This paper analyses magnetosphere-ionosphere (MI) coupling from a perspective that is independent of inertial reference frame, explicitly acknowledging the role of the principle of relativity in MI coupling. For the first time in the context of MI coupling, we discuss the literature on the low-velocity limit of the theory of special relativity applied to electrodynamics. In many MI coupling theories, a particular low-velocity limit applies, known as the “magnetic limit”. Two important consequences of the magnetic limit are: 1) Maxwell’s equations cannot contain a displacement current and be consistent with the magnetic limit and 2) the magnetic field is not modified by currents created by charge densities in motion, thus charge density is approximately zero. We show how reference frame-independent descriptions of MI coupling require that ion-neutral relative velocities and ion-neutral collisions are key drivers of the physics. Electric fields, on the other hand, depend on reference frame, and can be zero in an appropriate frame. Currents are independent of reference frame and will flow when the electric field is close to zero. Starting with the same momentum equations that are typically used to derive Ohm’s law, we derive an equation that relates the perpendicular current to collisions between ions and neutrals, and electrons and neutrals, without reference to electric fields. Ignoring the relative motion between ions and neutrals will result in errors exceeding 100% for estimates of high latitude Joule heating during significant geomagnetic storms when ion-neutral velocity differences are largest near the initiation of large-scale ion convection.

This study exploits the volumetric sampling capabilities of the Resolute Bay Incoherent Scatter Radar (RISR-N) in collaboration with all-sky imagery and in-situ measurements (DMSP) to examine the interplay between cold plasma transport and auroral precipitation during a high-latitude lobe reconnection event on the dawn side. The IMF had an impulsive negative excursion in B$_z$ embedded within a prolonged period of B$_z>0$ and B$_y<0$. The combined effects of transport and magnetic stress release associated with a reconnection pulse resulted in a co-mingling of plasma patches and soft electron precipitation, creating regions of elevated electron density and temperature. Altitude profiles of ionospheric parameters extracted in the rest frame of the drifting patch showed an increase in $T_e$ above 200 km and $N_e$ below 250 km (both hallmarks of soft precipitation), while also showing small and predictable changes in $N_e$ near the F-region peak over the 34-minute duration of the event. For the first time, we identified that the simultaneous appearance of elevated $T_e$ and elevated F-region $N_e$ (i.e., a ‘hot patch’), thus providing a new formation process for hot patches. The physics-based GEMINI model was used to explore the response to the observed precipitation as a function of altitude and time. Enhancements in $N_e$ in the topside ionosphere (e.g., DMSP altitudes) are caused by upward ambipolar diffusion induced by ionospheric heating and not impact ionization. The study highlights the importance of densely distributed measurements in space and time for understanding both mesoscale and small-scale ionospheric dynamics in regions subject to complex forcing.

An objective of the solar and space physics communities has been to predict the behavior of the interconnected physical systems that bring space weather to Earth. One approach is to use first-principles models that may predict behavior of the various space plasma regimes from the magnetized solar corona to Earth’s upper atmosphere. We focus on space weather forecasts in the thermosphere-ionosphere (T-I), with lead time based on the period following a solar eruption. There are generally 1-4 days lead time before the interplanetary coronal mass ejection (ICME) reaches the Earth’s magnetopause. Forecasting the behavior of the T-I with such multi-day lead times requires new ways of using and assessing first principles models, which are capable of predicting many details of the T-I response, including the time history of the global electron density distribution, neutral densities and neutral winds. All facets of the complex T-I system response must be predicted based on input solar and interplanetary parameters. Another influence on the forecast is the condition of the T-I at the time a forecast is produced (e.g. shortly after the CME eruption epoch). However, the role of such pre-conditioning is not well understood for lead times of a few days. To improve our understanding of these forecasts, we have submitted more than 120 multi-day simulation periods to NASA’s Community Coordinated Modeling Center, spanning three coupled T-I models. Approximately 40 T-I storms have been simulated, driven by solar wind and EUV parameters alone. We will present an analysis that characterizes how T-I models respond to the information content of the solar wind, mediated through climatological models of high latitude forcing, and the possible influence of pre-existing conditions. Smoothing across mesoscale variability is inevitable in this scenario. Analyzing the response across events and across models reveals critical information about the predictability of the T-I system as an ICME approaches.

Field-aligned currents (FACs), or the system of currents flowing along Earth’s magnetic field lines, are the dominant form of energy and momentum exchange between the magnetosphere and ionosphere. FACs are ubiquitous across the high-latitude region and have unique characteristics depending on the magnetospheric or solar wind source mechanism, and, therefore, mapping location in the ionosphere (i.e. auroral zone, polar cap, cusp). Further complicating the picture, FACs also exhibit a large range of spatial and temporal scales. In order to create new understanding of FAC spatial and temporal scales, their cross-scale effects, and the impact on the polar region, including on critical technologies, new data analysis approaches are required. This talk addresses a coherent progression of investigation in three parts: 1) an exploration of the characteristics, controlling parameters, and relationships of multiscale FACs using a rigorous, comprehensive analysis across multiple spacecraft observations; 2) augmentation of these statistical results with detailed case studies, fusing observations from diverse platforms and incorporating critical information about the high-latitude electrodynamics across scales; and 3) a quantitative investigation of the impact on Global Navigation Satellite System (GNSS) signals. We find that the relationships between FAC scales are complex and reveal new information about the connection between multiscale FACs and irregular space weather activity. Additionally, there are observable signatures of multiscale FACs and resultant electrodynamic activity in ionospheric data from GNSS signals, suggesting that these signals are affected distinctly according to scale size of the coupling process. Our results indicate that GNSS data may be a powerful source of information about the multiscale near Earth space environment.

Polar topside total electron content (TEC) enhancement (PTTE) above 1336 km altitude is reported for the first time. The results are based on measurements from 2008 to 2018 made using a GPS receiver onboard NASA’s Jason-2 satellite. The enhancement can exceed 5.5 TEC units or 78% relative to the dayside ambient state. Comparisons with COSMIC/FORMOSAT-3 topside TEC measurements confirm the PTTE events. Our statistical analysis reveals that PTTE mostly occurs in the southern dayside polar cap, with a seasonal preference of southern summer, regardless of geomagnetic conditions. Our case analysis indicates that PTTE is associated with the tongue of ionization. This suggests that the source of PTTE may be the dayside F region plasma that moves poleward following the anti-sunward plasma convection, and the plasma upflow driven by the polar wind may act to cause PTTE. The hemispheric asymmetry in PTTE occurrence remains to be a major unsolved puzzle.