? • The drivers of space weather —How are CMEs initiated and accelerated? —What is the origin of coronal shocks? —How are solar energetic particles in the heliosphere accelerated? • The physics of the quiet sun —How are the solar chromosphere and corona heated? —What is the origin of the solar wind? —What is the structure of prominences and filaments? 36  NRC, New Worlds, New Horizons, 2010, p. 191. 37  named because they were first discovered by the Extreme-ultraviolet Imaging Telescope (EIT) on the SOHO spacecraft. So

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318 SOLAR AND SPACE PHYSICS: A SCIENCE FOR A TECHNOLOGICAL SOCIETY BOX 10.2  FASR SPECIFICATIONS Angular resolution 20/nGHz arcsec Frequency range 50 MHz to 21 GHz Number of data channels 2 (dual polarization) Frequency bandwidth 500 MHz per channel Frequency resolution Instrumental: 4,000 channels Scientific: minimum (1%, 5 MHz) Time resolution About 1 s (full spectrum sweep) 20 ms (dwell) Polarization Full Stokes (intensity and linear polarization and circular polarization) Number of antennas deployed A (2-21 GHz): about 100 B (0.3-2.5 GHz): about 70 C (50-350 MHz): about 50 Size of antennas A (2-21 GHz): 2 m B (0.3-2.5 GHz): 6 m C (50-350 MHz): log-periodic dipole array Array size 4.25 km east-west x 3.75 km north-south Absolute positions 1 arcsec Absolute flux calibration <10% FASR comprises three antenna arrays that are designed to observe meter (FASR C), decimeter (FASR B), and centimeter wavelengths (FASR A). The instrument exploits the long heritage of Fourier synthesis imag- ing developed over several decades in radioastronomy. The techniques are mature, and the technologies robust. High-level instrument specifications are given in Box 10.2. 10.5.4.4  Coronal Solar Magnetism Observatory The SHP panel’s other high-priority candidate for the NSF midscale line is the COSMO large-aperture coronagraph and chromosphere and prominence magnetometer,38 which would complement the ATST and FASR. Until explosively released, most of the mass and energy that produce space weather events are stored in the coronal magnetic field. Coronal faintness is an observational challenge especially for sensitive magnetic and velocity measurements. Responding to a next-step suggestion of the 2003 decadal survey,39 COSMO is proposed as a suite of three instruments: a ground-based, 1.5-m-aperture solar coronagraph supported by a 12-cm-aperture white-light K-coronagraph (under construction) and a 20-cm-aperture chromosphere and prominence magnetometer. COSMO will be a facility for use by the solar physics research community. The facility will take continuous daytime synoptic measurements of magnetic fields 38  Tomczyk et al., COSMO, The Coronal Solar Magnetism Observatory, white paper submitted to the Decadal Strategy for Solar S. and Space Physics (Heliophysics), Paper 268; J. Burkepile et al., The Importance of Ground-Based Observations of the Solar Corona, white paper submitted to the Decadal Strategy for Solar and Space Physics (Heliophysics), Paper 25; S. McIntosh et al., The Solar Chromosphere: The Inner Frontier of the Heliospheric System, white paper submitted to the Decadal Strategy for Solar and Space Physics (Heliophysics), Paper 193. 39  NRC, The Sun to the Earth—and Beyond: A Decadal Research Strategy in Solar and Space Physics, 2003.

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REPORT OF THE PANEL ON SOLAR AND HELIOSPHERIC PHYSICS 319 in the solar corona and chromosphere to support understanding of solar eruptive events that drive space weather and investigation of long-term coronal phenomena. The large emission-line coronagraph will be the largest refracting telescope in the world. COSMO complements other facilities and missions by providing 300-days-per-year limb observations of the coronal magnetic field down to 1 Gauss over a 1° field of view. Long-term synoptic observations will directly address how the coronal magnetic field responds to the sunspot cycle and how the switch in polarity of the global field manifests itself in the heliosphere. On a shorter timescale, COSMO will provide new information on the evolution of and interactions between magnetically closed and open regions that determine the changing structure of the heliospheric magnetic field and provide verification of extrapolations of the photospheric field. COSMO will detect polarization signatures of nonpotential fields to afford insight into the roles of energy storage, magnetic reconnection, helicity creation and transport, and flux emergence in CME forma- tion. It will also provide white-light images of CMEs in the low corona needed to determine basic properties of CMEs in early stages of formation. Particles accelerated by CME-driven shocks have the highest particle energies and pose the greatest space weather hazards. COSMO can detect compressions and distortions in the field that are due to the formation and passage of a CME and associated waves. Density compres- sions resulting from shock formation can produce intensity enhancements in white-light coronal images. COSMO has the potential to detect shock and CME locations simultaneously. COSMO will provide routine observations of prominence, filament, and chromospheric magnetic fields and prominence flows. Those observations will constrain prominence densities and determine how prominence and coronal magnetic fields interact, how and where magnetic energy is stored (for example, by flux and helicity transport), and how it is released (for example, by instabilities, reconnection, or dissipa- tive heating). COSMO will provide the first routine high-time-cadence measurements of coronal magnetic fields in and around flares and associated CMEs as seen above the solar limb. The high-time-cadence observations can help to determine when, where, and how magnetic energy is released by CMEs and by dissipative processes that result in flares. 10.5.4.5  National Science Foundation Small-Grants Program SHP Imperative: To support the community effort required to analyze, interpret, and model the vast new solar and space physics data sets of the next decade, the SHP panel assigns high priority to NSF’s adopting the policy of doubling the size of its small-grants programs. Justification: The coming decade should see major advances in solar and space physics with new ground-based and space-based instrumentation coming on line, new computational technology becoming available, and new personnel in the nation’s universities and other institutions. Funding will be needed to achieve the science promise of the new capabilities and researchers. Core support for new researchers, especially in universities, comes from NSF small-grants programs, which include the CEDAR, GEM, SHINE, and base grants programs and associated postdoctoral and young-faculty programs. The NSF small-grants program is inadequate to cover the science requirements of existing facilities and personnel. Whether measured by publications, data analyzed, or students educated, increased investment in the small-grants program is by far the most effective strategy for NSF to use to achieve its science and education goals.

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320 SOLAR AND SPACE PHYSICS: A SCIENCE FOR A TECHNOLOGICAL SOCIETY 10.5.4.6  Broadening the Definition of the National Science Foundation’s Solar-Terrestrial Research Program to Include Outer-Heliosphere Research SHP Imperative: New scientific discoveries about the outer heliosphere may have important effects on the history and future of our planet, and this justifies broadening the scope of NSF’s Solar-Terrestrial Research program.40 Justification: NSF’s Solar-Terrestrial Research program is in the Geospace Section of the Atmospheric and Geospace Sciences Division. To be funded, proposals to the program must demonstrate direct relevance to solar-terrestrial science or be transformational in advancing understanding of the outer solar system. Even high-quality proposals in outer-heliospheric research may not be funded if they are not perceived to be directly relevant to changing terrestrial conditions. Outer-heliosphere research is not funded in other NSF programs and is “falling between the cracks” in NSF. Recent discoveries suggest that solar interac- tions with the local interstellar medium may play a much larger role in influencing terrestrial conditions than previously thought. In addition, this exciting and rapidly emerging field is providing new insights into processes occurring in the Sun, solar wind, planetary magnetospheres and atmospheres, and the galaxy. All that suggests that the definition of solar-terrestrial research in NSF should be broadened to include solar wind interactions with the local interstellar medium. 10.5.5  Multiagency Imperatives 10.5.5.1  Ground-Based Solar Observations SHP Imperative: The SHP panel gives high priority to NSF’s and other agencies’ support (where it is appropriate to their missions) of continuation of ground-based observations of the Sun.41 Justification: The Sun’s scientific and societal importance stimulates a broad array of research ap­ roaches. Much of the current understanding of the Sun originates in observations made on the ground. p Continuing ground-based observations serve crucial roles in studies of long-term variations of the Sun, in attaining the highest spatial resolution of solar features, in measuring wavelengths from the infrared to the radio, in exploring new ideas, in testing numerical models, in developing new instruments, and in verify- ing space-based results. National and university-based solar observatories are supported mainly by NSF, and support from mission-oriented agencies is sometimes available when specific mission objectives align with ground-based capabilities. In spite of an outstanding record of scientific accomplishments, support for ground-based observations and for research based on them has eroded. The SHP panel believes that agencies, especially NSF, should work to reverse that trend. 40 G.P. Zank, Role of the National Science Foundation ATM/GEO in Promoting and Supporting Space Physics, white paper submit- ted to the Decadal Strategy for Solar and Space Physics (Heliophysics), Paper 284. 41  Ayres and D. Longcope, Ground-based Solar Physics in the Era of Space Astronomy, white paper submitted to the Decadal T. Strategy for Solar and Space Physics (Heliophysics), Paper 3; F. Hill et al., The Need for Synoptic Optical Solar Observations from the Ground, white paper submitted to the Decadal Strategy for Solar and Space Physics (Heliophysics), Paper 108; A. Pevtsov, Cur- rent and Future State of Ground-based Solar Physics in the U.S., white paper submitted to the Decadal Strategy for Solar and Space Physics (Heliophysics), Paper 218; A.G. Kosovichev, Solar Dynamo, white paper submitted to the Decadal Strategy for Solar and Space Physics (Heliophysics), Paper 141.

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REPORT OF THE PANEL ON SOLAR AND HELIOSPHERIC PHYSICS 321 10.5.5.2  Laboratory Astrophysics and Calibration Facilities SHP Imperative: NASA, the National Oceanic and Atmospheric Administration (NOAA), and NSF are encouraged to continue their support of laboratory facilities for accurate measurement of atomic properties and for instrument calibrations as needed for several research programs and missions.42 Justification: Understanding the Sun and heliosphere requires observing them remotely. Diagnosing these observations requires both theoretical knowledge of radiation across the electromagnetic spectrum and well-calibrated instrumentation. Heliophysics research relies heavily on measurements of atomic and molecular collision physics, especially for highly charged ions that dominate X-ray and EUV produc- tion. Proper interpretation of observations requires cross sections for calculating excitation, direct and dielectronic recombination, single-charge and multiple-charge exchange, lifetimes, and other values. And calibration facilities (for example, at the National Institute of Standards and Technology) are required for accurate calibration and characterization of NASA and NOAA instrumentation before flight. Without such facilities, the science return from missions and ground-based remote-sensing observations can be substan- tially limited. The SHP panel assigns high priority to continued support of these facilities by NASA, NOAA, and NSF, preferably through budget line items for laboratory facilities. 10.5.5.3  Enhanced Space Weather Monitoring and Modeling SHP Imperative: To optimize space weather capabilities, the SHP panel recommends that all future solar and heliospheric space missions and ground-based facilities consider including capabilities for delivering space weather data products. It would be a benefit for NASA to develop multiagency missions whose primary purpose is space weather monitoring. An interagency clearinghouse and archive of space weather data would benefit forecasters, researchers, and model-builders. Justification: During the past decade, the direct application of solar and heliospheric physics to the protection of life and our high-technology society has demonstrated that the nation’s investment in the field is returning tangible benefits. The SHP panel recognizes the great benefit that would be realized if studies of new NASA missions considered adding space weather measurements and real-time data-transmitting capabilities where appropriate. Examples of possible missions include IMAP, SEE, and L5. The technical and financial effects of adding space weather instrumentation could be addressed by partnering with other NASA directorates or other agencies. Furthermore, the SHP panel recognizes a benefit in NASA consider- ation of partnering with other agencies to fly missions whose primary purpose is space weather operations but that also have science objectives, such as an L5 mission (§10.5.2.5). Currently, ground-based neutron monitors and solar optical telescopes and radiotelescopes provide unique real-time data. In the future, an expansion of SOLIS to a three-site network and completion of FASR and COSMO would provide key data. The panel encourages ground-based facilities to assess data products that could improve space weather capabilities. Finally, to expand the availability of space weather data to forecasters, researchers, and model-builders, the SHP panel encourages development of an interagency clearinghouse for real-time and near-real-time data and an active national archive of current and past space weather data. 42 F.G. Eparvier, The Need for Consistent Funding of Facilities Required for NASA Missions, white paper submitted to the Decadal Strategy for Solar and Space Physics (Heliophysics), Paper 69; A. Chutjian et al., Laboratory Solar Physics from Molecular to Highly- Charged Ions, Meeting Future Space Observations of the Solar Plasma and Solar Wind, white paper submitted to the Decadal Strategy for Solar and Space Physics (Heliophysics), Paper 39.

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322 SOLAR AND SPACE PHYSICS: A SCIENCE FOR A TECHNOLOGICAL SOCIETY 10.5.5.4  Continuity of Real-Time Solar Wind Data from L1 SHP Imperative: Maintaining the continuity of real-time solar wind data from L1 is essential for the preservation and improvement of current space weather forecasting capabilities. Justification: Observations of the solar wind and the Sun from 1 million miles upstream from Earth (orbiting the L1 Lagrangian point) have proved to be extremely valuable. The ACE mission has returned solar wind observations in real time since 1998, and the NOAA Space Weather Prediction Center uses them to drive 5 of its 11 space weather watches and warnings with a lead time of up to 60 minutes. The real-time data are also downloaded about 1 million times a month by about 25,000 unique customers, including deep-sea drilling, surveying, mining, and airline companies. NOAA, NASA, and the U.S. Air Force are refurbishing the DSCOVR spacecraft to provide operational real-time data to partially replace the data supplied by the aging ACE spacecraft. IMAP will be able to replace and expand on the suite of real-time space weather data provided by ACE and DSCOVR. 10.5.5.5  Preserving Key Solar-Heliospheric Data Sets SHP Imperative: Agencies that engage in solar-heliospheric research or use solar and heliospheric data products (such as NASA, NOAA, NSF, and DOD) are encouraged to initiate an internal or external study that would identify key long-term data records and recommend approaches to ensure that they are continued and archived.43 Justification: A number of long-term solar and heliospheric data sets are essential for tracking the evo- lution of the solar-heliosphere system on timescales ranging from minutes to millennia. Examples include neutron-monitor records of cosmic-ray variations, TSI measurements, and solar wind properties upstream of Earth. Some of the data sets are often in danger of being discontinued because of lack of funding or changes in agency priorities. 10.5.5.6  Laboratory Plasma Physics SHP Imperative: NASA and NSF are encouraged to continue supporting laboratory plasma-physics research at current or higher levels because it complements space- and ground-based measurements in efforts to understand basic heliophysical processes.44 Justification: Facilities that approximate solar and space plasma environments in the laboratory have long been part of the scientific investigation of space. Next-generation experiments have been emerging to provide experimental capabilities to study detailed processes directly relevant to space and solar plas- mas. Some fundamental plasma processes are difficult, if not impossible, to measure and confirm with spacecraft but are potentially within reach through laboratory experiments. Examples include studies of magnetic reconnection and associated particle acceleration, solar coronal loops, and large-scale dynamo experiments at the Madison Dynamo Experiment facility. Moderate funding for laboratory heliophysics in 43  J.M. Ryan et al., Ground-Based Measurements of Galactic and Solar Cosmic Rays, white paper submitted to the Decadal Strat- egy for Solar and Space Physics (Heliophysics), Paper 235; P. Pilewskie, The Total and Spectral Solar Irradiance Sensor: Response to the NAS Decadal Strategy for Solar and Space Physics, white paper submitted to the Decadal Strategy for Solar and Space Physics (Heliophysics), Paper 221; F. Hill et al., The Need for Synoptic Solar Observations from the Ground, white paper submitted to the Decadal Strategy for Solar and Space Physics (Heliophysics), Paper 108. 44  Brown et al., An Experimental Plasma Dynamo Program for Investigations of Fundamental Processes in Heliophysics, white B. paper submitted to the Decadal Strategy for Solar and Space Physics (Heliophysics), Paper 18; H. Ji et al., Next Generation Experiments for Laboratory Investigations of Magnetic Reconnection Relevant to Heliophysics, white paper submitted to the Decadal Strategy for Solar and Space Physics (Heliophysics), Paper 120.

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REPORT OF THE PANEL ON SOLAR AND HELIOSPHERIC PHYSICS 323 support of space-plasma and solar research, preferably through budget line items for laboratory facilities, would be beneficial. 10.5.5.7  Interagency Planning for a Future L5 Mission SHP Imperative: The SHP panel assigns high priority to the development by NASA, NOAA, and DOD of plans for a mission at the L5 Lagrangian point to conduct helioseismology studies and develop advanced capabilities to forecast space weather. Justification: From L5, it is possible to forecast the arrival of Earth-directed CMEs with high precision, to observe emerging or developed active regions and corotating interaction regions about 4 days earlier than from Earth, and to measure photospheric magnetic fields over about 60° additional longitude, improv- ing magnetic-field models of regions rotating toward Earth.45 In addition, stereohelioseismology studies combining L1 and near-Earth observations have the potential to enable even longer solar-activity forecasts (§10.3.1 and §10.5.2.5). The SHP panel encourages NASA, NOAA, and DOD to study means of achieving an L5 orbit for minimal cost and to define the spacecraft, instrument, and mission requirements needed to optimize the scientific and operational opportunities from a future L5 mission. 10.6  CONNECTIONS TO OTHER DISCIPLINES The SHP panel has interests that are connected to those of the Panel on Atmosphere-Ionosphere- Magnetosphere Interactions (AIMI) and the Panel on Solar Wind-Magnetosphere Interactions (SWMI). Solar photon radiation and energetic particle outputs are primary energy inputs into and thus drivers of dynamic processes in Earth’s atmosphere, ionosphere, and magnetosphere and those of other planets. The Sun varies on timescales of minutes (flares, CMEs, and SEPs), days (27-day solar rotation), years (11-year solar-activity cycle), and even longer. There are corresponding responses throughout the heliosphere, including at Earth and other planets. Successful space weather modeling and forecasting of magnetospheric and ionospheric events include continuous tracing through interplanetary space and monitoring of con- ditions upstream of Earth. Consequently, most SHP panel initiatives also support AIMI and SWMI goals. Robust observational and modeling programs of solar outputs and interactive collaborations among the SHP, AIMI, and SWMI communities are critically important for current and future heliophysics research and space weather operations. 10.6.1  Earth Science and Climate Change Solar-irradiance variations in the near-ultraviolet, visible, and near-infrared have direct forcing on Earth’s climate change because of energy deposition in the lower atmosphere and at the surface and oceans. The solar-energy input and other indirect forcings, such as top-down coupling of solar ultraviolet heating and photochemistry in the stratosphere, and the possible influence of galactic cosmic rays, affect both global climate changes and regional changes that are due to subtle changes in the atmosphere, ocean circulation patterns, and cloud cover. Solar-irradiance observations and reconstruction and modeling of long-term variations, such as improved solar-dynamo models, are important support for the Earth science 45  Vourlidas et al., Mission to the Sun-Earth L5 Lagrangian Point: An Optimal Platform for Heliophysics and Space Weather A. Research, white paper submitted to the Decadal Strategy for Solar and Space Physics (Heliophysics), Paper 273; N. Gopalswamy et al., Earth-Affecting Solar Causes Observatory (EASCO): A New View from Sun-Earth L5, white paper submitted to the Decadal Strategy for Solar and Space Physics (Heliophysics), Paper 99.

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324 SOLAR AND SPACE PHYSICS: A SCIENCE FOR A TECHNOLOGICAL SOCIETY goal of understanding natural influences on climate change. The SHP panel encourages enhanced col- laboration among the solar, heliosphere, Earth science, and climate-change communities, in particular between the NASA Heliophysics Living With a Star targeted research and technology and NASA Earth science radiation and stratosphere programs. 10.6.2 Astrophysics Understanding the Sun as a star, understanding how solar structure and dynamics are related to those of other stars, and understanding relationships between the heliosphere and astrospheres are examples of how solar, stellar, galactic, and heliospheric physics research efforts benefit each other. Basic plasma processes that include particle acceleration, reconnection, and turbulence in the heliosphere also occur in other astrophysical environments. Studies of stellar evolution, through asteroseismology—the study of a star’s internal structure by analyzing the frequency spectra of its oscillations—and other means, and improved understanding of the range of variability of Sun-like stars also benefit Sun-climate studies of long-term solar variations, such as the Maunder minimum.46 It is highly desirable to continue and improve collaborations between heliophysics and astrophysics programs in NSF. 10.6.3  Comparative Planetology and Astrospheres The magnetosphere represents a boundary in space plasmas created through the interaction of Earth’s magnetic field and solar wind. Comparable boundaries exist around planets, their moons, asteroids, comets, the heliosphere, and astrospheres. Detailed study of plasma boundaries mutually benefits understanding of boundaries surrounding Earth, planets (including exoplanets), moons, comets, the heliosphere, and astrospheres surrounding other stars. It is highly desirable to continue and improve collaborations among heliophysics, planetary science, and astrophysics programs to elevate and generalize understanding of planetary and astrophysical boundaries in space. 46  Schrijver et al., The Solar Magnetic Dynamo and Its Role in the Formation and Evolution of the Sun, in the Habitability of Its K. Planets, and in Space Weather around Earth, white paper submitted to the Decadal Strategy for Solar and Space Physics (Heliophys- ics), Paper 240.