Polar Perspectives Abstracts

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Tom Berger, CU Boulder

Title: SPOC: the Solar Polar Observing Constellation

Abstract: The most glaring gap in our ability to forecast space weather is the lack of a full-Sun magnetic field measurement: the synoptic magnetograms currently used to model solar wind and CME propagation are fictional constructs based on limited measurements from the Earth-Sun line in the ecliptic plane. Measurements of the solar polar magnetic fields from the ecliptic plane are highly inaccurate, leading to significant errors in predictions of heliospheric current sheet location and coronal hole structure and hence to large errors in predictions of solar wind high-speed stream (HSS) and co-rotating interaction region (CIR) events. Flux transport models and helioseismic reconstructions can be used to approximate the evolution of magnetic structure on the unseen hemisphere, but these will never achieve the accuracy of actual measurements. At the same time, the final frontier in solar exploration is the measurement of flows and magnetic field structure in the polar regions. We have tantalizing views of unexpected magnetic structure from Hinode/SP measurements and Solar Orbiter will achieve glimpses of the polar regions from its maximum inclination of 34 degrees. But as the Juno mission has shown, there is no substitute for achieving a true polar orbit if the goal is high-resolution measurements of flows and field structure. Here we present a mission concept for a constellation of four small satellites with a primary payload of an imaging magnetograph and a coronagraph placed into a low-eccentricity solar polar orbit using Jupiter gravitational assist with a final perihelion distance of approximately 0.5 AU. By phasing the satellites in longitude, the constellation will achieve a true synchronic measurement of the full solar magnetic field, including accurate polar fields, and provide novel multi-view CME measurements for improved forecasting of geomagnetic storm onset. Additional in-situ instrumentation will enable studies of solar wind and CME structure from unique vantage points and provide advanced warning of CME magnetic field orientation when one of the satellites is in, or close to, the Sun-Earth line. The SPOC mission exemplifies the kind of hybrid operational-research mission that fills gaps in space weather forecasting data while also providing discovery-level science observations. [Coauthors: Tom Berger (CU/SWx-TREC), Nicole Duncan (Ball Aerospace), Natasha Bosanac (CU/AES), Jeffrey Van Cleve (Ball Aerospace)]

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Aaron Birch, Max Planck Institute for Solar System Research

Title: Helioseismology from a polar perspective

Abstract: Measurements of flows at high latitudes promise to improve our understanding of solar convection and the solar cycle. Important open questions include the behavior of differential rotation, torsional oscillations, meridional circulation, and the supergranulation pattern at high latitudes. Local helioseismology, local correlation tracking, and direct Doppler observations can be used to measure these flow. Local helioseismology would require time-series of Dopplergrams with four arc-second resolution at a cadence of one minute or better. Correlation tracking would require pairs of intensity images with at least one arc-second resolution separated by no more than about one minute; the spacing between pairs could be much longer. Magnetograms would be required for context and if taken with a sufficient cadence and resolution could be used for correlation tracking as well. Stereoscopic helioseismology potentially provides access to acoustic wave ray paths that cannot be studied from a single vantage point. The benefit of stereoscopic helioseismology for learning about the solar interior is a current research topic. In addition, observations from out of the ecliptic plane could be used to obtain, in combination with simultaneous observations of the same portion of the Sun from along the Sun-Earth line, two components of Doppler velocity. These observations would enable studies of convection, the physics of p-modes, and oscillations in sunspots.

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Amir Caspi, SwRI

Title: The need for spectrally resolved soft X-ray observations of solar polar regions

Abstract: TBD

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Heather Elliott, SwRI

Title: Understanding the origin and acceleration of the fast solar wind: the need for new observations

Abstract: The solar wind emitted from large polar coronal holes is faster than the solar wind emitted from smaller equatorial coronal holes. Additionally, the wind emitted from the center of large polar coronal holes is faster than the wind emitted from the edges of the polar coronal holes. In the small equatorial holes there is a very small region with a similar temperature-speed relationship as observed in the center of the large polar coronal holes, but the edges of the equatorial holes have a different relationship. Several studies reveal that the heavy ion charge state density ratios change at the edges of holes, but the elemental abundance ratios are relatively flat across both the center and edges of the fast streams. These plasma and composition results indicate there could a boundary region emitting moderately fast wind near the outer edges of all coronal holes. Smaller holes may have a small core region and consist mostly of such a boundary region that emits moderately fast wind. Such a boundary region may form in the corona because the elemental abundances reflect the chromospheric properties and the charge state ratios reflect the coronal properties. Even over the middle of the large polar coronal holes Ulysses observations indicate there are small variations in the solar wind speed that exhibit compression and rarefaction signatures because as the solar wind speed rises (decreases) the density is elevated (reduced) as expected for compressions (rarefactions). Solar and coronal observations reveal that outflowing material may be intimately linked with the chromosphere network. By combining solar and coronal imaging with in situ observations from polar and midlatitude vantage points, firm links can be established between features on the Sun and the properties of the solar wind. We present compact particle instrumentation capable of addressing these open issues and the need for joint solar and heliospheric observations

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Bob Ergun, CU Boulder, LASP

Title: Planetary magnetospheres – The importance of the understanding noth the full system and the small details

Abstract: he Sun is a primary source of energy that drives a rich variety of processes in planetary magnetospheres beginning with a bow shock, generating of turbulence, promoting of magnetic reconnection, energizing particles, and ultimately causing spectacular aurorae in the polar areas. Almost all regions of Earth’s magnetosphere and much of Jupiter’s and Saturn’s magnetospheres now have been visited to some degree, which allows for a large-scale picture that includes the boundaries, identifies the critical processes in these boundary regions, and indicates how energy and mass is transferred between regions. These large-scale models have led to what I call a “2nd generation” science, which concentrates on the detailed physics that govern the interactions at the boundaries and dictate the evolution of the system. The combination of developing a large-scale model and investigating the detailed physics of the critical regions has been a highly successful method of advancing the understanding of magnetospheres. One can apply a similar argument for understanding the solar corona. While images of the equatorial regions of the Sun in a range of spectral bands with ever increasing resolution have been invaluable, a full picture that includes the polar regions is not available. Furthermore, many physical processes have not been fully detailed, largely due to the difficulties of in-situ observations. I show examples of work done at Earth and Jupiter that advocate a polar mission to the sun and advocate for more in-situ observations such as those to be made by Solar Probe.

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Sarah Gibson, NCAR/HAO

Title: Solar physics from unconventional viewpoints

Abstract: 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 (SEL). 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 & L5 Lagrange 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.

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Don Hassler, SwRI

Title: SOLARIS: A small-sat solar polar mission concept

Abstract: SOLARIS is a versatile small-sat mission concept that could fly as a stand-alone mission, or part of a constellation of 2-4 small-Sats, in response to near-term or future mission opportunities. SOLARIS could fly as a 3-axis stabilized or spinning spacecraft and include any combination of remote sensing and in-situ instruments, depending on the science objectives and mission constraints.

This talk will describe the SOLARIS mission concept and discuss various scientific drivers of such a mission to strategically complement and build upon the advances of Parker Solar Probe and Solar Orbiter. In particular, I will discuss scientific objectives that can only be addressed by a dedicated Solar Polar Mission, and what requirements these scientific objectives place on the observational, orbital and mission requirements for a small-Sat mission such as SOLARIS. [Coauthors: Donald M. Hassler (SwRI), Jeffrey Newmark (GSFC), Sarah Gibson (HAO/NCAR), Marco Velli (UCLA), Neil Murphy (JPL)]

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Carl Henney, AFRL

Title: Forecasting space weather with global solar magnetic maps

Abstract: Global solar magnetic maps, which provide estimates of the solar photospheric magnetic field distribution, are the primary input data driver of coronal and heliospheric models. Though full-disk solar magnetograms are now typically available with high temporal cadence, estimating the global magnetic field distribution continues to be a challenge since less than half of the solar surface is viewable with spectropolarimetric measurements at any given moment in time. The absence of solar far-side magnetic field observations and lack of quality polar data result in temporal and spatial discontinuities within global maps at the east-limb boundary and at the poles. Accounting for differential rotation, together with meridional and supergranulation flows, the flux transport component of the ADAPT (Air Force Data Assimilative Photospheric flux Transport) model evolves an ensemble of realizations to estimate the polar and far-side regions within global maps. In addition to coronal and solar wind models, global magnetic maps are utilized to forecast key space weather parameters using SIFT (Solar Indices Forecasting Tool). The SIFT empirical models utilize ADAPT global magnetic maps to predict typical input parameters to ionospheric and thermospheric models, e.g., selected bands (between 0.1 to 175 nm) of solar soft X-ray (XUV), far ultraviolet (FUV), and extreme ultraviolet (EUV) irradiance, along with observed F10.7 (solar 10.7 cm, 2.8 GHz, radio flux), the sunspot number (SSN), and the Mg II core-to-wing ratio. For the past few years, the ADAPT and SIFT models have been operating continuously in a prototype mode at the National Solar Observatory (NSO), generating global photospheric magnetic maps and F10.7 predictions in near real-time. Input to the ADAPT model includes photospheric magnetograms from the NISP (NSO Integrated Synoptic Program) ground-based instruments, GONG (Global Oscillation Network Group) and VSM (Vector SpectroMagnetograph). More recently, the ADAPT model has been updated to utilize line-of-sight and vector magnetograms from HMI. The benefits of including far-side flux evolution will be reviewed, along with the expected implications when full-disk magnetograms of the far-side and polar regions become available, e.g., from the Polarimetric and Helioseismic Imager (PHI) on Solar Orbiter.

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Neal Hurlburt, LMATC

Title: New observations for actionable space weather forecasts

Abstract: The architecture required for actionable space weather forecasts is actively being discussed by space weather community and government agencies around the world. There is a growing consensus that any architecture must include observations of the solar magnetic fields at the surface of the sun and of the surrounding corona from multiple viewpoints around the Sun. Understanding the magnetic field emerging from the solar surface and its interaction with the solar corona is essential for developing methods to forecast space weather. Accurate forecasts require a full knowledge of the global distribution of the magnetic field. STEREO EUVI observations have demonstrated the value of multiple views of the corona to assess trigger conditions for flares and CMEs, but to date, magnetograph observations and operational EUV observations, are only available from instruments located on the Sun-Earth line. We present concepts for the next-generation of space-based magnetographs and extended coronal imagers which could be deployed throughout the heliosphere on small sat constellations or larger observatories to enable greater observational coverage of the solar magnetic fields and a 3-dimensional view of coronal structures. We also discuss the results of extended coronal imaging out to 4 Rsun acquired by the SUVI instruments on GOES-16 and -17 and how both magnetographs and EUV imagers benefit space weather capabilities.

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Les Johnson, NASA MSFC

Title: Solar sail propulsion - status and mission applications

Abstract: Solar sail propulsion uses sunlight to propel vehicles through space by reflecting solar photons from a large, mirror-like sail made of a lightweight, highly reflective material. The continuous photonic pressure provides propellantless thrust to perform a wide range of advanced maneuvers, such as to hover indefinitely at points in space, or conduct orbital plane changes more efficiently than conventional chemical propulsion. Solar sails can play a critical role in enabling solar and heliophysics missions. Solar sail technology is maturing rapidly with the flight of IKAROS and NanoSail-D (2010), LightSail-A (2015) and the planned flight of NASA’s Near Earth Asteroid (NEA) Scout in 2020. Missions leveraging advances in solar sail technology to support Heliophysics Decadal Survey goals are now feasible.

Because of the continuous force provided by solar radiation pressure on a solar sail, solar sail spacecraft can fly in non-Keplerian orbits and can continually maneuver throughout flight without the use of (finite) propellant. A number of science mission concepts have been identified that make optimum use of solar sail technology as the next phase in the development of solar sail propulsion as the go-to technology for high C3 missions. Among them are Solar Polar Imager, GeoSail (McInnes, et al. 2001), Heliostorm, and Interstellar Probe (Mewaldt, et al 2001). The status and mission applicability of solar sail propulsion will be discussed.

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Michael Kirk, NASA GSFC / Catholic University of America

Title: An assessment of EUV polar coronal holes

Abstract: Polar coronal holes offer an indirect measurement of the polar magnetic flux, which is a significant component to our understanding of the solar cycle. Polar holes are prevalent during solar minimum, non-axisymmetric, and are stable. They are regularly observed capping the northern and southern solar poles in EUV images of the corona and are understood as the primary source of the fast solar wind. We make measurements of polar hole perimeter boundary with three EUV wavelengths from 1996 through 2017 using five different space-based imagers: SOHO EIT, STEREO A and B EUVI, PROBA2 SWAP, and SDO AIA. Each time series of coronal hole parameters produce a slightly different perspective on the polar hole. This produces a difficult data problem: how to reconcile multi-band, multi-instrument, heteroscedastic measurements with periodic signals. We separate the oscillations associated with systematic measurement errors from physical phenomena using a Tikhonov regularization scheme to generalize the conventional Lomb-Scargle method. Using this technique allows us to simultaneously analyze the physical properties of polar coronal holes and identify regular periodicities in our data from other systematic origins.

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Rudolf Komm / NSO

Title: Subsurface meridional flow at high latitudes

Abstract: We have estimated the meridional flow at high latitudes and found that the flow direction might change during the course of a solar cycle. To study the meridional flow during Solar Cycles 23 and 24, we have combined ring-diagram results derived from MDI, GONG, and SDO/HMI. GONG and MDI provide ring-diagram velocity measurements up to 52.5 degree latitude, while SDO/HMI provides flow up to 75 degree. For the meridional flow, we can assume that the values are zero at the poles on time scales of one solar rotation and longer and spatial scales similar to ring-diagram patches and fit the measured flows with an orthogonal polynomial expansion. These fits suggest that equatorward meridional flows (counter-cells) might exist at about 80 degree latitude except during the declining phase of the solar cycle.

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Vladimir Krasnoselskikh, LPCEE, CNRS, Orleans, France/ SSL, UCB, Berkeley, USA

Title: ICARUS mission, next step of coronal exploration after Solar Orbiter and Parker Solar Probe

Abstract: The primary scientific goal of ICARUS, a mother-daughter satellite mission, will be to determine how the magnetic field and plasma dynamics in the outer solar atmosphere give rise to the corona, the solar wind and the entire heliosphere. Reaching this goal will be a Rosetta-stone step, with results broadly applicab the le within the fields of space plasma physics and astrophysics. Within ESA’s Cosmic Vision roadmap,these science goals address the theme 2: How does the solar system work ?" by investigating basic processes occurring from the Sun to the edge of the Solar System. ICARUS will not only advance our understanding of the plasma environment around our Sun, but also of the numerous magnetically active stars with hot plasma coronae. ICARUS I will perform the first ever direct in situ measurements of electromagnetic fields, particle acceleration, wave activity, energy distribution and flows directly in the regions where the solar wind emerges from the coronal plasma. ICARUS I will have a perihelion at 1 Solar radius from its surface, it will cross the region where the major energy deposition occurs. The polar orbit of ICARUS I will enable crossing the regions where both the fast and slow wind are generated. It will probe local characteristics of the plasma and provide unique information about the physical processes involved in the creation of the solar wind. ICARUS II will observe this region using remote-sensing instruments, providing simultaneous information about regions crossed by ICARUS I and the solar atmosphere below as observed by solar telescopes. It will thus provide bridges for understanding the magnetic links between the heliosphere and the solar atmosphere. Such information is crucial to our understanding of the plasma physics and electrodynamics of the solar atmosphere. ICARUS II will also play a very important relay role, enabling the radio-link with ICARUS I. It will receive, collect and store information transmitted from ICARUS I during its closest approach to the Sun. It will also perform preliminary data processing before transmitting it to the Earth. Performing such unique in situ measurements in the region where presumably deadly solar energetic particles are energized, ICARUS will make fundamental contributions to our ability to monitor and forecast the space radiation environment. Such a knowledge is extremely important for future space explorations, especially for long-term manned space missions. [Co-authors: Bruce T. Tsurutani, Marco Velli, Milan Maksimovic, Mikhail Balikhin, Thierry Dudok de Wit, Matthieu Kretzschmar, and the ICARUS Team]

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Paulett Liewer, Jet Propulsion Laboratory, California Institute of Technology

Title: Solar polar concepts: Past studies and missions

Abstract: Our current understanding of the Sun, its atmosphere and interior, as well as its activity and space weather potential, is severely limited by the lack of good observations of the polar and far-side regions. Observations from a polar or high latitude (above 60°) vantage point would revolutionize our understanding of the mechanism of solar activity cycles, polar magnetic field reversals, the internal structure and dynamics of the Sun and its linkage to the heliosphere. While Solar Orbiter will provide out-of-the-ecliptic views up to about 30°, only with extended (many day) observations of the polar regions can the polar flows be determined down to the tachocline where the dynamo may originate. Over the years, various concepts for a mission to explore the polar regions of the Sun have been investigated. Solar sailing a conventional spacecraft to a polar or near-polar orbit has been investigated in depth. Several engineering studies of conventional spacecraft missions using a using a Jupiter gravity assist to get out of the ecliptic (ala Ulysses) have also been performed. More recently, concepts using constellations of small spacecraft to accomplish the same goals have been suggested. In this talk, I will present an overview of some of the various mission concepts that have been proposed, including their advantages and disadvantages and also present science objectives of polar missions.

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Chris Lowder, SwRI

Title: Open magnetic flux and coronal holes: Probing the polar regions

Abstract: Appearing as dark patches in EUV and X-ray imagery, coronal holes provide an observational signature of the roots of open magnetic field in the solar corona. Understanding the formation, evolution, migration, and solar cycle dependence of coronal holes provides an insight into the distribution of associated open magnetic flux and linked space weather impacts. Combining an automated detection methodology with EUV data from SOHO/EIT, SDO/AIA, and STEREO/EUVI A&B, coronal hole footprints were identified over the time span 1996 to 2014. Efforts are underway to modernize this database and extend the temporal range. With multiple spacecraft vantage points merged from mid-2010 onward, enhanced polar coverage improves estimates of coronal hole enclosed open magnetic flux, correcting issues with gaps in polar coverage from a single viewpoint limited to the Sun-Earth line. These improved estimates of open magnetic flux originating from the poles can improve modeling constraints, and highlight the importance of additional vantage points from which to observe solar activity at the poles.

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Chip Manchester, University of Michigan

Title: Polar observations: Impacts for coronal and solar wind modeling

Abstract: We outline how observations obtained from a solar polar perspective can complement simulations of the corona and solar wind transients to inform us of their structure and dynamics. We examine model results from a global coronal model, the Alfven Wave Solar Model (AWSoM) and consider how key features would appear from the poles. The AWSoM model includes low-frequency Alfven wave turbulence with wave reflection and counter-propagating waves, which lead to nonlinear wave dissipation. Thermodynamics are treated with a three temperature formalism: isotropic electron temperature and anisotropic proton temperatures (parallel and perpendicular) with field aligned heat conduction. With this model, a variety structures are produced that may be observed with heliospheric imagers (HIs). For example, dense streamers that can be observed simultaneously from multiple latitudes provide data for 3D tomographic reconstructions. Multiple view points including a polar perspective can also provide 3D localization of dense transient features such as coronal mass ejections (CMEs) and the dense pileups in stream interaction regions (SIRs). In situ instruments placed from a polar orbit would allow clear observations of coronal holes and high-speed streams where plasma wave observations can detect Alfven wave turbulence. Particle observations in turn provide charge state composition that can be used to probe the freeze in temperatures, while higher order velocity moments can also provide temperature anisotropies related to plasma instabilities.

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Scott McIntosh, NCAR/HAO

Title: Exploring longitudinal evolution

Abstract: In recent years we were able to observe the entire sun for the first time. We present just a few of the characteristics of Sun's longitudinal evolution that were readily extracted and also mirror those derived from archived observations. A solar polar mission will permit the characterization of longitudinal activity that could revolutionize (pardon the - intentional - pun) our understanding of the Sun on its own, valuable context for all stars, and for the national strategy to mitigate the impacts of space weather.

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Jeffrey Newmark, NASA GSFC

Title: Concept development for a solar polar mission: SOLar Polar EXplorer (SOLPEX)

Abstract: Understanding the generation of the solar magnetic field and its subsequent driver of activity remains a major outstanding question in heliophysics. Our current understanding of the Sun, its atmosphere, and the connection to the heliosphere is severely limited by the lack of good observations of the polar regions. The SOLar Polar EXplorer (SOLPEX) mission targets the unexplored polar regions and enables crucial observations not possible from lower latitude perspectives. The SOLPEX mission will use a combination of a Jovian gravity assist and solar electric propulsion to place a spacecraft in a 0.5 x 1.5 AU orbit with an inclination of ~90° with respect to solar equator. This challenging orbit is made possible by the recent maturation of solar electric propulsion. Just as our understanding of Jupiter is being revolutionized by the new observations from Juno (looking at the Jovian poles), our understanding of the Sun will be revolutionized by this mission. Through a combination of remote and in-situ sensors, we will observe the polar flows and fields, surface manifestations of magnetic activity, and solar wind structures throughout interplanetary space, connecting the solar interior to the heliosphere. Moreover, SOLPEX serves as a pathfinder for a permanent solar polar sentinel for space weather prediction

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Nariaki Nitta, LMATC

Title: Polar field measured by Hinode SP in comparison with other observations

Abstract: We present our ongoing work to systematically analyze SP data that have been taken under the two Hinode Observing Programs (HOPs) specifically designed to observe the polar field. Here we discuss how the radial field as measured by SP compares with the polar field in synoptic maps constructed from other full-disk magnetograms or magnetic maps that serve as lower-boundaries of MHD global heliospheric simulations. We also compare the long-term (solar cycle) variations of the magnetic field in polar regions as characterized by SP and other magnetographs in the context of other observables in the EUV and radio wavelengths.

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W. Dean Pesnell, NASA/GSFC

Title: Areas and shapes of polar coronal holes

Abstract: We are now watching as solar minimum approaches and the solar polar coronal holes develop for the third time in images using extreme ultraviolet light. During the first two minima, the polar coronal holes were about the same size even as the magnetic field threading the region decreased by 50% from Solar Cycle 23 to Solar Cycle 24. It appears that the polar magnetic field is larger this minimum than the last. How does this affect the areas of the current polar coronal holes? We have measured the areas and shapes of polar coronal holes using EUV imagers and the magnetic field to see whether the insensitivity to field strength continues. We have also noticed that filaments with overlying cavities are associated with the diminution of these longest-lived solar features. We will describe how the polar coronal holes are developing in this minimum. We will also describe what satellites flying above the poles can tell us about these features.

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Gordon Petrie, National Solar Observatory

Title: Towards mapping the Sun's polar magnetic field

Abstract: The Sun's polar field dominates the global structure of the corona and heliosphere over most of the solar cycle, supplies the bulk of the interplanetary magnetic field via the polar coronal holes, and is believed to provide the seed for the magnetic activity cycle that follows. We therefore need magnetograms with good coverage and resolution of the polar fields to study global solar magnetism on a sound observational basis. Present-day synoptic magnetogram observations do not have sufficient spatial resolution or sensitivity to diagnose accurately the polar radial magnetic flux distribution. Recent efforts to study the polar field using existing line-of-sight and high-resolution vector data, and to model full-disk magnetogram observations from elsewhere in the ecliptic, will be summarized. Possible science with a magnetograph flying over the polar caps will then be suggested.

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Vic Pizzo, NOAA

Title: Using an improved HI-1 instrument to advance CME and CIR forecasting

Abstract: While coronagraph imagery has long been used to derive observable forecasting inputs for Earth-directed CMEs in space weather applications, the STEREO mission has highlighted the complementary utility of heliospheric imagers for this purpose. In particular, observations of the type afforded by the HI-1 instruments show great potential for dramatically improving forecasts of CMEs in transit to Earth. The HI-1 FOV covers the important region extending from the outer edge of classic coronagraph domain out into interplanetary space to about 0.5 AU. This region is of great significance for estimating CME propagation, since that is where CMEs decelerate most rapidly due to momentum exchange with the background medium. Accurate knowledge of CME speed and direction in that regime should therefore enable much improved forecasts, since CMEs are largely coasting beyond that point.

Orbiting an updated, improved version of the HI-1 imager at high latitudes would enable several new approaches to CME and high-speed stream forecasting. As an example, HI-1A images processed by the SWRI Pipeline are presented to illustrate how improved sensitivity over this FOV may be used to characterize CMEs and CME morphology over the 0.1-0.5 AU range. For extremely impulsive events of most critical concern to space weather applications, such images enable accurate differentiation between the actual CME ejecta (what we normally think of as “the” CME) and the extended coronal disturbance (blast-wave-like component commonly visible as the faint, milky “halo” in standard coronagraphs) that accompanies them. Upgraded HI-1 imagery would enable these components to be reliably differentiated, and would also offer a new perspective on the 3D aspects of CME ejecta. Such an instrument, in conjunction with a standard coronagraph, should also provide a view of CIR spiral structure heretofore impossible to attain. Finally, used with similar observations from L5 (or even Earth), these observations would enable new types of analyses affording improved forecasts.

To achieve functional forecast capability two such spacecraft – properly phased in orbit – would be required. Given the funding hurdle that would impose, it is stressed that the knowledge to be drawn from a single s/c mission with an upgraded HI-1 imager and coronagraph would still yield a new understanding of CME dynamics and CIR evolution that would ultimately contribute substantially to forecasting aims.

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Nour E. Raouafi, JHUAPL

Title: What can the solar polar perspective bring to space weather research?

Abstract: Sustained remote sensing observations of the solar poles can have significant impact on several open questions in Space Weather research. For example, line of sight magnetograms from the poles (or high inclinations) record the transverse component of the field in active regions that closely corresponds to the Bz component of the erupting structure. This observation is almost impossible to make from the Ecliptic, particularly for Earth-direct Coronal Mass Ejections (CMEs). Coronal imaging can easily follow active regions as the emerge on the Earth’s farside and rotate over the East limb, greatly improving medium to long-term forecasting. Moving outwards, the imaging of the inner heliosphere from a polar perspective can readily decipher how CMEs interact with the ambient solar wind structure, or whether they deflect or distort. In this talk, we discuss these and other key observables for improving Space Weather research, and outline the proper strategy and instrumentation for extracting the maximum Space Weather benefit from a possible future polar mission.

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Pete Riley, Predictive Science Inc.

Title: Why we need sustained observations of the Sun’s polar regions: A modeling perspective

Abstract: The Sun’s polar regions, and in particular, the photospheric magnetic field, represent a crucial, yet largely unknown measurement for driving boundary conditions for global magnetohydrodynamic (MHD) models. In this presentation, with the aid of numerical models, we explore some of the scientific breakthroughs that would likely result from prolonged observations of the Sun’s polar regions. We illustrate the point by addressing one of the current major deficiencies of these models; an inability to reproduce the amplitude of the measured interplanetary magnetic field at 1 AU (or elsewhere in the heliosphere), often underestimating it by a factor of two or more. Some modelers have attempted to resolve this by “correcting” what they believe to be errors in the estimates of the photospheric field values. Others have simply multiplied interplanetary values by some correction (fudge) factor to match 1 AU values. Here, we explore the idea that this “missing flux” can be explained by a source of largely unobserved concentrated bundles of flux in the photosphere at latitudes too high to be adequately resolved by ground-based observatories or Earth-based spacecraft. Using potential field source surface and magnetohydrodynamic models, we investigate the level of additional flux necessary to resolve the missing flux problem. We show that MHD models that incorporate polar values near the level required are consistent with white-light coronagraph observations. A future solar polar mission, which included – at the least – a magnetograph, would be able to substantiate or refute this idea.

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Title: Zooming in on the coronal poles with solar orbiter

Abstract: The ESA Solar Orbiter mission is designed to determine how the Sun creates and controls the heliosphere. The spacecraft will bring a combination of in situ and remote sensing instruments out of the ecliptic (>30°) and close to the sun (0.3 solar-radii).

The Extreme Ultraviolet Imager is part of the remote-sensing package of Solar Orbiter, which will be operated during 3 periods of ten days during each 168-day orbit, nominally corresponding to perihelion and maximal solar latitude north and south. The Extreme Ultraviolet Imager is itself a suite of three UV and EUV telescopes that observe the solar atmosphere both globally as well as at very high resolution. EUI’s passbands cover the full range of conditions from the chromosphere to the outer corona. Thus EUI will observe and analyze the global morphology and local dynamics of the solar atmosphere, in particular at the base of the corona.

A Full Sun Imager (FSI), working at the 17.4 nm and 30.4 nm EUV passbands, named “FSI174/304”, will provide a global view of the solar atmosphere and is therefore an essential building block for the “connection science” in the key science questions of the Solar Orbiter mission. FSI will provide the connection between the in-situ instruments and the remote sensing instruments that observe the solar surface and outer corona. The FSI FOV is large enough that the full solar disk remains in the field of view, even for maximal off-points by Solar Orbiter. This large FOV and the FSI’s high sensitivity will allow to image the “transition corona” where the topology of streamers and pseudo-streamers fades in the solar wind. Furthermore, FSI will be the first to image this from a polar perspective. FSI will also play an important supportive role when the spacecraft is located at the far side of the Sun: FSI images of the solar back-side showing the location of coronal holes and active regions will support the interpretation of in-situ solar wind data.

Here we focus on the polar observations that EUI, and in particular FSI, will make from its out-of-ecliptic perspective. By manipulating existing EUV observations taken from within the ecliptic we anticipate the issues and opportunities that true polar observations will bring us.

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Karel Schrijver, LMSAL

Title: A solar-stellar perspective on solar polar views, magnetoconvection, stellar astrophysics, exoplanet properties and habitability

Abstract: The classical solar-stellar connection is the interdisciplinary exchange of information about the processes that power the magnetism of stars and about the impacts of that activity on the structure of, and radiation from, stellar atmospheres. Only the solar dynamo is accessible to in-depth scrutiny, and thus detailed knowledge of the drivers of the Sun's magnetism is key to the development and validation of a general theory of stellar dynamos. Transport processes throughout the Sun, including those at high latitudes need to be observed to achieve that goal. But with the discovery of a multitude of transiting exoplanets a modern-day solar-stellar connection has emerged that benefits planetary science and stellar astrophysics alike. Transit spectroscopy in principle yields information about exoplanet properties from body sizes to atmospheric properties, and does the same for the occulted structures on the stellar disks, but only if these two avenues are pursued in tandem. With the ensemble of transits probing the full range of stellar latitudes with varied obliquities, this provides information on (super-)granular properties in quiet regions as well as statistical information on (polar) starspot coverage, activity belts, nests, and plage and spot structures, and thereby constraints for exoplanetary habitability. This emerging wealth of new data on stellar activity can be harvested by the development of advanced radiative-magnetoconvective and dynamo models in conjuction with new spectral, magnetic, and helioseismic perspectives of the Sun.

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Leif Svalgaard, Stanford University

Title: The mysterious polar magnetic fields and their Use for solar sunspot cycle predictions

Abstract: The shape of the solar corona near minimum had already in the late 19th century led to suggestions that the sun had a General Magnetic Field. It was only in the 1950s that the Babcock father-son team succeeded in reliably measuring this field and found that it was concentrated around the poles. The observed (and unexpected) reversal of this Polar Field at solar maximum in ~1958 guided Babcock to his celebrated Solar Cycle Model in 1961 in which the polar fields at minimum serve as the seed for the generation of the magnetic sunspots in the following cycle as elaborated theoretically by Leighton in 1969. The basic ideas of this Babcock-Leighton model still today form the foundation for our description [‘understanding’] of the generation and evolution of the solar cycle, and led to the suggestion by Schatten, Scherrer, Svalgaard, & Wilcox (1978) that the magnitude of the polar fields near minimum could be used to predict the magnitude of the coming solar cycle. Observations have generally borne this suggestion out, especially the successful prediction of the now ending Cycle 24. Yet, many uncertainties and mysteries remain. The transportation of magnetic flux from the sunspot zones (the ‘toroidal’ flux) to the Polar Regions seems to be due to a meridional circulation that itself is poorly understood (how many cells? to what depth? etc.). How does the flux get into the deep interior? (advection and/or diffusion?). Can we model this process and from the observed or guessed distribution of active regions predict the polar fields and thus in turn the next cycle? How can the polar fields (and that in coronal holes generally) ‘live’ for years? Are there other processes that could maintain [or contribute to] the polar fields? Do the fields always reverse near solar maximum? even if solar activity is confined to one hemisphere only (as perhaps during the Maunder Minimum)? How do the polar fields extend into and help shape the heliospheric magnetic field? Can we reconstruct the polar fields in the past? These, and other, questions call for observations from better vantage points than the ecliptic. Understanding the polar fields seems to be key to unraveling the mystery of the solar cycle and the dynamo that drives it.

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Alan Title, LMATC

Title: 360 or bust

Abstract: Prediction of violent events on the sun is not possible without how and where the sun's magnetic field emerges and the role of convection in distributing the field over the solar surface. Examples will be shown to illustrate the difficulties.

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Lisa Upton, NCAR/HAO

Title: Observing the Sun’s poles: A new frontier

Abstract: Obtaining direct observations of the photospheric magnetic fields at the Sun’s poles represents a new frontier in solar physics. Surface flux transport models that simulate the evolution of the magnetic field, such as the Advective Flux Transport (AFT) model, offer glimpses of what we might expect to see with a magnetic imager at a polar vantage point. I will show the polar perspective of the Sun as realized in AFT simulations, focusing particularly on the reversals of the Sun's polar magnetic fields and I will show how these maps compare with observations. While this offers a tantalizing picture of what we might see, the limited polar observations that are currently available have already surprised us. I will discuss what types of polar observations are needed, some of the open questions that they would address, and why a solar mission with a polar vantage point is essential to answering these questions and to providing a complete global perspective of the Sun.

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Maria Weber, University of Chicago

Title: How a polar observing perspective could help constrain dynamo theory and the solar cycle origin

Abstract: Our solar dynamo perspective is driven almost entirely by observations taken within the ecliptic plane. The Ulysses mission, the most notable exception, provided insight about the solar wind at all latitudes, yet lacked an imager or Doppler magnetograph. Such high latitude observations are key to unlocking polar dynamics that are believed to play integral roles in the solar cycle. We review some open solar interior and dynamo questions that specific polar observations will address, including the high latitude structure of the meridional circulation, the role of convection and flux emergence in the near-polar region, and hints as to why there is a marked difference in solar phenomena above and below ~55 degrees latitude. Information we glean about solar irradiance at all latitudes will also impact our understanding of the Sun as a star, making connections between solar and stellar variability.

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Junwei Zhao, W.W. Hansen Experimental Physics Laboratory, Stanford University

Title: Polar observations and helioseismic measurements of interior meridional circulation

Abstract: Meridional circulation inside the Sun plays a crucial role in transporting magnetic flux and angular momentum. However, its precise determination is weakened by our limited observations of the Sun from only the ecliptic plane. Current observations not only limit our capability of deriving the circulation below 65 degree latitude, but also impose a systematic center-to-limb effect that greatly complicates the interpretation of the helioseismic measurements. An off-ecliptic observation, or even better, a polar mission will greatly enhance our capability of understanding the Sun's deep meridional circulation, in addition to our ability to better determine interior rotation and structures.

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