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We present a new technique for the upcoming tri‐static incoherent scatter radar system EISCAT 3D (E3D) to perform a volumetric reconstruction of the 3D ionospheric electric current density vector field, focusing on the feasibility of the E3D system. The input to our volumetric reconstruction technique are estimates of the 3D current density perpendicular to the main magnetic field, j⊥, and its covariance, to be obtained from E3D observations based on two main assumptions: (a) Ions fully magnetized above the E region, set to 200 km here. (b) Electrons fully magnetized above the base of our domain, set to 90 km. In this way, j⊥ estimates are obtained without assumptions about the neutral wind field, allowing it to be subsequently determined. The volumetric reconstruction of the full 3D current density is implemented as vertically coupled horizontal layers represented by Spherical Elementary Current Systems with a built‐in current continuity constraint. We demonstrate that our technique is able to retrieve the three dimensional nature of the currents in our idealized setup, taken from a simulation of an active auroral ionosphere using the Geospace Environment Model of Ion‐Neutral Interactions (GEMINI). The vertical current is typically less constrained than the horizontal, but we outline strategies for improvement by utilizing additional data sources in the inversion. The ability to reconstruct the neutral wind field perpendicular to the magnetic field in the E region is demonstrated to mostly be within ±50 m/s in a limited region above the radar system in our setup. Plain Language Summary: We introduce a novel method for the upcoming EISCAT 3D (E3D) radar system to reconstruct the 3D electric current density vector in Earth's ionosphere. Here we present the new technique and assess its feasibility for the E3D system. The input to the 3D reconstruction technique relies on estimates of the current density perpendicular to the Earth's magnetic field, obtained from the E3D observations. We include estimates of uncertainties originating from the observations of the 3D ion velocity vectors and electron density in our reconstruction. Comparisons with simulations of an active auroral ionosphere exemplify that our technique provides reasonably accurate estimates of current density, especially in the 90–150 km altitude range. Our results demonstrate success in retrieving the horizontal part of the electric current system in the E region, while the vertical part has more uncertainty. Our method offers insight into how electric currents flow in a specific region of the Earth's atmosphere. The results can be further improved with additional data sources; this flexibility is a significant advantage of our approach. Overall, our study facilitates the advanced knowledge of Earth's upper atmosphere using innovative radar observations in companion with advanced analysis techniques. Key Points: A technique for volumetric reconstruction of 3D electric current density from tri‐static incoherent scatter radar observations is presentedConsidering the anticipated noise levels, the radar system is likely to produce good current density estimates in a limited regionThe reconstruction technique is particularly well suited for inclusion of additional data sources that improve overall performance [ABSTRACT FROM AUTHOR]

Ground magnetic field variations have been used to investigate ionospheric dynamics for more than a century. They are usually explained in terms of an electric circuit in the ionosphere driven by an electric field, but this is insufficient to explain how magnetic field disturbances are dynamically established. Here we explain and simulate how the ionosphere dynamically responds to magnetospheric forcing and how it leads to magnetic field deformation via Faraday's law. Our approach underscores the causal relationships, treating the magnetic field and velocity as primary variables (the B, v paradigm), whereas the electric field and current are derived, in contrast to the E, j paradigm commonly used in ionospheric physics. The simulation approach presented here could be used as an alternative to existing circuit‐based numerical models of magnetosphere‐ionosphere coupling. Plain Language Summary: Ground magnetic field variations have been used to investigate ionospheric dynamics for more than a century. They are usually explained in terms of an electric circuit in the ionosphere driven by an electric field; similar to how we would explain the magnetic field of a current‐carrying wire. However, this approach oversimplifies the complex reality in space plasmas. Here, the relationship between currents and magnetic fields is reversed: currents should be understood as a consequence of the magnetic field, and not the other way around. In this paper we explain and simulate how the ionosphere dynamically responds to forcing from above, and how it leads to magnetic field deformation that corresponds to an electrical current. Key Points: We present a model and simulation of how the magnetic field in the ionosphere dynamically changes in response to external forcingOur model emphasizes the causal relationships, treating B and v as primary instead of E and j, as is commonly done in ionospheric physicsSimulation results highlighting the self‐consistent ionospheric response in the B, v paradigm are presented [ABSTRACT FROM AUTHOR]

Calculating the magnetic flux transfer across the open‐closed boundary (OCB) per unit time and distance—the reconnection electric field—is an important means of remotely monitoring magnetospheric dynamics. Ground‐based measurements of plasma convection velocities together with velocities of the OCB are commonly used to infer reconnection rates. However, this approach is limited by spatial coverage and often lacks robust uncertainty quantification. In this paper, we assimilate Super Dual Auroral Radar Network convection measurements, ground magnetometer data, and estimates of the conductance derived from the Imager for Magnetopause‐to‐Aurora Global Exploration satellite imagers, using the Local mapping of polar ionospheric electrodynamics (Lompe) framework over a region in North America. We present a new method to assess various contributions to uncertainties in the derived reconnection electric fields, including a novel approach to estimate uncertainties in conductance from global auroral imaging. Our method is demonstrated on a substorm event with an associated pseudobreakup during a period of favorable observational coverage. In this case study, the uncertainties in the reconnection electric field are ∼5–10 mV/m at the peak of substorm expansion, roughly 15% of the peak reconnection electric field. We find that the main contributor to the reconnection electric field estimates after substorm onset is the OCB motion, whereas during the pseudobreakup the main contributor is ionospheric plasma convection. Plain Language Summary: The solar wind is a stream of particles and magnetic field flowing away from the Sun. Under certain orientations of the solar wind magnetic field, magnetic reconnection can occur between the magnetic fields of the solar wind and Earth. Magnetic reconnection is the process by which oppositely directed magnetic field lines "break," then merge into a new configuration. Magnetic reconnection is the primary process responsible for coupling the solar wind energy to the Earth's magnetic field, and is ultimately the principal driver of space weather. In the Earth's magnetosphere, reconnection is associated with topological changes at both dayside and nightside, where stored magnetic energy is released through a global reconfiguration of the magnetosphere which is referred to as magnetospheric substorms. We can remotely monitor this reconnection from the ground by studying the transfer of magnetic flux across the boundary between open and closed magnetic field lines. In this study, we combined data from ground‐based radars, ground magnetometers, and space‐based auroral imaging to monitor the reconnection rate across the entire nightside auroral oval for a full substorm event. We additionally derived uncertainties in this reconnection rate stemming from uncertainties in the ionospheric velocities, the ionospheric conductances, and the open‐closed boundary motion. Key Points: We estimate Hall and Pedersen conductance uncertainties using global auroral satellite images from Imager for Magnetopause‐to‐Aurora Global Exploration (IMAGE) for an isolated substormWe calculate uncertainties in ionospheric reconnection electric fields related to conductance, open‐closed boundary (OCB) motion, and convectionWe find that the main contributor to the reconnection electric field estimates after onset is the OCB motion [ABSTRACT FROM AUTHOR]

The aurora often appears as an approximately oval shape surrounding the magnetic poles, and is a visible manifestation of the intricate coupling between the Earth's upper atmosphere and the near-Earth space environment. While the average size of the auroral oval increases with geomagnetic activity, the instantaneous shape and size of the aurora is highly dynamic. The identification of auroral boundaries holds significant value in space physics, as it serves to define and differentiate regions within the magnetosphere connected to the aurora by magnetic field lines. In this work, we demonstrate a new method to estimate the spatiotemporal variations of the poleward and equatorward boundaries in global UV images. We apply our method, which is robust against outliers and occasional bad data, to 2.5 years of UV imagery from the Imager for Magnetopause-to-Aurora Global Exploration satellite. The resulting data set is compared to recently published boundaries based on the same images (Chisham et al., 2022, https://doi.org/10.1029/2022JA030622), and shown to give consistent results on average. Our data set reveals a root mean square boundary normal velocity of 149 m/s for the poleward boundary and 96 m/s for the equatorward boundary and the velocities are shown to be stronger on the nightside than on the dayside. Interestingly, our findings demonstrate an absence of correlation between the amount of open magnetic flux and the amount of flux enclosed within the auroral oval. [ABSTRACT FROM AUTHOR]

Energetic Electron Precipitation (EEP) from the Earth's plasma sheet and the radiation belts is an important feature of atmospheric dynamics through their destruction of ozone in the lower thermosphere and mesosphere. Therefore, understanding the magnitude of the atmospheric impact of the Sun‐Earth interaction requires a comprehensive understanding of the intensity and location of EEP. This study improves the accuracy of a previous pressure‐corrected Dst model that predicts the equatorward extent of >43, >114, and >292 keV EEP using the measurements from the Medium Energy Proton Electron Detector detector of six National Oceanic and Atmospheric Administration/Polar Orbiting Environmental Satellites and EUMETSAT/METOP satellites. The improvement is achieved through multiple linear regression of pressure‐corrected Dst and pressure‐corrected Ring Current (RC) indices. The RC index mitigates the baseline variation of the Dst index that created an inherent solar cycle bias in the previous model. The new model is then extended to the Southern Hemisphere (SH) after removing the South Atlantic Anomaly longitudes from the data. More than 80% of the residuals lie within ±1.8° Corrected Geomagnetic Latitude (CGMLat) in the Northern Hemisphere and within ±1.98° CGMLat in the SH. Plain Language Summary: This study aims to construct a model that predicts the geographic extent of Energetic Electron Precipitation (EEP) from the Earth's radiation belts using measurements from the Medium Energy Proton Electron Detector detector of six National Oceanic and Atmospheric Administration/Polar Orbiting Environmental Satellites and EUMETSAT/METOP satellites. The study enhances the accuracy of the previous pressure‐corrected Dst model. This improvement is implemented using multiple linear regression of pressure‐corrected Dst and pressure‐corrected Ring Current (RC) indices. Additionally, the study extends the model to the Southern Hemisphere after removing the South Atlantic Anomaly longitudes from the data. The result resolves the solar cycle bias that existed in the previous study. Key Points: An updated model of the equatorward extent of >43 keV electron precipitation has been improved by successfully removing the solar cycle biasIncluding both the Dst* and the Ring Current index reduces the error estimate to ±1.8° Corrected Geomagnetic Latitude (CGMLat) over a full solar cycle (2004–2014)The model is extended to the Southern Hemisphere with an error estimate of ±1.98° CGMLat [ABSTRACT FROM AUTHOR]

An accurate description of the state of the ionosphere is crucial for understanding the physics of Earth's coupling to space, including many potentially hazardous space weather phenomena. To support this effort, ground networks of magnetometer stations, optical instruments, and radars have been deployed. However, the spatial coverage of such networks is naturally restricted by the distribution of land mass and access to necessary infrastructure. We present a new technique for local mapping of polar ionospheric electrodynamics, for use in regions with high data density, such as Fennoscandia and North America. The technique is based on spherical elementary current systems (SECS), which were originally developed to map ionospheric currents. We expand their use by linking magnetic field perturbations in space and on ground, convection measurements from space and ground, and conductance measurements, via the ionospheric Ohm's law. The result is a technique that is similar to the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) technique, but tailored for regional analyses of arbitrary spatial extent and resolution. We demonstrate our technique on synthetic data, and with real data from three different regions. We also discuss limitations of the technique and potential areas for improvement. Plain Language Summary: The ionosphere, where a small but significant fraction of the atmosphere is ionized, forms the edge of space. At only 100‐km altitude, it is the region in space which is by far best monitored by human instruments. Space scientists routinely use measurements that inform about specific aspects of the dynamics in the ionosphere, but not the whole picture. For example, magnetometers on ground measure one part of the electric current system while magnetometers on satellites measure another part. Radars measure the flow of charged particles in the ionosphere, while optical images and particle measurements can be used to estimate electric conductivity. In this paper, we present a technique that combines all these different types of measurements to give a complete picture of what takes place in the ionosphere. The technique is tailored for use in regions where the data density is high, and the spatial resolution and extent of the analysis region are flexible. Key Points: We present a technique to use disparate data types to produce local maps of polar ionospheric electrodynamicsΔB and convection measurements are related via ionospheric Ohm's law and spherical elementary current systemsWe demonstrate the technique on real and synthetic data, and discuss limitations and future development [ABSTRACT FROM AUTHOR]

Auroral substorm onset locations are highly unpredictable. Previous studies have shown that the By component of the interplanetary magnetic field (IMF) explains ∼5% of the variation in onset magnetic local time (MLT), while solar wind conditions and the other IMF components have even less explanatory power. In this study, we show that the level of geomagnetic activity before substorm onset, as indicated by the AL index, explains an additional ∼5% of the variation in onset MLT. We discuss our results with regard to recent modeling studies, which show that gradients in the ionospheric Hall conductance can lead to a duskward shift of the magnetotail dynamics. Our findings suggest that this magnetosphere‐ionosphere coupling effect may also influence the location of substorm onsets. Plain Language Summary: Substorms are explosive disturbances in our magnetotail that impact the earth's ionosphere. They happen on average several times per day and as a result of this phenomenon, we can see the marvelous aurora. Substorms happen on the nightside of the earth and can take place over a wide range of latitudes and longitudes. In this study, we show that substorms tend to begin at earlier local times during geomagnetically active times than during quiet times. We interpret this tendency as a sign that ionospheric conditions may play a role in determining where substorms occur. Key Points: Ionospheric conditions before substorm onset are different for substorms with an early local time onset versus late local time onsetSubstorm onsets tend to move to earlier local times with increasing geomagnetic activityWe suggest that higher ionospheric conductance leads to a duskward shift in magnetospheric substorm activity [ABSTRACT FROM AUTHOR]

Lobe reconnection is usually thought to play an important role in geospace dynamics only when the Interplanetary Magnetic Field (IMF) is mainly northward. This is because the most common and unambiguous signature of lobe reconnection is the strong sunward convection in the polar cap ionosphere observed during these conditions. During more typical conditions, when the IMF is mainly oriented in a dawn‐dusk direction, plasma flows initiated by dayside and lobe reconnection both map to high‐latitude ionospheric locations in close proximity to each other on the dayside. This makes the distinction of the source of the observed dayside polar cap convection ambiguous, as the flow magnitude and direction are similar from the two topologically different source regions. We here overcome this challenge by normalizing the ionospheric convection observed by the Super Dual Aurora Radar Network (SuperDARN) to the polar cap boundary, inferred from simultaneous observations from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE). This new method enable us to separate and quantify the relative contribution of both lobe reconnection and dayside/nightside (Dungey cycle) reconnection during periods of dominating IMF By. Our main findings are twofold. First, the lobe reconnection rate can typically account for 20% of the Dungey cycle flux transport during local summer when IMF By is dominating and IMF Bz ≥ 0. Second, the dayside convection relative to the open/closed boundary is vastly different in local summer versus local winter, as defined by the dipole tilt angle. Plain Language Summary: Reconnection of magnetic field lines at high latitudes, tailward of the magnetic poles, is most often thought to play a big role in near‐Earth space dynamics only when the magnetic field carried by the solar wind, the Interplanetary Magnetic Field or IMF, has a large northward component. This is because such conditions lead to the distinct strong sunward movement of plasma at polar latitudes in the ionosphere. During more typical conditions (when the IMF is dawn/dusk directed), identifying and quantifying the effect of such high‐latitude reconnection becomes much more challenging. This paper presents a new technique that enables this separation even when the dawn‐dusk component of the IMF is dominating, by normalizing the convection to the boundary between open and closed magnetic field lines. We make two main findings. First, the summer and winter dayside plasma flows near the boundary between open and closed magnetic field lines are vastly different. Second, plasma circulation at polar latitudes (interpreted as lobe reconnection rate) can on average account for ∼20% $\sim 20\%$ of the total plasma transport during local summer when IMF is mostly directed in the dawn‐dusk direction and IMF Bz is northward. Key Points: We demonstrate a novel technique to quantify the polar cap plasma circulation statisticallyDuring local summer and By dominated Interplanetary Magnetic Field (IMF), lobe reconnection is estimated to amount to ∼20% of the dayside reconnection rateIn the local summer hemisphere, dayside polar cap convection is more vortical compared to the local winter hemisphere during IMF By periods [ABSTRACT FROM AUTHOR]

North‐south asymmetries arise in the magnetosphere‐ionosphere system when a significant east‐west (By) component is present in the interplanetary magnetic field (IMF). During such conditions, a By component with the same sign as the IMF By component is induced in the magnetosphere, and the locations of conjugate magnetic footpoints are displaced between the two hemispheres. It has been suggested that these asymmetries are introduced into the closed magnetosphere by tail reconnection. However, recent studies instead suggest that asymmetric lobe pressure induces the asymmetries, which are then reduced during periods of enhanced tail reconnection. To address this, we use the Lyon‐Fedder‐Mobarry (LFM) model and initiate a loading‐unloading cycle in multiple runs by changing the IMF. Asymmetries are induced during the loading phase and reduced during the unloading phase. The model results thus suggest that asymmetries arise during periods with low tail reconnection and are reduced during periods with enhanced tail reconnection. Plain Language Summary: The aurora is a bright and beautiful manifestation of Earth's connection to space, and can light up the night sky in the high latitude regions in both hemispheres. However, auroral features do not always occur at the expected magnetic location in the two hemispheres, but are often displaced in the longitudinal direction between the Northern and Southern Hemisphere. The displacement is related to the orientation of the magnetic field in the solar wind, but the exact mechanisms responsible for causing and removing this displacement are debated. Previous simulations of the plasma environment around the Earth suggest that when this magnetic field intensifies in the dawn‐dusk direction, magnetic pressure builds up asymmetrically in each hemisphere, causing the displacement. Here we present new simulation results showing that the longitudinal displacement is reduced when magnetic reconnection happens in the Earth's magnetotail. Key Points: The evolution of the asymmetric state of the magnetosphere is examined by using the Lyon‐Fedder‐Mobarry model with non‐zero interplanetary magnetic field ByThe simulation shows a clear reduction of north‐south asymmetries associated with enhanced tail reconnectionThe modeling results are consistent with the evolution seen in interhemispheric observations of aurora [ABSTRACT FROM AUTHOR]

Substorm activity is heavily influenced by the Interplanetary Magnetic Field (IMF) Bz component and magnetospheric substorms occur most frequently when Bz is strongly negative. The substorm occurrence rate is also affected by the magnitude of the By component, but it is usually presumed that this contribution is independent of the sign of By. Using five independent substorm onset lists, we show that substorm activity does depend on the sign of By near the solstices. Specifically, we show that substorms occur more frequently when By and the dipole tilt angle Ψ have different signs as opposed to when they have the same sign. These results confirm that the magnetosphere exhibits an explicit dependence on the polarity of By for nonzero Ψ, as other recent studies have suggested, and imply variation in the dayside reconnection rate and/or the magnetotail response. On the other hand, we find no clear relationship between substorm intensity and By regardless of Ψ. Last, for the onset list based on identifying negative bays at auroral latitudes, we observe an overall trend of more frequent onsets for positive By, regardless of season. However, substorm frequency in the other four substorm lists does not exhibit an overall preference for positive By. We show that this phenomenon is very likely a consequence of the particular substorm identification method (i.e., identification of negative bays), which is affected by local ionospheric conditions that depend on By and Ψ. [ABSTRACT FROM AUTHOR]

This paper presents and discusses electron density depletion regions observed with the incoherent scatter EISCAT Svalbard Radar (ESR) located at 75.43°N geomagnetic latitude. The data include several decades of measurements, which make them suitable for studying statistical features and characteristics of the ionospheric parameters. Here we focus on the electron density depletions and their dependence on diurnal and seasonal variations and solar activity. An electron density depletion region is identified in the ESR data in the early morning sector. This depletion region seems to be clearest during equinox and winter and moderate/high solar activity. An enhancement in the ion temperature is often colocated with the electron density depletion region. The ion temperature enhancement could indicate that ion frictional heating is related to the electron density depletion region. However, during summer when the solar activity is low, the electron density depletion is not observed although the ion temperature is enhanced, suggesting that formation of the electron density depletion regions due to ion frictional heating may depend on the background effective temperature and O/N2 ratio. In addition, seasonal changes in the solar zenith angle could also contribute to the formation of the depletion region. [ABSTRACT FROM AUTHOR]

ZnO nanorods synthesised using an aqueous pH 11 solution are shown to exhibit surface-sensitive morphology post-annealing in oxygen, air, and nitrogen as shown by scanning electron microscopy and transmission electron microscopy analysis. Raman analysis confirms the nanorods were nitrogen-doped and that nitrogen incorporation takes place during the synthesis procedure in the form of N-Hx. A strong green photoluminescence is observed post-annealing for all samples, the intensity of which is dependent on the atmosphere of anneal. This luminescence is linked to zinc vacancies as recent reports have indicated that these defects are energetically favoured with the annealing conditions used herein. ZnO-nanorod/CuSCN diodes are fabricated to examine the effect of material properties on photodetector device performance. The devices exhibit a photocurrent at zero bias, creating a self-powered photodetector. A photocurrent response of 30 μA (at 6 mW cm-2 irradiance) is measured, with a rise time of ∼25 ns, and sensitivity to both UV and visible light (475-525 nm). [ABSTRACT FROM AUTHOR]

One of the primary mechanisms of loss of Earth's atmosphere is the persistent "cold" (T≲ 20 eV) ion outflow that has been observed in the magnetospheric lobes over large volumes with dimensions of order several Earth radii. As the main source of this cold ion outflow, the polar cap F region ionosphere and conditions within it have a disproportionate influence on these magnetospheric regions. Using 15 years of measurements of plasma density Ne made by the Swarm spacecraft constellation and the Challenging Mini Satellite Payload (CHAMP) spacecraft within the F region of the polar cap above 80° Apex magnetic latitude, we report evidence of several types of seasonal asymmetries in polar cap Ne. Among these, the transition between "winter‐like" and "summer‐like" median polar cap Ne occurs 1 week prior to local spring equinox in the Northern Hemisphere (NH) and 1 week after local spring equinox in the Southern Hemisphere (SH). Thus, the median SH polar cap Ne lags the median NH polar cap Ne by approximately 2 weeks with respect to hemispherically local spring and fall equinox. From interhemispheric comparison of statistical distributions of polar cap plasma density around each equinox and solstice, we find that distributions in the SH are often flatter (i.e., less skewed and kurtotic) than those in the NH. Perhaps of most significance to cold ion outflow, we find no evidence of an F region plasma density counterpart to a previously reported hemispheric asymmetry whereby cold plasma density is higher in the NH magnetospheric lobe than in the SH lobe. Plain Language Summary: The Earth's magnetic poles are not perfectly aligned with the Earth's geographic poles, and the degree of misalignment is greater in the Southern Hemisphere. Furthermore, as a result of the Earth's elliptical orbit around the Sun, summer and fall in the Northern Hemisphere together are approximately 1 week longer than summer and fall in the Southern Hemisphere, because the Earth is very slightly closer to the Sun around December solstice (summer in the Southern Hemisphere). These seasonal asymmetries, together with the asymmetric displacement of the Earth's magnetic poles relative to the geographic poles, suggest that the plasma density in the topside ionosphere's geomagnetic polar regions may also be subject to seasonal and hemispheric asymmetries. The polar regions are the primary site of loss of the Earth's atmosphere via so‐called ion outflow processes that, over geological time scales, are believed to lead to loss of the Earth's atmosphere. Using 15 years of plasma density measurements made by four different satellites to statistically study the plasma density of each hemisphere's geomagnetic polar cap ionosphere in the altitude range 350–520 km, we find that the polar cap ionosphere at these altitudes exhibits a variety of seasonal and hemispheric asymmetries. Key Points: Statistics of F region polar cap plasma density derived from 15 years of measurements exhibit several types of seasonal asymmetriesStatistics do not support the conjecture that limited plasma availability is the cause of observed hemispheric asymmetries in lobe densitySouthern Hemisphere polar cap plasma densities lag those in Northern Hemisphere by at least 2 weeks around local spring and fall equinox [ABSTRACT FROM AUTHOR]

A number of interdependent conditions and processes contribute to ionospheric‐origin energetic (∼10 eV to several keV) ion outflows. Due to these interdependences and the associated observational challenges, energetic ion outflows remain a poorly understood facet of atmosphere‐ionosphere‐magnetosphere coupling. Here we demonstrate the relationship between east‐west magnetic field fluctuations (ΔBEW) and energetic outflows in the magnetosphere‐ionosphere transition region. We use dayside cusp region FAST satellite observations made near apogee (∼4,180‐km altitude) near fall equinox and solstices in both hemispheres to derive statistical relationships between ion upflow and ΔBEW spectral power as a function of spacecraft frame frequency bands between 0 and 4 Hz. Identification of ionospheric‐origin energetic ion upflows is automated, and the spectral power PEWin each frequency band is obtained via integration of ΔBEW power spectral density. Derived relationships are of the form J‖,i=J0,iPEWγ for upward ion flux J‖,i at 130‐km altitude, with J0,i the mapped upward ion flux for a nominal spectral power PEW=1 nT 2. The highest correlation coefficients are obtained for spacecraft frame frequencies ∼0.1–0.5 Hz. Summer solstice and fall equinox observations yield power law indices γ≃ 0.9–1.3 and correlation coefficients r≥0.92, while winter solstice observations yield γ≃ 0.4–0.8 with r≳0.8. Mass spectrometer observations reveal that the oxygen/hydrogen ion composition ratio near summer solstice is much greater than the corresponding ratio near winter. These results reinforce the importance of ion composition in outflow models. If observed ΔBEW perturbations result from Doppler‐shifted wave structures with near‐zero frequencies, we show that spacecraft frame frequencies ∼0.1–0.5 Hz correspond to perpendicular spatial scales of several to tens of kilometers. Key Points: Summer/equinox outflows and east‐west magnetic field fluctuations are highly correlated (r>0.92)Winter outflows are poorer in oxygen and less correlated with magnetic field fluctuations (r>0.75)Power indices 0.7–1.2 characterize statistical relationship between outflows and magnetic field fluctuations [ABSTRACT FROM AUTHOR]

The Swarm satellites fly at altitudes that at polar latitudes are generally assumed to only contain currents that are aligned with the local magnetic field. Therefore, disturbances along the main field direction are mainly signatures of auroral electrojet currents, with a relatively smooth structure due to the distance from the currents. Here we show that superimposed on this smooth signal is an irregular pattern of small perturbations, which are anticorrelated with the plasma density measured by the Langmuir probe. We show that the perturbations can be remarkably well reproduced by assuming they represent a j × B force, which balances the plasma pressure gradient implied by the density variations. The associated diamagnetic current, previously reported to be most important near the equator, appears to be a ubiquitous phenomenon also at polar latitudes. A spectral analysis indicates that this effect dominates magnetic field intensity variations at small‐scale sizes of a few tens of kilometers. Plain Language Summary: The Swarm satellites fly at altitudes that at polar latitudes are generally assumed to only contain currents that are aligned with the local magnetic field. Therefore, disturbances in the magnetic field strength are mainly signatures of horizontal currents below the satellites. Such disturbances have a smooth structure due to the distance from the currents. Here we show that superimposed on this smooth signal is an irregular pattern of small perturbations, which are anticorrelated with the local plasma density. We show that this anticorrelation can be explained in terms of pressure balance between particles and the magnetic field. The electric currents that are associated with the magnetic field fluctuations, diamagnetic currents, have previously been reported to be most important near the equator. Our results show that they are a ubiquitous phenomenon at all latitudes and indicate that the diamagnetic effect dominates magnetic field intensity variations at small‐scale sizes of a few tens of kilometers. Key Points: Magnetic intensity variations associated with plasma pressure are ubiquitous in the polar F regionPlasma pressure effects are the dominating source of ‖B‖ variations at small spatial scalesThis finding may enable new ways of estimating ion temperature and plasma flow with Swarm data [ABSTRACT FROM AUTHOR]