Most ironically, the Sun knows how to keep perfect time. While the surface of the Sun has cycles of varying lengths, the long-term average of these cycles is apparently constant. This implies that the dynamo deep in the Sun is very periodic (Dicke, 1978). Why this fact is not perfectly evident to us is that the transport of magnetic flux from the dynamo to the surface is slow and irregular as the flux convects upward. Moreover, until recently, we knew the Sun only through phenomena on its surface. We could see the transport of magnetic flux on the surface, but not to the surface. For a while, observers confused this complex surface transport as pertaining to the flux generation rather than the flux annihilation. In fact, the visible surface phenomena gave only weak clues to the generation process. Fortunately, helioseismology has enabled us to peer inside the Sun. But the interior is complex. There is a rotating solid inner core and a fluid convective zone. This geometry and the rotation produce two high-latitude zones that communicate but poorly, and mid- and low-latitude convection zones that are responsible for space weather phenomena. And while helioseismology has been a boon to solar physics, it is difficult to use observations from the ecliptic plane to study high-latitude behavior. Further, as of recently, the convective zone mid- and low-latitude dynamics had not been separated into north and south hemisphere contributions. The equatorial regions that are best sampled to date, need yet better sampling, for another reason. In situ solar wind data measured at the Earth cannot easily be compared with terrestrial coronograph data. The in-situ data on the streams seen with terrestrial coronographs are better observed from L5 than L1. Thus we need complementary in-situ and remote sensing data obtained both at L1 and L5. Finally, we must not neglect the high-latitude region. The high-latitude ’cones’ seem separated, not only from each other, but also from the mid- and low-latitude circulation. We need high-latitude helioseismology and high-latitude plasma, field and particle data. We need a sunspot number cycle with comprehensive coverage at both low and high latitudes for at least a full sunspot number cycle but better, two. Observing the polar regions poses different problems because of the difficulty in launching observing platforms out of the ecliptic plane and because the core plus the solar rotation prevent the two polar regions communicating. The poles can be quite independent, so we need to observe both. Addressing the problems facing solar physics cannot be solved with a single spacecraft, but will require a comprehensive and therefore multinational campaign covering both poles, including helioseismology for the interior, as well as orthogonal, in situ observations, in the ecliptic plane.
NASA’s Parker Solar Probe, which launched on August 12, 2018, flew closer to our star than any spacecraft has come before. Parker Solar Probe completed two solar orbits and started the third one, all with a perihelion of 35.6 Solar Radii. The second Venus gravity assist will take place on December 26, 2019, after which the orbit perihelion will decrease to 27.8 Solar Radii. Parker will potentially revolutionize our understanding of this mysterious region by answering questions that puzzled scientists for decades: how the solar wind is heated and accelerated and how solar energetic particles are accelerated and transported throughout the heliosphere. Data from the first two orbits show plasma properties that have not been observed before in the solar wind. The initial results of the mission and the data from the first two orbits will be published in the fall. We provide an overview on the status and outlook of the mission after the first year of operation.
This mission to explore the Sun-Heliosphere connection is the first medium-class mission of ESA's Cosmic Vision 2015-2025 program and is being jointly implemented with NASA. The dedicated payload of 10 remote-sensing and in-situ instruments will orbit the Sun as close as 0.3 A.U. and will provide measurements from the photosphere into the solar wind. The three-axis stabilized spacecraft will use Venus gravity assists to increase the orbital inclination out of the ecliptic to solar latitudes as high as 34 degrees in the extended mission. Solar Orbiter's science team has been working closely with the Parker Solar Probe (PSP) scientists to coordinate observations between these two highly-complementary missions. In addition to providing a Solar Orbiter status update, I will present the exciting new science opportunities that the synergy between Solar Orbiter and PSP offer in the search to understand the origins of the heliosphere.
The Interstellar Mapping and Acceleration Probe (IMAP) is slated to launch in September 2024 and transit to orbit around L1 by the end of that year. IMAP follows on the revolutionary expansion in understanding of the outer heliosphere over the past decade from the Interstellar Boundary Explorer (IBEX), Voyagers 1 & 2, and other missions. Simultaneously, IMAP pushes forward our understanding of particle acceleration in the solar wind. Thus, IMAP simultaneously investigates two of the most important, and intimately coupled, research areas in Heliophysics today: 1) the acceleration of energetic particles and 2) the interaction of the solar wind with the very local interstellar medium. IMAP’s ten instruments provide a complete set of observations to simultaneously examine the particle injection and acceleration processes at 1 AU while remotely dissecting the global heliospheric interaction and its response to particle populations generated through these processes. This talk focuses on the great science return promised by the IMAP mission.
For more information about IMAP, see: McComas, D.J., et al., Interstellar mapping and acceleration Probe (IMAP): A New NASA Mission, Space Science Review, 214:116, doi: 10.1007/s11214-018-0550-1, 2018.
Open Access: https://link.springer.com/article/10.1007%2Fs11214-018-0550-1
In the framework of the Space Situational Awareness (SSA) Programme, European Space Agency (ESA) has started the development of the 'Lagrange' mission that will provide solar monitoring data for operational space weather applications from the L5 point. Lagrange mission will carry a holistic set of space weather instruments that allow remote sensing of the solar disc, solar corona and heliosphere between the Sun and the Earth. The mission will also carry a set of in-situ instruments providing data about the solar wind, interplanetary magnetic field and solar charged particle flux at L5 point. This mission will be the first dedicated space weather mission in L5 and the first ever deep space mission providing measurement data in Near Real-Time (NRT). The development of the Lagrange mission was started with Phase 0 mission feasibility studies in 2015-2016 during Period 2 of the SSA Programme. The successful feasibility studies paved way to the start of the Phase A/B1 studies for the spacecraft platform and payload instruments in SSA Period 3. The objective of the Programme is to complete the Phase B1 studies with a successful Initial System Requirements Review (ISRR) in September 2019. This will allow starting the mission Phase B2/C/D phases in 2020, subject to the approval of the mission proposal by ESA Member States in the Space 19+ Ministerial Council in November 2019. This presentation will provide an overview of the Lagrange mission objectives, payload instruments and mission return and ESA’s space weather system development plans over the coming years.
It has been more than 10 years since the launch of the STEREO spacecraft. A primary objective of STEREO is to characterize Sun-to-Earth propagation of coronal mass ejections (CMEs), the most spectacular eruptions in the corona and drivers of major space weather effects. This talk will focus on some key sciences on CME Sun-to-Earth propagation based on merged remote-sensing and in situ observations from STEREO, specifically: (1) CME interaction with the heliosphere; (2) interactions between CMEs and implications for space weather; and (3) a 'perfect storm' scenario for the generation of extreme space weather. Finally we will discuss Chinese efforts on a future L5/L4 mission, including a mission concept we have developed and our possible contributions if the mission is to be done with international collaborations.
NASA is a mission driven agency whose science is focused on discovering the secrets of the universe, looking for life elsewhere, and safeguarding and improving life on Earth. The Heliophysics System Observatory, with its 18 missions and 26 spacecraft, plays a key role in every aspect of the NASA science mission, including understanding the drivers of and enabling the prediction of space weather. Furthermore, Heliophysics has an established research program that motivates and funds solar and space physics. Recently, the Heliophysics Division established a Space Weather Science and Applications Program, SWxSA. The objective of this competed program is to enable the transition of the knowledge and understanding of space weather to operation environments, by partnering with national and international sister agencies, the commercial sector, and academia. SWxSA leverages relevant NASA capabilities to reach this objective. Key to the success of exploring and understanding the dynamic nature of the Sun, its impact throughout the solar system, and its interaction with various bodies, are the international and interagency partnerships that NASA leverages. This talk will provide NASA’s perspective of what various agencies and groups are planning relevant to exploration, space weather, and solar and space physics.
In 2024, NOAA will replace the current L1 monitoring observatory (DSCOVR) with the Space Weather Follow On - L1 (SWFO-L1) observatory. SWFO-L1’s complement of instruments consists of an interplanetary magnetic field instrument (MAG); a solar wind thermal plasma sensor (SWiPS); a supra-thermal ion sensor (STIS) and a coronagraph (CCOR). In addition, two instruments of opportunity are planned. SWFO-L1 will launch as a ride share with NASA’s IMAP mission, planned for October, 2024. In addition to the coronagraph on SWFO-L1, NOAA will integrate a coronagraph on the solar pointing platform of the GOES-U spacecraft, also planned for launch in 2024. Together with IMAP, this will result in a robust architecture for in-situ solar wind monitoring and for remote sensing coronagraph observations.
The Lagrange point L5 is a gravitationally stable location with two unique characteristics that make it ideally suited for solar observations relevant for space weather. Firstly, L5 provides a continuous view of the Sun-Earth line thus enabling system wide studies to establish causal connections between solar phenomena and their influence on the near-Earth space environment. Secondly, on-disk solar magnetic features visible from L5 rotate to face Earth about four days later, thereby providing opportunities for predicting geo-effective events few days in advance. Moreover, Sun-observing missions located at multiple vantage points (near-Earth, L1, L4, L5) provide a comprehensive view of solar dynamics and enables novel studies that are not possible with one-point observations. With these perspectives in mind the Indian solar physics community is exploring the possibility of a comprehensive L5 mission which is envisaged to measure full-disk vector magnetic fields, perform imaging of transients in the inner heliosphere and measure in-situ properties of the ambient plasma at L5. In this talk, I shall provide an overview of the envisaged science objections, perceived difficulties which need to be addressed to realize this mission, and opportunities for international cooperation that may be mutually beneficial to national efforts.
Multi-vantage observations of the Sun are critical both for research and space weather operational forecast. Recently, several spacefaring nations have expressed interest in developing observational platforms for non-Earth vantage observations. However, these plans are not well-coordinate. At the end of 2018, the International Living with a Star (ILWS) working group, which is comprised of members from (33) contributing agencies, created a task group on "Promoting international collaboration in multi-vantage observations of the Sun, with a special focus on unique scientific advantages of L4+L5 combined observations". I will provide a brief summary of this new ILWS task group, summarize its current activity, and the membership.
ESA’s L5 Lagrange mission is a dedicated, applied space weather mission carrying a payload that is tuned to space weather requirements and the provision of timely and regular data products for assessing near-Earth space environment conditions and the forecasting of potentially Earth-impacting solar events. Thus, whilst the payload includes remote sensing and in-situ instruments that are derived from space science missions such as STEREO and Solar Orbiter, the emphasis is on synoptic monitoring and robust operations rather than the observational flexibility that one associates with many space science instruments and missions. However, it is clear that the Lagrange payload, stationed at L5, provides new opportunities for scientific research, especially in conjunction with instrumentation near Earth. The scientific advantages of having an L5 platform are focused in particular on location (allowing greater coverage of the solar disc, allowing multiple viewpoint observations from widely-spaced instrumentation, and allowing a constant view of activity along the Sun-Earth line), and on long-term synoptic monitoring (e.g. providing unique opportunities for statistical analysis). It is these opportunities that will be discussed in this presentation.
PMI is a full-disk vector magnetograph which is studied in the framework of the A/B1 study of an ESA mission to L5. PMI is based on the heritage of the SO/PHI magnetograph for Solar Orbiter. It contrast to SO/PHI, PMI is aiming for increased on-board computational power in order to provide both low-latency (quasi-real-time) maps of physical quantities for space weather monitoring and, as a byproduct, high-cadence Dopplergrams and high precision vector magnetograms for scientific use. Here we will describe the studied magnetograph, the design advancements and the envisaged properties of the data products.
The STEREO mission has provided us ample opportunities for 3D reconstruction of coronal magnetic fields, which are particular valuable for calculation of free energies that can be dissipated during flares and produce space weather events. On the other side, the particular orbits of the two STEREO spacecraft A and B are not an ideal observatory for long-term studies and monitoring of the solar magnetic field. A realistic stereoscopic reconstruction method revealed that two spacecraft with about 5 degrees angular separation is about the most optimum strategy for a dual-spacecraft setup (Aschwanden, Schrijver, and Malanushenko 2015, Solar Physics 290, 2765), which moreover needs to be stationary (opposed to the Sun-circling orbits of STEREO A and B). For a triplet spacecraft configuration that includes both the L1 and L4 (or L5) points, complementary capabilities are provided to measure the magnetic field, the plasma parameters, the arrival velocity, and the arrival time of Earth-bound (geo-effective) CMEs,as well as flare forecasting before active regions rotate around the East limb.
It is seen in the full disk vector magnetograms that the east-west field changes its sign in the weak field regions after crossing the central meridian. In this presentation, we show possible reasons for causing this change and discuss potential for L5 mission to help address this issue.
The line-of-sight (LOS) component of the large-scale photospheric magnetic field has been observed since the 1950s. Calibrated digital LOS data are available from the late 1960s onwards, but the daily full-disk observations of the full vector magnetic field started only in 2010. Traditional synoptic maps show the so-called pseudo-radial field, which is derived from LOS observations under the assumption that the field is radial. These maps are widely used in solar research, especially in the modelling of the solar corona and solar wind, and in studies of space weather and space climate. While different magnetograph instruments show a closely similar large-scale structure and temporal evolution of the photospheric magnetic field, the measured magnetic field intensity varies significantly between the observations.We have recently suggested a new calibration method based on harmonic scaling, which scales any pair of synoptic pseudo-radial observations to the same absolute level. The harmonic scaling method also allows the maps of the two data sets to have different resolutions. After harmonic scaling of the photospheric observations, the scaled unsigned coronal flux densities agree very well with each other. However, despite the good agreement with the radial component, the meridional and zonal components of the photospheric magnetic field disagree between the different vector field data sets, especially outside the active regions. In addition, the zonal component derived from consecutive LOS observations disagrees with the vector field observations. This is due to different properties of noise in the LOS and in the transverse components of the magnetic field, which need to be addressed in future studies.We emphasize the need of continuing homogeneous synoptic observations of the photospheric magnetic field in the future, even if only at a rather coarse spatial accuracy. We also address the benefits of having synoptic observations at two vantage points.
The Air Force Data Assimilative Photospheric flux Transport (ADAPT) model generates synchronic (i.e., globally instantaneous) maps by evolving observed solar magnetic flux using relatively well understood transport processes when measurements are not available and then updating the modeled flux with new observations using data assimilation methods that rigorously take into account both model and observational uncertainties. These maps can then be used in the Wang-Sheeley-Arge (WSA) model to extrapolate the coronal magnetic field and predict solar wind conditions in the inner heliosphere. ADAPT has recently been upgraded to include reverse active region (RAR) modeling, which is a process to introduce active regions that emerged on the far-side of the Sun into the map and smoothly evolve them forward in time. Using newly developed tools for quantitatively comparing solar wind predictions with observations, we evaluate the impact of including far-side active regions in ADAPT on coronal and solar wind forecasts at Earth and STEREO A & B for the June-July 2010 time interval, when STEREO A & B were near the L4 and L5 Lagrange points, respectively.
We outline how observations obtained from L5 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 L5. 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 L5 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 at L5 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.
Remote sensing measurements play an essential role in models of the global solar corona and solar wind. Such models rely on surface magnetic field observations to define boundary conditions, and combinations of extreme ultraviolet (EUV), soft X-ray, and coronagraphic imaging provide essential constraints on model formulations and inputs. Using our recent effort to predict the structure of the corona during the July 2nd, 2019 eclipse to frame the discussion, we detail the many ways in which remote sensing data influences the construction of a state-of-the-art global magnetohydrodynamic (MHD) model of the corona. We discuss how the availability of hypothetical L5/L4 observations could influence model setup and quality, both for our eclipse prediction effort and for more practical modeling applications.
The far-side magnetic field is important for space weather forecasting and solar wind modeling; however, it is not observed directly and cannot be modeled reliably using flux-transport models. Recently, there has been substantial effort toward applying machine learning methods to calibrate far-side acoustic travel time maps (measured from near-side observations) to far-side magnetic field measurements, incorporating both STEREO data and flux transport model results. However, the limitations of the far-side data present difficulties for calibration. Indirect flux measurements from EUV images add processing layers to the acoustic-to-magnetic-flux learning algorithms, which contribute additional uncertainties to the calibration results. Furthermore, the relatively short duration of full STEREO far-side observations -- only about 4 years before communications were lost with STEREO-B -- provides a limited data set with which to train, test, and validate a machine learning algorithm. Direct, consistent magnetic field observations from non-Earth viewpoints spanning the solar far side are key to moving forward with both the machine learning approach in the future, and for coronal and solar wind modelling in the interim.
The magnetic field of Sun’s polar regions may play an important role in producing the solar activity cycles according to the dynamo model. In shorter time scales, the coronal holes sitting in polar regions are responsible for the fast solar wind that may have implications in space weather in the inner heliosphere. The underlying magnetic field of polar coronal holes is not well understood, in particular, in relation to the patches of strong radial magnetic field as revealed by the Hinode Spectro-Polarimeter (SP). The radial magnetic field near the poles is extremely hard to observe from the ecliptic plane because it appears as nearly transverse, needing either high-resolution vector measurements or large cosine of mu corrections on line-of-sight magnetograms. Following the above-mentioned revelation of the patches of strong radial magnetic field, observations of polar regions have become one of the highest priorities of the Hinode observing programs. We analyzed some of the Hinode SP data of polar regions taken during different phases of solar cycle 24. We also learned that the Helioseismic and Magnetic Imager (HMI) on the Solar Dynamics Observatory show essentially the same patches of strong radial field as Hinode SP, despite its somewhat poorer spatial resolution and more restricted Stokes polarimetry. The constant availability of full disk vector magnetograms every 12 minutes lets us study the time variability of the patches. Therefore we consider SP and HMI to be complementary. We will summarize new knowledge of the polar magnetic field on the basis of the vector data from SP and HMI, show what cannot be achieved by these data, and discuss how we need observations from platforms far from the ecliptic plane.
The magnetic field of the solar polar region expands and permeates the heliosphere. Its nature remains poorly understood due to unfavorable viewing angle from the ecliptic. Here we perform deep integration (96 minute) on the spectropolarimetry data from SDO/HMI, which significantly boosts the signal to noise ratio. For March 2015, the polar landscape is consistent with previous reports, where predominantly unipolar flux concentrations (UFCs) populate the entire region. Most UFCs have size of a few arc second, mean flux density a few hundred Gauss, and evolution time scale longer than the integration window. For UFCs with the strongest polarization signal (> 5x RMS), the inferred field vectors are radial with deviations typically less than 10 deg. Curiously, they also remain more inclined toward the plane of sky when compared to purely radial vectors regardless of the location. Such a bias can significantly alter the magnetic flux estimate. We argue that this effect may be inherent to observations with limited spatial/spectral resolution, and that caution needs to be exercised when interpreting the data. We discuss how out-of-ecliptic and higher-resolution observations can improve the polar field characterization.
The Sun’s polar regions remain one of its last unobserved frontiers. Observations of the magnetic field, convective flows, and coronal outflow conditions in the solar polar regions are the keys to accurately modeling and forecasting the solar cycle, solar wind conditions, and CME arrival times at Earth. This talk describes the Solar Polar Observing Constellation (SPOC), a mission that will for the first time enable continuous high-resolution imaging of magnetic field dynamics, high-latitude helioseismology, and coronal mass ejection tracking from a near-circular polar heliocentric orbit. SPOC will consist of two identical spacecraft, each equipped with a Compact Magnetic Imager (CMI, derived from the Solar Dynamics Observatory (SDO) Helioseismic and Magnetic Imager), the Naval Research Laboratory (NRL) Compact Coronagraph (CCOR), and in-situ solar wind and energetic particle instruments. Falcon Heavy launch vehicles will place the SPOC spacecraft into a Jupiter gravitational assist (JGA) orbit, achieving an 88-degree ecliptic inclination orbit, with the spacecraft passing over the solar poles within 4 years after launch. Ion engines will subsequently reduce the eccentricity of the orbits to below 0.05 at approximately 0.9 AU within 6 years after launch. Orbital phasing will place the spacecraft over alternate poles to enable continuous monitoring of the polar regions with operational-level redundancy of systems. The inclusion of CCOR will enable visualization and tracking of coronal mass ejections from above (or below) the ecliptic for the first time, greatly enhancing our ability to forecast CME arrival times at Earth or Mars. SPOC combines polar region trail-blazing, long-term polar helioseismology and magnetic imaging, and operational space weather monitoring in a single mission. Along with planned missions to the L1 and L5 Lagrangian points in the ecliptic, SPOC will enable an approach to the long-standing goal of continuous full-sphere measurements of the solar magnetic field, solar wind and CME outflow, and energetic particle flux - a goal that cannot be achieved with observations from the ecliptic plane alone.
The solar poles are one of the last unexplored regions of the solar system…one of the final frontiers of solar physics. Although Ulysses flew over the poles in the 1990s and early 2000s and defined our understanding of the fast and slow solar wind, it did not have any remote sensing instruments onboard to probe neither the Sun’s polar magnetic field nor the Sun’s surface and sub-surface flows and fields at the pole. We will discuss in this talk the Solaris solar polar mission concept to address some of the fundamental questions that can only be answered with remote sensing instruments from a polar vantage point. Solaris will obtain continuous, high latitude (>55 deg.) observations of the solar poles for multiple solar rotations, providing the continuity necessary to detect sub-surface flows and follow the evolution of solar transient activity. The Solaris mission will be able to obtain sustained coverage of the solar interior and atmosphere from high latitudes, providing a unique and comprehensive investigation of the global Sun and heliosphere. We will also discuss the Compact Doppler Magnetograph (CDM) instrument, developed to meet the requirements for a mission such as Solaris, which provides photospheric line-of-sight magnetic field and Doppler velocity measurements in a ~15 kg package, significantly less than other comparable instruments.
Solar space missions designed to observe away from the Sun-Earth line, such as at L5 or at high heliographic latitudes, promise to provide significant gains in our knowledge of solar physics and in our ability to forecast space weather events. A key contribution to this knowledge will be measurements of the Sun’s photospheric magnetic field, requiring a magnetograph as part of the instrumentation. Since the orbits needed to reach these vantage points demand high velocity, the mass of the spacecraft and instrumentation need to be minimized. To meet this requirement, we present here CMag, a magnetograph based on the GONG measurement principle with an estimated weight of 10-15 kg, substantially less than the 30-50 kg of solar magnetographs on HMI and Solar Orbiter. CMag uses a polarizing Michelson interferometer and liquid crystal variable retarders (LCVRs) to form an interference fringe that is swept in wavelength across a spectral region. A prototype is being developed and tested at NSO, LASP and SWRI.
We present progress on developing a novel magnetograph that leverage advances in photonics integrated circuits (PICs) and low noise lasers driven by the needs of the telecommunications industry. In our design, a single PIC replaces the traditional optical components by exploiting interferometric imaging techniques developed as part of the SPIDER project, a collaboration with LM and UC Davis. The PIC processes incoming signals via two, independent waveguide circuits for the two linear polarizations. Narrow band spectroscopy is achieved by heterodyning the signals with a common local oscillator using a tunable laser . The resulting signal is processed using standard techniques from radio astronomy and solar magnetometry.The optics package for our prototype system achieve 30 arc second resolution within a few tens of cubic centimeters - compared to tens of thousands need for traditional designs - with comparable savings in mass. Such devices could easily be deployed throughout the heliosphere on small-sat constellations. The associated electronics required for our prototype are challenging, but we present strategies for reducing their size, mass and power to reasonable levels.
Most of our knowledge about the Sun's interior, including dynamics andstructures on both global and local scales, has been gained from observationson the Earth, near the Earth, or along the Sun-Earth line. Observations fromanother vantage point off the Sun-Earth line will help us better monitor theSun and better understand its internal dynamics. Here, I outline fourhelioseismology research topics that can greatly benefit from suchobservations from a different vantage point. First, helioseismologyroutinely maps active regions on the Sun's far side before they rotate intothe Earth's view; however, the accuracy of these helioseismic maps andthe quantitative relationship between helioseismic phase shifts and magneticfield can only be evaluated with an L5 observation. Second, the currentdetection of the deep solar interior is limited by the surface area we canobserve; observations from L5 will allow us to analyze waves passing throughthe solar core, greatly enhancing our capability of investigating the Sun's deep interior. Third, current studies on the Sun's internal meridionalcirculation are significantly complicated by a systematic center-to-limbeffect; an off-Sun-Earth vantage point will help us understand the physicalcause of the effect, and hopefully design a more robust way to remove theeffect. Fourth, due to the Wilson Depression in sunspots and the inclinedmagnetic field lines in sunspot penumbrae, the observed line-of-sightoscillatory signals from sunspots are therefore from different atmosphericheights and are only a component of the complicated oscillations; anobservation from a different vantage point will likely help us disentanglethe complexity of the observed oscillations.
Meridional circulation is a crucial component of the Sun’s internal dynamics, but its inference in the deep interior is complicated by a systematic center-to-limb (CtoL) effect in helioseismic measurement techniques. The CtoL effect was first found in helioseismic measurements using time-distance method. Solar interior flows cause measurable travel-time shifts for acoustic waves propagating inside the Sun, and can thus be inverted for from the travel-time shifts. However, depending on the location where measurements are made, the CtoL effect adds an extra travel-time shifts entangling with and even largely overwhelming the flow-related travel-time shifts. Counterparts of the CtoL effect exists in other helioseismic methods, too. The removal of the CtoL effect is therefore a critical task in the interior flow measurements, but currently the CtoL effect is removed only empirically. There is evidence indicating that the CtoL effect is related to spectrum line formation height, but the physical cause of the effect is still not understood. Simultaneous observations of the same area of the Sun from both Earth and non-Earth vantage points can help to calibrate the CtoL effect for a more robust effect removal, as well as help to understand the cause of the effect.
Charting out the complex interactions between acoustic waves (p modes), flows and magnetic fields is important for progress in active region seismology as well as in studies of atmospheric dynamics, energy transport and heating mechanisms. Further, there are systematics in several helioseismic observables that depend on the viewing angle or center-to-limb distance. We present a modeling of Doppler observations (with the photospheric Fe I 6173 A line) at two viewing angles -- 0 deg (Sun - Earth) and 60 deg (L5/L4) using 3D magnetohydrodynamic (MHD) simulations (with the CO5BOLD code) of near-surface layers covering the photosphere to chromosphere (with convection, acoustic waves, vortex flows and associated MHD wave motions). We present here some preliminary results on retrieving the 3D velocity field. This is with the aim of developing a method to combine two-vantage Doppler observations towards the above science.
The predictions of CME arrival to the Earth and the southward magnetic field brought by the CMEs are one of crucial tasks for space weather forecast.We have developed a MHD simulation capable of reproducing the interplanetary propagation of multiple CMEs with internal magnetic flux rope (Shiota & Kataoka 2016) called as SUSANOO-CME. The simulation solves propagation of solar wind and CMEs in the inner heliosphere from 25 solar radii. The information of solar wind and CME is specified at the inner boundary with empirical and analytical models using real-time observations of the Sun and the corona.Recently, we have been constructing a new prediction system of CME impacts utilizing SUSANOO-CME with the real-time solar observations for the purpose of use in space weather forecast in NICT. The system is capable of performing ensemble simulation with different sets of multiple CME input parameters on the basis of those derived from the observations. The results of ensemble simulation can be evaluated with IPS observation in Nagoya University. We will introduce the current status of the development and discuss expectations for observations in Lx missions.
Coronal mass ejections (CMEs) are the most energetic and dynamic phenomena in our solar system. Presenting massive clouds of magnetized plasma with speeds up to a few thousand km/s, they may propagate over Sun-Earth distance within less than a day and may cause strong geomagnetic disturbances (Space Weather). As CMEs are optically thin, measurements of their intrinsic properties such as speed, width, propagation direction, density etc. are severely affected by projection effects. Hence, observations from single vantage points observe these extended objects projected onto the plane-of-sky and therefore miss valuable information. Forecasting CME impacts at Earth by using sophisticated CME propagation models, have to face the fact that observational input values, especially coming from single spacecraft, are of high uncertainty. This strongly limits the reliability and accuracy of the model results, hence, the forecast itself. Using multi-viewpoint observations from missions in the L4/L5 Lagrange points or out of the Sun-Earth ecliptic plane (polar mission) would provide significant additional information by enabling CME 3D analyzes, and with that facilitate a better quantification of the uncertainties in the observational measurements. The talk will cover the benefits of combined multi-viewpoint/multi-wavelength data that would improve our understanding of CME initiation and propagation, and Space Weather forecasting capabilities.
Because of the nature of the coronagraph observations from the Sun-Earth line, it is difficult to observe Earth-directed coronal mass ejections (CMEs). Such CMEs could become very faint when the CME material reaches above the coronagraph occulting disk. Yashiro et al. (2005) estimated the CME visibility rate using the flare-CME association. They reported that all CMEs associated with X-class flares are detected by the LASCO coronagraphs, while half (25-67%) of CMEs associated with C-class flares are invisible. Here we report that the visibility of the Earth-directed CMEs using STEREO observations. During 2009 October - 2012 July, STEREO observed the Earth-directed CMEs as limb events, so the CME properties can be obtained without the projection effects. There were 260 wide CMEs whose angular width was equal or greater than 60 degree from the STEREO view. We examined their LASCO counterparts and found that LASCO could detect 218 CMEs. We could not identify the erupting feature in the LASCO images in the remaining 42 CMEs. Therefore, the visibility rate of the wide CMEs is 84%. We will present how the obtained CME properties are different between the CME observations from the Sun-Earth line and from the L4/L5 points. The importance of the coronagraph observation from the L4/L5 points for the space weather forecast will be discussed.
The payload complements specified for most L5 Lagrange point space weather mission concepts include a white-light coronagraph as the primary means to detect the eruption of coronal mass ejections (CMEs) and to establish their initial trajectory into interplanetary space. The design goal outer field of view for an L5 coronagraph is typically about 25 RSun. Once an Earth-directed CME leaves the L5 coronagraph’s outer field of view, it loses track of the event and no information about its trajectory or speed is available to operational heliospheric disturbance propagation codes. Forecasters would be blind until the CME reaches the L1 Lagrange point along the Sun-Earth line, where the in-situ measurements would provide only 30-45 minutes of actionable lead time prior to the CME impact at Earth. Adding a heliospheric imager to the instrument suite of an L5 space weather mission will enhance its ability to continuously track CMEs as they leave the L5 coronagraph field of view, improving CME trajectory determination, CME arrival time estimation, and ultimately the accuracy of geomagnetic storm forecasts. The Compact Heliospheric Imager (CHI) is a dual-telescope instrument concept with 30° fields of view that is an ideal candidate for this role on an L5 space weather mission. CHI will image interplanetary space in white light (500-700 nm) between 4.5°-64.5° elongation from L5. This combined field of view encompasses the entire Sun-Earth line with Earth just inside the outer field of view cut off. CHI’s enclosed design allows it to be placed close to other spacecraft components or instruments without those components interfering with CHI’s imaging performance. This provides a great deal of flexibility in placement of CHI on a spacecraft since its only requirement is to have an unobstructed field of regard (FOR) in the Sun-facing hemisphere. CHI’s compact design and low power requirements make it an ideal instrument candidate for an L5 space weather mission.
The Space Weather (SWE) element of ESA’s Space Situational Awareness (SSA) - now Space Safety - programme was established to address the increasing risk of solar effects on human technological systems and health. Within its Period 3, the SSA programme was extended to include an additional element (LGR) targeted towards the development of a space weather monitoring mission - Lagrange - to L5. It is envisaged that Lagrange will operate in coordination with a US-led mission to L1. Under the auspices of LGR, a number of Phase A/B1 studies have been undertaken; these studies, recently completed, cover the remote-sensing payload, the in-situ payload, and overall Lagrange system. The remote-sensing instrument package for the Lagrange mission includes a Coronagraph (COR) and Heliospheric Imager (HI). These instruments are based on heritage from the Solar Coronagraph for Operations (SCOPE) concept study and the HI instruments on-board the Solar Terrestrial Relations Observatory (STEREO) spacecraft, respectively. In this presentation, we will review the observational requirements for Lagrange COR and HI. We will then present their optical, mechanical, thermal and electrical designs - as well as their operations concepts - developed to meet these observational requirements and those of the Lagrange mission. Differences between the requirements, and design, of the Lagrange COR and HI instruments and those of their heritage instruments will be highlighted.
Many astrophysical missions benefit from operating well separated from the Earth. In particular, exoplanet imaging missions can take advantage of this environment. A fiducial Earthlike exoplanet would be ~10^-10 fainter than their parent star and at angular separations of a tenth of an arcsecond. I will review exoplanet imaging basics and discuss two key concepts. The first are starshades - steerable deployed spacecraft that operate in tandem with a telescope. A starshade occulter blocks the target star while allowing nearby planets to remain visible. A typical starshade is ~30m in diameter, operates tens of thousands of km away from the telescope, and requires positional accuracy of ~1 m - clearly impractical in most Earth orbits and are typically designed for L2. Internal coronagraphs instead use masks in the telescope focal and pupil planes, together with deformable mirrors, to achieve high contrast. These missions require extreme thermal stability and are similarly proposed for L2.
The mission concept for the STEREO mission included the plan to understand the 3D structure of CMEs. This was to be accomplished by two identical spacecraft viewing the solar corona and its ejecta from two vantage points. The two spacecraft, STEREO-A and -B, were launched into heliospheric orbits, one trailing Earth and the other leading, and both separating from Earth at the rate of about 22.5deg per year. The mission lifetime was 2.5 years, which put the separation of the spacecraft at 45deg from Earth, and 90deg from each other. Prior to SOHO, the CME had been interpreted as planar structures, 3D structures, such as a cone and MHD coronal disturbances. The difficulty with single point observations, such as from SOHO alone, is that the projection of the 3D scattered light distribution onto the 2D detector plane leads to non-unique interpretation. With SOHO and STEREO together, the 3D geometry and the propagation direction could be determined using the framework of the GCS model. Thus STEREO was able to live up to its concept and has established the magnetic flux rope as the primary, if not the only, type of CME. But the kinematics of any particular CME can only be defined as projections, which is not sufficient for space weather predictions. Having the STEREO/SOHO configuration is almost ideal - one clearly defines the symmetry relative to the Sun-Earth line and the other clearly showing the direction and the two defining the shape, the orientation and the true speed. This effort has been supported by the NASA STEREO/SECCHI program.
Although the current NASA Heliophysics System Observatory (HSO) has provided unprecedented coverage of the Sun and its impact on Earth, the planets, and other small bodies (e.g., comets) in the solar system, it is an ad hoc network of satellites that is not set up to safeguard astronauts as they explore the solar system, particularly as they move away from the Earth-Sun Line. Here we describe a Design Reference Mission (DRM) for an autonomous space weather constellation, which would consist of a fleet of spacecraft in different orbits offering a simultaneous 4pi steradian view of the Sun. Its aim would be filling the gaps in our observational capabilities to facilitate validated, near real-time, data-driven models of the Sun’s global corona, heliosphere, and associated space-weather effects. This DRM will help focus technological developments to enable the autonomous capabilities needed to address space weather nowcasting and forecasting needs. In addition, similar and more advance autonomy technology will benefit another exploration mission such as the Interstellar Probe, the first robotic mission to explore beyond our solar system.
Solar magnetism defines the heliosphere and is responsible for a vast number of Heliophysical processes. Helioseismic studies have led to the conclusion that the site of the solar dynamo is at the base of the convection zone. All the knowledge we have gained so far on the magnetic field in the solar interior is from observations along the Sun-Earth line. In order to make rapid progress in understanding the magnetic coupling between the solar interior and atmosphere/heliosphere, we need to make observations from off the Sun-Earth line such as L5 and/or L4. By combining Doppler measurements from L5/L4 and Sun-Earth line (e.g., GONG, HMI) one can use helioseismology techniques to track subsurface signatures of active regions and derive physical properties of the convection zone. Detailed information on the life cycle of active regions is important for tracking polar field build up, a key feature of the solar dynamo. Measurements of meridional flow and its spatial structure using the larger range of ray paths, depths and lat/lon extents available from the multiview (L5/L4 and Sun-Earth line combination) are critical in discriminating Dynamo models. Once the active regions are on the surface, how they erupt and disturb the heliosphere can be best tracked using multiview observations, as demonstrated by the STEREO mission. In particular, we can determine the acceleration profile of coronal mass ejections (CMEs) by combining wide-field EUV images and coronagraph images to identify the forces acting on CMEs. We can identify and track the evolution of CME flux ropes fully characterized using flare reconnection flux derived from EUV post-eruption arcades and compare them with in-situ flux ropes. This paper describes a mission concept known as Sun-Earth Lagrangian Explorer (SELEX) that will observe signatures of magnetic coupling from the solar interior to the inner heliosphere.
Despite recent advances in observations, modeling, and theoretical work, there remain many critical uncertainties regarding topology and evolution of solar surface magnetic field as well as the 3D structure of CMEs and ICMEs. Having multi-vantage observations would allow developing new understanding of the creation, structure, and variability of solar surface magnetic fields, resolving disparate processes in the corona that energize, accelerate, and direct coronal eruptions, and exploring physical processes fundamental to predictive models of the corona, solar wind, and ICMEs. What topological changes of the photospheric magnetic fields occur during emergence, evolution, and decay of active regions, and how do they contribute to the large-scale magnetic field pattern? What physical processes produce CMEs and their associated shocks and how do they evolve in the solar corona, as seen from multiple viewpoints? How do CMEs and their associated shocks evolve as they propagate to 1 AU through their interaction with the ambient solar wind and/or other CMEs, as seen from multiple viewpoints? To answer these and other science questions, the team will employ observations from four MagEx instruments (Compact Magnetograph for measuring photospheric magnetic fields, the Sun’s Coronal Eruption Tracker with solar extreme ultraviolet imager and irradiance spectrograph, dual FluxGate Magnetometers for in situ magnetic fields, and the Solar Wind Sensor for in situ solar wind protons) in combination with state-of-the-art modeling.
The complex interactions of the Sun’s magnetic fields that generate solar wind and coronal mass ejections (CMEs) are inherently 3-dimensional, requiring observations off the Sun-Earth Line (SEL) to fully interpret. Multipoint solar magnetic field observations combined with multipoint in situ measurements will revolutionize our understanding of magnetic connectivity in the solar atmosphere, its role in eruptive processes, and propagation of solar wind and CME disturbances to 1 AU. We have developed the Magnetic Explorer (MagEx) mission concept with the goal of using another vantage point to achieve new understanding of the origins of solar activity and variations of the space environment. While traveling to the Lagrange L5 point, MagEx will observe the photospheric magnetic fields and coronal structures necessary to understand, reconstruct, and model the complex 3-D dynamics of solar magnetic fields, answering outstanding questions on how these fields evolve, interact with distant active regions, and reconnect to create the powerful releases of energy that drive flares and CMEs. Similarly, MagEx’s in situ measurements enable understanding and reconstruction of the temporal and spatial evolution of stream interaction regions (SIRs) and interplanetary CMEs (ICMEs). MagEx can be a pathfinder for more comprehensive L5 missions in the future to study the 3-D magnetic topology of the Sun and space weather. MagEx is an innovative, affordable PI-led small mission. The spacecraft uses high-heritage components and subsystems and a tailored Class D management approach to enable a low-cost deep space mission. It is proposed as a rideshare opportunity with the Interstellar Mapping and Acceleration Probe (IMAP). After deployment near L1 in fall 2024, MagEx maneuvers to L5 and inserts into a halo orbit about L5 in 2026, providing views that complement near-Earth operational observatories (e.g. GOES in GEO, IMAP and DSCOVR at L1, and the GONG ground network). These views enable broader longitudinal coverage and longer continuous observations, earlier awareness of potentially geoeffective solar activity, multiple views of CMEs that enable their 3-D reconstruction, and improved predictive models of solar wind and ICMEs at 1 AU. MagEx’s vanguard mission to L5 has four instruments: the Compact Magnetograph (CMAG) for measuring photospheric magnetic fields, the Sun’s Coronal Eruption Tracker (SunCET) with solar extreme ultraviolet imager and irradiance spectrograph for observing CME initiation and acceleration, dual FluxGate Magnetometers (FGM) for in situ magnetic fields, and the Solar Wind Sensor (SWS) for in situ solar wind protons (density, velocity, temperature). The MagEx instrumentation will directly observe the origins and evolution of solar active regions (closed magnetic fields), the solar wind sources (open magnetic fields), and the energetics and evolution of CMEs (eruptions that transition from closed to open fields).
This presentation will review the scientific key diagnostics provided by hard X-ray instrumentations on L5/L4 missions. Besides the scientific benefits, I will discuss different instrument design options such as spectrometers, locators, and imaging spectrometers based on the RHESSI and Solar Orbiter STIX indirect imaging technique, including the required resources such as mass, power, and telemetry.
While there have been significant advances in our understanding of impulsive energy release at the Sun through the combination of RHESSI X-ray observations and SDO/AIA EUV observations, there is a clear science need for significantly improved X-ray and EUV observations. These new observations must capture the full range of emission in flares and CMEs (e.g., faint coronal sources near bright chromospheric sources), connect the intricate evolution of energy release with dynamic changes in the configuration of plasma structures, and identify the signatures of impulsive energy release in even the quiescent Sun. The Fundamentals of Impulsive Energy Release in the Corona Explorer (FIERCE) MIDEX mission concept makes these observations by combining the two instruments previously proposed on the FOXSI SMEX mission concept - a focusing hard X-ray spectroscopic imager and a soft X-ray spectrometer - with a high-resolution EUV imager that will not saturate for even intense flares. All instruments observe at high cadence to capture the initiation of solar transient events and the fine time structure within events. FIERCE would launch in mid-2025, near the peak of the next solar cycle, which is also well timed with perihelions of Parker Solar Probe and Solar Orbiter. The goals of FIERCE include improving our understanding of the genesis of space-weather events, and FIERCE obserations would vitally complement observations by other observatories both near Earth and elsewhere in the heliosphere.
A Space Weather nature of the mission to L5 requires good description of a nonthermal populations of electrons produced during a solar flare. Therefore measurements of X-ray spectra is necessary, this can be achieved with a small X-ray photometer-spectrometer equipped with three solid state detectors: two with silicon crystal as a detecting medium and additional with a CdTe crystal. This solution will broaden the spectral response of the instrument up to ~80 keV as well as allow to observe wide range of solar X-ray fluxes, from a quiescent Sun up to strongest flares. The instrument will require minimal amount of allocated telemetry by adopting e.g. STIX/Solar Orbiter compression algorithms.
I will discuss some possible advantages of observing high-energy charged particles, such as solar-energetic particles (SEP) and cosmic rays, from vantage points off of, but in addition to the Sun-Earth line. One topic is the longitudinal transport of solar-energetic particles associated with compact sources on the Sun, such as small solar flares. Such events observed by spacecraft near Earth and L4/L5, for example, allow for a critical measure of the longitudinal transport of the particles arising from cross-field diffusion. Another topic is the variation of large, gradual SEP events associated with shocks driven by coronal mass ejections. As the CME-driven shock moves outward from the Sun, the angle-between the unit normal to the shock and the interplanetary magnetic field varies along the shock in a manner that is depends on helio-longitude. The rate of acceleration depends on this angle leading also to a variation in the particle distribution along the shock. The L1-L4/5 separation is ideal to study this since most large CMEs have an angular extent that is of the same order, or exceeds this separation. Other possible topics include: (a) the distribution of very intense SPE (solar-energetic proton) events in helio-longitude, and (b) the variation in galactic cosmic rays associated with solar transient phenomena, such as Forbush decreases.
Depending on the phase of the solar activity cycle, hazardous space weather at Earth is largely associated with either coronal mass ejections (CMEs) or corotating interaction regions (CIRs), while increased levels of harmful particulate radiation are caused by Solar Energetic Particles or SEPs that are accelerated by powerful CME-driven shocks that plough through the solar corona and interplanetary space. Despite decades of observations and significant advances in our understanding of these phenomena, our ability to predict their occurrences and impacts remains hampered by the lack of simultaneous observations at appropriate locations, such as the Sun-Earth Lagrange points. This talk describes two low-resource, compact instruments with flight heritage and high Technological Ready Level (>6+) that can provide the comprehensive measurements of the solar wind, suprathermal, and energetic protons, alphas, and electrons that are required for Space Weather research and predictions at high sensitivity and high time resolution. The Ion and Electron Sensor (IES) is a compact, dual-electrostatic analyzer and microchannel plate-based sensor that measures solar wind ions and electrons between ~10 eV/e to 33 keV/e, thus encompassing the full range of proton energies required to measure solar wind speeds, including extremely fast CMEs, up to ~2500 km/s. IES draws its heritage from the Rosetta mission, and can provide accurate measurements of the speed, density, and temperature of the bulk solar wind plasma. The Miniaturized Electron and Ion Telescope (MErIT), developed for the CeRES and CuSP CubeSat missions, combines state-of-the-art avalanche photo-diode detectors with traditional solid-state detectors in a compact telescope configuration. MErIT covers 5 orders of magnitude in energy range for protons between ~10 keV to 100 MeV, and 4 orders of magnitude in energy range for electrons between ~10 keV - 8 MeV, thus covering the suprathermal through relativistic energy ranges that are required to achieve the following objectives: 1) provide advance warning of potentially geoeffective CME shocks; 2) predict the arrival of hazardous SEP protons by measuring the intensity and rise times of the earlier arriving relativistic electrons above ~1 MeV; and 3) characterize the radiation levels associated with the ~10-100 MeV SEP protons.
The in-situ measurement of the magnetic field in the solar wind is a key measurement for shocks, coronal mass ejections, corotating interaction regions, particle propagation and pitch angle, etc. This presentation will focus on the magnetic field data from an L5 mission, regarding its contribution as in-situ measurements and terrestrial space weather prediction. The NASA/GSFC magnetometers have flown on many missions; for Parker Solar Probe the two FIELDS MAGs represent the 80th and 81st flight magnetometers built by the NASA/GSFC Magnetometer Team. As part of this presentation, I will present magnetic field data results acquired by Parker Solar Probe, which show how the solar wind differs close to the Sun, compared to near 1 AU magnetic field measurements.
140 years of imaging data of the Sun and related data science dating back to the turn of the 20th century indicate that the sun has an incredibly regular background variation. That variation contains the ingredients responsible for the sun’s decadal variability and the strongly longitudinal processes that govern space weather conditions on shorter timescales. I’ll discuss the data, the related determinations, what is coming, and propose observing strategies to monitor the variability across scales.
Eruptive events are pervasive throughout the solar atmosphere, occurring on time scales from as short as minutes, to as long as many hours. The most spectacular such events are large-scale eruptions that produce major solar flares and coronal mass ejections (CMEs). Recently it has been recognized that smaller versions of such eruptions occur on the size scale of supergranules, producing coronal jets. How the energy that powers these eruptions is accumulated, stored, and triggered to release, are still questions lacking complete answers. One certainty though is that all of these eruptions are a consequence of a catastrophic release of free energy in non-potential magnetic fields. A vantage point from east of the Earth-Sun line, in particular L5, will allow us to observe the evolution of eruption-prone magnetic regions from before they rotate around the east limb from the viewpoint of Earth-Sun-line-based instruments, until they are poised to erupt aimed in Earth’s direction. This will open up fresh avenues to both new research investigations into the build-up/storage/release mechanisms of eruptive events, and our ability to predict when large eruptions that drive severe space weather are or are not likely to be launched toward Earth.
Until recently, extreme ultraviolet solar coronal imagers have generally focused on exploring the physics of the low corona, observing phenomena such as coronal loops, coronal holes, and solar flares below about 1.3 Rsun. In the past decade, however, imagers such as PROBA2/SWAP and GOES/SUVI have arrived with both larger fields of view and the ability to off-point to observe out to heights greater than two Rsun. Observations from this new generation of imagers have revealed both the surprising visibility of the EUV corona to large heights, and the complex structure and dynamics of this poorly explored region sometimes referred to as the middle corona. Additional imagers, both proposed and in active development, such as Solar Orbiter/EUI, COSIE, SunCET, and others, promise to further advance the boundaries of our understanding of the corona and its large-scale connections to the heliosphere. These new imagers offer the opportunity for considerable progress in our understanding of a hard to observe region where it is thought the solar wind is accelerated, where stored magnetic energy is released during solar eruptions, and where the interplay between both magnetically and gas dynamics dominated plasma gives the corona its large-scale shape. In this talk we discuss both current and prospective EUV observations of the corona on large scales and their value for science. We discuss the benefits and limitations of EUV observations in contrast to visible light coronagraphic observations, as well as some particularly unique opportunities for both research and operational observations of the large scale EUV corona from L5.
Space observations taken at vantage points off the Sun-Earth line have a multitude of scientific and societal values. We present four examples to demonstrate that such observations can provide crucial new information for solving some of the most outstanding puzzles in solar physics and beyond. (1) Prominence bubbles (e.g., Berger et al. 2011, Nature; 2017, ApJ) are intriguing, dome-shaped intrusions into the cold and dense prominence material from below. They have so far been observed only at the solar limb with favorable contrasts from the background. They are hypothesized to be a result of magnetic flux emergence into the corona and can play an important role in the so-called chromosphere-corona mass cycle. Measurements of the solar surface magnetic field at the limb are essential to validate this hypothesis and can be obtained from spacecraft at a quadrature angle from the Earth. (2) By the same token, such observations are required to shed light on (a) the physical nature and causes of coronal rain that is best seen off-limb (e.g., Antolin et al. 2010; Mason et al. 2019), (b) flares on the far side of the Sun occulted by the solar limb partially (e.g., Liu et al., 2008; Krucker & Lin 2008; Effenberger et al. 2017, ApJ) or completely, in particular those so-call behind-the-limb (BTL) gamma-ray flares detected by Fermi (e.g., Pesce-Rollins et al. 2015; Jin et al. 2018, ApJ); and (c) global EUV waves as solar analogs of terrestrial Tsunamis that are triggered by seemingly localized eruptions and can traverse the entire outer atmosphere of the Sun (e.g., Thompson et al. 1998, GeoRL; Liu et al. 2012 ApJ). These examples demonstrate the strong scientific needs for missions to off-Sun-Earth-line vantage points that will have the potential to bring breakthroughs in a wide range of sciences.
wide array of interesting and important science questions can be addressed from unique vantage points in the heliosphere that are far from Earth. L5 and other L* locations can also provide invaluable additional information essential for improved space weather forecasting. As we have heard at this meeting, nations and agencies around the globe are developing plans for such missions. The U.S. science community is a little past the mid-point of implementing the 2012 Solar and Space Physics Decadal survey and the National Science and Technology Council released the latest National Space Weather Strategy and Action Plan in March, 2019. What can we do to advocate for these critical observations?
The model contouring the dynamics of transient nonlinear interaction between the high frequency extraordinary-elliptically polarized Laser and low-frequency Kinetic Alfven Wave dynamics in the overdense plasma is the focal point of the present investigation. By virtue of this transient feedback, filamentation of HFXPL pump takes place, which is responsible for the progression of magnetic turbulence in laser-plasma interaction. The quasistatic ponderomotive force driven by the high frequency pump wave induces density cavitation and humps in the low-frequency Kinetic Alfven wave. The requisite dimensionless equations are solved by using numerical methods in the nonlinear stage, to inquest the intricate localized structures of pump wave that evolve with time. The rendered investigations follow direct relevance to the experimental observations and are imperative in understanding turbulence in astrophysical scenarios.
Modeling the space weather conditions for the near-Earth environment depends on a proper representation of magnetic fields on the Sun. Observations from a single (L1) vantage point are insufficient to characterize rapid changes in magnetic field on the far side of the Sun. Nor can they represent well the polar fields near both poles. However, if the changes in sunspot activity were moderate, how well would our predictions of the solar wind work? How much improvement could we see by adding magnetograph observations from L5, L4, and even L3? We will present the results of our recent modeling, which show the level of improvement in forecasting the properties of the solar wind at Earth by having additional observations from different vantage points during a period of moderate evolution of sunspot activity.
Previous studies have characterized the properties of stream interaction regions/corotating interaction regions (SIRs/CIRs) over two solar cycles enabling a degree of empirical prediction as to the properties of SIRs/CIRs as a function of solar cycle phase [e.g., Mason et al., 2012; Filwett et al., 2017; Jian et al., 2019; Allen et al., 2019]. However, a focused investigation of the likelihood that an L5 monitor will be able to serve as an advanced warning buoy for SIRs/CIRs that will affect the near-Earth space environment has yet to be extensively performed. Having advanced warning of an CIR impinging upon the magnetosphere of Earth is important for predictive space weather warnings, due to SIRs/CIRs ability to trigger geomagnetic storms [e.g., Tsurutani & Gonzalez, 1997; Turner et al., 2006; Richardson, 2018] and affect ionospheric compositions and winds [e.g., Chen et al., 2014]. Through comparing 11 years of SIRs/CIRs observed at ACE and STEREO, we have investigated the probability of detecting a SIRs/CIRs at two locations as a function of the difference in heliospheric longitude between the two spacecraft. By examining the detection and properties of SIRs/CIRs using variable separation between the two observations points, this work seeks to estimate the utility of an L5 monitor for SIR/CIR predictability.
Major solar activity (Flares and Coronal Mass Ejections; CMEs) has long been attributed to the rapid magnetic energy release governed by ideal and/or resistive MHD processes. Such activities may occur [1] in Active Regions (ARs) where magnetic field concentrations emerge and evolve, but also [2] in other locations where magnetic fields decay, such as decaying ARs/plage. For the first case, not all ARs are flare and CME productive; ARs that exhibit compact polarity inversion lines (PILs) are known to be very flare productive. However, the physical mechanisms behind this statistical inference have not been demonstrated conclusively due to the lack of continuous observations of a large sample of ARs in the rotating frame of the sun as observed by the Earth’s position. For complex ARs, which were well-observed since the beginning of their emergence phase, it has been shown that such PILs can occur owing to the collision between at least two emerging flux tubes nested within the same AR (Chintzoglou et al 2019). However, many potent ARs rotate into Earth view already developed and thus assessing how they evolve in becoming eruptive is as of now not possible. In the second case, eruptive activity can also occur in decaying ARs hosting an energized magnetic structure known as filament channel (or coronal cavity when seen at the limb), which eventually erupts as a CME. Observations of the formation of filament channels remain scarce (only a handful of publications), primarily due to the time-scale of the evolution that appears to last longer than the maximum observing period from Earth’s vantage point (half solar rotation period). For either source of major solar activity, a quantity that plays central role is the magnetic flux content and spatial distribution with time. Measurements of the true radial component of the photospheric magnetic field (requiring a vector magnetograph) of almost all the emerging and decaying ARs seen from Earth and from a different vantage point (L5) are therefore crucial in our quest to understand the cause of major solar activity."