A systems science approach based on canonical correlation analysis (CCA) is applied as a new, behavioral way to validate global geospace models. The biggest novelty of the technique is that it validates models at a system level, whereby a side-by-side comparison is performed of CCA applied to a 30-day observational and the corresponding simulation data sets comprising quiet, moderate and active times. The simulation used the Multiscale Atmosphere-Geospace Environment (MAGE) model. It is shown that (a) CCA must be combined with sensitivity analysis to be effective, (b) the MAGE model generally reproduces the observed behavior (more so for quieter time intervals), quantified by the intercorrelations between different variables and (c) the technique identifies the SuperMAG SML index as a quantity for which refinements of the model are needed.

The simple problems of the solar wind number density driving the plasma sheet number density and the solar wind speed driving the plasma sheet temperature are examined. To ensure that the central plasma sheet is studied, 1017 current sheet crossings in the plasma sheet are collected from 10.8 RE to 76.9 RE downtail, and 3-s resolution ion and electron measurements from THEMIS-B and THEMIS-C are compared with time-lagged solar wind number densities and speeds. The central plasma sheet measurements are taken from the solar minimum years of 2007–2009. Three correlation methods are used: (1) Pearson (univariate) linear correlations; (2) multivariate linear correlations; (3) canonical correlation analysis. For both ions and electrons, knowing the solar wind speed adds insignificant information to the solar wind density versus plasma sheet density correlations. Likewise, for both ions and electrons, knowing the solar wind density adds insignificant information to the solar wind speed versus plasma sheet temperature correlations. The standard two problems (1) the density of the solar wind driving the density of the plasma sheet and (2) the velocity of the solar wind driving the temperature of the plasma sheet, appear to be completely unrelated, even though the solar wind density and the solar wind velocity have a strong anticorrelation. Future work is outlined.

For community use, a new composite whole-Earth index E(1) and its matching composite solar wind driving function S(1) are derived. A system science methodology is used based on a time-dependent magnetospheric state vector and a solar wind state vector, with canonical correlation analysis (CCA) used to reduce the two state vectors to the two time-dependent scalars E(1)(t) and S(1)(t). The whole-Earth index E(1) is based on a diversity of measures via six diverse geomagnetic indices that will be readily available in the future: SML, SMU, Ap60, SYMH, ASYM, and PCC. The CCA-derived composite index has several advantages: 1) the new “canonical” geomagnetic index E(1) will provide a more powerful description of magnetospheric activity, a description of the collective behavior of the magnetosphere–ionosphere system. 2) The new index E(1) is much more accurately predictable from upstream solar wind measurements on Earth. 3) Indications are that the new canonical geomagnetic index E(1) will be accurately predictable even when as-yet-unseen extreme solar wind conditions occur. The composite solar wind driver S(1) can also be used as a universal driver function for individual geomagnetic indices or for magnetospheric particle populations. To familiarize the use of the new index E(1), its behavior is examined in different phases of the solar cycle, in different types of solar wind plasma, during high-speed stream-driven storms, during CME sheath-driven storms, and during superstorms. It is suggested that the definition of storms are the times when E(1) >1.

This white paper summarises the Seven Sisters solar wind (SW) mission concept and engineering report.The mission will collect critical measurements of the thermal and suprathermal plasma, and magnetic fields utilizing Venus-Sun Lagrange (VL) points, to resolve the science enabling eventual operational space weather mission and next generation space weather model development.Mission will uncover fundamental plasma physical processes responsible for particle acceleration and transport in the SW and enable > 50 Earth days/year collection of data in Geoeffective region (GER) for the development of algorithms for 7 hr to 2 day advanced prediction of IMF orientation at Earth and properties of geoeffective SW structures.The 7 spacecraft mission will launch in 2029, it will arrive to VL1 point in August 2030, and eventually occupy also VL3, VL4, and VL5 orbits.Different mission phases enable 1) 3D volumetric measurements at different scales, and 2) simultaneous large (> 0.6 AU) and intermediate-(≈ 2-100 Mm)-scale azimuthal and radial measurements.The total cost of the 7 year mission is < $ 560 M.

EDITORIAL article Front. Astron. Space Sci., 11 May 2023Sec. Space Physics Volume 10 - 2023 | https://doi.org/10.3389/fspas.2023.1195579

Insufficiently accurate magnetic-field-line mapping between the equatorial magnetosphere and the ionosphere prevents us from determining the cause of many types of aurora and ionospheric phenomena and from knowing many of the connections in the magnetosphere-ionosphere-thermosphere system.The bold MIO mission concept is to operate a powerful 1-MeV electron accelerator on a main spacecraft in the equatorial nightside magnetosphere: with the beam directed into the atmospheric loss cone the accelerator deposits energy of ionizing electrons in the atmosphere sufficient to optically illuminate the magnetic footpoint of the spacecraft while 4 nearby daughter spacecraft make equatorial magnetospheric measurements.A network of ground-based imagers in Alaska and Canada will locate the optical beamspot thereby unambiguously establishing the connection between equatorial magnetospheric measurements and ionospheric phenomena.Critical gradient and boundary measurements will be made to discern magnetospheric generator mechanisms and boundary mapping.This enables the magnetospheric drivers of various aurora, ionospheric phenomena, and field-aligned currents to be determined.

The cold particle populations (with energy less than ~100 eV) of the Earth's magnetosphere are sparsely measured and very poorly understood but play critical roles in the dynamics of the magnetosphere-ionosphere-thermosphere system, both locally and globally.A research plan combining the development of new measurement techniques, data analysis, and theory and modeling, culminating with a dedicated space mission, is necessary to definitively understand the cold particle populations and should be one of the focuses of the next decade.Without such understanding, the magnetosphere-ionosphere system cannot be fully understood.

The Sun and the heliosphere is a system-of-systems, where the physics of cross-regional and cross-scale coupling determines the state of the system.We describe the outstanding questions of solar wind physics as well as potential solutions, summarized broadly as two overarching issues.The first issue is that there is insufficient data coverage and computational power to measure and model cross-scale and cross-regional feedback.The second issue is that the understanding of the Sun and heliosphere has traditionally existed in knowledge silos, primarily as the independent study of the Sun and the solar atmosphere with remote measurements, versus the independent study of the solar wind and heliosphere with in situ measurements.To address these issues, we call for:-Measurement coverage of the Sun and heliosphere in 4pi steradian, with measurements over the solar poles having the most potential for discovery science.-Cross-regional and cross-scale measurement coverage, especially via constellations measuring the mesoscales in the inner heliosphere, matched compositional measurements, and continuous remote imaging through the middle corona.-Solving the coronal heating problem and Huygens Probes at the Sun.-Modeling, data delivery and data assimilation that captures the cross-regional and crossscale coupling.-Training and retaining the next generation of Heliophysicists that can bring together the necessary broad range of expertise to solve these problems.Together, this need for coordinated observations, modeling, and data architecture calls for an umbrella program such as: ISTPNext, enhanced DRIVE Centers, Centers of Excellence, University Departments of Heliophysics, etc.The Current State.The Sun and heliosphere is a system-of-systems: the solar interior/dynamo; the solar atmosphere, consisting of the photosphere, chromosphere, transition region, low, middle and upper corona; and the solar wind/heliosphere.Cross-regional and cross-scale coupling is crucial to the physical state of this system.Emergent phenomena, i.e., physical behaviors that emerge only when the parts interact in a wider whole, are revealed when studying cross-scale and cross-regional feedback.The Sun's magnetic field, generated in the solar interior, and threading through the solar atmosphere and out into solar wind, produces much of the coupling.Due to the complexity and feedback of this system-of-systems, there are major outstanding questions regarding solar wind formation, and its evolution as it advects through the heliosphere.Synthesizing inputs from the solar wind research community, nine outstanding questions of solar wind physics from a recent AGU Grand Challenges review paper (Viall & Borovsky 2020) are described in this white paper, as well as potential solutions.The formation of the solar wind and its evolution as it flows away from the Sun is fundamental to how the Sun and stars get rid of stressed magnetic fields, and involves physical processes that operate throughout the universe.Additionally, the solar wind constantly bombards Earth's magnetic field and plasma environment, as well as other planetary bodies, driving dynamic space weather.The solar wind is the medium through which larger space weather events from solar storms (e.g.CMEs and SEPs) propagate.Understanding the solar wind is therefore key for understanding universal plasma physics, stars and how they form their astrospheres, and space weather and the space environment around Earth.

Operational space weather requires understanding the solar wind-magnetosphere interaction not only during the typical solar wind conditions, but also those that may be more rare but particularly geoeffective.The space weather phenomena associated with meso-scale solar wind structures, that can have size comparable to the magnetospheric scale, have been largely ignored, as the standard procedure is to determine what are the solar wind conditions, based on a single monitor at L1, impacting the magnetosphere at any point in time.Moving forward, it is important to ask what are the solar wind conditions and what location of the magnetosphere is expected to be impacted.This also leads to the question of how the magnetosphere is configured globally when there are different solar wind conditions on the dawn-vs-dusk flanks.Future space weather monitoring missions should be adequately equipped to predict the impact of meso-scale solar wind structures, well in advance of the current ~1 hr window.Magnetospheric constellation missions and global magnetosphere simulations, using different plasma approximations, can be used to understand the associated space weather effects.

This paper summarizes the Seven Sisters solar wind mission concept and the outstanding science questions motivating the mission science objectives. The Seven Sisters mission includes seven individual spacecraft designed to uncover fundamental physical processes in the solar wind and provides up to ≈ 2 days of advanced space weather warnings for 550 Earth days during the mission. The mission will collect critical measurements of the thermal and suprathermal plasma and magnetic fields, utilizing, for the first time, Venus–Sun Lagrange points. The multi-spacecraft configuration makes it possible to distinguish between spatial and temporal changes, define gradients, and quantify cross-scale transport in solar wind structures. Seven Sisters will determine the 3-D structure of the solar wind and its transient phenomena and their evolution in the inner heliosphere. Data from the Seven Sisters mission will allow the identification of physical processes and the quantification of the relative contribution of different mechanisms responsible for suprathermal particle energization in the solar wind.

EDITORIAL article Front. Astron. Space Sci., 22 February 2023Sec. Space Physics Volume 10 - 2023 | https://doi.org/10.3389/fspas.2023.1149649

Mesoscale dynamics are fundamental in space physics, but fall within an observational gap of current and planned missions.Particularly in the solar wind, measurements at the mesoscales (100's RE to a few degrees heliographic longitude at 1 au) are crucial for understanding the connection between the corona and an observer anywhere within the heliosphere.Mesoscale dynamics may also be key to revealing the currently unresolved physics regulating particle acceleration and transport, magnetic field topology, and the causes of variability in the composition and acceleration of solar wind plasma.Studies using single-point observations do not allow for investigations into mesoscale solar wind dynamics and plasma variability, nor do they allow for the exploration of the sub-structuring of large-scale solar wind structures like coronal mass ejections (CMEs), co-rotating/stream interaction regions (CIR/SIRs), and the heliospheric plasma sheet.To address this fundamental gap in our knowledge of the heliosphere at these scales, new dedicated mesoscale missions are required in the next decade.This white paper outlines the current gaps in our understanding resulting from limited measurements at this critical scale and the need for an asserted effort in addressing these gaps.

∗ Primary Author 1 Astrophysical and Planetary Sciences Department, University of Colorado, Boulder, CO 2 Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO 3 Southwest Research Institute, San Antonio, TX 4 Space Science Research Institute, Boulder, CO 5 NASA Marshall Spaceflight Research Center, Huntsville, AL 6 Los Alamos National Laboratory, Los Alamos, NM 7 Space Sciences Laboratory, University of California, Berkeley, Berkeley, CA 8 College of Engineering, Boston University, Boston, MA

The Earth’s magnetic field shields the planet and its atmosphere from the solar wind. However, this magnetic shielding is not perfect. A fraction of the mass, energy, and momentum from the solar wind can transfer to the magnetosphere and ionosphere through processes that are often referred to as solar wind-magnetosphere interactions (see, for example, reviews in Akasofu, (1981); Rostoker et al. (1988); Gonzalez et al. (1999); Jordanova, (2003); Watermann et al. (2009); Wing et al. (2014); Johnson et al. (2014); Kilpua et al. (2017); Borovsky (2020); Zhang et al. (2022)). The solar-wind-magnetosphere interactions form a basic foundation for the studies of space physics, magnetospheric physics, ionospheric physics, and space weather. The goals of this Frontiers Research Topic on Solar Wind–Magnetosphere Interactions are 1) to publish research at the forefront of this important topic, 2) to assess the state of knowledge, 3) to point out new directions in research, 4) to apply new mathematical and data-analysis techniques, and 5) to discuss needs for the future. Seventeen papers on solar wind–magnetosphere interactions are contained in this electronic book. Synopses of the seventeen papers are as follows, ordered by papers that focus on 1) the Sun 2) solar wind, 3) magnetosphere, and 4) ionosphere. Chapman builds on her previous work that shows that they can map sunspot record, which has irregular cycle duration, onto a regular “clock” where each cycle has the same duration in Hilbert analytic phase. The quiet interval of the solar cycle is located at a fixed phase interval of this solar cycle clock. In the present work, she shows that such mapping can be done without using the Hilbert transform. There is a clear geomagnetically active-quiet switch-off and quiet-active switch-on activity and the times for this on and off switch can be directly determined from the sunspot time-series without performing Hilbert transform. The switch-off and switch-on of activity can be mapped from the clock back into the timedomain to create a cycle-by-cycle chart of activity, which can be useful for space weather assessment. Sivadas and Sibeck study how simultaneous measurements of different L1 solar wind monitors differ due spatial and temporal structure of solar wind. They point out that this inherent uncertainty in L1 solar wind measurements may lead to bias in various studies utilizing correlations between solar wind and magnetospheric variables. By numerical experiments Sivadas and Sibeck show that this so-called regression bias may lead to an OPEN ACCESS

There is a general consensus that fluctuations in the solar wind magnetic field and/or the Alfvenicity of the solar wind drive a solar wind-magnetosphere interaction. 11 years of hourly-averaged solar wind and magnetospheric geomagnetic indices are used to further examine this hypothesis in detail, confirming that geomagnetic activity statistically increases with the amplitude of upstream fluctuations and with the Alfvénicity, even when solar-wind reconnection driver functions are weak and reconnection on the dayside magnetopause should vanish. A comparison finds that the fluctuation-amplitude effect appears to be stronger than the Alfvénicity effect. In contradiction to the generally accepted hypothesis of driving an interaction, it is also demonstrated that many solar wind parameters are correlated with the fluctuation amplitude and the Alfvénicity. As a result, we caution against immediately concluding that the latter two parameters physically drive the overall solar-wind/magnetosphere interaction: the fluctuation amplitude and Alfvénicity could be acting as proxies for other more-relevant variables. More decisive studies are needed, perhaps focusing on the roles of ubiquitous solar-wind strong current sheets and velocity shears, which drive the measured amplitudes and Alfvénicities of the upstream solar-wind fluctuations.

Relatively few studies have focused on the cold plasma populations of the magnetosphere due to difficulties associated with obtaining measurements.The cold particle populations are defined here as those with total energy approximately <100 eV which is an energy range for which measurements are difficult (regardless of species), but which often make up the bulk of the plasma density.These populations have known and suspected impacts on the structure and dynamics of the magnetosphere.Unfortunately, the lack of accurate measurements of the cold ion and cold electron populations through the magnetosphere makes closure of these science questions extremely difficult if not impossible.In a complex system of interconnected parts like the Earth's magnetosphere, a lack of understanding of one part of the system (the cold electron and ion populations) is disabling.Hence, until cold electron and cold ion measurements are obtained robustly with every mission, the magnetospheric plasma environment cannot be completely understood.This will require innovations in plasma spectrometers and associated techniques required to obtain high-fidelity in-situ measurements of the cold ion and cold electron populations in the magnetosphere.This paper seeks to review the instruments and techniques that have been used to date and present possible options for future missions.