The Next Decade of Discovery in Solar and Space Physics Exploring and Safeguarding Humanity's Home in Space (2025) / Chapter Skim
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Appendix C: Report of the Panel on the Physics of Magnetospheres
Pages 315-380

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From page 315...
... Strong, sustained southward interplanetary magnetic fields drive geomagnetic storms, which result in intense currents both around Earth (the ring current) , along the magnetic field lines, and through the ionosphere, causing magnetic disturbances on the ground.
From page 316...
... C.1.1 Inner Magnetosphere The inner magnetosphere includes different interrelated, overlapping particle populations: the radiation belts at the highest (MeV and above) energies, the hot ring current and warm plasma cloak at lower (few eV to hundreds
From page 317...
... Understanding the dynamics of the radiation belts was a key goal of the Van Allen Probes mission because of the severe space weather impacts this energetic population can have on operating spacecraft. Van Allen Probes showed definitively that local acceleration by wave particle interactions is occurring in the center of the radiation belts, causing fast local changes in the belts.
From page 318...
... In addition, Van Allen Probes measurements showed that mesoscale energetic particle injections associated with magnetic field dipolarizations can also increase the ring current pressure and are also associated with direct outflow of O+ into the inner magnetosphere. This outflow has only a small impact on the ring current pressure owing to its low energy but is likely a source for the warm plasma cloak and perhaps the oxygen torus, a population of warm (<50 eV)
From page 319...
... As shown in Figure C-4, for the first time, observations directly captured the electron diffusion region (EDR) of magnetic reconnection, where magnetic field lines can break and reform, explosively releasing magnetic energy into bulk flows, heating, and the acceleration of particles, and ultimately allowing solar wind energy to enter the magnetosphere and driving space weather events.
From page 320...
... Building on this discovery, the community made novel measurements identifying the long-ranging effects of these twisted magnetic structures -- for example, releasing energetic particle injections and seeding ultra-low frequency waves that echo throughout the magnetosphere. • Magnetotail transport and dynamics: A growing number of multisatellite studies leveraging serendipitous arrangements of magnetospheric assets (e.g., THEMIS, Van Allen Probes, MMS, Arase, Geostationary Operational Environmental Satellites [GOES]
From page 321...
... • Energetic particle acceleration: Modeling studies, constrained by data from missions including THEMIS and MMS, have discovered that coherent dipolarization fronts or dipolarizing flux bundles can carry energetic electrons and ions earthward by trapping them in drifts around localized "magnetic islands." This may play an important role in the energization and transport of particles from the tail into the inner magnetosphere. • Structure of the substorm current wedge: New results from THEMIS, ground-based magnetometers, and all-sky imagers (ASIs)
From page 322...
... Major progress has been made in understanding the transfer of mass, momentum, and energy between the magnetosphere and ionosphere/thermosphere. Significant achievements and landmark discoveries over the past decade include the following: • Kinetic and electromagnetic energy deposition in the ionosphere and thermosphere: Patchy processes with transverse scales in the topside ionosphere (100 km can be associated with extreme Poynting fluxes >170 mW/m2.
From page 323...
... These results have opened new debates as to whether these extreme polar acceleration regions may actually serve as a source of Jupiter's extreme radiation belts. C.2 PRIORITY SCIENCE GOALS FOR MAGNETOSPHERIC PHYSICS Section C.1 highlights the tremendous progress that has been made in the past decade, particularly in understanding the dynamics of the radiation belts and the microphysics of magnetic reconnection.
From page 324...
... While the general topic of acceleration is not a focus for the coming decade, some important aspects of question 5, targeting particle acceleration, are included under the other questions: in particular, acceleration of ionospheric ions to create ion outflow is included in question 2, and acceleration and heating through reconnection, turbulence and shocks is included in question 4, and dynamics of radiation belts in other systems such as Jupiter is included in question 6. Investigations into all aspects of acceleration in the magnetosphere are still supported.
From page 325...
... to minutes Temporal energetic particle flux Injections (at satellite) enhancements; observed in the near tail and inner magnetosphere NOTE: Acronyms defined in Appendix H
From page 326...
... to better understand energy transfer from the solar wind to the magnetospheric system, the transition from the plasma sheet to the inner magnetosphere to better understand how the tail supplies the radiation belts and ring current with particles and energy, and the connection between the magnetosphere and the ionosphere as a coupled system. Current Research Activity Operating and Past Missions Many serendipitous spatial arrangements of current (and past)
From page 327...
... Although its primary focus is the solar wind, it will also spend time in the magnetosphere where it can probe magnetospheric turbulence. With apogee at almost lunar distances and perigee near 15 RE, HelioSwarm will not directly study the energy/mass/momentum transfer from the solar wind to the magnetosphere nor from the plasma sheet to the inner magnetosphere (or ionosphere)
From page 328...
... The lack of a self-consistent treatment of the transition region limits not only the ability to understand the coupling between the magnetotail and inner magnetosphere, but also a critical feedback loop spanning the magnetosphere, ionosphere, and thermosphere. The challenge of modeling the transition region is that this requires both highly resolved spatial scales over geospace timescales of several days and kinetic physics that goes beyond the typical ideal fluid treatments currently used.
From page 329...
... (See Table C-2.) The focus of these observations and modeling needs to be of the "transition regions" within geospace -- that is, the dayside where solar wind impinges on the magnetosphere, the magnetic field transition region between the magnetotail plasma sheet and the inner magnetosphere (including the radiation belts and ring current)
From page 330...
... or can be lost to space on polar field lines connected to the interplanetary magnetic field. In situ observations have revealed the presence of ionospheric plasma throughout the magnetosphere, extending more than 200 RE down the tail.
From page 331...
... The combination of FAST measurements of outflow at ~4,000 km altitude, Cluster measurements over the polar cap and into the lobe and plasma sheet, MMS measurements in the equatorial plasma sheet and Van Allen Probes in the inner magnetosphere has provided an extensive database of ion measurements for statistically tracking the transport paths of ions through the magnetosphere. In addition, ENA imaging from both IMAGE and TWINS have provided a global perspective on the evolution of ions in the inner magnetosphere during storms, including differences in H+ and O+ behavior.
From page 332...
... Over the past decade, tremendous progress has been made in developing complex frameworks that allow for the exchange of information between global magnetosphere models and those focused on specific regions, such as the polar wind, plasmasphere, ionospheric electrodynamics, and inner magnetosphere. These frameworks enable self-consistent coupling between the plasma and electromagnetic fields and involve different levels of sophistication in modeling collisionless plasma dynamics, ranging from ideal MHD to fully electromagnetic kinetic plasma models (PIC or Maxwell-Vlasov)
From page 333...
... Current Research Activity Missions and Facilities Addressing This Goal While there are no currently flying NASA missions devoted to studying M-I coupling, there are several currently in development that will make significant contributions to addressing part of this priority goal. First, the multisatellite GDC mission would provide unprecedented multiscale I-T measurements and has the appropriate instrumentation to determine the energy deposition and response of the I-T system to energy input from the
From page 334...
... mission was recommended in the 2013 solar and space physics decadal survey (NRC 2013; hereafter the "2013 decadal survey") and the subsequent midterm assessment, Progress Toward Implementation of the 2013 Decadal Survey for Solar and Space Physics: A Midterm Assessment (NASEM 2020)
From page 335...
... Assuming that Joule heating in the ionosphere equals the input energy, Joule heating and, thus, conductance and convection electric field have often been calculated to estimate the input energy by ignoring neutral winds. However, the lack of global specification of both conductivity and neutral wind distributions at any timescale have introduced considerable uncertainties in quantifying the energy deposition into the I-T system and its response.
From page 336...
... Thus, more global coverage from a combination of satellites and ground-based instruments is needed to improve mapping between the magnetosphere and ionosphere, along with modeling capabilities that can account for an altitude-resolved ionosphere. C.2.4 Priority Science Goal 4: What Are the 3D Global Properties of Turbulence, Magnetic Reconnection, and Shocks, and What Is Their Role in Coupling Energy in the Magnetosphere?
From page 337...
... However, as with reconnection, a global characterization of the bow shock and the resulting turbulence is missing. The conversion of solar wind kinetic energy into heating and compression of the plasma strongly affects the geospace response and may contribute to negative space weather consequences.
From page 338...
... The energy conversion mechanisms have been directly measured, including such mechanisms as a cross-shock electrostatic potential, current-driven instabilities (e.g., the Buneman and electron-cyclotron drift instabilities) , electron-only magnetic reconnection in the shock transition region, other WPIs, and particle acceleration and reflection.
From page 339...
... At the other extreme, global magnetospheric MHD simulations and associated computational frameworks (e.g., MAGE, Open Geospace General Circulation Model [OpenGGCM] , and Space Weather Modeling Framework [SWMF]
From page 340...
... Science Centers -- is improving modeling of the mesoscale dynamics of the plasma sheet and its connection to the inner magnetosphere, a topic at the heart of PSG 1. One unique challenge in addressing PSG 3 relates to the emphasis of some programs on projects that primarily involve satellite data analysis efforts with little or no support for combined efforts involving both space- and ground-based data.
From page 341...
... Throughout the solar system, researchers can combine the ground truth of in situ particle measurements with simultaneous remote measurements equivalent to what is done for extrasolar objects. So much more can be learned about the fundamental physical processes in the universe by adding in situ measurements from additional data points to those of Earth, specifically those that may be more analogous to other astrophysical systems (i.e., with relativistic particle acceleration, very strong and rapidly rotating magnetic fields, synchrotron electromagnetic emissions, natural X-ray sources)
From page 342...
... As with many things, Jupiter has the most intense auroral emission in the solar system, which seems to be largely decoupled from solar wind interactions and is instead dominated by internal processes. However, new results suggest that extreme auroral energies at Jupiter may provide a seed mechanism for the acceleration of the energetic particles in its radiation belts.
From page 343...
... Research and Analysis and Development Grant Programs Comparative planetary magnetosphere studies are supported by several rather focused opportunities across funding agencies. At NASA, the most explicit opportunities for broad comparative studies are the Heliophysics Division's LWS Program -- where a strategic science area focuses on topics such as atmospheric depletion and stripping and magnetospheric shielding that readily support investigation of varying magnetospheric configurations and characteristics and the Planetary Science Division's Solar System Workings Program -- which tends to accept a very wide scope of planetary science investigations.
From page 344...
... As has been the case for several decades, the space physics community also took advantage of serendipitous opportunities for collaborations with the Planetary Science Division, largely stemming from long cruise durations (e.g., Juno, BepiColombo, JUICE, and Europa Clipper) , unique access to regions of the outer solar system (e.g., New Horizons)
From page 345...
... Furthermore, magnetic fields of rocky planets are thought to play an essential role in planetary habitability, as they may regulate the interaction between a planet and the stellar wind, hence the global distribution of energy dissipated into the planetary atmosphere by the stellar wind. Conversely, the absence of an intrinsic magnetic field may make a planet more prone to atmospheric ablation because it allows for direct interaction between the stellar wind and the neutral atmosphere.
From page 346...
... • Data assimilation: Ingesting observations into models has shown promise for radiation belt and ionospheric environments. The community is developing data assimilation techniques for the magnetosphere as well as advanced techniques such as OSEs and OSSEs.
From page 347...
... The release has enabled intercalibrations with sensors at GEO and LEO, increased radiation belt model accuracy, and an improved understanding of acceleration and loss processes in the heart of the outer belt. Use Cases and Relation to Priority Science Goals In a typical scenario, a commercial satellite system may provide in situ or remote sensing data such as the plasma density, particle flux, ambient magnetic field, and/or auroral and airglow imagery.
From page 348...
... high-frequency noise Particle flux Radiation belts: particle GPS Spacecraft charging acceleration, transport, and loss Thermospheric density, O/N2 Thermospheric processes Starlink Satellite drag ratio Ionospheric electrodynamics Spacecraft charging Ionospheric parameters including magnetosphere– ionosphere coupling NOTE: Acronyms defined in Appendix H The relation between measured quantities, the science involved, and benefits for space weather nowcasting and forecasting are myriad.
From page 349...
... Given that there are lower-cost versions of multiple sensors that are mainstays of solar and space physics research -- GNSS receivers, magnetometers, all-sky cameras, ionosondes, and so on -- efforts have recently begun to create multi-instrument platforms with multiple low-cost sensors. Analogous to platforms that are widely deployed by volunteers to study terrestrial weather, these platforms provide one avenue for significantly improving the ability to address PSGs 1–4.
From page 350...
... gas populations immersed in electromagnetic fields evolve on a wide range of length and timescales. Usually, the dynamics of the large (macro-)
From page 351...
... This transition region between the plasma sheet and inner magnetosphere acts as the "gateway" to the inner magnetosphere, providing the population that creates the ring current that drives geomagnetic storms as well as seeding particles that fill the radiation belts. It is also where many intense auroral forms are driven, as flow braking and dipolarization drive FACs that cause aurora, and more recent results suggest it is where an instability forms that creates a bead-like structure on the substorm's quiet auroral arc.
From page 352...
... How is the 1.a. Scale size and evolution • Magnetic field, plasma density and velocity along the • Global magnetosphere models incorporating solar wind energy input of transfer processes at the dayside magnetopause with spatial resolution of 0.5 RE the physics and the requisite resolution to to the magnetosphere magnetopause spanning a spatial region or FOV of 4–5 RE.
From page 353...
... Common processes across • Magnetospheric plasma and energetic particle • Advancements in MHD models of other planets' magnetospheric planetary magnetospheres (tens ke–V–MeV) populations, including composition, planetary magnetospheres to allow more characteristics and and electromagnetic fields from each planetary system direct comparisons to those of Earth.
From page 354...
... Although these structures are known to exist, their global impact on the flow of energy into and through the magnetosphere and ionosphere is linked to their temporal frequency and spatial extent which has not been observed. Although the list of science questions that Links could address is exciting and long, the consolidated main science objectives are the following: • Determine how plasma sheet mesoscale structures transport and energize particles from the plasma sheet to the inner magnetosphere.
From page 355...
... to view the plasma sheet with a 50° × 50° field of view centered on the Sun–Earth line, and one wide-angle ENA camera for viewing the ring current with a 90° × 120° field of view. The magnetotail is wide compared to the size of the meso-scale structures of interest (~40 RE versus 1–3 RE)
From page 356...
... Incorporating the mesoscales into future (or current) models would be a new system science capability which could lead to better operational space weather prediction.
From page 357...
... To accomplish this goal, the mission targets four more specific science objectives: • Determine how magnetospheric and solar energy inputs cause outflow of ionospheric plasma into the magnetosphere. • Determine the mechanisms that drive refilling and isotropization of the plasmasphere.
From page 358...
... The aim is to have M5 in the same orbital plane as M1 and M2, such that it can measure outflowing ions that have been energized and transported in the lobes, plasma sheet, and cloak. It again includes the Fields Suite (like M1, M2, and M4)
From page 359...
... It addresses the fundamental processes of ion acceleration across the exobased transition region as well as those driving plasmaspheric refilling, isotropization, and erosion. Progress on all these processes would advance the understanding of fundamental physics present throughout solar and space physics.
From page 360...
... The instrumentation, which has a high heritage from previous missions such as IMAGE, FAST, ICON, MMS, Van Allen Probes, and Juno, includes a plasma instrument, an electromagnetic fields instrument, and a UV imager. The plasma instrument measures 3D distributions of electrons and ions (with composition)
From page 361...
... The solar and space physics environment offers a front-row seat where detailed, multipoint, in situ measurements can be made to provide insight that can be applied to a wide range of systems. With a variable incident solar wind, regular measurements from a dedicated mission can probe the physics over a wide range of plasma beta and Mach number, as well as incident magnetic field geometries.
From page 362...
... Jupiter is a natural stepping stone beyond Earth because it boasts the strongest magnetic field; largest magnetosphere; the most active moon, Io, which is the primary plasma source for the system; the fastest rotation; and the most powerful aurora and radiation belts. Additionally, Jupiter's environment continually exhibits extreme regimes that cannot be emulated even during the most extreme geomagnetic storms at Earth.
From page 363...
... The fact that Jupiter's magnetosphere greatly exceeds the energies and intensities found in any other planetary environment despite its high density of neutrals that absorb and cool charged particles remains one of the largest mysteries in planetary magnetospheres. Balancing losses with acceleration and source processes is critical for establishing and sustaining robust planetary radiation belts.
From page 364...
... It will study how Jupiter accelerates charged particles to such exceptionally high energies and how moon and ring materials in the Jovian space environment help create the radiation belts even though they simultaneously limit them. It will further reveal the processes seeding Jupiter's unique, intense radiation belts and the loss processes of relativistic charged particles in Jupiter's magnetosphere and the resulting X-ray emission.
From page 365...
... By providing measurements of both steady and rapidly varying flows and electric fields, this network of radars provides crucial information needed to quantify the relative importance of electric field variations with different spatial and temporal scales for overall energy deposition rates. Working together with the Distributed Network and satellite missions such as Links, studies using the existing SuperDARN network can also identify the causes of ionospheric electric field variations and their effect on multiscale energy dissipation on the M-I system.
From page 366...
... Therefore, IS radars are essential ground-based instruments for understanding the energy and mass transfer between the M-I-T-M system. More specifically, IS radars can contribute to planned and proposed magnetosphere missions, space weather studies, and other solar and space physics disciplines, such as I-T-M.
From page 367...
... Combined with other measurements, such as the SuperDARN convection, they could also be used to determine how global DC Poynting flux evolves in response to changing solar wind and magnetosphere conditions. More specifically, AMPERE-NEXT can contribute to planned and proposed magnetospheric missions, space weather studies, and other solar and space physics disciplines, such as ITM.
From page 368...
... is in need of a technology boost and that (b) could have a substantial impact in solar and space physics.
From page 369...
... Particle flux data are needed to constrain inner magnetospheric models of the radiation belts, ring current and low-energy populations, and for understanding particle acceleration, transport, and loss. Magnetic field data are needed for understanding the field configuration at key locations (e.g., GEO, LEO, and ground)
From page 370...
... Monitoring the heart of the radiation belts at L~4 would require at least two spacecraft either at geosynchronous transfer orbit (GTO)
From page 371...
... -- would provide detailed physical insight into multiple global magnetospheric processes of relevance to both the planetary science and space physics communities.
From page 372...
... It would also be beneficial to leverage international partnerships to extend the Distributed Network to include coverage in Greenland and other areas so that a wider range of M-I dynamics sampled by Links and other missions and projects are captured. This would also better constrain global conductance, auroral precipitation, and other parameters to more comprehensively address PSGs 1 and 3.
From page 373...
... It will then study the links between the plasma sheet in the stretched magnetotail and the radiation belts and ring current in the dipolar inner magnetosphere, learning how the solar wind's energy that was stored in the tail is transferred to the inner magnetosphere across Earth's transition region. Last, it will study the links between the magnetosphere and ionosphere by simultaneously measuring magnetospheric phenomenology with its auroral counterpart.
From page 374...
... The Cluster mission is only expected to operate until September 2024, which will leave no spacecraft in polar orbit. MMS and THEMIS provide critical fields and waves, plasma, and energetic particle measurements in the near-equatorial plane; however, they are not designed for measuring the inner magnetosphere and its intense radiation belts.
From page 375...
... These examples share another similarity: both GNSS receivers and magnetometers are frequently deployed by geoscience research groups seeking to address questions unrelated to solar and space physics. For example, GNSS receivers are frequently deployed by the cryosphere research community to study ice sheet dynamics.
From page 376...
... For example, FAST data in the auroral acceleration region and Van Allen Probes data in the inner magnetosphere provide observations that are still highly relevant to the PSGs. A second gap is that there is no apparent NASA opportunity that encourages equal analysis of both planetary science and heliophysics data for comparative magnetospheres studies.
From page 377...
... One possible solution may be to create a network of all institutions with publicly available data sets under a standard solar and space physics framework so each institutional site can operate by itself while utilizing data from and sharing data with the entire network. Storing data sets in a cloud gives researchers access to all the subscribing data sets within a unified framework, as well as cloud computing tools which drastically reduces the analysis times of tera- or petabyte data sets through parallel processing.
From page 378...
... These measurements are also crucial to the ITM and space weather communities; for example, distributed networks of GNSS TEC receivers in Antarctica enable studies of north-south hemisphere asymmetries in polar cap patches, tongues of ionization, and other I-T phenomena, while neutron monitors provide crucial information relevant to space weather nowcasts/forecasts. To mitigate some of these issues, international collaborations could be used to share logistical resources and access regions of Antarctica that are becoming less accessible to USAP.
From page 379...
... • Cooperation between the NASA Heliophysics Division and Planetary Science Division to ensure that future planetary missions include appropriate space physics instrumentation when feasible. The panel eagerly looks forward to the implementation of a program addressing many of these goals.
From page 380...
... 2017. "A New Physical Model of the Electron Radiation Belts of Jupiter Inside Europa's Orbit." Journal of Geophysical Research: Space Physics 122.5:5148–5167.


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