The Solar Dynamics Observatory (SDO) has been the pillar of NASA's Heliophysics Systems Observatory since it began operations in 2010.The three science instruments aboard SDO -the Atmospheric Imaging Assembly (AIA), the Helioseismic and Magnetic Imager (HMI) and the Extreme-ultraviolet Variability Experiment (EVE) -have monitored the state and evolution of the solar magnetic field, atmosphere, and radiative output with unprecedented resolution, cadence and accuracy, providing powerful insight into the drivers of space weather.In addition to obtaining high-quality, consistent data on its own, SDO has demonstrated the value of continuous synoptic observations of a set of critical observables, to serve as a context tying together more specialized observations, and as inputs to machine learning models that rely on robust datasets for deriving conclusions.Moreover, the lessons of SDO have illuminated the global nature of dynamic solar phenomena that cause space weather, and ultimately underscored the need for a more comprehensive picture of the sun's activity.Simultaneously, technology and the accelerating commercialization of space have transformed how precision flight instrumentation is built and operated.Lower launch costs and improved propulsion systems make escaping Earth orbit more feasible than ever before.More capable instruments can now be made smaller, lighter and more quickly than in the past.And advances in flight computing hardware and algorithms enable on-board data reduction, sensor fusion and data analysis to reduce telemetry requirements and improve the applicability of spacecraft data products.To take advantage of the convergence of these trends, the Solar Dynamics Constellation (SDC) mission concept has been developed.It is a mission architecture that will significantly advance the understanding of the global nature of solar activity and that can also dramatically improve the power, relevance, and resiliency of the space weather data that the scientific community and the nation rely on.This constellation is:• Global: Using 6 small spacecraft in solar orbit, the SDC will deliver views of the full sun, enabling advance warning of developing features and providing comprehensive coverage of the energetic events that can trigger sympathetic, geoeffective eruptions; • Intelligent: With robust on-board computing hardware capable of implementing solar models and computer vision algorithms, the SDC spacecraft will maximize scarce telemetry resources by transmitting actionable information directly; • Flexible: The SDC observatories can take advantage of rideshare opportunities for rapid, low-cost deployment to a variety of heliospheric vantage points.Instruments use proven designs and modular components and can be hosted on other platforms to allow crosscalibration and extension of the constellation.The data products are standardized, to enable interoperability with other instruments, or with future science missions with similar observables.• Integrated: The data generated by the SDC can easily be included into the well-structured data archive developed for SDO, which is widely used for space weather research and operations.SDC measurements of magnetic field and coronal structures are designed to be incorporated in the state-of-the-art numerical models that are essential for extending our understanding of the processes that create CMEs, particle events, and flares.

This chapter summarizes how observations of the Sun from space have revolutionized the understanding of our star. In space, instruments can observe the Sun in spectral regions that are absorbed by the Earth's atmosphere. Equally important is the ability to make long-duration, high-spatial, and spectral-resolution observations that are impossible to obtain on the ground even with a network of telescopes that span the Earth. It is impossible to cover the hundreds of rocket, balloon, and satellite missions that have contributed to our current knowledge of solar processes, but an attempt has been made to capture how data from space have increased our understanding of the Sun. The chapter also tries to put the development of space solar physics into the context of national and international political, national security, and scientific goals. Early in the Space Age, an "open sky policy" was accepted internationally: space has no national boundaries. The chapter also tracks how the traditional science policy of data ownership by the developers of experiments evolved into open data policies that were gradually supported by national governments that funded the scientists.

We explore new opportunities for solar physics that could be realized by future missions providing sustained observations from vantage points away from the Sun-Earth line. These include observations from the far side of the Sun, at high latitudes including over the solar poles, or from near-quadrature angles relative to the Earth (e.g., the Sun-Earth L4 and L5 Lagrangian points). Such observations fill known holes in our scientific understanding of the three-dimensional, time-evolving Sun and heliosphere, and have the potential to open new frontiers through discoveries enabled by novel viewpoints.

ABSTRACT With the global view and high-cadence observations from Solar Dynamics Observatory/Atmospheric Imaging Assembly and Solar TErrestrial RElations Observatory, many spatially separated solar eruptive events appear to be coupled. However, the mechanisms for “sympathetic” events are still largely unknown. In this study, we investigate the impact of an erupting flux rope on surrounding solar structures through large-scale magnetic coupling. We build a realistic environment of the solar corona on 2011 February 15 using a global magnetohydrodynamics model and initiate coronal mass ejections (CMEs) in active region 11158 by inserting Gibson–Low analytical flux ropes. We show that a CME’s impact on the surrounding structures depends not only on the magnetic strength of these structures and their distance to the source region, but also on the interaction between the CME and the large-scale magnetic field. Within the CME expansion domain where the flux rope field directly interacts with the solar structures, expansion-induced reconnection often modifies the overlying field, thereby increasing the decay index. This effect may provide a primary coupling mechanism underlying the sympathetic eruptions. The magnitude of the impact is found to depend on the orientation of the erupting flux rope, with the largest impacts occurring when the flux rope is favorably oriented for reconnecting with the surrounding regions. Outside the CME expansion domain, the influence of the CME is mainly through field line compression or post-eruption relaxation. Based on our numerical experiments, we discuss a way to quantify the eruption impact, which could be useful for forecasting purposes.

The Interface Region Imaging Spectrograph (IRIS) reveals small-scale rapid brightenings in the form of bright grains all over coronal holes and the quiet Sun. These bright grains are seen with the IRIS 1330, 1400, and 2796 Å slit-jaw filters. We combine coordinated observations with IRIS and from the ground with the Swedish 1 m Solar Telescope (SST) which allows us to have chromospheric (Ca ii 8542 Å, Ca ii H 3968 Å, Hα, and Mg ii k 2796 Å) and transition region (C ii 1334 Å, Si iv 1403 Å) spectral imaging, and single-wavelength Stokes maps in Fe i 6302 Å at high spatial ( 0 &farcs; 33 ?> ), temporal, and spectral resolution. We conclude that the IRIS slit-jaw grains are the counterpart of so-called acoustic grains, i.e., resulting from chromospheric acoustic waves in a non-magnetic environment. We compare slit-jaw images (SJIs) with spectra from the IRIS spectrograph. We conclude that the grain intensity in the 2796 Å slit-jaw filter comes from both the Mg ii k core and wings. The signal in the C ii and Si iv lines is too weak to explain the presence of grains in the 1300 and 1400 Å SJIs and we conclude that the grain signal in these passbands comes mostly from the continuum. Although weak, the characteristic shock signatures of acoustic grains can often be detected in IRIS C ii spectra. For some grains, a spectral signature can be found in IRIS Si iv. This suggests that upward propagating acoustic waves sometimes reach all the way up to the transition region.

Spectroscopic observations of prominence eruptions associated with coronal mass ejections (CMEs), although relatively rare, can provide valuable plasma and three-dimensional geometry diagnostics. We report the first observations by the Interface Region Imaging Spectrograph mission of a spectacular fast CME/prominence eruption associated with an equivalent X1.6 flare on 2014 May 9. The maximum plane-of-sky and Doppler velocities of the eruption are 1200 and 460 km s(-1), respectively. There are two eruption components separated by similar to 200 km s(-1) in Doppler velocity: a primary, bright component and a secondary, faint component, suggesting a hollow, rather than solid, cone-shaped distribution of material. The eruption involves a left-handed helical structure undergoing counterclockwise (viewed top-down) unwinding motion. There is a temporal evolution from upward eruption to downward fallback with less-than-free-fall speeds and decreasing nonthermal line widths. We find a wide range of Mg II k/h line intensity ratios (less than similar to 2 expected for optically-thin thermal emission): the lowest ever reported median value of 1.17 found in the fallback material, a comparably high value of 1.63 in nearby coronal rain, and intermediate values of 1.53 and 1.41 in the two eruption components. The fallback material exhibits a strong (>5 sigma) linear correlation between the k/h ratio and the Doppler velocity as well as the line intensity. We demonstrate that Doppler dimming of scattered chromospheric emission by the erupted material can potentially explain such characteristics.

Solar magnetism displays a host of variational timescales of which the enigmatic 11-year sunspot cycle is most prominent. Recent work has demonstrated that the sunspot cycle can be explained in terms of the intra- and extra-hemispheric interaction between the overlapping activity bands of the 22-year magnetic polarity cycle. Those activity bands appear to be driven by the rotation of the Sun’s deep interior. Here we deduce that activity band interaction can qualitatively explain the ‘Gnevyshev Gap’—a well-established feature of flare and sunspot occurrence. Strong quasi-annual variability in the number of flares, coronal mass ejections, the radiative and particulate environment of the heliosphere is also observed. We infer that this secondary variability is driven by surges of magnetism from the activity bands. Understanding the formation, interaction and instability of these activity bands will considerably improve forecast capability in space weather and solar activity over a range of timescales.

The High-Resolution Coronal Imager (Hi-C) was flown on a NASA sounding rocket on 11 July 2012. The goal of the Hi-C mission was to obtain high-resolution (≈ 0.3 – 0.4′′), high-cadence (≈ 5 seconds) images of a solar active region to investigate the dynamics of solar coronal structures at small spatial scales. The instrument consists of a normal-incidence telescope with the optics coated with multilayers to reflect a narrow wavelength range around 19.3 nm (including the Fe xii 19.5-nm spectral line) and a 4096×4096 camera with a plate scale of 0.1′′ pixel−1. The target of the Hi-C rocket flight was Active Region 11520. Hi-C obtained 37 full-frame images and 86 partial-frame images during the rocket flight. Analysis of the Hi-C data indicates the corona is structured on scales smaller than currently resolved by existing satellite missions.

The Interface Region Imaging Spectrograph (IRIS) small explorer spacecraft provides simultaneous spectra and images of the photosphere, chromosphere, transition region, and corona with 0.33-0.4 arcsec spatial resolution, 2 s temporal resolution and 1 km/s velocity resolution over a field-of-view of up to 175 arcsec x 175 arcsec. IRIS was launched into a Sun-synchronous orbit on 27 June 2013 using a Pegasus-XL rocket and consists of a 19-cm UV telescope that feeds a slit-based dual-bandpass imaging spectrograph. IRIS obtains spectra in passbands from 1332-1358, 1389-1407 and 2783-2834 Angstrom including bright spectral lines formed in the chromosphere (Mg II h 2803 Angstrom and Mg II k 2796 Angstrom) and transition region (C II 1334/1335 Angstrom and Si IV 1394/1403 Angstrom). Slit-jaw images in four different passbands (C II 1330, Si IV 1400, Mg II k 2796 and Mg II wing 2830 Angstrom) can be taken simultaneously with spectral rasters that sample regions up to 130 arcsec x 175 arcsec at a variety of spatial samplings (from 0.33 arcsec and up). IRIS is sensitive to emission from plasma at temperatures between 5000 K and 10 MK and will advance our understanding of the flow of mass and energy through an interface region, formed by the chromosphere and transition region, between the photosphere and corona. This highly structured and dynamic region not only acts as the conduit of all mass and energy feeding into the corona and solar wind, it also requires an order of magnitude more energy to heat than the corona and solar wind combined. The IRIS investigation includes a strong numerical modeling component based on advanced radiative-MHD codes to facilitate interpretation of observations of this complex region. Approximately eight Gbytes of data (after compression) are acquired by IRIS each day and made available for unrestricted use within a few days of the observation.

We present the first results of sunspot oscillations from observations by the Interface Region Imaging Spectrograph. The strongly nonlinear oscillation is identified in both the slit-jaw images and the spectra of several emission lines formed in the transition region and chromosphere. We first apply a single Gaussian fit to the profiles of the Mg II 2796.35 angstrom, C II 1335.71 angstrom, and Si IV 1393.76 angstrom lines in the sunspot. The intensity change is similar to 30%. The Doppler shift oscillation reveals a saw tooth pattern with an amplitude of similar to 10 km s(-1) in Si IV. The Si IV oscillation lags those of C II and Mg II by similar to 6 and similar to 25 s, respectively. The line width suddenly increases as the Doppler shift changes from redshift to blueshift. However, we demonstrate that this increase is caused by the superposition of two emission components. We then perform detailed analysis of the line profiles at a few selected locations on the slit. The temporal evolution of the line core is dominated by the following behavior: a rapid excursion to the blue side, accompanied by an intensity increase, followed by a linear decrease of the velocity to the red side. The maximum intensity slightly lags the maximum blueshift in Si IV, whereas the intensity enhancement slightly precedes the maximum blueshift in Mg II. We find a positive correlation between the maximum velocity and deceleration, a result that is consistent with numerical simulations of upward propagating magnetoacoustic shock waves.

The Interface Region Imaging Spectrograph (IRIS) is a NASA Small Explorer Mission (SMEX) launched on 27 June 2013 with the goal to discover how the outer atmosphere of the Sun is energized. It is designed to accomplish this by combining IRIS's on-orbit imaging and spectral measurements with simultaneous observations from the JAXA /ISAS HINODE and NASA SDO missions. These observations when combined with a new generation of sophisticated computer models using code developed by an international team, will allow, for the first time, the determination of the physical processes responsible for the activity in the outer solar atmosphere that result from the transfer of energy from turbulent convection to non-thermal energy release in the chromosphere and corona. The IRIS is a collaboration of Lockheed Martin Advance Technology Center(LMATC) and Space and Electronic Systems(LM S&ES), the University of Montana (UM), the Smithsonian Astrophysical Observatory (SAO), NASA Ames Research Center (AMES), the University of Oslo (UIO), and the Norwegian Space Center (NSC). Here we outline the IRIS and the ground and space supporting observations as well as comparisons of the observations with numerical simulations of both images and spectra.

![Figure][1] NASA/GSFC/CI LAB The Sun has been the subject of human curiosity since the dawn of time. It provides the energy that makes Earth habitable and is also the closest star to Earth. The Sun thus acts as a laboratory that provides detailed views of physical processes that occur in other, much more distant, astrophysical objects. Much progress has been made in understanding how nuclear fusion powers the Sun's 15-million-degree core and the mechanisms that transport this energy to the visible surface, where most of the light that reaches Earth is released. However, major unresolved questions linger about how the heliosphere, the Sun's outer atmosphere in which we live, is shaped and powered. We do not understand the counterintuitive rise of temperature from the 6000-K surface to millions of degrees in the Sun's outer atmosphere or corona. Equally puzzling is the solar wind, a high-speed continuous stream of particles that permeates space around Earth. These are not academic problems: Violent explosions such as flares and coronal mass ejections cause bouts of bad space weather that threaten power grids, satellites, and astronauts. These eruptions originate in and travel through this poorly understood solar atmosphere and wind. An important step in our quest to better understand such violent events is then to explore what drives the quiescent state of the solar atmosphere. In June 2013, NASA launched the Interface Region Imaging Spectrograph (IRIS), an Earth-orbiting small explorer satellite with a 20-cm telescope onboard. IRIS uses gratings to split the Sun's near- and far-ultraviolet light into its constituent wavelengths, in order to remotely probe the physical conditions in the interface region that consists of the chromosphere and transition region. Recent research suggested that it is here, at the interface between surface and corona, that answers to some of the more vexing unresolved questions in solar physics might be found. In this special section of Science , five Reports exploit the high-resolution images and spectra obtained with IRIS to present major advances toward a comprehensive understanding of how the solar atmosphere is energized ([sciencemag.org/special/iris][2]). Testa et al. find compelling evidence for the presence of high-energy particles generated during coronal nanoflares, small-scale heating events long hypothesized to drive coronal heating through the release of energy when magnetic field lines reconnect. These results provide constraints for models of the poorly understood mechanism that accelerates these electrons to such high energies and that probably acts under many other astrophysical conditions. Hansteen et al. reveal the presence of small-scale magnetic loops in high-resolution images of IRIS and advanced three-dimensional numerical models, resolving a long-standing debate about the nature of the transition region emission. These results vindicate the view that much of this emission does not originate in the “classical” transition region between the surface and the hot loops. Rather, the emission occurs in “unresolved fine structure” that has now been spatially resolved, thereby removing a major impediment to the modeling of coronal loops. Peter et al. exploit the power of high-resolution spectroscopy to reveal a solar atmosphere turned upside down: Hot plasma at 100,000 K is found closer to the solar surface than previously imagined, sandwiched by cool plasma both below and above. The hot plasma is heated by “bombs” in which the reconnection of magnetic fields leads to rapid heating. These unexpected results will likely lead to a reassessment of other phenomena in the low solar atmosphere, such as the mysterious Ellerman bombs discovered almost a century ago. De Pontieu et al. describe a chromosphere that is replete with twisting motions on very small scales that are associated with the heating of plasma to transition region temperatures. They are the signature of propagating Alfven wave pulses and provide support for recently developed models of atmospheric heating and dynamics and insight into the transport of helicity in the solar atmosphere. Tian et al. find evidence of high-speed jets at the root of the solar wind, fountains of plasma that appear to undergo rapid heating from chromospheric to transition region temperatures. These observations provide support for recent suggestions that the solar wind does not necessarily originate only from gentle evaporation in funnels rooted in strong field regions. Together, these results provide critical pieces in the still-unsolved puzzle of fully understanding of how the Sun shapes and affects the heliosphere. With solar activity at high levels, more advances from the imaging spectrograph onboard IRIS can be expected, especially with respect to flares and coronal mass ejections. [1]: pending:yes [2]: http://sciencemag.org/special/iris

The High-resolution Coronal Imager (Hi-C) flew aboard a NASA sounding rocket on 2012 July 11 and captured roughly 345 s of high-spatial and temporal resolution images of the solar corona in a narrowband 193 Å channel. In this paper, we analyze a set of rapidly evolving loops that appear in an inter-moss region. We select six loops that both appear in and fade out of the Hi-C images during the short flight. From the Hi-C data, we determine the size and lifetimes of the loops and characterize whether these loops appear simultaneously along their length or first appear at one footpoint before appearing at the other. Using co-aligned, co-temporal data from multiple channels of the Atmospheric Imaging Assembly on the Solar Dynamics Observatory, we determine the temperature and density of the loops. We find the loops consist of cool (∼105 K), dense (∼1010 cm−3) plasma. Their required thermal energy and their observed evolution suggest they result from impulsive heating similar in magnitude to nanoflares. Comparisons with advanced numerical simulations indicate that such dense, cold and short-lived loops are a natural consequence of impulsive magnetic energy release by reconnection of braided magnetic field at low heights in the solar atmosphere.

We present an overview of solar sounding rocket instruments developed jointly by NASA Marshall Space Flight Center and the University of Alabama in Huntsville. The High Resolution Coronal Imager (Hi-C) is an EUV (19.3 nm) imaging telescope which was flown successfully in July 2012. The Chromospheric Lyman-Alpha SpectroPolarimeter (CLASP) is a Lyman Alpha (121.6 nm) spectropolarimeter developed jointly with the National Astronomical Observatory of Japan and scheduled for launch in 2015. The Marshall Grazing Incidence X-ray Spectrograph is a soft X-ray (0.5-1.2 keV) stigmatic spectrograph designed to achieve 5 arcsecond spatial resolution along the slit.

Plasma flows within prominences/filaments have been observed for many years and hold valuable clues concerning the mass and energy balance within these structures. Previous observations of these flows primarily come from H-alpha and cool EUV lines (e.g., 304A) where estimates of the size of the prominence threads has been limited by the resolution of the available instrumentation. Evidence of `counter-steaming' flows has previously been inferred from these cool plasma observations but now, for the first time, these flows have been directly imaged along fundamental filament threads within the million degree corona (at 193A). In this work we present observations of an active region filament observed with Hi-C that exhibits anti-parallel flows along adjacent filament threads. Complementary data from SDO/AIA and HMI are presented. The ultra-high spatial and temporal resolution of Hi-C allow the anti-parallel flow velocities to be measured (70-80 km/s) and gives an indication of the resolvable thickness of the individual strands (0.8'' +/- 0.1''). The temperature distribution of the plasma flows was estimated to be log T(K) = 5.45 +/- 0.10 using EM loci analysis. We find that SDO/AIA cannot clearly observe these anti-parallel flows nor measure their velocity or thread width due to its larger pixel size. We suggest that anti-parallel/counter-streaming flows are likely commonplace within all filaments and are currently not observed in EUV due to current instrument spatial resolution.

The high-cadence, comprehensive view of the solar corona by SDO/AIA shows many events that are widely separated in space while occurring close together in time. In some cases, sets of coronal events are evidently causally related, while in many other instances indirect evidence can be found. We present case studies to highlight a variety of coupling processes involved in coronal events. We find that physical linkages between events do occur, but concur with earlier studies that these couplings appear to be crucial to understanding the initiation of major eruptive or explosive phenomena relatively infrequently. We note that the post-eruption reconfiguration timescale of the large-scale corona, estimated from the extreme-ultraviolet afterglow, is on average longer than the mean time between coronal mass ejections (CMEs), so that many CMEs originate from a corona that is still adjusting from a previous event. We argue that the coronal field is intrinsically global: current systems build up over days to months, the relaxation after eruptions continues over many hours, and evolving connections easily span much of a hemisphere. This needs to be reflected in our modeling of the connections from the solar surface into the heliosphere to properly model the solar wind, its perturbations, and the generation and propagation of solar energetic particles. However, the large-scale field cannot be constructed reliably by currently available observational resources. We assess the potential of high-quality observations from beyond Earth's perspective and advanced global modeling to understand the couplings between coronal events in the context of CMEs and solar energetic particle events.

The current generation of space and ground-based experiments in solar physics produces any megabyte-sized image data arrays. Optical disk technology is the leading candidate for convenient analysis, distribution, and archiving of these data. We have been developing data analysis procedures which use both analog and digital optical disks for the study of solar phenomena. The analog disks allowed us to view movies much more effectively than video tape. In particular, it has been possible to develop a PC-based movie control program for interactive analysis of movies. The digital disks make it easy to have many, very large image data bases on the computer without loading numerous tapes. Our experience indicates that both the system design and software must be developed based on studying real data. Our basic approach to learning about managing large blocks of image data is to: (1) produce, analyze, and publish the high resolution movies from observing runs at Sacramento Peak Observatory with a tunable filter and a charge coupled device (CCO) camera; (2) collaborate with the Swedish Solar Observatory to obtain high resolution movies in the solar continuum; and (3) study three-dimensional Fourier filtering techniques for hydrodynamic studies and suppression of atmospheric seeing.

This paper presents a study of a large sample of global disturbances in the solar corona with characteristic propagating fronts as intensity enhancement, similar to the phenomena that have often been referred to as Extreme Ultraviolet Imaging Telescope (EIT) waves or extreme-ultraviolet (EUV) waves. Now EUV images obtained by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory provide a significantly improved view of these large-scale coronal propagating fronts (LCPFs). Between 2010 April and 2013 January, a total of 171 LCPFs have been identified through visual inspection of AIA images in the 193 angstrom channel. Here we focus on the 138 LCPFs that are seen to propagate across the solar disk, first studying how they are associated with flares, coronal mass ejections (CMEs), and type II radio bursts. We measure the speed of the LCPF in various directions until it is clearly altered by active regions or coronal holes. The highest speed is extracted for each LCPF. It is often considerably higher than EIT waves. We do not find a pattern where faster LCPFs decelerate and slow LCPFs accelerate. Furthermore, the speeds are not strongly correlated with the flare intensity or CME magnitude, nor do they show an association with type II bursts. We do not find a good correlation either between the speeds of LCPFs and CMEs in a subset of 86 LCPFs observed by one or both of the Solar and Terrestrial Relations Observatory spacecraft as limb events.

The High-resolution Coronal Imager (Hi-C) has provided Fe XII 193A images of the upper transition region moss at an unprecedented spatial (~0.3-0.4 arcsec) and temporal (5.5s) resolution. The Hi-C observations show in some moss regions variability on timescales down to ~15s, significantly shorter than the minute scale variability typically found in previous observations of moss, therefore challenging the conclusion of moss being heated in a mostly steady manner. These rapid variability moss regions are located at the footpoints of bright hot coronal loops observed by SDO/AIA in the 94A channel, and by Hinode/XRT. The configuration of these loops is highly dynamic, and suggestive of slipping reconnection. We interpret these events as signatures of heating events associated with reconnection occurring in the overlying hot coronal loops, i.e., coronal nanoflares. We estimate the order of magnitude of the energy in these events to be of at least a few $10^{23}rg, also supporting the nanoflare scenario. These Hi-C observations suggest that future observations at comparable high spatial and temporal resolution, with more extensive temperature coverage are required to determine the exact characteristics of the heating mechanism(s).