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Abstract The Global‐scale Observations of Limb and Disk (GOLD) and Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instruments were used to investigate the thermospheric composition and temperature responses to the geomagnetic storm on 23–24 April, 2023. Global‐scale Observations of Limb and Disk observed a faster recovery of thermospheric column density ratio of O to N₂(ΣO/N₂) in the southern hemisphere (SH) after the storm ended at 12 Universal time (UT) on 24 April. After 12 UT on 25 April, ΣO/N₂had mostly recovered in both hemispheres. Global‐scale Observations of Limb and Disk also observed an increase of middle thermospheric temperature (140–200 km) (Tdisk) on 24 April with a maximum of 340 K. Within 4–6 hr of the storm ending on 24 April, Tdisk enhancement persisted between 30°N and 60°N, 100°W and 30°W, while Tdisk lower than pre‐storm quiet day (17 April) was observed between 45°W and 15°W, 40°S and 50°N. Tdisk recovered between 100°W and 45°W, 30°N and 55°S. On 25 April, Tdisk was lower than on 17 April across the entire GOLD Field‐of‐Regard (FOR) by ∼50–110 K. Additionally, solar irradiance decreased by 15%–20% from 17 to 25 April, indicating that the lower Tdisk on 25 April resulted from both storm and solar irradiance variations. Latitudinal variations of Tdisk and the SABER observed Nitric Oxide (NO) cooling rate revealed that NO cooling is crucial for the lower Tdisk in the northern hemisphere (NH) mid‐high latitudes on 25 April. These results provide direct evidence of decreased thermospheric temperature during storm recovery phase than pre‐storm quiet times. 

Abstract Geomagnetic storms transfer massive amounts of energy from the sun to geospace. Some of that energy is dissipated in the ionosphere as energetic particles precipitate and transfer their energy to the atmosphere, creating the aurora. We used the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mosaic of all‐sky‐imagers across Canada and Alaska to measure the amount of energy flux deposited into the ionosphere via auroral precipitation during the 2013 March 17 storm. We determined the time‐dependent percent of the total energy flux that is contributed by meso‐scale (<500 km wide) auroral features, discovering they contribute up to 80% during the sudden storm commencement (SSC) and >∼40% throughout the main phase, indicating meso‐scale dynamics are important aspects of a geomagnetic storm. We found that average conductance was higher north of 65° until SYM‐H reached −40 nT. We also found that the median conductance was higher in the post‐midnight sector during the SSC, though localized conductance peaks (sometimes >75 mho) were much higher in the pre‐midnight sector throughout. We related the post‐midnight/pre‐dawn conductance to other recent findings regarding meso‐scale dynamics in the literature. We found sharp conductance peaks and gradients in both time and space related to meso‐scale aurora. Data processing included a new moonlight removal algorithm and cross‐instrument calibration with a meridian scanning photometer and a standard photometer. We compared ASI results to Poker Flat Incoherent Scatter Radar (PFISR) observations, finding energy flux, mean energy, and Hall conductance were highly correlated, moderately correlated, and highly correlated, respectively. 

Abstract We investigated the effects of storm‐time diffuse auroral electron precipitation on ionospheric Pedersen and Hall conductivity and conductance during the CME‐driven St. Patrick's Day storms of 2013 (minDst = −131 nT) and 2015 (minDst = −233 nT). These storms were simulated using the magnetically and electrically self‐consistent RCM‐E model with STET modifications, alongside the B3C auroral transport code to compute ionospheric conductivities and height‐integrated conductance. The simulation results were validated against conductance inferred from Poker Flat Incoherent Scatter Radar (PFISR) and Millstone Hill Incoherent Scatter Radar (MHISR) measurements. Our simulations show that the magnetic latitude and local time distribution of Pedersen and Hall auroral conductance strongly correlate with diffuse electron precipitation flux, with the plasmapause marking the low‐latitude boundary of conductance. Simulated Pedersen/Hall conductance agrees reasonably well with PFISR measurements at 65.9° MLAT during diffuse auroral precipitation. During the intense 2015 storm, diffuse aurora extended down to 52.5° MLAT, with simulated conductance agreeing within a factor of two with MHISR observations. Discrete auroral arcs observed during both storms enhanced PFISR conductance by tens of siemens, though these enhancements were not captured by the model. Additionally, the simulated electric intensity showed development of sub‐auroral polarization streams (SAPS) and dawn SAPS features and followed the general trend of Poker Flat electric intensity at 65.9° MLAT during diffuse aurora, despite being updated every 5 min. The overall agreement between simulated ionospheric conductance and electric intensity with observations highlights the model's capability during diffuse auroral precipitation. 

Microelectromechanical Systems (MEMS) energy harvesters have been extensively investigated over the past decade, but increasing power density and long-term reliability under high acceleration and low frequency are still major concerns. This study focused on the development of a low-frequency lead zirconate titanate (PZT) based energy harvester capable of operating at high acceleration >4 g with high power density performance. This study investigates the performance effects of altering the electrode configuration and poling configuration to maximize power density. The study investigated using four different types of electrode configuration consisting of long and short interdigitated electrodes (IDE) to operate in d 33 mode, and traditional parallel plate configuration to operate in d 31 mode. The results were numerically and experimentally validated. The results illustrate that the d 33 mode configuration was able to generate >3200 μW mm -3 with good reliability of up to 4 g. 

Abstract Most ionospheric models cannot sufficiently reproduce the observed electron density profiles in the E‐region ionosphere, since they usually underestimate electron densities and do not match the profile shape. Mitigation of these issues is often addressed by increasing the solar soft X‐ray flux which is ineffective for resolving data‐model discrepancies. We show that low‐resolution cross sections and solar spectral irradiances fail to preserve structure within the data, which considerably impacts radiative processes in the E‐region, and are largely responsible for the discrepancies between observations and simulations. To resolve data‐model inconsistencies, we utilize new high‐resolution (0.001 nm) atomic oxygen (O) and molecular nitrogen (N₂) cross sections and solar spectral irradiances, which contain autoionization and narrow rotational lines that allow solar photons to reach lower altitudes and increase the photoelectron flux. This work improves upon Meier et al. (2007,https://doi.org/10.1029/2006gl028484) by additionally incorporating high‐resolution N₂photoionization and photoabsorption cross sections in model calculations. Model results with the new inputs show increased O⁺production rates of over 500%, larger than those of Meier et al. (2007,https://doi.org/10.1029/2006gl028484) and total ion production rates of over 125%, while production rates decrease by ∼15% in the E‐region in comparison to the results obtained using the cross section compilation from Conway (1988,https://apps.dtic.mil/sti/pdfs/ADA193866.pdf). Low‐resolution molecular oxygen (O₂) cross sections from the Conway compilation are utilized for all input cases and indicate that is a dominant contributor to the total ion production rate in the E‐region. Specifically, the photoionization contributed from longer wavelengths is a main contributor at ∼120 km. 

Abstract E‐region models have traditionally underestimated the ionospheric electron density. We believe that this deficiency can be remedied by using high‐resolution photoabsorption and photoionization cross sections in the models. Deep dips in the cross sections allow solar radiation to penetrate deeper into the E‐region producing additional ionization. To validate our concept, we perform a study of model electron density profiles (EDPs) calculated using the Atmospheric Ultraviolet Radiance Integrated Code (AURIC; D. Strickland et al., 1999,https://doi.org/10.1016/s0022-4073(98)00098-3) in the E‐region of the terrestrial ionosphere. We compare AURIC model outputs using new high‐resolution photoionization and photoabsorption cross sections, and solar spectral irradiances during low solar activity with incoherent scatter radar (ISR) measurements from the Arecibo and Millstone Hills observatories, Constellation Observing System for Meteorology Ionosphere and Climate (COSMIC‐1) observations, and outputs from empirical models (IRI‐2016 and FIRI‐2018). AURIC results utilizing the new high‐resolution cross sections reveal a significant difference to model outputs calculated with the low‐resolution cross sections currently used. Analysis of AURIC EDPs using the new high‐resolution data indicate fair agreement with ISR measurements obtained at various times at Arecibo but very good agreement with Millstone Hills ISR observations from ∼96–140 km. However, discrepancies in the altitude of the E‐region peak persist. High‐resolution AURIC calculations are in agreement with COSMIC‐1 observations and IRI‐2016 model outputs between ∼105 and 140 km while FIRI‐2018 outputs underestimate the EDP in this region. Overall, AURIC modeling shows increased E‐region electron densities when utilizing high‐resolution cross sections and high‐resolution solar irradiances, and are likely to be the key to resolving the long standing data‐model discrepancies. 

Abstract The ionospheric O⁺number density can be measured remotely during the day by observing its optically thick 83.4 nm radiance. Some ambiguity is present in the process of retrieving the density due to uncertainties in the initial excitation rate. This can be removed by observing a companion optically thin emission at 61.7 nm originating from the O⁺(3s²P) state, providing that the ratio of the initial excitation rates is known. Analyses of ICON EUV data using an 83.4/61.7 emission ratio of order 10 result in O⁺densities lower by ∼2 than other measurements. Key to relating the two emissions is accurate knowledge of the partial photoionization cross sections and the spectroscopy of O⁺—the topic of this paper. Up to now, no independent evaluation of the ratio of the 83.4/61.6 emission ratio exists. The recent availability of state‐of‐the‐art calculations of O partial photoionization cross sections into a variety of O⁺states presents an opportunity to evaluate the O⁺(2p⁴⁴P)/O⁺(3s²P) ionization rate ratio. We calculate excitation of these parent states of the emissions including both direct and cascade excitation from higher lying O⁺energy states. The resulting theoretical prediction gives ratios that range from 13.5 to 12 from solar minimum to maximum, larger than the value of 10 used by the ICON 83.4 and 61.7 nm algorithm. The higher theoretical values for the ratio reconcile the ∼2 discrepancy between simultaneous ICON and other electron density measurements. 

The MicroBooNE experiment is an 85 tonne active mass liquid argon time projection chamber neutrino detector exposed to the on-axis Booster Neutrino Beam at Fermilab. One of MicroBooNE’s physics goals is the precise measurement of neutrino interactions on argon in the 1 GeV energy regime. Building on the capabilities of the MicroBooNE detector, this analysis identifies $K^{+}$mesons, a key signature for the study of strange particle production in neutrino interactions. This measurement is furthermore valuable for background estimation for future nucleon decay searches and for improved reconstruction and particle identification capabilities in experiments such as the Deep Underground Neutrino Experiment. In this Letter, we present the first-ever measurement of a flux-integrated cross section for charged-current muon neutrino induced $K^{+}$production on argon nuclei, determined to be $7.93\pm 3.22\left(\mathrm{stat}\right)\pm 2.83\left(\mathrm{syst}\right)\times {10}^{-42}{\mathrm{cm}}^2/\mathrm{nucleon}$based on an analysis of $6.88\times {10}^{20}$protons on target. This result was found to be consistent with model predictions from different neutrino event generators within the reported uncertainties. 

Abstract The existence of three distinct neutrino flavours,ν_e,ν_μandν_τ, is a central tenet of the Standard Model of particle physics^1,2. Quantum-mechanical interference can allow a neutrino of one initial flavour to be detected sometime later as a different flavour, a process called neutrino oscillation. Several anomalous observations inconsistent with this three-flavour picture have motivated the hypothesis that an additional neutrino state exists, which does not interact directly with matter, termed as ‘sterile’ neutrino,ν_s(refs. ^3–9). This includes anomalous observations from the Liquid Scintillator Neutrino Detector (LSND)³experiment and Mini-Booster Neutrino Experiment (MiniBooNE)^4,5, consistent withν_μ → ν_etransitions at a distance inconsistent with the three-neutrino picture. Here we use data obtained from the MicroBooNE liquid-argon time projection chamber¹⁰in two accelerator neutrino beams to exclude the single light sterile neutrino interpretation of the LSND and MiniBooNE anomalies at the 95% confidence level (CL). Moreover, we rule out a notable portion of the parameter space that could explain the gallium anomaly^6–8. This is one of the first measurements to use two accelerator neutrino beams to break a degeneracy betweenν_eappearance and disappearance, which would otherwise weaken the sensitivity to the sterile neutrino hypothesis. We find no evidence for eitherν_μ → ν_eflavour transitions orν_edisappearance that would indicate non-standard flavour oscillations. Our results indicate that previous anomalous observations consistent withν_μ → ν_etransitions cannot be explained by introducing a single sterile neutrino state. 

We report results from an updated search for neutral current (NC) resonant $\mathrm{\Delta }\left(1232\right)$baryon production and subsequent $\mathrm{\Delta }$radiative decay (NC $\mathrm{\Delta }\to N\gamma$). We consider events with and without final state protons; events with a proton can be compared with the kinematics of a $\mathrm{\Delta }\left(1232\right)$baryon decay, while events without a visible proton represent a more generic phase space. In order to maximize sensitivity to each topology, we simultaneously make use of two different reconstruction paradigms, Pandora and Wire-Cell, which have complementary strengths, and select mostly orthogonal sets of events. Considering an overall scaling of the NC $\mathrm{\Delta }\to N\gamma$rate as an explanation of the MiniBooNE anomaly, our data exclude this hypothesis at 94.4% CL. When we decouple the expected correlations between NC $\mathrm{\Delta }\to N\gamma$events with and without final state protons, our data exclude an interpretation in which all excess events have associated protons at $2.0\sigma$, and are consistent with an interpretation in which all excess events have no associated protons at  $0.63\sigma$.