When a linearly polarized radio wave travels down a magnetic field line through a plasma, Faraday rotation causes its polarization plane to rotate by an amount proportional to the integrated Total Electron Content (TEC) along the path. This effect can be measured by a simple cross-yagi antenna, and given a known initial polarization can be used to derive TEC. We present work from the GIRAFF sounding rocket (mission 36.381, Michell) where the Faraday rotation from a linearly polarized beacon carried by the rocket, as measured by three ground-based receivers, was used to construct a 2d tomographic reconstruction of ionospheric plasma density. Despite severe limitations on reconstruction accuracy imposed by the opportunistic use of the GIRAFF launch, the resulting density map agrees reasonably well with the Poker Flat Incoherent Scatter Radar. Implications for the upcoming GNEISS sounding rocket mission, which will replicate this idea on a larger scale and with much better accuracy, are discussed.

The physical trigger of substorm onset remains one of the key unresolved problems in magnetospheric physics. Understanding how, when, and why stored energy in Earth’s magnetotail is explosively released is central to space-weather science. To identify the instability responsible for detonation, recent studies have focused on the earliest auroral signatures of onset—small-scale, quasi-periodic structures known as auroral beads. Previous work has linked these beads to plasma instabilities and to magnetotail dynamics through kinetic Alfvén waves.To further understand the substorm onset mechanism, we use new measurements from a narrow-field, high-cadence auroral imager. By extending the Kalmoni et al. (2018) methodology, we track the temporal evolution and dispersion characteristics of “mini beads”, in effect beads-within-beads. Our analysis shows that all types of beads move in the same eastward direction but that mini beads precede the larger beads by at least one minute. However, in contrast to larger-scale beads, mini beads obey different dispersion relations, suggesting that mini beads arise from a distinct physical process and represent an earlier or new stage of the instability development leading to substorm onset. This means that we need to understand the near-Earth transition region on multiple scales far earlier than currently thought, challenging all current substorm onset paradigms. We discuss the implications of this analysis for determining the role of multi-scale physical processes in substorm onset for multi-spacecraft missions such as Plasma Observatory.

The Systematic Study of lower Thermosphere Energetics by a Rocket (SYSTER) is a multi-payload sounding rocket designed to study Joule heating at auroral latitudes. SYSTER provides pathfinder measurements for a future thermospheric ’dipper’ spacecraft, currently being evaluated by the ESA-NASA Lower Thermosphere-Ionosphere Science (ENLOTIS) working group.

We investigated the pulsating aurora observed on 7 January 2014, by a narrow field-of-view (FOV) high-time resolution ground-based white-light imager and all-sky low-time-resolution imager operated at Poker Flat, AK (geographic: 65.1°N, 147.4°W). The pulsating aurora showed very notable characteristics, such as frequency drift in their pulsation with time and drifting of the entire pulsating auroral structure in space. We find that (i) the entire pulsating auroral patch was observed to drift northward at a velocity of approximately 76 m/s, which aligns closely with the local convection velocities obtained from Super Dual Auroral Radar Network (SuperDARN) data, consistent with the idea that the patch motion is primarily due to E×B convection. (ii) The duration of persistence for each pulsation in the pulsating aurora is found to be ∼1 s (iii) The auroral pulsation frequency abruptly increases from ∼0.0625 Hz to ∼0.5 Hz, closely aligning with the broadening of the frequency band observed at the Dawson (DAWS) ground magnetometer location. Wavelet analysis of DAWS magnetic field data, recorded at similar magnetic local time (MLT) and L-values, reveals the presence of Pc-1 geomagnetic pulsation (Pc-1). This connection suggests that the drift in auroral pulsation frequency may be driven by the evolution of Pc-1 waves, which are influenced by changes in the local plasma environment. The broadening of the frequency band may indicate dynamic variations in magnetospheric ion composition or plasma density. This interplay underscores the role of Pc-1 waves and magnetospheric dynamics in determining the auroral pulsation characteristics.

Our study presents the first simultaneous multi-point observations of the local-time asymmetry of 10's-100's of keV energy particle pitch angle distributions (PADs), and associated wave activity during the main phase of the geomagnetic storm that occurred on 7 September 2017. This study is a companion to Pandya et al. (2025), who identified a rare conjunction in which RBSP-A and RBSP-B were located in the evening and morning sectors, respectively, enabling the comparison of ion populations across local time. Building on that work, we identify an additional rare conjunction during the same interval in which RBSP-A and MMS-1 were co-located in the evening sector for similar to 15 min (2,325-2340 UT) within Delta L < 0.2, Delta MLT < 2 min and Delta MLAT similar to 20 degrees. Our analysis shows strong local time asymmetries. Protons in the evening sector exhibited freshly injected, enhanced fluxes with nearly isotropic PADs at >60 keV energies and pancake PADs at <60 keV energies, whereas dawn-noon proton fluxes retained pancake PADs characteristic of older populations. In contrast, electrons showed a significant flux decrease in the evening sector and isotropic enhancement in the morning sector, consistent with their eastward gradient-B and curvature drifts. Concurrent wave observations revealed strong ULF, magnetosonic and hiss waves in the evening sector, while hiss waves dominated in the morning sector. Our results demonstrate that storm-time magnetic field reconfiguration, rather than wave-particle interactions, primarily governs keV particle PAD asymmetries. The findings highlight the importance of coordinated multi-point measurements for advancing our understanding of ring current asymmetries and storm-time particle transport. Plain Language Summary During geomagnetic storms, particles trapped in Earth's magnetic field are strongly energized and redistributed differently at different magnetic local times (MLTs). In this study, we investigate the 7 September 2017 geomagnetic storm using the multi-spacecraft conjunction. Previous work (Pandya et al., 2025) reported a unique event in which the two RBSP observatories were located on opposite sides of Earth, allowing direct comparison of particle behavior across local time. Building on that study, we identify a second rare conjunction in which the RBSP-A and MMS-1 spacecraft were located in nearly the same region of the evening sector at the same time. These coordinated measurements show that protons and electrons responded very differently at different local times during the storm. Protons were enhanced and nearly isotropic in the evening sector but weakened in the dawn sector, while electrons showed the opposite trend. These asymmetries were accompanied by different wave activity on the dawn and dusk sides of the magnetosphere. Our results suggest that the reconfiguration of the Earth's magnetic field during the storm, rather than wave-particle interactions, was the dominant factor shaping these particle distributions. This study highlights the importance of multi-point observations for understanding the Earth's near-space environment.

Our study presents the first simultaneous multi‐point observation of the local‐time asymmetry of 10's–100's of keV energy ion fluxes during the main phase of the geomagnetic storm that occurred on 7 September 2017. During this event, Van Allen Probe‐A and Van Allen Probe‐B observed two different tendencies. The ion fluxes increased by an order of magnitude in the noon‐dusk sector, while decreasing by one order or more in the dawn‐noon sector, offering a unique opportunity to investigate this asymmetry. Numerical simulations employing the Comprehensive Inner Magnetosphere‐Ionosphere model with time‐dependent electric fields from Global Magnetohydrodynamic (MHD) simulations revealed that the local time asymmetry in ion fluxes is associated with a sharp southward turning of the interplanetary magnetic field (IMF) and long‐duration persistent westward electric field. These factors cause ions to drift toward the dusk sector, while preexisting ions on the dayside drift sunward and escape the inner magnetosphere. Our findings provide the first direct observational evidence of ring current asymmetry, complementing and supporting prior statistical studies and simulation results.

Cold plasma of ionospheric origin has recently been found to be a much larger contributor to the magnetosphere of Earth than expected1, 2-3. Numerous competing mechanisms have been postulated to drive ion escape to space, including heating and acceleration by wave-particle interactions4 and a global electrostatic field between the ionosphere and space (called the ambipolar or polarization field)5,6. Observations of heated O+ ions in the magnetosphere are consistent with resonant wave-particle interactions7. By contrast, observations of cold supersonic H+ flowing out of the polar ionosphere8,9 (called the polar wind) suggest the presence of an electrostatic field. Here we report the existence of a +0.55 +/- 0.09 V electric potential drop between 250 km and 768 km from a planetary electrostatic field (E parallel to circle plus = 1.09 +/- 0.17 mu V m-1) generated exclusively by the outward pressure of ionospheric electrons. We experimentally demonstrate that the ambipolar field of Earth controls the structure of the polar ionosphere, boosting the scale height by 271%. We infer that this increases the supply of cold O+ ions to the magnetosphere by more than 3,800%, in which other mechanisms such as wave-particle interactions can heat and further accelerate them to escape velocity. The electrostatic field of Earth is strong enough by itself to drive the polar wind9,10 and is probably the origin of the cold H+ ion population1 that dominates much of the magnetosphere2,3.

High Altitude Reflection Potential Structures (HARPS) with typical magnitudes of a few tens of volts have been frequently detected above Earth's sunlit polar cap. They are thought to be electrostatic structures forming between 1 to several Earth radii in altitude. Previous satellite studies have been unable to probe the temporal variability of their magnitude owing to their fast motion through the region of observation. In this study, we present a similar to ${\sim} $10 min time series of observations of HARPS from NASA's Endurance sounding rocket. These observations were made from a spatially localized region, enabling the first experimental investigation of the temporal variability of HARPS. The magnitude of the potential drop was found to vary unexpectedly rapidly between 15.5 and 23.7 V on a time cadence of <= 10 ${\le} 10$ s. We additionally find an inverse correlation between polar rain precipitating flux and reflection potential magnitude, consistent with predictions from prior theoretical work.

AbstractUsing NASA's Global‐scale Observations of the Limb and Disk (GOLD) imager, we report nightside ionospheric changes during the G5 super geomagnetic storm of 10 and 11 May 2024. Specifically, the nightside southern crest of the Equatorial Ionization Anomaly (EIA) was observed to merge with the aurora near the southern tip of South America. During the storm, the EIA southern crest was seen moving poleward as fast as 450 m/s. Furthermore, the aurora extended to mid‐latitudes reaching the southern tips of Africa and South America. The poleward shift of the equatorial ionospheric structure and equatorward motion of the aurora means there was no mid‐latitude ionosphere in this region. These observations offer unique insights into the ionospheric response to extreme geomagnetic disturbances, highlighting the complex interplay between solar activity and Earth's upper atmosphere.

Wave-particle interaction processes in the equatorial magnetosphere initiate time-dependent electron precipitation in the pulsating aurora. These electrons enter loss-cone and bounce between the two magnetically conjugate hemispheres, collide with the atmospheric constituents, and introduce additional time scales in electron precipitation dynamics. In this letter we present preliminary results of pulsating aurora formation using the time-dependent SuperThermal Electron Transport code, which considers the magnetosphere-ionosphere-atmosphere energy coupling between the two magnetically conjugate regions and discuss their contribution to the peculiarities of electron distribution function formation within the pulsating aurora.

In this study, we report observations made by filtered (557.7 and 630.0 nm) All-Sky Imagers located at Poker Flat, Alaska alongside Poker Flat Incoherent Scatter Radar data for an event observed on 5 February 2017. Together, the data indicate ion upflow in the vicinity of pulsating aurora. Additionally, the data show a strong 630.0 nm (red-line) auroral emission. Observations of pulsating aurora are typically reported at 557.7 and 427.8 nm, as these wavelengths are more sensitive to high-energy (∼ tens of keV) electron precipitation. In contrast, 630.0 nm emission is generated preferentially by low-energy soft electron precipitation (∼ hundreds of eV), and is less commonly observed. The All-Sky Imager data discussed here are unusual in that they suggest regions of enhanced soft electron precipitation in conjunction with enhanced ambipolar electric fields, which are a known factor contributing to ion outflow.

NASA’s Endurance sounding rocket (yard No. 47.001) will launch from Ny Ålesund, Svalbard in May 2022 on a solid fueled Oriole III-A launch vehicle. Its $\sim19$ minute flight will carry it to an altitude of $\sim780~\text{km}$ above Earth’s sunlit polar cap. Its objective is to make the first measurement of the weak “ambipolar” electric field generated by Earth’s ionosphere. This field is thought to play a critical role in the upwelling and escape of ionospheric ions, and thus potentially in the evolution of Earth’s atmosphere. The results will enable us to determine the importance to ion escape of this previously unmeasured fundamental property of our planet, which will aid in a better understanding of what makes Earth habitable. Endurance will carry six science instruments (with 16 sensors) that will measure the total electrical potential drop below the spacecraft, and the physical parameters required to understand the physics of what generates the ambipolar field. The mission will be supported by simultaneous observations of solar and geomagnetic activity.

Abstract Photoelectrons are crucial to atmospheric physics. They heat the atmosphere, strengthen planetary ambipolar electric fields, and enhance the outflow of ions to space. However, there exist only a handful of measurements of their energy spectrum near the peak of photoproduction. We present calibrated energy spectra of pristine photoelectrons at their source by a prototype Dual Electrostatic Analyzer (DESA) instrument flown on 11 July 2021 aboard the Dynamo‐2 sounding rocket (NASA № 36.357). Photopeaks arising from 30.4 nm He‐II spectral line were observed throughout the flight above 120 km. DESA also successfully resolved the rarely observed N2 absorption feature. Below 10 eV observations were in good agreement with the GLOW suprathermal electron. Above 10 eV fluxes substantially deviated from the model by as much as an order of magnitude.

Studies have shown a broad correlation between pulsating aurora, chorus waves, and electron scattering, but most studies have used either low time resolution waveform data, high time resolution waveform data over short periods of time, or waveform data without direct crossover of an all sky camera field of view. For the present study, we analyze three nights in Oct 2016 with conjugate Van Allen Probe (VAP) chorus wave observations and HAARP all sky camera (ASC) pulsating aurora observations. We use VAP burst mode waveform data collected for about an hour at 16,000 samples/s during direct VAP crossover of the HAARP ASC FOV in Gakona, AK. Our high-resolution analysis indicates a more complicated relationship between individual aurora pulsations and chorus wave elements. We show in previous study that for each VAP ASC crossover event on October 16 2016, the chorus wave elements observed by VAP do not correspond well to the detailed dynamics of the pulsating aurora. We compare the individual chorus wave elements to the extracted all sky camera optical intensity fluctuations along the mapped magnetic footpoint determined by four separate field line models. Our Poynting flux analysis shows chorus wave propagation towards the northern hemisphere. Based on previous results using THEMIS data, we would expect to see good correlation between the observed chorus waves above the magnetic equator and the pulsating aurora dynamics in the northern hemisphere. However, observed chorus waves may be distorted during propagation away from the generation region or non-linear wave effects may play a role. In this study we extend our analysis to the VAP ASC crossover events on October 13 and 19 2016. We expand our methodologies for optical intensity extraction of ASC images. We seek to draw connections between the characteristics of the individual chorus wave elements and the correlation to pulsating aurora dynamics to better identify particular chorus wave electron resonance conditions.

We use the Geospace Environment Model of Ion-Neutral Interactions (GEMINI) to create three-dimensional, time-dependent simulations of auroral ionospheric parameters in the localized, several 100 km region surrounding auroral arcs observed during a winter 2017 sounding rocket campaign, resolving three-dimensional features of fine-scale (km) flow structures in the vicinity of an auroral arc. The three-dimensional calculations of GEMINI allow (with sufficient driving data) auroral current closure to be investigated without idealizing assumptions of sheet-like structures or height integrated ionospheres. Datamaps for two nearly sheet-like arcs are reconstructed from replications of the Isinglass sounding rocket campaign data, and combined with camera-based particle inversions into a set of driving inputs to run the 3D time-dependent model. Comparisons of model results to radar density profiles and to in situ magnetometry observations are presented. Slices of volumetric current, flow, and conductance structures from model outputs are used to interpret closure currents in an auroral arc region, and are compared to original in situ measurements for verification. The predominant source of return current region field aligned current closure for these slow time variation events is seen to be from the conductance gradients, including the Hall. The importance of the backward difference sigma H versus backward difference sigma P terms in the determination of the current structure provides a more complicated picture than a previous GEMINI study, which relied predominantly on the divergence of the electric field to determine current structure. Sensitivity of data-driven model results to details of replication and reconstruction processes are discussed, with improvements outlined for future work.

This article presents the results of a spectroscopic observations of faint meteors made from Arecibo during an observing campaign in May 2012. The scientific interest is reduced because the authors have not clearly identified the origin of the meteors studied, and the paper lacks of clear goals, more than a presentation of results. I also found that the paper lacks of scientific justification for many of the results presented. On the other hand, the manuscript doesn’t include a proper citation of previous literature on the topic. Finally, the scientific discussion and the conclusions are too vague as well. In these circumstances, I think that the authors should rewrite the entire manuscript. In order to help them to make it publishable, let me provide a detailed review with major and minor issues.

Earth’s primary ionospheric loss process is the polar wind, which flows outwards along open magnetic field lines above our polar caps. One key component critical to the formation of this outflow is thought to be a weak ambipolar electric field. The potential drop resulting from this electric field is thought to assist terrestrial atmospheric escape since it reduces the potential barrier required for heavier ions (such as O+) to escape and accelerates light ions (such as H+) to escape velocity. Although a key component to atmospheric loss, Earth’s ambipolar electric field has never been measured due to its weak strength. We announce the NASA Endurance mission, launching in 2022, which will attempt to make the first direct in-situ observations of Earth’s ambipolar electric field. Endurance launch from Ny-Ålesund, Svalbard, and soar across the exobase to altitudes greater than 800km. The spacecraft will be equipped with a new type of scientific instrument which will enable the Endurance to measure the total electric potential drop below her. She will also be equipped with a full array of sensors that will enable the science team to self-consistently model the polar wind during the flight to test our current theoretical understanding of the physical processes which generate Earth’s ambipolar electric field. Endurance will perform groundbreaking discovery science, measuring a fundamental property of Earth for the first time: the strength of the ambipolar electric field generated by its ionosphere. The results will provide us with a better understanding of atmospheric escape at Earth, and why our planet is habitable.

This chapter reviews fundamental properties and recent advances of diffuse and pulsating aurora. Diffuse and pulsating aurora often occurs on closed field lines and involves energetic electron precipitation by wave-particle interaction. After summarizing the definition, large-scale morphology, types of pulsation, and driving processes, we review observation techniques, occurrence, duration, altitude, evolution, small-scale structures, fast modulation, relation to high-energy precipitation, the role of ECH waves, reflected and secondary electrons, ionosphere dynamics, and simulation of wave-particle interaction. Finally we discuss open questions of diffuse and pulsating aurora.