Omega bands are an auroral structure which consist of upward and downward field aligned currents (FACs) which are formed in the boundary between the region 1 and region 2 FACs in the dawn sector. They are characterised by their wave-like structure, which is often described as looking like a chain of the Greek letter Ω, with luminous extensions of the aurora protruding poleward. Omega bands cause ground based perturbations as they drift eastward, which can have large dB/dt values and hence are a potential source of geomagnetically induced currents (GICs). GICs are a hazard to our infrastructure, as currents can be induced in power grids, railways and pipelines. In this study, we investigate several cases of omega bands using ground and spaced based observations to examine their properties. Observations from the European Incoherent SCATter (EISCAT) radar show enhancements in electron density, which alongside measurements of FACs from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) can be used to study the intensity of different events. We use the IMAGE magnetometer network across Scandinavia to explore the latitudinal extend of omega bands as well as see their drift speed and dB/dt strength. SuperDARN and DMSP ion drift meter measurements help us to determine if the omega bands are embedded in the convection flow. Data from the DMSP Special Sensor Ultraviolet Spectrographic Imager (SSUSI) show the auroral data associated with omega bands. We present a study of omega bands from 2010 onwards.

Here we consider initial steps of how upcoming data from the SMILE Soft X-ray Imager and Ultraviolet Imager may be combined with additional data sources to provide a more holistic view of the coupled magnetosphere-ionosphere system. The Ground-based and Additional Science Working Group aims to embed SMILE in a multi-scale and holistic view of the Earth’s magnetosphere by exploring coordination of ground-based and other spacecraft’s data with SMILE. This working group is one of four working groups within the SMILE Science Working Team who are tasked with preparing all aspects of the mission. Adequate preparation is essential to optimise the tools, multiple instrument campaigns and procedures to allow the maximum science return from SMILE in the context of the entire available range of temporal and spatial scales in the terrestrial system. SMILE instruments will not work in isolation from each other, nor from other spacecraft or ground-based experiments. Synergies with other missions and ground-based experimentation will be fundamental for full science exploitation of the data. In this paper, we expand on the previous publications by the Ground-Based and Additional Science working group, by exploring the possibilities of using a two-way approach to deriving scientific results from SMILE, using a small isolated substorm as a case study. We use knowledge of the contemporaneous solar wind conditions during the substorm to simulate SMILE Soft X-ray Imager data. We also use observed ultraviolet auroral emissions and field-aligned current data as measured in the high-latitude polar regions to act as either a proxy for the SMILE Ultraviolet Imager, or an alternative source of information for the open-closed field line boundary. The observational data is used to constrain the minimisation of the two-dimensional X-ray images, leading to an improvement in the derived shape of the flank magnetopause position. We also comment on mission’s possibilities to inspire the public through various engagement programmes, and current activities to involve diverse communities in the preparations and science exploitation of SMILE.

State-of-the-art numerical models have been developed to reproduce magnetospheric dynamics in response to solar wind variations. However, we do not understand how accurate the predictions of the models would be in different solar wind and magnetospheric conditions. In this study, we consider the two relatively simple cases with southward interplanetary magnetic field turnings which have been simulated by several MHD models (SWMF, LFM, PPMLR-MHD, PLUTO). We compare numerical results with observations in terms of global magnetospheric characteristics such as the polar cap open flux and the indices of magnetospheric activity. Our purpose is to understand why some models can make better predictions. To answer this question we also compare the results of the same MHD model with different numerical resolutions and ionospheric conductances and show that both resolution and conductance are important for accurate predictions. By comparing simulations with observations, we can figure out the optimal parameters in the models which should be used in the future.

Coronal Mass Ejections (CMEs), and ever-changing solar wind conditions, drive processes in the Earth’s space-environment (the magnetosphere and ionosphere) which can strongly affect satellite communications, navigation systems, and power grids upon which society relies. Mitigation strategies are heavily dependent on accurate forecasting of the likely impact of space-weather conditions on operations. The tracking of plasma structures, and turbulence within, in the inner-heliosphere is now made possible by the LOw Frequency ARray (LOFAR, the world’s largest low-frequency radio-telescope) through observations of the scintillation of radio waves from astronomical sources propagating through these plasma structures. Information obtained through LOFAR can be augmented with in situ measurements from existing missions and the planned ESA Vigil mission to be stationed at L5, as well as other remote-sensing techniques, to provide an unprecedented advance warning of space weather detrimental to society. The Radio Investigations for Space Environment Research (RISER) project will provide a comprehensive understanding of the Earth’s space-environment through the use of novel radio observations and modelling techniques to investigate coupling between solar-driven inner-heliospheric structures and the Earth. RISER will address the following key questions in the space-weather domain: How can we better attribute magnetospheric-ionospheric response to inner-heliospheric variability? How well can we establish a direct connection between parameters that characterise structures in the inner-heliosphere with the geo-effectiveness of geomagnetic disturbances? How can we identify and track plasma structures in the inner-heliosphere using scintillation data from low-frequency radio telescopes in a systematic way before they reach Earth? What is the value of improved forecasts of adverse space weather conditions when using radio-telescope observations and enhanced science of the inner heliosphere- magnetosphere-ionosphere system? Here, we give an overview of RISER, its high-level objectives, the importance and relevance to advancing our understanding of space-weather science and impacts, as well as a brief overview of the LOFAR-UK upgrades.

The structure and dynamics of the magnetosphere are significantly different during intervals of northward interplanetary magnetic field (IMF) compared to when the IMF is southward. Under northward IMF, reconnection occurs at higher latitudes tailward of the cusps. High latitude reconnection occurring simultaneously in both hemispheres can close significant amounts of open flux in the magnetospheric lobes resulting in an almost entirely closed magnetosphere and has been linked to characteristic auroral signatures, such as cusp-aligned arcs.Under northward IMF the magnetosphere becomes dominated by closed magnetic flux with associated trapped particles populations which are thought to provide the source particle population for auroral cusp-aligned arcs (Milan et al., 2023; Mooney et al, 2024). However, the structure and properties of the distant magnetotail under northward IMF are poorly understood. We have performed a statistical analysis of ARTEMIS crossings of the distant magnetotail (XGSE ~ -60 RE) between 2011 - 2016 to investigate the magnetic field and plasma characteristics in the magnetotail under northward IMF conditions compared to southward IMF conditions. Under southward IMF, the magnetotail is dominated by magnetic pressure with no significant associated plasma population. However, under northward IMF we find that statistically the central distant magnetotail contains denser, hotter plasma and that the plasma pressure in the magnetotail is typically larger than the magnetic pressure. We suggest that the observed hotter, denser plasma population in the central magnetotail could indicate that the plasma sheet extends down to the distant magnetotail under northward IMF.

High-latitude ionospheric convection is a useful diagnostic of solar wind-magnetosphere interactions and nightside activity in the magnetotail. For decades, the high-latitude convection pattern has been mapped using the Super Dual Auroral Radar Network (SuperDARN), a distribution of ground-based radars which are capable of measuring line-of-sight (l-o-s) ionospheric flows. From the l-o-s measurements an estimate of the global convection can be obtained. As the SuperDARN coverage is not truly global, it is necessary to constrain the maps when the map fitting is performed. The lower latitude boundary of the convection, known as the Heppner-Maynard boundary (HMB), provides one such constraint. In the standard SuperDARN fitting, the HMB location is determined directly from the data, but data gaps can make this challenging. In this study we evaluate if the HMB placement can be improved using data from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE), in particular for active time periods when the HMB moves to latitudes below 55 degrees $55{}<^>{\circ}$. We find that the boundary as defined by SuperDARN and AMPERE are not always co-located. SuperDARN performs better when the AMPERE currents are very weak (e.g., during non-active times) and AMPERE can provide a boundary when there is no SuperDARN scatter. Using three geomagnetic storm events, we show that there is agreement between the SuperDARN and AMPERE boundaries but the SuperDARN-derived convection boundary mostly lies similar to 3 degrees ${\sim} 3{}<^>{\circ}$ equatorward of the AMPERE-derived boundary. We find that disagreements primarily arise due to geometrical factors and a time lag in expansions and contractions of the patterns.

Iridium satellites in low-Earth orbit have transformed our knowledge of geospace by enabling the AMPERE dataset. We employ AMPERE data from October 2009 to December 2021 to examine the interhemispheric asymmetry in Birkeland currents over the span of a solar cycle. We take daily averages of the upward and downward current in both hemispheres and examine the systematic asymmetry by removing the seasonal trend. We find that Birkeland currents are stronger in the Northern Hemisphere than in the South after removing the seasonal trend, consistent with Coxon et al. (2016). We explore how this asymmetry manifests over a solar cycle and compare the variation of the asymmetry to other parameters.

We present the first observations of a three-hour quasi-periodic intensification of the polar auroras during a prolonged interval of strongly-northward interplanetary magnetic field (IMF). This takes the form of a localised spot of auroral emission that appears near the pole which subsequently spreads sunwards and antisunwards to produce a sun-aligned auroral arc. This arc eventually merges with the dayside and nightside auroral zones. Twin reverse-cell convection in the noon-sector ionosphere suggests that this occurs during on-going dual-lobe magnetic reconnection which has closed the magnetosphere. We propose that the polar auroral dynamics are an indication of reconnection in the magnetotail, bearing similarities to southwards-IMF substorms. We further suggest that this process may be responsible for the cusp-aligned auroral morphology frequently observed when the IMF is directed northwards.

We present an analysis of radar blackouts observed by MARSIS on Mars Express and SHARAD on Mars Reconnaissance Orbiter for the interval 2006 – 2017. The period of interest encompasses the extended solar minimum between solar cycles 23 and 24 as well as the solar maximum of cycle 24. Blackouts have been identified by eye through scanning daily plots of the surface reflection for both radars. A blackout occurs when, for no apparent instrumental reason, the surface reflection normally expected is either not observed (total) or when the surface reflection is seen for only part of the orbit or the surface reflection is both weaker and spread over a significant time delay (partial). Such blackouts are caused by enhanced ionisation at altitudes below the main ionospheric electron density peak resulting in increased absorption of the radar signal. There are more occurrences observed by MARSIS than SHARAD, which is expected due to the lower absorption at the higher operating frequency of SHARAD. We also observe more blackouts during solar maximum than solar minimum. Indeed, there are no total blackouts during the extended solar minimum, although both radars do have partial blackouts. There is no apparent relationship between blackout occurrence and crustal magnetic fields. Following previous work, which has indicated that solar energetic particles, specifically electrons are responsible for the enhanced ionisation in the atmosphere, we also present the analysis of the MAVEN SEP electrons between 20 keV and 2 MeV during events when all three spacecraft were operational. We find that the SEP electron flux-energy relationship is much enhanced during the total blackouts, in particular where both radars are impacted, while for partial blackouts the flux-energy spectrum is closer to those from orbits where no blackout occurs. We also find that for certain events, the average spectrum which result in a blackout is particularly enhanced at the higher energy end of the spectrum, above 50 keV. The average spectra from each condition is presented. We conclude that there is a higher probability of a radar blackout during solar maximum, that crustal magnetic fields play no apparent role in the their observational occurrence, that the higher energy (< 50 keV) electrons are responsible, and that for events where both radars observe a radar blackout the SEP electron fluxes are at their highest.

We propose a mechanism for the formation of the horse-collar auroral configuration during periods of strongly northwards interplanetary magnetic field, invoking the action of dual-lobe reconnection (DLR). Auroral observations are provided by the Imager for Magnetopause-to-Auroras Global Exploration (IMAGE) satellite and spacecraft of the Defense Meteorological Satellite Program (DMSP). We also use ionospheric flow measurements from DMSP and polar maps of field-aligned currents (FACs) derived from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE). Sunward convection is observed within the dark polar cap, with antisunwards flows within the horse-collar auroral region, together with the NBZ FAC distribution expected to be associated with DLR. We suggest that newly-closed flux is transported antisunwards and to dawn and dusk within the reverse lobe cell convection pattern associated with DLR, causing the polar cap to acquire a teardrop shape and weak auroras to form at high latitudes. If the process continues, the cusp-aligned arcs auroral configuration ensues. Horse-collar auroras and cusp-aligned arcs are a common feature of the quiet magnetosphere, and this model provides a first understanding of their formation, resolving several outstanding questions regarding the nature of DLR and the magnetospheric structure and dynamics during northwards IMF. The model can also provide insights into the trapping of solar wind plasma by the magnetosphere and the formation of a low-latitude boundary layer and cold, dense plasma sheet.

We use MHD simulations to study the time sequence of magnetospheric responses to a synthetic event with a southward interplanetary magnetic field (IMF) turning. The onset of dayside magnetopause reconnection launches a weak rarefaction wave and sunward flow in the equatorial magnetosphere simultaneously with a tailward flow through the polar cap. This convection results in the accumulation of magnetic flux in the tail lobes and thinning of the tail current layer which provides favorable conditions for the onset of nightside reconnection. The onset of nightside reconnection about 40 min later closes the Dungey convection cycle, resulting in a second increase in the sunward flow in the equatorial plane. Variations of the magnetopause standoff distance as well as the size of the polar cap (PC) may indicate the onsets of the dayside and nightside reconnections. We compare the results of two MHD models and discuss their differences. The auroras and other space weather phenomena are produced by the interaction of the solar wind with the Earth's magnetic environment. The fundamental plasma process of magnetic reconnection modulates this interaction, which then drives a circulation of magnetic field and plasma within the magnetosphere known as the Dungey cycle. Reconnection occurs when the magnetic field in the solar wind points southwards but turns off when it is northwards. The sequence of events within the magnetosphere in response to a southwards turning of the magnetic field is currently poorly understood. In this study, we model the interaction with two magnetohydrodynamic simulation codes. These show a rarefaction wave from the front of the magnetosphere toward the magnetotail in response to the turn-on of reconnection. Thereafter magnetic reconnection occurs in the magnetotail to complete the cycle. Although the simulations differ in the details, the two agree on this sequence of events, providing new insights into the dynamics of the magnetosphere. We investigate magnetospheric convection after southward turning and highlight the differences between the two MHD models Two-step response in convection after dayside and nightside reconnection Variations in the magnetopause standoff distance may indicate variations in the magnetic flux

We investigate the causes of large $dB/dt$ events observed by SuperMAG, by comparing with the time-series of different types of geomagnetic activity, or “convection state”, for the duration of 2010. Spikes are found to occur predominantly in the pre-midnight and dawn sectors. We find that pre-midnight spikes are associated with substorm onsets. Dawn sector spikes are not directly associated with substorms, but with auroral activity occurring within the westward electrojet region. Azimuthally-spaced auroral features drift sunwards, producing Ps6 (10-20 min period) magnetic perturbations on the ground. The magnitude of $dB/dt$ is determined by the flow speed in the convection return flow region, which in turn is related to the strength of solar wind-magnetospheric coupling. Pre-midnight and dawn sector spikes can occur at the same time, as strong coupling favours both substorms and westward electrojet activity; however, the mechanisms that create them seem somewhat independent. The dawn auroral features share some characteristics with omega bands, but can also appear as north-south aligned auroral streamers. We suggest that these two phenomena share a single underlying cause.

Whitepaper #420 in the Decadal Survey for Solar and Space Physics (Heliophysics) 2024-2033. Main topics: basic research; infrastructure/workforce/other programmatic. Additional topics: planetary magnetospheres; system science; space-based missions/projects; research tools […]

During the long main phase of the St Patrick’s Day storm on March 17, 2015, we found three separate enhancements of the westward electrojet. These enhancements are observed in the ionospheric equivalent currents computed using geomagnetic data over Fennoscandia. Using data from the IMAGE magnetometer network, we identified localised field-aligned current (FAC) systems superimposed on the pre-existing ionospheric current system. We suggest that these localised current systems are wedgelets and that they can potentially contribute to a larger-scale structure of a substorm current wedge (SCW). Each wedgelet is associated with a negative B X spike. Each spike is recorded at a higher latitude than the former one and all three are very localised over Fennoscandia. The first spike occurred at 17:34 UT and was observed at Lycksele, Rørvik and Nurmijärvi, the second spike was recorded at 17:41 UT and located at Lycksele and Rørvik, whereas the last spike occurred at 17:47 UT and was observed at Kevo and Abisko. Simultaneous optical auroral data and electron injections at the geosynchronous orbit indicate that one or more substorms took place in the polar ionosphere at the time of the wedgelets. This study demonstrates the occurrence of small and short-lived structures such as wedgelets at different locations over a short time scale, 15 min in this case.

We study the magnetospheric response to solar wind discontinuities with a southward interplanetary magnetic field (IMF) turning. We find two events characterized by a strong positive IMF Bz before the discontinuity and a strong negative Bz after the discontinuity. The magnetosphere stays in quiet conditions until the southward turning in both cases, then the dayside reconnection starts and the electromagnetic energy is accumulated in the magnetotail. We simulate these cases using several MHD models and compare numerical predictions of the global parameters such as the magnetopause standoff distance, open flux in the polar cap, auroral indices, and cross polar cap potential. We also make several runs of one model with different spatial resolutions and ionospheric conductivities. Summarizing this study, we discuss the differences between the MHD models and speculate about the reasons why one model is able to better predict observations than the other. We also discuss the reasons for different magnetospheric responses observed in two cases.

High-Intensity Long-Duration Continuous AE Activity (HILDCAA) intervals are driven by High Speed solar wind Streams (HSSs) during which the rapidly-varying interplanetary magnetic field (IMF) produces high but intermittent dayside reconnection rates. This results in several days of large, quasi-periodic enhancements in the auroral electrojet (AE) index. There has been debate over whether the enhancements in AE are produced by substorms or whether HILDCAAs represent a distinct class of magnetospheric dynamics. We investigate sixteen HILDCAA events using the expanding/contracting polar cap model as a framework to understand the magnetospheric dynamics occurring during HSSs. Each HILDCAA onset shows variations in open magnetic flux, dayside and nightside reconnection rates, the cross-polar cap potential, and AL that are characteristic of substorms. The enhancements in AE are produced by activity in the pre-midnight sector, which is the typical substorm onset region. The periodicities present in the intermittent IMF determine the exact nature of the activity, producing a range of behaviours from a sequence of isolated substorms, through substorms which merge into one-another, to almost continuous geomagnetic activity. The magnitude of magnetic fluctuations, $dB/dt$, in the pre-midnight sector during HSSs is sufficient to produce a significant risk of Geomagnetically Induced Currents, which can be detrimental to power-grids and pipelines.

Earth’s atmosphere provides the background for the “sea of plasmas” surrounding Earth via its Ionosphere and the upper and middle Atmosphere, providing an interface layer through which a broad diversity of solar-terrestrial energy transfer processes takes place. Developing an integrative understanding of global geospace energy transfer processes affecting this layer is a major scientific challenge with important societal implications. The disciplines covering this interaction have a large, diverse and active international community, with significant expertise and heritage in the European Space Agency and Europe. Several ESA directorates have activities directly connected with this topic, and an ESA Heliophysics Working group has been appointed by several ESA Directors, under the direction of the ESA Director General, to work on optimizing synergies and to act as a focus for discussion, inside ESA, of the scientific interests of the Heliophysics community.Very recently, a Forum at the International Space Science Institute was set up, involving some of the above WG, to look towards developing a deeper understanding of the solar-terrestrial interactions between the Ionosphere and the upper- and middle atmosphere, thus possibly enabling the detection of signatures by natural and anthropogenic hazards.This presentation will provide a brief introduction to ongoing internal ESA cross discipline approaches, and then note some of the outcomes of this recent ISSI forum to set out a pathway to address this intriguing topic.

We study the dependencies of Earth’s magnetosphere on Universal Time, UT . These are introduced because Earth’s magnetic axis is not aligned with the rotational axis and complicated because it is eccentric, which makes the offset of the magnetic and rotation poles considerably greater in the Southern hemisphere and the longitudinal separation of the magnetic poles less than 180°: hence consequent UT variations in the two hemispheres are not in equal in amplitude nor in exact antiphase and do not cancel, as they would for a geocentric dipole. We use long series of a variety of geomagnetic data to demonstrate the inductive effect of motions of the polar caps in a “geocentric-solar” frame, which is phase-locked to the Russell-McPherron (R-M) effect on solar-wind magnetosphere coupling. This makes the response of the magnetosphere-ionosphere system different for the two polarities of the Y-component of the Interplanetary Magnetic Field in the GSEQ reference frame, explaining the difference in response to the March and September equinox peaks in solar wind forcing. The sunward/antisunward pole-motion effect is detected directly in satellite transpolar voltage data and is shown to have a greater effect on the geomagnetic data than the full dipole tilt effect which generates the equinoctial pattern, the potential origins of which are discussed in terms of the dipole tilt effect on ionospheric conductivities and the stability of the near-Earth tail. Persistent UT variations in Region-1 and Region-2 field-aligned currents and in partial ring current indices are presented: their explanation is an important challenge for numerical modelling of the magnetosphere-ionosphere-thermosphere system which we need to quantify the relative contributions of the various mechanisms and to give understanding of the effect of arrival time on the response of the system to large, geoeffective disturbances in interplanetary space. Plain language summary : The effect on terrestrial space weather of Earth’s magnetic axis not being aligned with the rotational axis is investigated. It is complex because not only do these two axes not align in direction (the “dipole tilt”), the magnetic axis does not pass through the centre of the Earth, which sets a requirement for an “eccentric” model of the field and not the commonly-used “geocentric” one. For many years, it has been known that the dipole tilt gives a peak in geomagnetic activity at the equinoxes (the semi-annual variation) through the “Russell-McPherron” (R-M) effect. However, although the variation with Universal Time is consistent with the R-M effect for the September equinox, it is not for the March equinox. We here solve this long-standing puzzle by investigating the effects of the motions of the two poles in a frame fixed with respect to both the Earth and the Sun for an eccentric dipole model. But solving one puzzle generates many others. We present observations of the Universal Time variations that these mechanisms combine to generate, which set an important challenge to the numerical modelling of the near-Earth space environment.