Search

The Arase satellite observed the precipitation of monoenergetic electrons accelerated from a very high altitude above 32,000 km altitude on 16 September 2017. The event was selected in the period when the high‐angular resolution channel of the electron detector looked at pitch angles within ∼5° from the ambient magnetic field direction, and thereby was the first to examine the detailed distribution of electron flux near the energy‐dependent loss cone at such high altitudes. The potential energy below the satellite estimated from the observed energy‐dependence of the loss cone was consistent with the energy of the upgoing ion beams, indicating that ionospheric ions were accelerated by a lower‐altitude acceleration region. The accelerated electrons inside the loss cone carried a significant net field‐aligned current (FAC) density corresponding to ionospheric‐altitude FAC of up to ∼3μA/m2. Based on the anisotropy of the accelerated electrons, we estimated the height of the upper boundary of the acceleration region to be >∼2 RE above the satellite. The height distribution of the acceleration region below the satellite, estimated from the frequency of auroral kilometric radiation, was ∼4,000–13,000 km altitude, suggesting that the very‐high‐altitude acceleration region was separated from the lower acceleration region. Additionally, we observed time domain structure (TDS) electric fields on a subsecond time scale with a thin FAC indicated by magnetic deflections. Such a TDS may be generated by the formation of double layers in the magnetotail, and its potential drop could significantly contribute (∼40%–60%) to the parallel energization of precipitating auroral electrons. Plain Language Summary: The auroral arc is produced by electrons in the magnetosphere accelerated downward by a quasi‐static electric field. The region of the electric field, so called the auroral acceleration region, is typically located just above the ionosphere, at altitudes of a few thousand kilometers. However, recent studies have shown that it can be extended to altitudes higher than 30,000 km. The mechanism and impact of such a very‐high‐altitude acceleration region remain a mystery. The high‐angular resolution electron detector on board the Arase satellite successfully measured current and energy flows carried by the electron accelerated at the very‐high‐altitude acceleration region above the satellite altitude of 32,000 km. This acceleration at very‐high‐altitudes contributed significantly to the energy flow into the ionosphere. Based on the anisotropy of the accelerated electrons, the frequency of auroral kilometric radiation, and the presence of spiky electrostatic waves, we estimate that the very‐high‐altitude acceleration region was located more than 12,000 km above the satellite as a thin charge separation layer, apart from the acceleration region below the satellite. Our results suggest that localized electric fields at very high altitudes, which were not previously associated with the aurora, can energize auroral electrons and affect auroral visibility. Key Points: We comprehensively analyzed a very‐high‐altitude (>32,000 km) auroral acceleration eventNet precipitation of accelerated electrons significantly contributes to the field‐aligned current and energy flux into the ionosphereDouble layers in the magnetotail are possible candidates for very‐high‐altitude auroral accelerations [ABSTRACT FROM AUTHOR]

Polarization and propagation characteristics of ultra‐low frequency (ULF, ≃1−1000 $\simeq 1-1000$ mHz) waves are conventionally studied using arrays of ground‐based magnetometers. However, the ground magnetometer observations are subject to distortions due to polarization rotation and spatial integration effects caused by the transition of the magnetohydrodynamic wave into an electromagnetic wave at the lower ionospheric boundary. In contrast, high‐frequency (3–30 MHz) radars, like those comprising the Super Dual Auroral Radar Network (SuperDARN), are capable of direct observations of the ULF wave characteristics at ionospheric altitudes via measuring plasma drift velocity variations caused by the wave's electric field. In this work, we use multi‐beam data from SuperDARN Hokkaido East, Hokkaido West, and Christmas Valley West radars to identify the dominant polarization modes as well as azimuthal wave numbers of evening‐night‐side‐morning ULF waves in the Pc5 frequency band (1.67–6.67 mHz) propagating over sub‐auroral and mid‐latitude regions. The observed statistical characteristics of these waves point at the solar wind dynamic pressure variations and Kelvin‐Helmholtz instability at the magnetopause as their potential principal sources, although the drift‐bounce resonance with trapped energetic ions may contribute to the small‐scale part of the observed Pc5 wave population. Plain Language Summary: Ultra‐low frequency waves (ULF, ≃1−1000 $\simeq 1-1000$ mHz) are large‐scale hydromagnetic waves, which are generated by different mechanisms and propagate in the near‐Earth's plasma environment. They contain important information about Space Weather phenomena and have been intensively studied since the late 1950s. ULF waves are routinely studied using ground‐based magnetometers, which provide data with relatively low spatial resolution and geographic coverage restricted to landmasses. In this work, we mitigate these problems by using high‐frequency (3–30 MHz) ground‐based radars comprising the Super Dual Auroral Radar Network, which provides superior spatial resolution and covers inaccessible geographic regions like the sea or mountains. Using more than 10 years of mid‐latitude data from the Hokkaido East and Hokkaido West radars (Japan) and the Christmas Valley West radar (US), we performed detailed statistical studies of ULF wave propagation characteristics in the Pc5 frequency range (1.67–6.67 mHz). These studies provide important information about the possible generation and propagation of Pc5 ULF waves in the near‐Earth's plasma environment. Key Points: Statistical characteristics of Pc5 ultra‐low frequency (ULF) waves at mid‐latitude and sub‐auroral ionosphere was studied using Super Dual Auroral Radar Network radarsObserved occurrence rate, frequency, polarization, and azimuthal m $m$‐number point at a common source of these wavesSolar wind dynamic pressure variations and Kelvin‐Helmholtz instability at the magnetopause may be the principal generation mechanisms [ABSTRACT FROM AUTHOR]

Pulsating Aurora (PsA) is one of the major classes of diffuse aurora associated with precipitation of a few to a few tens of keV electrons from the magnetosphere. Recent studies suggested that, during PsA, more energetic (i.e., sub‐relativistic/relativistic) electrons precipitate into the ionosphere at the same time. Those electrons are considered to be scattered at the higher latitude part of the magnetosphere by whistler‐mode chorus waves propagating away from the magnetic equator. However, there have been no actual cases of simultaneous observations of precipitating electrons causing PsA (PsA electrons) and chorus waves propagating toward higher latitudes; thus, we still do not quite well understand under what conditions PsA electrons become harder and precipitate to lower altitudes. To address this question, we have investigated an extended interval of PsA on 12 January 2021, during which simultaneous observations with the Arase satellite, ground‐based all‐sky imagers and the European Incoherent SCATter (EISCAT) radar were conducted. We found that, when the PsA shape became patchy, the PsA electron energy increased and Arase detected intense chorus waves at magnetic latitudes above 20°, indicating the propagation of chorus waves up to higher latitudes along the field line. A direct comparison between the irregularities of the magnetospheric electron density and the emission intensity of PsA patches at the footprint of the satellite suggests that the PsA morphology and the energy of PsA electrons are determined by the presence of "magnetospheric density ducts," which allow chorus waves to travel to higher latitudes and thereby precipitate more energetic electrons. Plain Language Summary: Pulsating Aurora (PsA) is a kind of diffuse aurora associated with periodic precipitation of energetic electrons from the near‐Earth space into the atmosphere. Recent research has shown that, during PsA events, energetic particles at the sub‐relativistic energy range precipitate into the atmosphere. We speculate that such particles are scattered by wave‐particle resonance with natural electromagnetic waves, called chorus waves, at higher magnetic latitude regions. However, there has been no experimental case of PsA during which propagation of the chorus waves to higher magnetic latitudes was confirmed; thus, we still do not fully understand when and why PsA electrons become more energetic. Here, we investigate a PsA event on 12 January 2021, simultaneously observed by the Arase satellite, ground‐based all‐sky imagers and the European Incoherent SCATter (EISCAT) radar. We found that, when the PsA shape was patchy, the energy of precipitating electrons increased and chorus waves were observed at high latitudes in the magnetosphere. Comparing the magnetospheric electron density with the PsA brightness seen from the ground, we suggest that both the PsA shape and the energy of precipitating electrons were influenced by the so‐called magnetospheric ducts, which guide chorus waves to high‐latitudes regions where they interact with more energetic electrons. Key Points: Examined simultaneous observations of Pulsating Aurora (PsA) with the Arase satellite, ground‐based all‐sky imagers, and the EISCAT radarFound a relationship among the patchy PsA, the enhanced energy of PsA electrons, and the chorus wave propagation to high‐latitudes (>20°)Arase observations suggest that the observed relationship can be explained by the ducted propagation of chorus waves [ABSTRACT FROM AUTHOR]

Recent simulation studies using the RAM‐SCB model showed that proton precipitation contributes significantly to the total energy flux deposited into the subauroral ionosphere thereby affecting the magnetosphere‐ionosphere coupling. In this study, we use the BATS‐R‐US + RAM‐SCB model to understand the evolution of ElectroMagnetic Ion Cyclotron (EMIC) waves in the inner magnetosphere, their correspondence to the proton precipitation into the subauroral ionosphere, and to assess the performance of the model in reproducing the EMIC wave‐particle interactions. During the 27 May 2017 storm, Arase and RBSP‐A satellites observed typical signatures of EMIC waves in the inner magnetosphere. Within this interval, Defense Meteorological Satellite Program (DMSP) and National Oceanic and Atmospheric Administration (NOAA)/MetOp satellites observed significant proton precipitation in the dusk‐midnight sector. Simulation results show that H‐ and He‐band EMIC waves are excited within regions of strong temperature anisotropy near the plasmapause. The simulated growth rates of EMIC waves show a similar trend to that of the EMIC wave power observed by the Arase and RBSP‐A satellites, suggesting that the model can reproduce the EMIC wave activity qualitatively. The simulated H‐band waves in the dusk sector are stronger than He‐band waves possibly due to the presence of excess protons in the boundary conditions obtained from the BATS‐R‐US code. The precipitating proton fluxes reproduced by the simulation with EMIC waves are found to agree reasonably well with the DMSP and NOAA/MetOp satellite observations. It is suggested that EMIC wave scattering of ring current ions can account for proton precipitation observed by the DMSP and MetOp satellites during the 27 May 2017 storm. Plain Language Summary: During geomagnetic storms, plasma waves are generated in the Earth's magnetosphere. Among these waves, ElectroMagnetic Ion Cyclotron (EMIC) waves can scatter protons from the ring current, causing them to precipitate into the subauroral ionosphere. Such precipitation not only affects the midlatitude ionosphere but also impacts the dynamics of the magnetosphere. Understanding the origin of magnetospheric plasma waves and how they interact with the magnetospheric populations, along with their subsequent impact on the ionosphere, is crucial for predicting space weather accurately. In our study, we combined ground and satellite observations with simulations using the BATS‐R‐US + RAM‐SCB to investigate EMIC wave‐particle interactions in the inner magnetosphere and the resulting proton precipitation during the 27 May 2017 storm. We found that EMIC waves were excited in the dusk‐midnight sector during the storm's main phase, within the regions of strong temperature anisotropy. The simulations reproduced the proton precipitation observed in the dusk‐midnight sector by the Defense Meteorological Satellite Program /National Oceanic and Atmospheric Administration MetOP satellites fairly well. The model qualitatively captured the growth of the EMIC waves during the storm and showed that the EMIC waves, by scattering the ring current, were responsible for the proton precipitation into the dusk‐midnight sector during the storm. Key Points: ElectroMagnetic Ion Cyclotron (EMIC) wave activity and proton precipitation were observed simultaneously in the dusk‐midnight sector during the 27 May 2017 stormThe BATS‐R‐US + RAM‐SCB model can capture the EMIC wave growth during the storm qualitativelyThe EMIC wave scattering of ring current ions can account for the proton precipitation in the dusk‐midnight sector during the storm [ABSTRACT FROM AUTHOR]

This is the first report of significant energization (up to 7,000 eV) of low‐energy He+ ions, which occurred simultaneously with H‐band electromagnetic ion cyclotron (EMIC) wave activity, in a direction mostly perpendicular to the ambient magnetic field. The event was detected by the Arase satellite in the dayside plasmatrough region off the magnetic equator on 15 May 2019. The peak energy of the He+ flux enhancements is mostly above 1,000 eV. At some interval, the He+ ions are energized up to ∼7,000 eV. The H‐band waves are excited in a frequency band between the local crossover and helium gyrofrequencies and are close to a linear polarization state with weakly left‐handed or right‐handed polarization. The normal angle of the waves exhibits significant variation between 0° and 80°, indicating a non‐parallel propagation. We run a hybrid code with parameters estimated from the Arase observations to examine the He+ energization. The simulations show that cold He+ ions are energized up to more than 1,000 eV, similar to the spacecraft observations. From the analysis of the simulated wave fields and cold plasma motions, we found that the ratio of the wave frequency to He+ gyrofrequency is a primary factor for transverse energization of cold He+ ions. As a consequence of the numerical analysis, we suggest that the significant transverse energization of He+ ions observed by Arase is attributed to H‐band EMIC waves excited near the local helium gyrofrequency. Key Points: Strong H‐band EMIC waves were detected in the dayside plasmatrough region off the magnetic equator by the Arase spacecraftThe H‐band waves energize cold He+ ions to levels above ∼1,000 eV in the direction perpendicular to the background magnetic fieldSimulation indicates that the ratio of the wave frequency to He+ gyrofrequency is a primary factor in the strong energization of He+ ions [ABSTRACT FROM AUTHOR]

We present the first direct evidence of an in situ excitation of drift‐compressional waves driven by drift resonance with ring current protons in the magnetosphere. Compressional Pc4–5 waves with frequencies of 4–12 mHz were observed by the Arase satellite near the magnetic equator at L ∼ 6 in the evening sector on 19 November 2018. Estimated azimuthal wave numbers (m) ranged from −100 to −130. The observed frequency was consistent with that calculated using the drift‐compressional mode theory, whereas the plasma anisotropy was too small to excite the drift‐mirror mode. We discovered that the energy source of the wave was a drift resonance instability, which was generated by the negative radial gradient in a proton phase space density at 20–25 keV. This proton distribution is attributed to a temporal variation of the electric field, which formed the observed multiple‐nose structures of ring current protons. Plain Language Summary: During magnetic storms and substorms, energetic ions are sporadically injected into the geospace, which distorts the stable population and velocity distributions of ions in space. At these moments, various plasma instabilities lead to ultra‐low frequency (ULF) wave excitations. The lowest‐frequency waves in the ULF range have a wavelength comparable to the size of the Earth and are typically analyzed using magnetohydrodynamic principles. This approach considers the plasma environment using macroscale parameters such as pressure and density. In this paper, we report a spacecraft observation of a broadband compressional ULF wave that cannot be interpreted using magnetohydrodynamics. Such waves have rarely been reported and analyzed; however, their interaction with energetic ions is important to understand magnetospheric energy dynamics. The plasma conditions were described using the kinetic theory, which involves particle velocity distributions. We observed that a drift resonance occurred between the energetic protons and waves, while the gradient instability condition was satisfied for a part of time. Therefore, we concluded that the wave was in a drift‐compressional mode excited through drift resonance and gradient instability. The interpretation of compressional waves via satellite observations of energetic ions has been receiving increasing attention to understand their excitation mechanism. Key Points: Pc4–5 compressional ultra‐low frequency waves with an azimuthal wave number of −130 were observed in the nose structure on dusksideTheoretically predicted values of drift‐compressional mode frequency match the observed wave frequencyBoth radial ion temperature gradient and drift resonance of 20–25 keV protons serve as energy sources of the wave [ABSTRACT FROM AUTHOR]

Using the Arase and Van Allen Probes satellite observations, we investigate the nonlinear electromagnetic ion cyclotron (EMIC) rising‐tone (RT) emissions with an increase of the solar wind dynamic pressure in the dayside magnetosphere. We find that EMIC RT emissions are accompanied by the extended dayside uniform zone (DUZ) over |MLAT| < 25° due to the dayside magnetospheric compression by an increase in Pdyn. Using the observed plasma and magnetic field data, we modeled the threshold amplitude for the nonlinear EMIC waves and compared it with the observation. The small gradient of the ambient magnetic field strongly contributes to the reduction in the threshold amplitude of nonlinear wave growth compared to other parameters. When the threshold amplitude falls to comparable level of pre‐existing EMIC waves, EMIC RT emissions are immediately triggered, suggesting direct evidence that the DUZ is the preferred condition to cause the nonlinear EMIC RT emission in the dayside magnetosphere. Plain Language Summary: Electromagnetic ion cyclotron (EMIC) waves play an important role in controlling the dynamics of charged particles in the inner magnetosphere. Especially, nonlinear EMIC rising‐tone (RT) emissions can cause the rapid loss of relativistic electrons and ring current ions. Here, we present direct evidence demonstrating that the distortion of the dayside magnetic field causes nonlinear EMIC RT emission in response to the intensification of the solar wind dynamic pressure. Remarkably, these nonlinear EMIC waves are generated through a reduction in the threshold wave amplitudes by the distortion of the magnetic fields, even in the absence of any significant change in the pre‐existing EMIC wave amplitude. The present result provides new insights into a triggering process of nonlinear plasma waves in the magnetosphere. Key Points: Electromagnetic ion cyclotron (EMIC) waves with rising‐tone (RT) elements were observed in the dayside magnetosphere during an increase in the solar wind dynamic pressureIncreasing solar wind dynamic pressure extends the dayside uniform zone of the magnetic field to higher magnetic latitudesThe uniform zone leads to the reduction of the nonlinear threshold wave amplitude, which triggers nonlinear EMIC RT emissions [ABSTRACT FROM AUTHOR]

Although many substorm‐related observations have been made, we still have limited insight into propagation of the plasma and field perturbations in Pi2 frequencies (∼7–25 mHz) in association with substorm aurora, particularly from the auroral source region in the inner magnetosphere to the ground. In this study, we present conjugate observations of a substorm brightening aurora using an all‐sky camera and an inner‐magnetospheric satellite Arase at L ∼ 5. A camera at Gakona (62.39°N, 214.78°E), Alaska, observed a substorm auroral brightening on 28 December 2018, and the footprint of the satellite was located just equatorward of the aurora. Around the timing of the auroral brightening, the satellite observed a series of quasi‐periodic variations in the electric and magnetic fields and in the energy flux of electrons and ions. We demonstrate that the diamagnetic variations of thermal pressure and medium‐energy ion energy flux in the inner magnetosphere show approximately one‐to‐one correspondence with the oscillations in luminosity of the substorm brightening aurora and high‐latitudinal Pi2 pulsations on the ground. We also found their anti‐correlation with low‐energy electrons. Cavity‐type Pi2 pulsations were observed at mid‐ and low‐latitudinal stations. Based on these observations, we suggest that a wave phenomenon in the substorm auroral source region, like ballooning type instability, play an important role in the development of substorm and related auroral brightening and high‐latitude Pi2, and that the variation of the auroral luminosity was directly driven by keV electrons which were modulated by Alfven waves in the inner magnetosphere. Plain Language Summary: One of the most frequent disturbances in the Earth's magnetosphere is called substorm. Through Earth's magnetic field line, the development of a magnetospheric substorm is projected onto Earth's high‐latitude ionosphere as auroral evolution. During a substorm, the energy in the tail of the magnetosphere is released to the earth, and quite a part of this energy is transmitted as different types of wave phenomena. These wave oscillations can be observed by magnetometers on the ground and satellites in the magnetosphere. It is still uncertain what mechanisms trigger these substorm‐related waves, how these waves correlate with other substorm phenomena, and how they transmit and dissipate, especially for the wave phenomena at ∼4–7 Earth radii away from the Earth. This paper presents a case study of such substorm event, where we show the variation of magnetic field and auroral luminosity on the ground, and the electromagnetic wave that is called as Pi2 pulsations and oscillation of plasma flux in the inner magnetosphere. We demonstrate that there are one‐to‐one correspondences in these oscillations. We suggest the possibility that a ballooning plasma instability triggers the observed oscillations in particle flux, as well as the electromagnetic wave that modulates the auroral luminosity. Key Points: Observations of plasma and field characteristics near the source region of a substorm auroral brightening at L ∼ 5Pi2, auroral luminosity variation and fluctuations of in‐situ electromagnetic field and particle flux were observed during substorm onsetCorrespondence between these fluctuations suggest waves in the magnetosphere like ballooning instability control auroral intensity [ABSTRACT FROM AUTHOR]

Using Arase observations of the inner magnetosphere during 26 CIR‐driven geomagnetic storms with minimum Sym‐H between −33 and −86 nT, we investigated ring current pressure development of ions (H+, He+, O+) and electron during prestorm, main, early recovery and late recovery phases as a function of L‐shell and magnetic local time. It is found that during the main and early recovery phase of the storms the ion pressure is asymmetric in the inner magnetosphere, leading to a strong partial ring current. The ion pressure becomes symmetric during the late recovery phase. H+ ions with energies of ∼20–50 keV and ∼50–100 keV contribute more to the ring current pressure during the main phase and early/late recovery phase, respectively. O+ ions with energies of ∼10–20 keV contribute significantly during main and early recovery phase. These are consistent with previous studies. The electron pressure was found to be asymmetric during the main, early recovery and late recovery phase. The electron pressure peaks from midnight to the dawn sector. Electrons with energy of <50 keV contribute to the ring current pressure during the main and early recovery phase of the storms. Overall, the electron contribution to the total ring current is found to be ∼11% during the main and early recovery phases. However, the electron contribution is found to be significant (∼22%) in the 03–09 MLT sector during the main and early recovery phase. The results indicate an important role of electrons in the ring current build up. Key Points: The first statistical study of both ring current ions (H+, He+, O+) and electrons during corotating interaction region driven storms using Arase observationsH+ is the major contributor to the total pressure with E = 20–50 keV while O+ pressure with E = 10–20 keV contributed more during main phaseElectron (E < 50 keV) contributes ∼20% to the total ring current pressure in 03–09 MLT during main and early recovery phase [ABSTRACT FROM AUTHOR]

A physical mechanism to produce pulsating aurora (PsA) has been considered to be the interaction of the electron and the chorus wave generated near the equatorial plane of the magnetosphere. A recent observation of high temporal resolution of chorus waves by the Arase satellite revealed that the presence or absence of the internal modulation of PsA, which is a characteristic sub‐second scintillation at 3 ± 1 Hz within each optical pulsation, is closely related to the discreteness of the element structure of the chorus wave. However, it is still unclear what parameters (or conditions) control the discreteness of the element and the existence of the internal modulation of PsA. In this study, we discuss parameters that determine the presence or absence of the internal modulation of PsA and element structure of chorus by showing a conjugate observation of PsA/chorus by ground‐based cameras and the Arase satellite. During the event, the occurrence of internal modulation increased temporally. The wave data from the satellite show that the repetitive frequency of elements was ∼6 Hz when the internal modulation was indistinct, while the repetitive frequency was ∼3 Hz when the internal modulation was distinct. The particle measurements suggest that this difference was caused by changes in the density and the temperature anisotropy of the hot electron. The internal modulation was clearly observed when the density of hot electrons decreased and the temperature anisotropy relaxed after the injection. Observations of internal modulations from the ground might allow us to estimate the parameters such as energetic electron density and temperature anisotropy in the magnetosphere. Key Points: We analyzed a pulsating aurora (PsA) event in which the occurrence frequency of internal modulation increased significantly with timeA conjugate observation with Arase suggests that a sudden enhancement of energetic electrons by the injection caused non‐modulated PsAsThe internal modulation may be more often observed after the injection as the density of energetic electrons decreases in the magnetosphere [ABSTRACT FROM AUTHOR]

We performed a statistical study of electromagnetic ion cyclotron (EMIC) wave distributions and their coupling with energetic protons in the inner magnetosphere using the Arase satellite data from May 2017 to December 2020. We investigated the energetic proton pitch‐angle distributions and partial thermal pressures associated with EMIC waves using inter‐calibrated proton data in the energy range of 30 eV/q–187 keV/q. With a cold plasma approximation, we computed the proton minimum resonance energies using the observed EMIC wave frequency and plasma density values. We found that the EMIC waves had left‐handed polarization near the magnetic equator close to the threshold of proton cyclotron instability, and propagated to higher latitudes along the field line with polarization reversal. H‐EMIC waves showed two peak occurrence regions in the morning and noon sectors at L = 7.5–9 outside the plasmasphere. The flux enhancements associated with morning side H‐EMIC waves appeared at E < 1 keV/q among all pitch angles, while H‐EMIC waves in the noon sector exhibited flux enhancement in field‐aligned directions at E = 1–100 keV/q. He‐EMIC waves showed a broad occurrence region from 12 to 20 magnetic local time at L = 5.5–8.5 inside the plasmasphere with strong flux enhancements at all pitch‐angle ranges at E = 1–100 keV/q. The proton minimum resonance energy using the obtained central frequency was consistent with the observed flux enhancements at different peak occurrence regions. We conclude that the free energy sources of EMIC waves in different geomagnetic environments drive various types of EMIC waves, and they interact with energetic protons at different energy ranges. Plain Language Summary: Electromagnetic ion cyclotron (EMIC) waves are considered to play an important role in controlling magnetospheric plasma dynamics. Specifically, EMIC wave‐particle interactions can cause the loss of energetic protons and relativistic electrons in the Earth's magnetosphere, and the scattered particles precipitate into the ionosphere, creating isolated proton auroras at sub‐auroral latitudes (55–65 geomagnetic latitudes). To understand the coupling of EMIC waves with energetic protons in the inner magnetosphere, we performed a statistical study of proton distributions associated with EMIC waves using a 4‐year in‐situ observation obtained by the Arase satellite. We observed dawn‐dusk asymmetric EMIC wave distributions depending on the wavebands. We also found three significantly different regions of EMIC waves showing different characteristics. EMIC waves were inferred to be generated near the magnetic equator and propagate to higher magnetic latitudes along the field line. Furthermore, EMIC waves in different regions were proposed to interact with energetic protons at different energy ranges. The Arase satellite observations used in this study provided new insights into the dynamics of EMIC waves in the inner magnetosphere. Key Points: H‐ (He‐) electromagnetic ion cyclotron (EMIC) waves are observed in the morning‐noon (afternoon) sector outside (inside) the plasmasphereEMIC waves are generated at the magnetic equator near the threshold of proton cyclotron instability and propagate to higher latitudesThe energy ranges of the observed proton pitch angle scatter coincide with the resonance energy using the central EMIC wave frequency [ABSTRACT FROM AUTHOR]

Auroral brightening is one of the most common phenomena that occur during substorm onset and is usually recognized as a projection of the substorm‐associated magnetospheric plasma dynamics to the ionosphere. However, electromagnetic fields and plasma features associated with the substorm brightening arc have not been well understood. In this study, we present a comprehensive observation of the source plasma and field variations of a substorm brightening aurora in the inner magnetosphere. We performed a unique conjugate observation of a substorm brightening auroral arc observed by a ground‐based camera and by the Arase satellite in the magnetospheric source region at L ∼ 6. The event was observed at Tromsø (69.6°N, 19.2°E), Norway, on 12 October 2017. The brightening arc indicates east‐west structures with longitudinal scales of ∼0.5°–2.0°. Field‐aligned bi‐directional electrons with an energy range between 66 and 1,800 eV were detected by the satellite, simultaneously with the appearance of the brightening arc in the camera. These electrons were probably supplied from the auroral brightening region in the ionosphere, indicating that the satellite was on the same field line of the brightening aurora. The magnetic and electric field data show characteristic fluctuations and earthward Poynting flux around the time that the satellite crossed the aurora. Anti‐phase oscillations between the thermal pressure and the magnetic pressure are also reported. Based on these observations, we suggest the possibility that a ballooning instability occurred in the source region of the substorm brightening arc in the inner magnetosphere at L ∼ 6. Plain Language Summary: A frequently occurring source of variations in the magnetosphere is the substorm, a process that causes energy dissipation into the atmosphere. Substorm is presented as the development of aurorae at high latitudes in the ionosphere. The study of substorm processes helps in understanding the near‐Earth space environment and the space weather. Along Earth's magnetic field lines, the aurora at a latitude of ∼65°N can be traced to ∼4–7 Earth radii away from the Earth at the equatorial plane in space. Using a ground‐based auroral camera, we can construct the correspondence between auroral motion and field and plasma variation at the satellite. This study reports such a unique event of substorm brightening arc observed at Tromsø, Norway, on 12 October 2017. Satellite observed bi‐directional electrons prove the connection between aurora break‐up at ∼100 km altitude and its source region in the magnetosphere at ∼30,000 km away from Earth. Based on the magnetic wave spectrograms, auroral bead‐like structures and other observational results, we suggest the possibility that a ballooning plasma instability occurred in the source region of the substorm brightening arc in the inner magnetosphere. Key Points: Observation of plasma and field features in the source region of a sudden brightening auroral arc during a minor substorm onset at L ∼ 6Energization of particles, field‐aligned electrons, and electromagnetic field fluctuations were observed during the arc crossing by AraseSeveral observational facts indicate the possibility of ballooning instability occurring at this substorm onset [ABSTRACT FROM AUTHOR]

Microbursts are impulsive (<1 s) injections of electrons into the atmosphere, thought to be caused by nonlinear scattering by chorus waves. Although attempts have been made to quantify their contribution to outer belt electron loss, the uncertainty in the overall size and duration of the microburst region is typically large, so that their contribution to outer belt loss is uncertain. We combine datasets that measure chorus waves (Van Allen Probes [RBSP], Arase, ground‐based VLF stations) and microburst (>30 keV) precipitation (FIREBIRD II and AC6 CubeSats, POES) to determine the size of the microburst‐producing chorus source region beginning on 5 December 2017. We estimate that the long‐lasting (∼30 hr) microburst‐producing chorus region extends from 4 to 8 Δ ${\Delta}$MLT and 2–5 Δ ${\Delta}$L. We conclude that microbursts likely represent a major loss source of outer radiation belt electrons for this event. Plain Language Summary: Microbursts are short‐duration (<1 s) bursts of electrons that precipitate from the magnetosphere into the atmosphere. Microbursts are thought to be a result of scattering by a plasma wave called chorus. Attempts have been made to understand the contribution microburst precipitation has on electron loss, which helps the outer radiation belt recover after enhancements during storms. The contribution depends on the overall size and duration of the microburst region. We combine datasets that measure chorus waves and microburst precipitation to determine the size and duration of a microburst region beginning on 5 December 2017. Our results show that microbursts are likely a significant source of electron loss. Key Points: We use multipoint observations to estimate the size of a long‐lasting microburst‐producing chorus region beginning on 5 December 2017We estimate that the microburst‐producing chorus region for this event extends from 4 to 8 Δ ${\Delta}$MLT and 2–5 Δ ${\Delta}$LMicroburst precipitation from this event likely constitutes a major source of electron loss from the outer radiation belt [ABSTRACT FROM AUTHOR]

Plasmaspheric hiss can cause energetic electron precipitation from the magnetosphere to the Earth's upper atmosphere and affect the ionospheric electron density profiles. In this study, we use Arase satellite measurements in the dayside plasmasphere to model the electron precipitation and the resultant ionospheric response, and compare the results to the electron density measured by the Poker Flat Incoherent Scatter Radar (PFISR). We analyzed two close conjunction events between Arase and PFISR at L ∼ 6 in the afternoon sector, when Arase was in the outer plasmasphere and traveled into the plasmaspheric plumes. Modest or strong hiss waves were observed with amplitudes higher than 50 pT during both events. Quasilinear modeling suggests that the hiss waves could cause intense electron precipitation ranging from several keV to several hundred keV energies. The electron density profiles at 60–90 km modeled by the Boulder Electron Radiation to Ionization (BERI) model suggest significant electron density enhancements due to the precipitating electrons. PFISR simultaneously observed electron density enhancements during both events, and provided evidence for the electron precipitation at altitudes down to <70 km. The temporal modulation of hiss caused the modulated density profiles in BERI modeling, but was not evident in PFISR observations. The modeled altitude profiles of the perturbed electron density overall agree with PFISR observation. At altitudes below 75 km, the modeled electron densities are lower than the observation, suggesting additional high energy electron precipitation possibly due to low frequency (<50 Hz) waves or hiss wave powers ducted to high latitudes. Key Points: Two Poker Flat Incoherent Scatter Radar (PFISR)‐Arase conjunction events are identified at the dayside plasmasphere when hiss wave amplitudes reach 50–100 pT at L ∼ 6Hiss‐driven electron precipitation obtained from quasilinear simulation is used to model ionospheric density profiles at 60–90 km altitudeModeled electron densities overall agree with PFISR observations with differences in the temporal modulation and at altitudes below 75 km [ABSTRACT FROM AUTHOR]

We present an example of one‐to‐one correspondence between poleward moving auroral arcs (PMAAs) and Pc5 oscillations observed at the Time History of Events and Macroscale Interactions during Substorms (THEMIS) Ground Based Observatory station Gillam. The PMAAs consisted of four successive intensifications (named PMAA1, PMAA2, PMAA3 and PMAA4) with a period of 3∼4 min over the magnetic latitudes from 68° to 70° in the auroral oval and varied coherently with the H‐component of magnetic field Pc5 oscillations. PMAA1 and PMAA2 appeared clearly at the magnetic latitude ∼69°, and the following two PMAAs, which were dimmer, appeared at the magnetic latitude ∼68°. PMAA1 and PMAA2 exhibited features of field‐line resonances with the maximum luminosity at the magnetic latitude ∼69.5° and ∼69.4°, respectively. The ground Pc5 oscillations were concurrent with toroidal mode Pc5 oscillation observed at the THEMIS‐D, ‐E, and ‐A satellites at ∼4 MLT in the outer magnetosphere. The magnetic and electric field oscillations at THEMIS were synchronized with the PMAAs. The magnetic energy of the THEMIS Pc5 oscillations is estimated using a numerical model of damped toroidal oscillations and compared with the kinetic energy of precipitating electrons associated with the field aligned current carried by the toroidal oscillations. The result reveals that the Pc5 magnetic energy is much larger than the kinetic energy, implying the magnetic energy is important for producing auroral emissions in the ionosphere. We also perform a simulation of the relationship between PMAAs and toroidal mode Pc5 oscillations. The simulation explains the observed spatial and temporal structures of the PMAAs. Plain Language Summary: Aurora are a fascinating phenomenon observed in the polar region of the earth. The auroral emission is caused by the excitation of neutral oxygen atoms and nitrogen molecules in the ionosphere through collision with precipitating electrons from higher altitudes traveling along the magnetic field lines. The precipitating electrons need to have energies of order keV in order to produce auroral emissions. The energy is higher than that of solar wind electrons even after they are heated on passing through the bow shock in front of the magnetosphere. However, how the electrons gain the required high energy is not fully understood. The present study discusses a possible mechanism for the electron acceleration through analysis of the relationship between periodic auroral brightening detected by an all‐sky imager and ultralow frequency hydromagnetic (Alfvén) waves detected by the THEMIS spacecraft and a ground magnetometer. The emphasis is placed on the importance of the magnetic energy of Alfvén waves. We find that the magnetic energy is larger than the kinetic energy of the precipitating electrons, implying that the magnetic energy is important for acceleration of auroral electrons. A simulation of this process explains the spatial and temporal structure of the observed auroral emissions. Key Points: We observed concurrent occurrence of poleward moving auroral arcs (PMAAs) and Pc5 oscillations on the ground and in the magnetosphereWe evaluated magnetic energy of Pc5 oscillations and compared it with kinetic energy of precipitating electrons along the field lineThe magnetic energy of Pc5 oscillations is important for auroral emission and simulated the spatial and temporal structures of PMAAs [ABSTRACT FROM AUTHOR]

The auroral acceleration region plays an important role in the magnetosphere‐ionosphere coupling system. In this study, signatures of an auroral U‐shaped potential structure were found for the first time in the near‐equatorial inner magnetosphere by the Arase satellite at ∼6.0 RE geocentric distance and 11° magnetic latitude. The observed magnetic and electric field variations corresponded to the equatorward motion of the upward field‐aligned current and converging perpendicular electric field. Examining the three‐dimensional velocity distribution function of H+ and O+ ions, we demonstrate that upflowing ion beams were significantly deflected in an east‐west direction with a perpendicular velocity up to ∼80 km/s, which is consistent with the ExB drift velocity. A simple particle drift model with the inferred auroral perpendicular potential presents a new kink‐like drift path of ions from the magnetotail, implying that the auroral potential structure has a great impact on particle dynamics in the near‐earth plasma sheet. Plain Language Summary: The auroral arc involves multiple physical processes over a wide altitude range in the upper atmosphere. While the primary energy sources are at high altitudes, the accelerated electrons that are directly responsible for auroral emissions are mainly produced at lower altitudes. In the region where the electrons are accelerated downward, known as the auroral acceleration region, a peculiar electric field structure is formed. We clarified whether this electric field structure exists up to near the energy source region and how it affects the plasma dynamics by an in situ observation by the Arase satellite. We found for the first time that ions accelerated from below the satellite were supplied to the energy source region, and were deflected by the observed auroral electric field structure. Our model calculation shows that the electric field structure can significantly meander the motion of the entire near‐Earth space plasma as it flows toward the Earth. Our result invites a new perspective that the structure of the electric field from low altitudes associated with the auroral arc has a significant impact on the dynamics of near‐Earth space plasmas. Key Points: Signatures of an auroral U‐shaped potential structure were found first in the near‐equatorial inner magnetosphere by the Arase satelliteUpflowing ion beams, especially O+ ion beams, were significantly deflected from field lines by a converging perpendicular electric fieldThe converging electric field and ion beam potentially affect the particle dynamics in the near‐Earth plasma sheet [ABSTRACT FROM AUTHOR]

We conduct a statistical analysis on nighttime medium‐scale traveling ionospheric disturbances (MSTIDs) using the Super Dual Auroral Radar Network (SuperDARN) Hokkaido East (43.53°N, 143.61°E) high‐frequency (HF) radar data from 2009 to 2019 and the SuperDARN Hokkaido West (43.54°N, 143.61°E) HF radar data from 2016 to 2019. We analyze the line‐of‐sight Doppler velocity data, corresponding to the magnitude of the polarization electric field associated with nighttime MSTIDs. We find that the propagation direction of the nighttime MSTIDs is mainly southwestward and rotates clockwise with progressing local time. In addition, we identify a negative correlation between the nighttime MSTIDs amplitude and the solar F10.7 index. These tendencies can be explained by the Perkins instability, which is considered to be associated with the growth of nighttime MSTIDs. This study is the first to find the solar activity dependence of the polarization electric field fluctuations associated with the nighttime MSTIDs. Plain Language Summary: Medium‐scale traveling ionospheric disturbances (MSTIDs) are propagating wave‐like electron density disturbances in the ionosphere. Previous studies have shown nighttime MSTIDs propagate mainly southwestward and the propagation direction changes clockwise with progressing local time at mid‐latitude. However, statistical studies using long‐term data are few in number, and long‐term trends, such as solar activity dependence, are still unknown. In this study, we report the results of statistical analysis on the characteristics of nighttime MSTIDs using long‐term data from the Super Dual Auroral Radar Network (SuperDARN) Hokkaido pair of radars. The nighttime MSTIDs in the northern region of Hokkaido have the same propagation characteristics with the MSTIDs in the other midlatitude region. In addition, the nighttime MSTID amplitude has a negative correlation with solar activity. Key Points: Long‐term analysis on nighttime medium‐scale traveling ionospheric disturbances (MSTIDs) was conducted using the SuperDARN Hokkaido pair of radarsSeasonal and local time dependences were analyzed and these results were consistent with theoretical expectations of the Perkins instabilityNegative correlation between the MSTID amplitude and solar activity was found [ABSTRACT FROM AUTHOR]

We present an observation of rapid flux depressions in relativistic electrons, which is referred to as "EMIC‐induced drifting electron holes (EDEHs)." The Arase, Van Allen Probes, and THEMIS detected simultaneously electron flux fluctuations. The time variation of flux shows depressions of 1‐min scale with energy dispersion, which appear only in the relativistic energy range and small pitch angles. These characteristics of the flux depression indicate that electromagnetic ion cyclotron waves caused pitch angle scattering on a short time scale in a longitudinally limited region. The Arase satellite detected the local depression of the phase space density of 1,000 MeV/G electron, indicating that EMIC waves cause the true loss of electrons. Tracing the energy dispersion profile of EDEHs, we show that EDEHs are formed at localized region in the dusk side. Multisatellite observations demonstrate that a series of EDEHs eventually cause a substantial depression of the radiation belt on 1‐hr time scale. Plain Language Summary: This study focuses on the electrons with energies ranging from hundreds of keV to several MeV in the Earth's radiation belt. This study reports the observation of "EMIC‐induced drifting electron holes (EDEHs)" in electron flux near‐simultaneously detected by four satellites: Arase, Van Allen Probes A and B, and THEMIS‐A. EDEHs were caused by localized electron precipitation induced by structured electromagnetic ion cyclotron waves. The observation of EDEHs clearly shows the energy range of the loss process, the magnitude of the loss, and the longitudinal range. Our results highlight that the detection of EDEHs provides a way of monitoring the macroscopic dynamics of the magnetosphere through particle acceleration, loss, and transport. Key Points: "EMIC‐induced drifting electron hole (EDEH)" was simultaneously detected by four satellites in the radiation beltThe radial profiles of phase space density indicate the local losses of relativistic electrons caused by EMIC wavesMultisatellite observations reveal that the flux at L* = 5.2–5.4 gradually decreases in a few tens of minutes [ABSTRACT FROM AUTHOR]

Flux enhancements of field‐aligned low‐energy O+ ion (FALEO) are simultaneously observed by Arase, Van Allen Probes A and B in the nightside inner magnetosphere during 05–07 UT on September 22, 2018. FALEOs appear after a magnetic dipolarization signature with approximately 6–20 min delay. It has the energy‐dispersion signature from a few keV to ∼100 eV only in the direction parallel to the magnetic field at Arase, while it decreases its energy from a few keV down to 10 eV in both the parallel and antiparallel directions at Probes A and B. We perform a numerical simulation to trace trajectories of test O+ ions in a model magnetosphere, which are launched from above the ionosphere 3–15 min after a substorm. Flying virtual satellites that have the same orbits as the real satellites, we create virtual energy‐time spectrograms of O+ ions to compare with the observed ones. Results show a very good correspondence between them, indicating that FALEOs originate from ionospheric O+ ions that are extracted from the upper ionosphere at substorm onset and flow along the magnetic field toward the geomagnetic equator. It is also revealed that 3–9 hr after their launch, test O+ ions less than 400 eV have a spatial distribution in the inner magnetosphere which is similar to those of the warm plasma cloak and the oxygen torus. We therefore conclude that FALEO is a source of those cold ion populations. Key Points: Flux enhancements of field‐aligned low‐energy O+ ion (FALEO) are simultaneously observed by Arase, Van Allen Probes A and BNumerical simulation well reproduces observed energy‐time spectrograms of FALEO with the energy‐dispersed signature from 1 keV to 10 eVFALEO is a source of the warm plasma cloak and the oxygen torus that appear in the dawn to noon sectors [ABSTRACT FROM AUTHOR]

O+ ions make a significant contribution to plasma pressure in the inner magnetosphere during magnetic storms. The storm-time O+ enhancements are primarily caused by enhanced supply from the ionosphere and preferential energization in the magnetotail. In order to characterize the magnetotail process that dominates the energization, we examine differences in energy spectra of energetic 10-180 keV/q ions between different ion species, namely H+, He++, He+. O++, and O+. We use observations made by the MEP-i instrument on the Arase (ERG) spacecraft on the nightside in the radial distance range of ~5-~7 Re during the main and early recovery phases of the May and July 2017 storms. The comparisons of energy spectra show that, for the same charge states, heavier ions are more energized than lighter ions. For the same mass, lowercharge-state ions are more energized than higher-charge-state ions. The spectra exhibit a sharp decrease at high energies for all ion species, while the spectra for more energized ions were shifted toward higher energies, compared to those for less energized ions. The results suggest that the preferential energization is due to temperature increases rather than the generation of energetic ions in the high-energy tail. Considering temporal and spatial scales of heavy ion kinetic motions, we conclude that the preferential energization of lowercharge-state heavier ions occurs during the course of dipolarization, likely due to non-adiabatic heating in the near-Earth plasma sheet, effective trapping during transport by localized flow channels, and/or non-adiabatic acceleration within the near-Earth flow-braking region. Plain Language Summary Plasma in the Earth's magnetosphere consists primarily of electrons, protons, and singly charged oxygen ions of ionospheric origin, O+, but other ions such as He++ of solar wind origin and He+ and O++ of ionospheric origin exist and are observable. The shape and evolution of an energy spectrum, which presents the number of particles as a function of particle kinetic energy, help us identify physical processes of plasma transport, heating, and acceleration in the magnetosphere. This study compares energy spectra between different mass or charge state ions observed by the Arase spacecraft during two magnetic storms that occurred in 2017. The differences seen in the spectral shape indicate that lower-chargestate heavier ions gain more energy in the near-Earth magnetotail. The preferential energization likely occurs during the course of magnetic field reconfiguration (from stretched to dipole-like), suggesting the importance of local kinetic motions of heavy ions in global magnetotail-inner magnetospheric dynamics. [ABSTRACT FROM AUTHOR]

We present observations of an equatorward detachment of the auroral arc from the main oval and magnetically conjugate measurements made by the Arase satellite in the inner magnetosphere. The all‐sky imager at Gakona (magnetic latitude = 63.6°N), Alaska, shows the detachment of the auroral arc in both red and green lines at local midnight (∼0130–0230 MLT) on 30 March 2017. The electron density derived from the Arase in‐situ observations shows that this arc occurred outside the plasmapause. At the arc crossing, the electron flux of energies ∼0.1–2 keV is found to be locally enhanced at L∼4.3–4.5. We estimated auroral intensities for both red and green lines by using the Arase low‐energy (0.1–19 keV) electron flux data. The peak latitude of the estimated intensity shows reasonably good correspondence with the observed intensity mapped at the ionospheric footprints of the Arase satellite. These findings indicate that the observed arc detachment at Gakona was associated with the localized enhancement of low‐energy electrons (∼0.1–2 keV) at the inner edge of the electron plasma sheet. Further, we employ the simulation results of the Community Coordinated Modeling Center (CCMC), the BATS‐R‐US–CIMI 3‐D MHD code to understand the conditions in the inner magnetosphere around the time of detachment. Although the simulation could not reproduce the lower‐energy component responsible for the arc detachment, it successfully reproduced two earthward convection events at the lower radial distance (R) (R ≤ ∼4) around the time of arc detachment and the features of enhanced convection in similarity with the observations. Key Points: Conjugate measurements of an equatorward detachment of the auroral arc from the main oval and the Arase satellite in the inner magnetosphereEquatorward detachment of the auroral arc coincided with a localized enhancement of electrons of energies ∼0.1–2 keV deeper down to L∼4.3–4.5BATS‐R‐US–CIMI model successfully reproduced the enhancement of lower‐energy electrons (∼8–40 keV) at a lower radial distance (R < 4) [ABSTRACT FROM AUTHOR]

Resonant interactions of energetic electrons with electromagnetic whistler‐mode waves (whistlers) contribute significantly to the dynamics of electron fluxes in Earth's outer radiation belt. At low geomagnetic latitudes, these waves are very effective in pitch angle scattering and precipitation into the ionosphere of low equatorial pitch angle, tens of keV electrons and acceleration of high equatorial pitch angle electrons to relativistic energies. Relativistic (hundreds of keV), electrons may also be precipitated by resonant interaction with whistlers, but this requires waves propagating quasi‐parallel without significant intensity decrease to high latitudes where they can resonate with higher energy low equatorial pitch angle electrons than at the equator. Wave propagation away from the equatorial source region in a non‐uniform magnetic field leads to ray divergence from the originally field‐aligned direction and efficient wave damping by Landau resonance with suprathermal electrons, reducing the wave ability to scatter electrons at high latitudes. However, wave propagation can become ducted along field‐aligned density peaks (ducts), preventing ray divergence and wave damping. Such ducting may therefore result in significant relativistic electron precipitation. We present evidence that ducted whistlers efficiently precipitate relativistic electrons. We employ simultaneous near‐equatorial and ground‐based measurements of whistlers and low‐altitude electron precipitation measurements by ELFIN CubeSat. We show that ducted waves (appearing on the ground) efficiently scatter relativistic electrons into the loss cone, contrary to non‐ducted waves (absent on the ground) precipitating only <150 keV electrons. Our results indicate that ducted whistlers may be quite significant for relativistic electron losses; they should be further studied statistically and possibly incorporated in radiation belt models. Key Points: Near‐equatorial and ground‐based measurements of whistler‐mode waves are accompanied by relativistic electron precipitationIn the presence (absence) of ducted wave propagation, as monitored by propagation to the ground, the precipitating electron energies are above (below) 150 keVDucted whistler‐mode waves may play a key role in relativistic electron loss in the inner magnetosphere [ABSTRACT FROM AUTHOR]

The present study examines the low‐energy ion flux variations observed by the Arase satellite in the inner magnetosphere. From the magnetic field and ion flux data obtained by the fluxgate magnetometer and the low‐energy particle experiments–ion mass analyzer onboard Arase, we find 55 events of the low‐energy O+ flux enhancement accompanied with magnetic field dipolarization in the periods of April 1–October 31, 2017 and July 1, 2018–January 31, 2019. The low‐energy O+ flux enhancements (a) start a few minutes after the dipolarization onset, (b) have energy‐dispersed signatures with decreasing energy from a few keV down to ∼10 eV, (c) are observed in both storm and non‐storm periods, (d) have a field‐aligned distribution (α ∼ 0° in the southern hemisphere and α ∼ 180° in the northern hemisphere), (e) are accompanied by the low‐energy H+ flux enhancements that have lower energies than O+ by a factor of 3–10, and (f) increase the O+ density and the O+/H+ density ratio by ∼10 times and 4–5 times, respectively. We perform a numerical simulation to trace ion trajectories forward in time from the Arase positions. It is revealed that both H+ and O+ ions drift eastward and reach the dawn‐to‐morning sector without being lost in the ionosphere, if the pitch angle scattering effect is considered near the equatorial plane. This result suggests that these low‐energy field‐aligned ions can contribute to formation of the warm plasma cloak. Key Points: O+ flux enhancements that have energy‐dispersed signatures at <∼5 keV appear a few minutes after magnetic field dipolarizationThe lowest energy of ∼10 eV and a field‐aligned distribution of the O+ flux enhancements suggest prompt extraction from the ionosphereThe field‐aligned low‐energy O+ flux enhancements can be a source of the warm plasma cloak [ABSTRACT FROM AUTHOR]

This study investigates the characterization and calibration of the high‐energy electron experiments (HEP) instrument onboard the exploration of energization and radiation in geospace (ERG). Two detector modules, HEP‐L and HEP‐H, which employ stacks of multichannel silicon strip detectors, detect electrons in the energy ranges of 70 keV–1 MeV and 700 keV–2 MeV, respectively. The detector response to electron irradiation needs to be assessed to obtain accurate electron fluxes from these detectors. In this study, we perform Monte Carlo simulations using the Geant4 particle simulation tool to reconstruct incident electron fluxes from detected count rates. Based on the simulation results, we investigate the response characteristics of the detectors when electrons with a certain range of energy are irradiated onto them. A response function is constructed by combining the simulation results for different incident energies. A response matrix is calculated by binning the response function according to the energy channels of the detector, and an inverse matrix derived from the response matrix is used to calibrate the observational data. Compared with the data obtained from another electron instrument onboard the Arase satellite (MEP‐e), whose energy range overlaps with that of the HEP, the differential flux data for the overlapping energy range (85–95 keV) are consistent with each other. The basic characteristics of the HEP detectors are thus confirmed to provide well‐calibrated data. Key Points: Arase high‐energy electron instrument (HEP) observational data (70 keV–2 MeV) is calibrated using a Geant4 simulationA new "inverse matrix calibration" method is developed for this calibrationThe calibrated HEP data shows good agreement with the data from MEP‐e that is a lower energy electron instrument onboard Arase satellite [ABSTRACT FROM AUTHOR]

An energy spectrum of electrons from 180 to 550 keV precipitating into the dayside polar ionosphere was observed under a geomagnetically quiet condition (AE ≤ 100 nT, Kp = 1‐). The observation was carried out at 73–184 km altitudes by the HEP instrument onboard the RockSat‐XN sounding rocket that has been launched from Andøya, Norway. The observed energy spectrum of precipitating electrons follows a power law of −4.9 ± 0.4 and the electron flux does not vary much over the observation period (∼274.4 s). A nearby ground‐based VLF receiver observation at Lovozero, Russia shows the presence of whistler‐mode wave activities during the rocket observation. A few minutes before the RockSat‐XN observation, POES18/MEPED observed precipitating electrons, which also suggest whistler‐mode chorus wave activities at the location close to the rocket trajectory. A test‐particle simulation for wave‐particle interactions was carried out using the data of the Arase satellite as the initial condition which was located on the duskside. The result of the simulation shows that whistler‐mode waves can resonate with sub‐relativistic electrons at high latitudes. These results suggest that the precipitation observed by RockSat‐XN is likely to be caused by the wave‐particle interactions between whistler‐mode waves and sub‐relativistic electrons. Plain Language Summary: Sub‐relativistic electrons precipitating into the Earth's dayside polar ionosphere are observed by a sounding rocket under geomagnetically quiet conditions. An energy spectrum of these electrons in an energy range from 180 to 550 keV is reported at the rocket altitude. A possible mechanism for generating this precipitation is the resonance scattering of electrons by whistler‐mode waves, which we conducted a test‐particle simulation based on the ground and satellite observations. Key Points: A sounding rocket observed an energy spectrum of sub‐relativistic electron precipitation in the dayside polar ionosphere during quiet timeGround and satellite observations suggest that the precipitation observed by RockSat‐XN was caused by the whistler‐mode wavesA test‐particle simulation for wave‐particle interactions based on the data of the Arase satellite supports the RockSat‐XN observation [ABSTRACT FROM AUTHOR]

We present the results of a multi‐point and multi‐instrument study of electromagnetic ion cyclotron (EMIC) waves and related energetic proton precipitation during a substorm. We analyze the data from Arase (ERG) and Van Allen Probes (VAPs) A and B spacecraft for an event of 16 and 17 UT on December 1, 2018. VAP‐A detected an almost dispersionless injection of energetic protons related to the substorm onset in the night sector. Then the proton injection was detected by VAP‐B and further by Arase, as a dispersive enhancement of energetic proton flux. The proton flux enhancement at every spacecraft coincided with the EMIC wave enhancement or appearance. This data show the excitation of EMIC waves first inside an expanding substorm wedge and then by a drifting cloud of injected protons. Low‐orbiting NOAA/POES and MetOp satellites observed precipitation of energetic protons nearly conjugate with the EMIC wave observations in the magnetosphere. The proton pitch‐angle diffusion coefficient and the strong diffusion regime index were calculated based on the observed wave, plasma, and magnetic field parameters. The diffusion coefficient reaches a maximum at energies corresponding well to the energy range of the observed proton precipitation. The diffusion coefficient values indicated the strong diffusion regime, in agreement with the equality of the trapped and precipitating proton flux at the low‐Earth orbit. The growth rate calculations based on the plasma and magnetic field data from both VAP and Arase spacecraft indicated that the detected EMIC waves could be generated in the region of their observation or in its close vicinity. Plain Language Summary: Electromagnetic ion cyclotron (EMIC) waves are believed to play a significant role in the dynamics of energetic protons and relativistic electrons in the Earth's magnetosphere. The properties of these waves are being intensively studied. We consider the conditions of the EMIC wave generation and the dynamics of the wave source during a substorm event using a unique configuration of three spacecraft (Arase and two Van Allen Probes). All spacecraft were at approximately the same distance from the Earth, forming a chain across the evening local time sector. Analyzing parameters of the wave generation obtained from in situ measured proton distribution function, we came to the conclusion that the waves could be generated within the substorm area, sometimes close to, but not necessary at the spacecraft location. As the substorm expands in longitude, the EMIC wave source exhibits a longitudinal drift. When substorm expansion stops, the wave generation region expands due to the magnetic drift of protons injected during the substorm. The observed wave properties show that the waves are able to precipitate energetic protons into the atmosphere. This is confirmed by observations of low orbiting satellites measuring proton precipitating fluxes. Key Points: Westward propagation of the EMIC wave generation region is due to both the substorm expansion and azimuthal drift of injected protonsStrong pitch‐angle diffusion regime is confirmed by observations of proton fluxes at low altitude and the diffusion coefficient calculationThe diffusion coefficient maximum corresponds well to the energy range of the observed proton precipitation [ABSTRACT FROM AUTHOR]

Understanding the physical processes that control the dynamics of energetic particles in the inner magnetosphere is important for both space-borne and ground-based assets essential to the modern society. The storm time distribution of ring current particles in the inner magnetosphere depends strongly on their transport in the evolving electric and magnetic fields along with particle acceleration and loss. In this study, we investigated the ring current particle variations using observations and simulations. We compared the ion (H+, He+, and O+) and electron flux and plasma pressure variations from Arase observations with the self-consistent inner magnetosphere model: Ring current Atmosphere interactions Model with Self Consistent magnetic field (RAM-SCB) during the 7-8 November 2017 geomagnetic storm. We investigated the contribution of the different species (ions and electrons) to the magnetic field deformation observed at ground magnetic stations (09°-45° MLat) using RAM-SCB simulations. The results show that the ions are the major contributor with ~88% and electrons contribute ~12% to the total ring current pressure. It is also found that the electron contribution is non-negligible (~18%) to the ring current in dawn-side during the main phase of the storm. Thus, the electron contribution to the storm time ring current is important and should not be neglected. [ABSTRACT FROM AUTHOR]

During the magnetic storm starting on September 7, 2017, the MEP‐i instrument onboard the Arase (ERG) satellite observed molecular ions (O2+/NO+/N2+) in the ring current. The molecular ions were observed by Arase in four orbits during this magnetic storm. This indicates that there was a continuous molecular ion supply from the ionosphere. During the storm main phase around the second Dst minimum (∼−100 nT) on September 8, 2017, the European Incoherent Scatter (EISCAT) radar observed the ion upflow (∼50–150 m s−1) in the low‐altitude (250–350 km) ionosphere together with strong ion heating up to >2,000 K. The convective electric field derived from the electron heating observed by EISCAT at an altitude of approximately 110 km was also enhanced by a factor of 2. The observations suggest that the additional ion heating at low altitudes helps to cause the fast upflow and transport molecular ions upward. The flux decreases from 280 to 350 km altitudes due to the dissociative recombination was estimated to be approximately two orders of magnitude. This resulted in significant molecular ion flux remaining at 350 km altitude. These results suggest that the low‐altitude ion upflow caused by the ion frictional heating enables molecular ions to escape to space against rapid loss by the dissociative recombination. Plain Language Summary: Molecular ions (O2+/NO+/N2+) in the ring current are sometimes observed during magnetic storms. These molecular ions come from the deep ionosphere and considered good tracers of escape mechanisms from the Earth's ionosphere to the magnetosphere. However, it has not been revealed how these molecular ions are transported upward, especially by ion upflows in the low‐altitude ionosphere (∼250–350 km). It is difficult to transport sufficient flux of molecular ions due to deceleration by the strong gravitational force and rapid decrease by dissociative recombination even during magnetic storms. In this paper, we report the analysis results of the fast ion upflow (∼100 m s−1) event in the low‐altitude ionosphere observed by the European Incoherent Scatter (EISCAT) radar, while the Arase (ERG) satellite observed molecular ions in the inner magnetosphere during the magnetic storm starting on September 7, 2017. The results suggest that ion frictional heating created the ion upflow and could be a source of outflows at higher altitudes in the ionosphere to supply the molecular ions into the magnetosphere. Key Points: Arase satellite observed molecular ions in the ring current during the magnetic storm starting on September 7, 2017An ion upflow from the deep ionosphere was observed with enhancements of electric field and ion temperature by EISCATThe fast upflow caused by the ion frictional heating enables molecular ions to escape to space against dissociative recombination [ABSTRACT FROM AUTHOR]

The temporal variation of the energetic electron flux distribution caused by whistler mode chorus waves through the cyclotron resonant interaction provides crucial information on how electrons are accelerated in the Earth's inner magnetosphere. This study employs a data-driven test-particle simulation which demonstrates that the rapid change of energetic electron distribution observed by the Arase satellite cannot be simply explained by a quasi-linear diffusion mechanism, but is essentially caused by nonlinear scattering: the phase trapping and the phase dislocation. In response to upper-band whistler chorus bursts, multiple nonlinear interactions finally achieve an efficient flux enhancement of electrons on a time scale of the chorus burst. A quasi-linear diffusion model tends to underestimate the flux enhancement of energetic electrons as compared with a model based on the realistic dynamic frequency spectrum of whistler waves. It is concluded that the nonlinear phase trapping plays an important role in the rapid flux enhancement of energetic electrons observed by Arase. [ABSTRACT FROM AUTHOR]

Whistler mode chorus waves scatter magnetospheric electrons and cause precipitation into the Earth's atmosphere. Previous measurements showed that nightside chorus waves are indeed responsible for diffuse/pulsating aurora. Although chorus waves and electron precipitation have also been detected on the dayside, their link has not been illustrated (or demonstrated) in detail compared to the nightside observations. Conventional low-altitude satellite observations do not well resolve the energy range of 10–100 keV, hampering verification on resonance condition with chorus waves. In this paper we report observations of energetic electrons with energies of 30–100 keV that were made by the electron sensor installed on the NASA's sounding rocket RockSat-XN. It was launched from the Andøya Space Center on the dayside (MLT ∼ 11 h) at the L-value of ∼7 on January 13, 2019. Transient electron precipitation was observed at ∼50 keV with the duration of <100 s. The VLF receiver of a ground station at Kola peninsula in Russia near the rocket's footprint observed intermittent emissions of whistlermode waves at the VLF frequency range simultaneously with the rocket observations. The energy of precipitating electrons is consistent with those derived from the quasilinear theory of pitch angle scattering by chorus waves through cyclotron resonance, assuming a typical dayside magnetospheric electron density. Precise interaction region is discussed based on the obtained energy spectrum below 100 keV. [ABSTRACT FROM AUTHOR]

Auroral arcs and diffuse auroras are common phenomena at high latitudes, though characteristics of their source plasma and fields have not been well understood. We report the first observation of fields and particles including their pitch‐angle distributions in the source region of auroral arcs and diffuse auroras, using data from the Arase satellite at L ~ 6.0–6.5. The auroral arcs appeared and expanded both poleward and equatorward at local midnight from ~0308 UT on 11 September 2018 at Nain (magnetic latitude: 66°), Canada, during the expansion phase of a substorm, while diffuse auroras covered the whole sky after 0348 UT. The top part of auroral arcs was characterized by purple/blue emissions. Bidirectional field‐aligned electrons with structured energy‐time spectra were observed in the source region of auroral arcs, while source electrons became isotropic and less structured in the diffuse auroral region afterwards. We suggest that structured bidirectional electrons at energies below a few keV were caused by upward field‐aligned potential differences (upward electric field along geomagnetic field) reaching high altitudes (~30,000 km) above Arase. The bidirectional electrons above a few keV were probably caused by Fermi acceleration associated with the observed field dipolarization. Strong electric‐field fluctuations and earthward Poynting flux were observed at the arc crossing and are probably also caused by the field dipolarization. The ions showed time‐pitch‐angle dispersion caused by mirror reflection. These results indicate a clear contrast between auroral arcs and diffuse auroras in terms of source plasma and fields and generation mechanisms of auroral arcs in the inner magnetosphere. Plain Language Summary: Auroral arcs or curtains are a familiar phenomenon seen at high latitudes, and aurora is also present in diffuse form. In near‐Earth space, plasmas and electric and magnetic fields are known to have interactions that cause the auroral phenomena, but a direct link between measurements in space and the corresponding auroras near the surface has been hard to make. The Arase satellite carries advanced plasma and field instruments allowing detailed study of conditions in space, so campaign observations were carried out at Nain, Canada, in September 2018, at a time when it was expected to be connected to the region by following magnetic field lines. Both discrete and diffuse auroras were observed from the ground, while in space electrons and ions were observed, whose characteristics changed depending on whether the spacecraft was lined up with discrete auroras, or later, with diffuse auroras. The auroras and particles changed with time due to a "substorm," which made the auroras brighten while making the particles more energetic. The observations suggest mechanisms by which the particles may be energized during substorms, with direct measurements in the source region. Key Points: This is the first observation of the source plasma features of auroral arcs and diffuse auroras in the inner magnetosphere by AraseUnique purple/blue auroral arcs appeared in association with an arrival of corotating interaction region (CIR) in the solar windDuring the arc crossing, field‐aligned electrons, time‐pitch‐angle dispersion of ions, and strong electric field variations were observed [ABSTRACT FROM AUTHOR]

Energetic O+ outflow is observed from both the dayside cusp and the nightside aurora, but the relative importance of these regions in populating the plasma sheet and ring current is not known. During a storm on 16 July 2017, the Arase and MMS satellites were located in the near‐earth and midtail plasma sheet boundary layers (PSBL). During the storm main phase, Arase and MMS both observe O+ in the lobe entering the PSBL, followed by a time period with energy‐dispersed bursts of tailward‐streaming O+. The ions at MMS are at higher energies than at Arase. Trajectory modeling shows that the ions coming in from the lobe are cusp origin, while the more energetic bursty ions are from the nightside aurora. The observed and simulated energies and temporal dispersion are consistent with these sources. Thus, both regions directly contribute O+ to the plasma sheet during this storm main phase. Plain Language Summary: The magnetosphere is the region of space encompassed by Earth's magnetic field. The plasma trapped in the magnetosphere can come both from the Sun and from the ionosphere, the ionized layer of the atmosphere. The ionospheric contribution to the plasma increases during geomagnetic storms. These ions get energized in the auroral oval and flow out along magnetic field lines. During storms, this outflow can contain a large fraction of O+. There are two particular regions where this O+ outflow occurs, one on the dayside and one on the nightside. This study looks at the contribution of O+ from these two regions. Two spacecraft in different locations in the magnetosphere during the storm were able to observe the signatures of ions from both regions indicating that both regions are important during the peak of the storm. Key Points: Arase and MMS are fortuitously located in the near‐Earth and midtail plasma sheet boundary layer during the main phase of a stormBoth spacecraft observe O+ from both the nightside aurora and the cusp, with higher energies observed at greater distancesThe energy differences and timing of the O+ at the two spacecraft are consistent with modeled transport [ABSTRACT FROM AUTHOR]

Drastic variations of radiation‐belt/ring current electrons are the result of competing processes of acceleration, transport, and loss. For subrelativistic energetic electrons (10–100 keV), one of the promising loss mechanisms is precipitation into the atmosphere due to pitch angle scattering by whistler mode chorus waves. The efficiency of the scattering has yet to be quantified by direct observations, however. Using in situ measurements by the ERG (Arase) spacecraft in the midnight‐to‐dawn sector at and around the magnetic equator, we demonstrate that the full filling of energetic electron loss cones occurs commonly, associated with typical‐amplitude (greater than 50 pT) chorus waves. The spatial distribution of the loss cone filling indicates that the efficient scattering is limited to |MLAT|< 10°. Plain Language Summary: Drastic variations of high‐energy (10–100 keV) electrons in the Earth's magnetosphere are the result of competing processes of acceleration, transport, and loss. In order to understand their dynamics, therefore, it is important to quantify each process. One of the promising loss mechanisms is precipitation into the atmosphere due to the interaction with electromagnetic waves called "chorus waves." However, the precipitation rate has yet to be quantified by direct observations in the interaction region. Using in situ measurements by the ERG (Arase) spacecraft in the magnetosphere, we demonstrate that the full throttle precipitation occurs commonly, associated with typical‐amplitude (greater than 50 pT) chorus waves. The observed spatial distribution indicates that the efficient interaction is confined at/around the magnetic equator. Key Points: Spatial distribution of medium‐energy loss cone electrons in the low‐latitude magnetosphere is shown for the first timeThe strong diffusion is common when chorus waves are activeStrong scattering occurs only at the near‐equatorial region (|magnetic latitude|< 10°) in the midnight‐to‐dawn sector [ABSTRACT FROM AUTHOR]

We report the electron flux modulations without corresponding magnetic fluctuations from unique multipoint satellite observations of the Arase (Exploration of Energization and Radiation in Geospace) and the Van Allen Probe (Radiation Belt Storm Probe [RBSP])‐B satellites. On 30 March 2017, both Arase and RBSP‐B observed periodic fluctuations in the relativistic electron flux with energies ranging from 500 keV to 2 MeV when they were located near the magnetic equator in the morning and dusk local time sectors, respectively. Arase did not observe Pc5 pulsations, while they were observed by RBSP‐B. The clear dispersion signature of the relativistic electron fluctuations observed by Arase indicates that the source region is limited to the postnoon to the dusk sector. This is confirmed by RBSP‐B and ground‐magnetometer observations, where Pc5 pulsations are observed to drift‐resonate with relativistic electrons on the duskside. Thus, Arase observed the drift‐resonance signatures "remotely," whereas RBSP‐B observed them "locally." Plain Language Summary: Magnetohydrodynamic waves in the outer radiation belt with periods of ~150–250 s occasionally cause the acceleration of energetic electrons drifting eastward around the Earth. We examined the longitudinal distributions of the interaction region in which magnetohydrodynamic waves with periods of ~150–250 s interacted with energetic electrons on 30 March 2017, using simultaneously observed data by multisatellite observations from the Arase and the Radiation Belt Storm Probe (RBSP)‐B satellites. Both satellites observed radiation belts at different local times but at almost the same Earth radii. The Arase satellite located in the dawn sector observed energetic electron flux modulations that had clear energy dispersion signatures, while magnetohydrodynamic waves with the same period were not identified. However, the RBSP‐B located in the dusk sector simultaneously observed magnetohydrodynamic waves and the energetic electron modulations with the characteristics of the interaction. This multipoint measurement indicates that the interaction region is limited from the postnoon to the dusk sector. Key Points: Arase observed flux modulations of relativistic electrons at 04 MLT without variations in the ambient magnetic and electric fieldsTime‐of‐flight analysis from the energy dispersion of relativistic electrons identified the drift‐resonant region to be 14–18 MLTThe interactions between Pc5 waves and relativistic electrons occurred at a limited local time even though the estimated m number is small [ABSTRACT FROM AUTHOR]

Molecular ions in the magnetosphere can be a tracer of fast ion outflows from the deep ionosphere. Statistical properties of molecular ions (O2+/NO+/N2+) in the ring current are investigated based on ion composition measurements (<180 keV/q) by medium‐energy particle experiments‐electron analyzer and low‐energy particle experiments‐ion mass analyzer instruments on board the Arase (Exploration of energization and Radiation in Geospace, ERG) satellite. The investigated period from late March to December 2017 includes 11 geomagnetic storms with the minimum Dst index less than −40 nT. The molecular ions are observed in the region of L = 2.5–6.6 and clearly identified at energies above ~12 keV during most magnetic storms. During quiet times, molecular ions are not observed. The average energy density ratio of the molecular ions to O+ is ~3%. The ratio tends to increase with the size of magnetic storms. Existence of molecular ions even during small magnetic storms suggests that the fast ion outflow from the deep ionosphere occurs frequently during geomagnetically active periods. Plain Language Summary: Molecular ions usually exist only in the low‐altitude (< 300 km) deep ionosphere and cannot escape to space without a fast ion outflow to overcome a rapid loss due to dissociative recombination. Thus, molecular ion escape from the terrestrial atmosphere to space can be used as a tracer of effective ion loss from the deep ionosphere. Here we report new observations by Arase satellite that enables definitive identification of molecular ions by frequent time‐of‐flight mode observations. The statistical analysis shows that molecular ions exist in near‐Earth space during most magnetic storms, while they are not detected during geomagnetically quiet periods. The existence of molecular ions even during small magnetic storms suggests that the magnetic storm is an effective driver of the ion loss from the deep terrestrial ionosphere. Key Points: Frequent TOF‐mode ion composition measurements by Arase revealed statistical properties of molecular ions in the ring currentThe molecular (O2+/NO+/N2+) ions are commonly observed during geomagnetically active periods even during small magnetic stormsThe results suggest that the rapid ion outflow from the deep ionosphere occurs frequently during active periods [ABSTRACT FROM AUTHOR]

We examined the average meridional distribution of middle‐energy protons (10–180 keV) and pressure‐driven currents in the nightside (20–04 hr magnetic local time) ring current region during moderately disturbed times using the Arase satellite's data. Because the Arase satellite has a large inclination orbit of 31°, it covers the magnetic latitude (MLAT) in the range of −40° to 40° and a radial distance of <6RE. We found that the plasma pressure decreased significantly with increasing MLAT. The plasma pressure on the same L* shell at 30° < MLAT < 40° was ∼10–60% of that at 0° < 4 MLAT < 10°, and the rate of decrease was larger on lower L* shells. The pressure anisotropy, derived as the perpendicular pressure divided by the parallel pressure minus 1, decreased with radial distance and showed a weak dependence on MLAT. The magnitude of the plasma beta at 30°

Super Dual Auroral Radar Network (SuperDARN) observations show that ionospheric flow fluctuations of millihertz or lower‐frequency range with horizontal velocities of a few hundred meters per second appeared in the subauroral to midlatitude region during a magnetic storm on 27 March 2017. A set of the radars have provided the first ever observations that the fluctuations propagate azimuthally both westward and eastward simultaneously, showing bifurcated phase propagation associated with substorm expansion. Concurrent observations near the conjugate site in the inner magnetosphere made by the Arase satellite provide evidence that multiple drifting clouds of electrons in the near‐Earth equatorial plane were associated with the electric field fluctuations propagating eastward in the ionosphere. We interpret this event in terms of mesoscale pressure gradients carried by drifting ring current electrons that distort field lines one after another as they drift through the inner magnetosphere, causing eastward propagating ionospheric electric field fluctuations. Plain Language Summary: Midlatitude ionospheric radars called SuperDARN observed azimuthally propagating fluctuations of ionospheric plasma flow in association with substorm expansion during a magnetic storm on 27 March 2017. The radar observations have shown for the first time that the flow fluctuations bifurcate toward eastward and westward simultaneously. The Arase satellite in the near‐conjugate site of the eastward propagating ionospheric flow fluctuations in the inner magnetosphere saw repeated flux enhancement of energetic electrons. The good satellite‐radar conjunction gives observational evidence that the eastward propagating ionospheric flow fluctuations are driven by eastward drifting pressure bumps of electrons injected into the inner magnetosphere upon substorm expansion. Key Points: This study shows the first ever comprehensive observation of azimuthal bifurcation of substorm‐associated ionospheric flow fluctuationsThe eastward propagating portion of the flow fluctuations can be mapped to electron pressure enhancements in the inner magnetosphereWe propose that multiple pressure bumps of drifting energetic electrons directly cause the observed ionospheric flow fluctuations [ABSTRACT FROM AUTHOR]

We examine magnetic and electric field perturbations associated with a sudden commencement (SC), caused by an interplanetary (IP) shock passing over the Earth's magnetosphere on 16 February 2013. The SC was identified in the magnetic and electric field data measured at Time History of Events and Macroscale Interactions during Substorms (THEMIS-E; THE-E: magnetic local time (MLT) = 12.4, L = 6.3), Van Allen Probe-A (VAP-A: MLT = 3.2, L = 5.1), and Van Allen Probe-B (VAP-B: MLT = 0.2. L = 4.9) in the magnetosphere. During the SC interval, THE-E observed a dawnward-then-duskward electric ( E) field perturbation around noon, while VAP-B observed a duskward E field perturbation around midnight. VAP-A observed a dawnward-then-duskward E field perturbation in the postmidnight sector, but the duration and magnitude of the dawnward E perturbation are much shorter and weaker than that at THE-E. That is, the E field signature changes with local time during the SC interval. The Super Dual Auroral Radar Network radar data indicate that the ionospheric plasma motions during the SC are mainly due to the E field variations observed in space. This indicates that the SC-associated E field in space plays a significant role in determining the dynamic variations of the ionospheric convection flow. By comparing previous SC MHD simulations and our observations, we suggest that the E field variations observed at the spacecraft are produced by magnetospheric convection flows due to deformation of the magnetosphere as the IP shock sweeps the magnetopause. [ABSTRACT FROM AUTHOR]

Contents In this study, sperms collected from the right and left cauda epididymis were grouped into having canine prostatic fluid ( PF) sensitization or not diluted with egg yolk Tris-fructose citrate extender, and stored at 4°C. The necessity of canine PF in cooled preservation was determined by elucidating the sperm quality after the storage. As a result, while there was no difference among all groups up to 48 hr of storage, after storage for 96 hr and more, a significantly lower sperm motility was observed in the group without being sensitized to PF than the groups with being sensitized to PF ( p < .05, p < .01). Although sperm abnormality increased in all groups with increased storage time, the group without being sensitized to PF showed significantly higher sperm abnormality than did the groups with being sensitized to PF after storage for 24 hr and more ( p < .01). From these findings, we concluded that PF was necessary for the cooled preservation of the canine sperm because these sperms were protected from any effects of low temperatures by being sensitized to PF. [ABSTRACT FROM AUTHOR]

We investigate spatial and temporal evolution of large-scale electric fields in the magnetosphere and ionosphere associated with sudden commencements (SCs) using multipoint equatorial magnetospheric (THEMIS, RBSP, and GOES) and ionospheric (C/NOFS) satellites with radars (SuperDARN). A distinct SC event on 17 March 2013 shows that the magnetospheric electric field in the equatorial plane propagates from dayside toward nightside as a fast-mode wave. The ionospheric electric field responds ~41 s after the onset of dayside magnetospheric electric field, which can be explained by the propagation of the Alfvén wave along magnetic field lines. The wavelet analysis shows that the Alfvén wave is dominant in the plasmasphere. Poynting fluxes toward the ionosphere support these propagations. From a statistical analysis of response time, tailward propagation speed is estimated at about 1000-1100 km/s. We also statistically derive a spatial distribution and time evolution of the magnetospheric electric field in the dawn-dusk direction ( E y). Our result shows that negative E y (dawnward) propagates from noon toward the magnetotail, followed by positive E y (duskward). The propagation characteristics of electric fields in the equatorial plane depend on magnetic local time. At noon, negative E y lasts for about 1 min, and positive E y becomes dominant about 2 min after the SC onset. Negative E y soon attenuates in the nightside region, while the positive E y propagates fairly well to the premidnight or postmidnight regions while maintaining a certain amplitude. The enhancement of positive E y is due to the enhancement of magnetospheric convection associated with the main impulse of SCs. [ABSTRACT FROM AUTHOR]

The article presents a case study of a 5-month-old girl who was presented having a history of yellowish papules in the extremities, trunk, face and scalp. The lesions became itchy with the development of weals around the papules through scratching when the patient was 15 months old. The patient was given a polymorphic maculopapular cutaneous mastocytosis (MPCM) diagnosis, according to classification of CM.

We present the results from our Suzaku observations of the Galactic black hole binary 4U 1630-47. 4U 1630-47 was observed in the very high state (VHS) during the 2012 September-October outburst. The inner disk appears slightly truncated by comparison with a previous high/soft state (HSS) of this source, even by taking into account energetic coupling between the disk and corona. The spectra do not show the Doppler-shifted emission lines indicating baryonic jets that were seen four days previously in an XMM-Newton observation, despite the source being in a similar state. There are no significant absorption lines from highly ionized iron ions. We also observed 4U 1630-47 in the HSS simultaneously with Suzaku and NuSTAR in an early epoch of the 2015 outburst. All Suzaku spectra in the HSS show variable iron-K absorption line features. We find that the ionization state of the disk wind rapidly increased when the continuum showed significant spectral hardening. This behavior is consistent with that expected from a thermally driven wind. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Background Vonoprazan is a novel potassium-competitive acid blocker which may provide clinical benefit in acid-related disorders. Aim To verify the non-inferiority of vonoprazan vs. lansoprazole in patients with erosive oesophagitis (EE), and to establish its long-term safety and efficacy as maintenance therapy. Methods In this multicentre, randomised, double-blind, parallel-group comparison study, patients with endoscopically confirmed EE (LA Classification Grades A-D) were randomly allocated to receive vonoprazan 20 mg or lansoprazole 30 mg once daily after breakfast. The primary endpoint was the proportion of patients with healed EE confirmed by endoscopy up to week 8. In addition, subjects who achieved healed EE in the comparison study were re-randomised into a long-term study to investigate the safety and efficacy of vonoprazan 10 or 20 mg as maintenance therapy for 52 weeks. Results Of the 409 eligible subjects randomised, 401 completed the comparison study, and 305 entered the long-term maintenance study. The proportion of patients with healed EE up to week 8 was 99.0% for vonoprazan (203/205) and 95.5% for lansoprazole (190/199), thus verifying the non-inferiority of vonoprazan (P < 0.0001). Vonoprazan was also effective in patients with more severe EE (LA Classification Grades C/D) and CYP2C19 extensive metabolisers. In the longterm maintenance study, there were few recurrences (<10%) of EE in patients treated with vonoprazan 10 or 20 mg. Overall, vonoprazan was well-tolerated. Conclusions The non-inferiority of vonoprazan to lansoprazole in EE was verified in the comparison study, and vonoprazan was well-tolerated and effective during the long-term maintenance study. [ABSTRACT FROM AUTHOR]

Contents Human chorionic gonadotropin ( hCG) is a glycoprotein used in the treatment of spermatogenic dysfunction. However, previous studies performed in dogs show that repeated administration of large doses of hCG produces antibodies against hCG. In this study, we examined the efficacy of low-dose injections of hCG in four male dogs with spermatogenic dysfunction and low plasma testosterone ( T) levels. We administered 100 IU hCG per animal, five times at 3-day intervals, and evaluated the changes in semen quality and plasma T levels. The total number of sperm in ejaculate, the percentage of progressively motile sperm and the plasma T levels had increased by 3-5 weeks after the first injection of hCG in three of the four dogs, but were unchanged in the fourth dog. These findings indicate that temporary improvement of the semen quality of dogs with spermatogenic dysfunction and low plasma T levels is possible after five low-dose injections of hCG. [ABSTRACT FROM AUTHOR]

Background Hepatic arterial reconstruction during living donor liver transplantation ( LDLT) is a very delicate and technically complicated procedure. Post- LDLT hepatic arterial complications are associated with significant morbidity and mortality. Methods We retrospectively analyzed the details of post-operative hepatic arterial complications in 673 consecutive adult LDLT recipients between January 1996 and September 2009. Results Hepatic arterial complications occurred in 43 of 673 adult recipients (6.4%) within a median of 13 post-transplant days (range, 1-63). These included hepatic artery thrombosis (including anastomotic stenosis) in 33 cases, anastomotic bleeding in seven cases, and rupture of anastomotic aneurysm in three cases. To treat these complications, surgical re-anastomosis was performed in 26 cases, while the other 17 cases underwent conservative therapies, including four angioplasties by interventional radiology. Biliary complications after hepatic arterial complications occurred in 17 cases. The overall survival rate after LDLT was significantly lower in the hepatic arterial complication group compared with that in the non-complication group (60.7% vs. 80.1% at one yr, 44.3% vs. 74.2% at five yr, respectively; p < 0.001). Multivariate analysis showed that the extra-anatomical anastomosis (p = 0.011) was the only independent risk factor for hepatic arterial complications. Conclusion Because hepatic arterial complications after LDLT are associated with poor patient survival, early diagnosis and immediate treatment are crucial. The anatomical anastomosis may be the first choice for the hepatic arterial reconstruction to the extent possible. [ABSTRACT FROM AUTHOR]

Contents This study investigated the duration of the interval between the onset of vulval bleeding at pro-oestrus and ovulation estimated from the plasma progesterone concentration in a large number of beagle bitches. The influence and association of individual variation, ageing and duration of the oestrous cycle were also investigated. The mean time of ovulation after the onset of vulval bleeding was 11.1 ± 0.2 days, but it widely ranged from 3 to 31 days. This timing was not influenced by age or duration of the oestrous cycle, and within-individual variation was small. As there has been no previous report in which the ovulation day was investigated by the age, these data may be very valuable. [ABSTRACT FROM AUTHOR]

Contents As a step towards elucidation of the timing and mechanism of the determination of the number of ovulated ova in dogs, we excised one ovary 2, 5 and 8 days after the beginning of vulval bleeding and examined whether the lost ovulation function, assessed by estimating the number of ovulated oocytes, would be compensated for by the remaining ovary. The number of ovulated ova was maintained by the remaining ovary in the group that underwent unilateral ovariectomy 2 days after the beginning of vulval bleeding. However, in the groups ovariectomized 5 or 8 days after the beginning of vulval bleeding, no compensation for the number of ova that would have been ovulated from the lost ovary was observed; ova were ovulated only from the follicles 3 mm or greater in diameter observed in the remaining ovary at unilateral ovariectomy. Thus, in dogs, the number of ovulated ova is considered to be determined within 5 days after the beginning of vulval bleeding. [ABSTRACT FROM AUTHOR]