A comparative overview of Terrestrial and Martian space weather is presented, with emphasis on applying the tools of complexity and nonlinear dynamics to study the spatiotemporal dynamics and structures of sun-Earth and sun-Mars space environment. The following topics are reviewed: (1) complex systems approach to solar atmosphere and solar wind; (2) complex systems approach to planetary bow shock and magnetosphere-ionosphere; (3) Martian space weather, bow shock, and magnetosphere-ionosphere; (4) imaging planetary magnetosphere-ionosphere.

In the domain of space science, numerous ground-based and space-borne data of various phenomena have been accumulating rapidly, making analysis and scientific interpretation challenging. However, recent trends in the application of artificial intelligence (AI) have been shown to be promising in the extraction of information or knowledge discovery from these extensive data sets. Coincidentally, preparing these data for use as inputs to the AI algorithms, referred to as AI-readiness, is one of the outstanding challenges in leveraging AI in space science. Preparation of AI-ready data includes, among other aspects: 1) collection (accessing and downloading) of appropriate data representing the various physical parameters associated with the phenomena under study from different repositories; 2) addressing data formats such as conversion from one format to another, data gaps, quality flags and labeling; 3) standardizing metadata and keywords in accordance with NASA archive requirements or other defined standards; 4) processing of raw data such as data normalization, detrending, and data modeling; and 5) documentation of technical aspects such as processing steps, operational assumptions, uncertainties, and instrument profiles. Making all existing data AI-ready within a decade is impractical and data from future missions and investigations exacerbates this. This reveals the urgency to set the standards and start implementing them now. This article presents our perspective on the AI-readiness of space science data and mitigation strategies including definition of AI-readiness for AI applications; prioritization of data sets, storage, and accessibility; and identifying the responsible entity (agencies, private sector, or funded individuals) to undertake the task.

Past advances in Solar and Space Physics have primarily leveraged single point observations or ad hoc combinations of spacecraft, while missions such as Cluster, MMS, and THEMIS have paved the way toward a "constellation era" in Heliophysics.This new era allows for unprecedented advancements into our understanding of the fundamental spatiotemporal nature of Solar and Space Physics, but presents its own set of unique challenges.This white paper seeks to outline the benefits and challenges of constellations, ranging from the Heliophysics System Observatory, to constellations consisting of a small number of spacecraft, to large-number constellations.In moving toward this constellation era, investments are required by our sponsors to best enable our continued scientific advancement in Solar and Space Physics.

The behavior of energetic particles in the Earth's dipole and stretched magnetic‐field models is explored with a focus on the shift of the atmospheric loss cone away from the magnetic‐field direction and on non‐adiabatic behavior occurring when the particle gyroradius becomes comparable with the gradient scale length of the local magnetic field. It is shown that the equatorial loss cone is aberrated away from the magnetic‐field direction (pitch angle of 0°) by the perpendicular drift of a charged particle (which is referred to as the “Mozer transform” described in Mozer (1966, https://doi.org/10.1029/JZ071i011p02701 ). It is found that the Mozer coordinate transformation in pitch‐angle/gyrophase‐angle space better organizes the behavior of bounce times, mirror altitudes, drift speeds, and first adiabatic invariant. It also describes the loss‐cone shift accurately for a certain range of values of the adiabaticity parameter ϵ , defined by the ratio of the particle gyroradius to the local radius of curvature of the magnetic field. For particles with larger ϵ , the Mozer transform (evaluated with the standard gradient‐curvature drift) breaks down and the “central trajectory” theory can be used to calculate the angular shift of the loss cone, which now includes an Earthward shift. When ϵ becomes relatively large, stochastic field line curvature (FLC) scattering occurs: we show the intimate connection between the strength of FLC scattering and the loss‐cone shift. By comparing ion orbits in the dipole and Tsyganenko (Ts89 and Ts04) magnetic fields, we conclude that the loss cone of ring‐current ions is significantly modified during geomagnetically active times.

This is the set of simulation data of the equatorial thermal plasma density, provided by the activity-dependent Ober 1997 model.

Abstract In a perspective fashion, viewpoints on three research topics are presented, advice is given for early researchers and for not‐so‐early researchers, comments are made about the impacts of luck and hard work on a science career, and a lifetime of colleagues is discussed.

We describe the use of information-theoretic methodologies to characterise statistical dependencies of energetic electron fluxes (130 keV and >1 MeV) with a wide range of solar wind and magnetospheric drivers. We focus specifically on drivers associated with radial diffusion processes and revisit the events studied by Rostoker et al. Geophys. Res. Lett. (1998) in terms of mutual information. The main benefit of mutual information, in comparison to the Pearson correlation and other linear measures, lies in the capacity to distinguish nonlinear statistical dependencies from linear ones. We find that observed enhancement in relativistic electron fluxes correlate weakly, both linearly and nonlinearly, with the ULF power spectrum, whereas less energetic electron fluxes show stronger statistical dependency with both ground and in situ ULF wave power. Our results are indicative of the need to incorporate data analysis tools that can distinguish between interdependencies of various solar wind drivers.

Using a magnetohydrodynamic simulation of magnetotail reconnection, flow bursts, and dipolarization, we further investigate the current diversion and energy flow and conversion associated with the substorm current wedge (SCW) or smaller-scale wedgelets. Current diversion into both Region 1 (R1) and Region 2 (R2) sense systems is found to happen inside (that is, closer to the center of the flow burst) and equatorward of the R1 and R2 type field-aligned currents. In contrast to earlier investigations the current diversion takes place in dipolarized fields extending all the way toward the equatorial plane. An additional FAC system with the signature of Region 0 (R0) (same sense as R2) is found at higher latitudes in taillike fields. The diversion into this system takes place in layers equatorward of the R0 currents but outside the equatorial plane. Whereas the diversion into R1 and R2 systems is pressure gradient dominated, the diversion into the R0 system is inertia dominated and may persist only during flow burst activity. While azimuthally diverging flows near the dipole contribute to the buildup of R1 and R2 systems, converging flows at larger distance contribute to the buildup of R0 and R1 systems. In contrast to the current diversion regions inside the current wedge, generator regions are found on the outside of the wedge, similar to earlier results. Within the tail domain covered, these regions are overpowered by load regions, such that additional generator regions must be expected closer to Earth, not covered by the present simulation.

Five decades of satellite data confirm that the solar wind contains many boundaries separating flow with distinct magnetic and plasma properties. Some speculate the boundaries in the solar wind found at Earth originate at the solar surface and are carried along with the expanding solar wind as fossil structures to 1 AU. This begs the question, is it the physics and magnetic structure above the photosphere that creates well‐defined boundaries between different magnetic flux regions at 1 AU in the solar wind? Magnetic boundaries in the corona exist all the time as topological features of null points in the field. These topological magnetic boundaries seem to be likely locations for plasma boundaries. It can be expected that these boundaries are typical locations where field line‐integrated quantities, such as field‐aligned current, experience large and abrupt changes. We perform three‐dimensional resistive magnetohydrodynamic simulations of the solar corona driven by photospheric foot point motions. We find that large and abrupt changes occur for field line‐integrated quantities across a magnetic topological boundary and the cause for these changes is the discontinuous mapping for magnetic field lines and thus for Alfvén waves across these boundaries. It is also demonstrated via in situ properties that thin layers of field‐aligned and perpendicular currents are frequently located at or close to topological boundaries.

The idea of using a high-power electron beam to actively probe magnetic-field-line connectivity in space has been discussed since the 1970’s. It could solve longstanding questions in magnetospheric/ionospheric physics by establishing connectivity and causality between phenomena occurring in the magnetosphere and their image in the ionosphere [1]. However, this idea has never been realized onboard a magnetospheric spacecraft because the tenuous magnetospheric plasma cannot provide the return current necessary to keep the charging of the spacecraft under control.Recently, Delzanno et al. [2] have proposed a spacecraft-charging mitigation scheme to enable the emission of a high-power electron beam from a magnetospheric spacecraft. It is based on the contactor plasma, i.e. a high density neutral plasma emitted prior to and with the electron beam. The contactor acts as an ion emitter (not as an electron collector, as previously thought): a high ion current can be emitted off the quasi-spherical contactor surface, where the space-charge limits are higher than those typical of planar ion beams, and the electron-beam current can be compensated.In this work, we present a simple model to interpret the results of [2]. The model is in spherical geometry and the contactor is represented by only two surfaces (its quasi-neutral surface and the front of the outermost ions), whose dynamics is coupled to the beam and the Child-Langmuir law. It captures the results of self-consistent Particle-In-Cell (PIC) simulations with reasonable accuracy and highlights the physics behind the charge-mitigation scheme clearly. PIC simulations connecting the 1D model to the actual geometry of the problem will also be presented to obtain the scaling of the spacecraft potential varying contactor emission area.

The storm-substorm relationship is one of the most controversial aspects of geospace magnetic storm dynamics and one of the unresolved topics of solarterrestrial coupling. Here we investigate the statistical dependencies between storm and substorm indices in conjunction with multiple relevant solar wind variables with an information-theoretic causal inference approach. We find that the vertical component of the interplanetary magnetic field (IMF) is the strongest driver of both storms and substorms. Importantly, this common driver explains the transfer of entropy between substorms and storms found by a previous bivariate analysis. These results hold during two years close to solar maximum (2001) and minimum (2008), respectively, and suggest that, at least based on the analyzed indices, there is no statistical evidence for a direct or indirect dependency between substorms and storms. A physical mechanism by which substorms drive storms or vice versa is, therefore, unlikely.

The effects of the leading edge stream interface of high-speed solar-wind streams (HSSs) upon the Earth's magnetosphere have been extensively documented. The arrival of HSSs leads to significant changes in the plasmasphere, plasma sheet, ring current, and radiation belts, during the evolution from slow solar wind to persistent fast solar wind. Studies have also documented effects in the lower ionosphere and the neutral atmosphere. However, only cursory attention has been paid to the trailing-edge stream interface during the transition back from fast solar wind to slow solar wind. Here we report on the statistical changes that occur in the plasmasphere, plasma sheet, ring current, and electron radiation belt during the passage of the trailing-edge stream interface of HSSs, when the magnetosphere is in most respects in an extremely quiescent state. Counterintuitively, the peak flux of similar to 1MeV electrons is observed to occur at this interface. In contrast, other regions of the magnetosphere demonstrate extremely quiet conditions. As with the leading-edge stream interface, the occurrence of the trailing-edge stream interface has a periodicity of 27days, and hence, understanding the changes that occur in the magnetosphere during the passage of trailing edges of HSSs can lead to improved forecasting and predictability of the magnetosphere as a system.

Knowledge of the plasma fluxes at geosynchronous orbit is important to both scientific and operational investigations. We present a new empirical model of the ion flux and the electron flux at geosynchronous orbit (GEO) in the energy range similar to 1 eV to similar to 40 keV. The model is based on a total of 82 satellite years of observations from the magnetospheric plasma analyzer instruments on Los Alamos National Laboratory satellites at GEO. These data are assigned to a fixed grid of 24 local times and 40 energies, at all possible values of Kp. Bilinear interpolation is used between grid points to provide the ion flux and the electron flux values at any energy and local time, and for given values of geomagnetic activity (proxied by the 3h Kp index), and also for given values of solar activity (proxied by the daily F-10.7 index). Initial comparison of the electron flux from the model with data from a Compact Environmental Anomaly Sensor II, also located at geosynchronous orbit, indicates a good match during both quiet and disturbed periods. The model is available for distribution as a FORTRAN code that can be modified to suit user requirements.

We investigated mass density rho(m) and O+ concentration eta(O+) = n(O+)/n(e) (where n(O+) and n(e) are the O+ and electron density, respectively) during two events, one active and one more quiet. We found rho(m) from observations of Alfven wave frequencies measured by the GOES, and we investigated composition by combining measurements of rho(m) with measurements of ion density n(MPA, i) from the Magnetospheric Plasma Analyzer (MPA) instrument on Los Alamos National Laboratory spacecraft or n(e) from the Radio Plasma Imager instrument on the Imager forMagnetopause-to-Aurora Global Exploration spacecraft. Using a simple assumption for the He+ density at solar maximum based on a statistical study, we found eta(O+) values ranging from near zero to close to unity. For geostationary spacecraft that corotate with the Earth, sudden changes in density for both rho(m) and n(e) often appear between dusk and midnight magnetic local time, especially when Kp is significantly above zero. This probably indicates that the bulk (total) ions have energy below a few keV and that the satellites are crossing from closed or previously closed to open drift paths. During long periods that are geomagnetically quiet, the mass density varies little, but ne gradually refills leading to a gradual change in composition from low-density plasma that is relatively cold and heavy (high-average ion mass M = rho(m)/n(e)) to high-density plasma that is relatively cold and light (low M) plasmasphere-like plasma. During active periods we observe a similar daily oscillation in plasma properties from the dayside to the nightside, with cold and light high-density plasma (more plasmasphere-like) on the dayside and hotter and more heavy low-density plasma (more plasma sheet-like) on the nightside. The value of ne is very dependent on whether it is measured inside or outside a plasmaspheric plume, while rho(m) is not. All of our results were found at solar maximum; previous results suggest that there will be much less O+ at solar minimum under all conditions.

Much attention has been focused on the reaction of the magnetosphere to the solar wind during the recent extended solar minimum (2006–2010). Although this period was exceptionally quiet when categorized by some parameters (e.g., the number of sunspots) the solar wind still contained features which impacted the Earth's magnetosphere and caused geomagnetic disturbances. Recurrent corotating interaction regions (CIRs) and associated high‐speed solar wind streams (HSSs) are typically associated with the declining phase of the solar cycle and were a regular feature of the solar wind during the most recent solar minimum. Here we compare and contrast strong and weak HSSs in the solar wind and their subsequent effect within the Earth's magnetosphere. We find significant differences between strong and weak HSS effects in the plasmasphere, in the ion and electron plasma sheets, and in the outer electron radiation belt. A density‐temperature description of the outer radiation belt is shown to shed light on why the radiation belt flux is observed to return at a higher level after the arrival of strong HSSs than before strong HSSs and why the flux is observed to return at a lower level after the arrival of weak HSSs than before weak HSSs.