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We made observations of magnetic field variations in association with pulsating auroras with the magneto‐impedance sensor magnetometer (MIM) carried by the Loss through Auroral Microburst Pulsations (LAMP) sounding rocket that was launched at 11:27:30 UT on 5 March 2022 from Poker Flat Research Range, Alaska. At an altitude of 200–250 km, MIM detected clear enhancements of the magnetic field by 15–25 nT in both the northward and westward components. From simultaneous observations with the ground all‐sky camera, we found that the footprint of LAMP at the 100 km altitude was located near the center of a pulsating auroral patch. The auroral patch had a dimension of ∼90 km in latitude and ∼25 km in longitude, and its major axis was inclined toward northwest. These observations were compared with results of a simple model calculation, in which local electron precipitation into the thin‐layer ionosphere causes an elliptical auroral patch. The conductivity within the patch is enhanced in the background electric field and as a result, the magnetic field variations are induced around the auroral patch. The model calculation results can explain the MIM observations if the electric field points toward southeast and one of the model parameters is adjusted. We conclude that the pulsating auroral patch in this event was associated with a one‐pair field‐aligned current that consists of downward (upward) currents at the poleward (equatorward) edge of the patch. This current structure is maintained even if the auroral patch is latitudinally elongated. Magneto‐impedance (MI) sensor was carried by a sounding rocket and first applied to magnetic field measurement in spaceMagnetic field variations were observed when the footprint of the payload was located near the center of an auroral patchThe magnetic field variations are thought to be caused by field‐aligned currents flowing at the edges of the pulsating auroral patch Magneto‐impedance (MI) sensor was carried by a sounding rocket and first applied to magnetic field measurement in space Magnetic field variations were observed when the footprint of the payload was located near the center of an auroral patch The magnetic field variations are thought to be caused by field‐aligned currents flowing at the edges of the pulsating auroral patch

During geomagnetic storms, some fraction of the solar wind energy is coupled via reconnection at the dayside magnetopause, a process that requires a southward interplanetary magnetic field Bz. Through a complex sequence of events, some of this energy ultimately drives the generation of electromagnetic ion cyclotron (EMIC) waves, which can then scatter energetic electrons and ions from the radiation belts. In the event described in this paper, the interplanetary magnetic field remained northward throughout the event, a condition unfavorable for solar wind energy coupling through low‐latitude reconnection. While this resulted in SYM/H remaining positive throughout the event (so this may not be considered a storm, in spite of the very high solar wind densities), pressure fluctuations were directly transferred into and then propagated throughout the magnetosphere, generating EMIC waves on global scales. The generation mechanism presumably involved the development of temperature anisotropies via perpendicular pressure perturbations, as evidenced by strong correlations between the pressure variations and the intensifications of the waves globally. Electron precipitation was recorded by the Balloon Array for RBSP Relativistic Electron Losses balloons, although it did not have the same widespread signatures as the waves and, in fact, appears to have been quite patchy in character. Observations from Van Allen Probe A satellite (at postmidnight local time) showed clear butterfly distributions, and it may be possible that the EMIC waves contributed to the development of these distribution functions. Ion precipitation was also recorded by the Polar‐orbiting Operational Environmental Satellite satellites, though tended to be confined to the dawn‐dusk meridians. Solar wind pressure fluctuations were directly transferred to the magnetosphere and then propagated throughout the magnetosphereGlobal pressure perturbations provided temperature anisotropies that drove EMIC waves throughout the magnetosphereElectron precipitation was recorded by the BARREL balloons, although it did not have the same widespread signatures as the wave signatures

Narrow bandwidth, whistler‐like spectral features in the extremely low frequency (ELF) range were recorded at South Pole Station over the duration of 2004. A full year of observation shows a distinct lack of activity over the Antarctic winter season. A calculation of solar zenith angle at the time of detection illustrates a connection between the occurrence of ELF whistlers and a sunlit ionosphere. ELF whistlers detected at low latitude follow a similar general trend between ELF whistler occurrence rate and changing solar zenith angle, but with an additional persistence of detections after local sunset. Temporal profiles from the International Reference Ionosphere 2016 show that the peaks in ELF whistler occurrence align with times of changing ionospheric composition. Correlation with solar activity per the F10.7index shows no connection to daily variations in activity, and the consistency of solar flux levels throughout 2004 appears insufficient to explain the absence of events during the winter blackout. These observations place new physical constraints on the conditions necessary for detecting ELF whistlers and suggest the potential for localized generating mechanisms due to plasma instabilities in the ionosphere. ELF whistlers are detected at the South Pole only when the local ionosphere is sufficiently sunlitPeak occurrence times of ELF whistlers align with times of composition change in the local ionosphereDaily solar flux levels do not correlate with daily occurrence rate of ELF whistlers

Relativistic electron microbursts are a known radiation belt particle precipitation phenomenon; however, experimental evidence of their drivers in space have just begun to be observed. Recent modeling efforts have shown that two different wave modes (whistler mode chorus waves and electromagnetic ion cyclotron (EMIC) waves) are capable of causing relativistic microbursts. We use the very low frequency/extremely low frequency Logger Experiment and search coil magnetometer at Halley, Antarctica, to investigate the ground‐based wave activity at the time of the relativistic microbursts observed by the Solar Anomalous Magnetospheric Particle Explorer. We present three case studies of relativistic microburst events, which have one or both of the wave modes present in ground‐based observations at Halley. To extend and solidify our case study results, we conduct superposed epoch analyses of the wave activity present at the time of the relativistic microburst events. Increased very low frequency wave amplitude is present at the time of the relativistic microburst events, identified as whistler mode chorus wave activity. However, there is also an increase in Pc1–Pc2 wave power at the time of the relativistic microburst events, but it is identified as broadband noise and not structured EMIC emissions. We conclude that whistler mode chorus waves are, most likely, the primary drivers of relativistic microbursts. However, case studies confirm the potential of EMIC waves as an occasional driver of relativistic microbursts. Case studies of relativistic microbursts with EMIC and/or chorus waves occurring are presentedStatistically, there is an increase in VLF wave amplitude at the time of relativistic microbursts, consistent with chorusStatistically, there is no increase in EMIC activity at the time of relativistic microbursts

We report on simultaneous observations of electromagnetic ion cyclotron (EMIC) waves associated with traveling convection vortex (TCV) events caused by transient solar wind dynamic pressure (Pd) impulse events. The Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft located near the magnetopause observed radial fluctuations of the magnetopause, and the GOES spacecraft measured sudden compressions of the magnetosphere in response to sudden increases in Pd. During the transient events, EMIC waves were observed by interhemispheric conjugate ground‐based magnetometer arrays as well as the GOES spacecraft. The spectral structures of the waves appear to be well correlated with the fluctuating motion of the magnetopause, showing compression‐associated wave generation. In addition, the wave features are remarkably similar in conjugate hemispheres in terms of bandwidth, quasiperiodic wave power modulation, and polarization. Proton precipitation was also observed by the DMSP spacecraft during the wave events, from which the wave source region is estimated to be 72°–74° in magnetic latitude, consistent with the TCV center. The confluence of space‐borne and ground instruments including the interhemispheric, high‐latitude, fluxgate/induction coil magnetometer array allows us to constrain the EMIC source region while also confirming the relationship between EMIC waves and the TCV current system. EMIC waves were observed by interhemispheric magnetometer arrays in association with transient solar wind pressure changes and TCVsThe waves are well correlated with fluctuating motion of the magnetopause, suggesting compression‐associated wave generationThe multipoint observations show wave events over an extensive latitudinal (L= 6–10) and longitudinal (6 h in MLT) range

Auroral pulsations are a convenient diagnostic of wave‐particle interactions in the magnetosphere. A case study of a daytime Pc3 (22–100 mHz) auroral pulsation event, measured with a ~2 Hz sampling all‐sky camera at South Pole Station (74.4°S magnetic latitude) on 17 May 2012, is presented. The daytime Pc3 auroral pulsations were most active in a closed field line region where the aurora was dominated by diffuse green‐line emissions and within ±2 h of magnetic local noon. Usually, but not always, the corresponding periodic variations were recorded with a colocated search coil magnetometer. Of particular interest is the two‐dimensional auroral signature, indicating that the temporal luminosity variations at a given point were due to repeated formation and horizontal motion of faint, nonpulsating auroral patches with scale sizes of ~100 km. The individual patches propagated equatorward with speeds of 15 km s−1up to 20–25 km s−1one after another along the magnetic meridian through local magnetic zenith. These properties differ considerably from typical pulsating aurorae, being periodic on‐off luminosity variations in a particular auroral patch and drifting in accordance with the convection electric field in the magnetosphere. We speculate that such repetitive patterns of the fast‐moving auroral patches, being another aspect of the daytime Pc3 auroral pulsations, may be a visible manifestation of compressional Pc3 waves which propagate earthward and cause modulation of precipitating keV electron fluxes in the dayside outer magnetosphere. Daytime Pc3 auroral pulsations occurred over South Pole Station, AntarcticaThe auroral pulsations result from repetitive episodes of fast‐moving diffuse auroral patchesThe spatiotemporal behavior of the auroral patches may be a visible manifestation of compressional Pc3 waves in the outer magnetosphere

Electromagnetic ion cyclotron (EMIC) waves are believed to be an important source of pitch angle scattering driven relativistic electron loss from the radiation belts. To date, investigations of this precipitation have been largely theoretical in nature, limited to calculations of precipitation characteristics based on wave observations and small-scale studies. Large-scale investigation of EMIC wave-driven electron precipitation has been hindered by a lack of combined wave and precipitation measurements. Analysis of electron flux data from the POES (Polar Orbiting Environmental Satellites) spacecraft has been suggested as a means of investigating EMIC wave-driven electron precipitation characteristics, using a precipitation signature particular to EMIC waves. Until now the lack of supporting wave measurements for these POES-detected precipitation events has resulted in uncertainty regarding the driver of the precipitation. In this paper we complete a statistical study comparing POES precipitation measurements with wave data from several ground-based search coil magnetometers; we further present a case study examining the global nature of this precipitation. We show that a significant proportion of the precipitation events correspond with EMIC wave detections on the ground; for precipitation events that occur directly over the magnetometers, this detection rate can be as high as 90%. Our results demonstrate that the precipitation region is often stationary in magnetic local time, narrow in L, and close to the expected plasmapause position. Predominantly, the precipitation is associated with helium band rising tone Pc1 waves on the ground. The success of this study proves the viability of POES precipitation data for investigating EMIC wave-driven electron precipitation. POES-based electron precipitation triggers most likely caused by EMIC waves detected on the groundEMIC-IPDP repeatedly triggered at a single MLT closely tied to POES-detected electron precipitationEMIC waves detected via POES-detected electron precipitation are primarily helium band IPDP waves

Morphological behavior of black aurora as it relates to pulsating aurora is investigated by examining a collection of ground‐based observations from January 2007 in support of the Rocket Observations of Pulsating Aurora rocket campaign. Images were sampled from video recorded by a Xybion intensified camera (30 fps) at Poker Flat Research Range, AK. The primary observations of black aurora recorded during the substorm recovery phase were between separate patches of pulsating aurora as well as pulsating aurora separated from diffuse aurora. In these observations the black aurora forms an apparent firm boundary between the auroral forms in a new behavior that is in contrast with previously reported observations. Also presented for the first time are black curls in conjunction with pulsating aurora. Curl structures that indicate shear plasma flows in the ionosphere may be used as a proxy for converging/diverging electric fields in and above the ionosphere. This new subset of black auroral behavior may provide visual evidence of black aurora as an ionospheric feedback mechanism as related to pulsating aurora. Observations show new behavior of black aurora associated with pulsating auroraBlack curls reported for the first time in conjunction with pulsating auroraNew behavior a possible indicator of ionospheric feedback mechanism

Electromagnetic ion cyclotron (EMIC) waves have been studied for decades, though remain a fundamentally important topic in heliospheric physics. The connection of EMIC waves to the scattering of energetic particles from Earth's radiation belts is one of many topics that motivate the need for a deeper understanding of characteristics and occurrence distributions of the waves. In this study, we show that EMIC wave frequencies, as observed at Halley Station in Antarctica from 2008 through 2012, increase by approximately 60% from a minimum in 2009 to the end of 2012. Assuming that these waves are excited in the vicinity of the plasmapause, the change in Kpin going from solar minimum to near solar maximum would drive increased plasmapause erosion, potentially shifting the generation region of the EMIC to lower Land resulting in the higher frequencies. A numerical estimate of the change in plasmapause location, however, implies that it is not enough to account for the shift in EMIC frequencies that are observed at Halley Station. Another possible explanation for the frequency shift, however, is that the relative density of heavier ions in the magnetosphere (that would be associated with increased solar activity) could account for the change in frequencies. In terms of effects on radiation belt dynamics, the shift to higher frequencies tends to mean that these waves will interact with less energetic electrons, although the details involved in this process are complex and depend on the specific plasma and gyrofrequencies of all populations, including electrons. In addition, the change in location of the generation region to lower Lshells means that the waves will have access to higher number fluxes of resonant electrons. Finally, we show that a sunlit ionosphere can inhibit ground observations of EMIC waves with frequencies higher than ∼0.5 Hz and note that the effect likely has resulted in an underestimate of the solar‐cycle‐driven frequency changes described here. EMIC wave frequencies are directly correlated to solar wind cyclesFrequencies related to radiation belt precipitation must also have this dependenceSunlit ionosphere screens observations of wave >0.5 Hz

Intervals of pulsations of diminishing periods (IPDPs) are a subtype of electromagnetic ion cyclotron (EMIC) waves that can be triggered by substorm onset. Pi1B waves are ultralow frequency (ULF) broadband bursts that are well correlated with substorm onset. IPDPs are associated with increased fluxes of 40–60 keV substorm‐injected protons which undergo gradient‐curvature drifting and interact with the cold plasmasphere population. While particle trajectories and the generation of IPDPs have been modeled in the past, those models neglect the role that drift shell splitting plays in the process. This research investigates the different pathways that Pi1B and IPDPs take from their shared origin in substorm onset to their distinct observations on the ground, including the effects of drift shell splitting en route. This paper presents two case studies using data from an array of four ground‐based Antarctic magnetometers that cover the evening sector, as well as in situ magnetometer data, proton fluxes, and proton pitch angles from the Van Allen Probes spacecraft. These observations identify a separation in geomagnetic latitude between Pi1Bs and IPDPs, and pinpoint a separation in magnetic local time (MLT). From these observations we model the drift shell splitting which injected particles undergo post‐onset. This study shows that simulations that incorporate drift shell splitting across a full injection front are dominated by injection boundary effects, and that the inclusion of drift shell splitting introduces a slight horizontal component to the time axis of the time–frequency dependence of the IPDPs. Pi1Bs and IPDPs observed from Antarctic ground stations occur simultaneously with particle injections from substorm onsetWe simulate the trajectories of particle injections from substorm onset as subject to drift shell splitting across a full injection frontParticle trajectories are dominated by injection boundary effects, but drift shell splitting affects the time‐frequency features of IPDPs Pi1Bs and IPDPs observed from Antarctic ground stations occur simultaneously with particle injections from substorm onset We simulate the trajectories of particle injections from substorm onset as subject to drift shell splitting across a full injection front Particle trajectories are dominated by injection boundary effects, but drift shell splitting affects the time‐frequency features of IPDPs

We report on observations of electromagnetic ion cyclotron (EMIC) waves and their interactions with injected ring current particles and high energy radiation belt electrons. The magnetic field experiment aboard the twin Van Allen Probes spacecraft measured EMIC waves near L= 5.5–6. Particle data from the spacecraft show that the waves were associated with particle injections. The wave activity was also observed by a ground‐based magnetometer near the spacecraft geomagnetic footprint over a more extensive temporal range. Phase space density profiles, calculated from directional differential electron flux data from Van Allen Probes, show that there was a significant energy‐dependent relativistic electron dropout over a limited L‐shell range during and after the EMIC wave activity. In addition, the NOAA spacecraft observed relativistic electron precipitation associated with the EMIC waves near the footprint of the Van Allen Probes spacecraft. The observations suggest EMIC wave‐induced relativistic electron loss in the radiation belt. Electromagnetic waves caused by plasma particles in the Earth's magnetic fields are known to interact with high energy particles in the Earth's radiation belts, leading to loss of the particles into the Earth's atmosphere. We report on observations of the wave phenomena and their interaction with radiation belt particles using data from NASA's twin spacecraft mission called Van Allen Probes. Particle detectors aboard the spacecraft measured the increased flux of particles, providing the source energy to generate electromagnetic waves. Such wave activity was also observed by instruments on the ground. A parameter calculated using data from various instruments aboard the spacecraft enabled us to quantitatively assess how the radiation belt electron population changes over time. This analysis reveals that the wave event caused the radiation belt electrons of certain energies to decay over a limited spatial extent. In addition, particle data from low earth orbiting spacecraft show an increase in particle flux, which appears to be associated with the wave activity. The observations suggest that the wave can contribute to loss of electrons in the radiation belts. A radiation belt electron dropout was observed during injection‐associated electromagnetic ion cyclotron (EMIC) wavesL‐shell and energy‐dependent electron dropout indicates EMIC‐wave induced scattering of radiation belt electronsNOAA spacecraft data show relativistic electron precipitation during the dropout event A radiation belt electron dropout was observed during injection‐associated electromagnetic ion cyclotron (EMIC) waves L‐shell and energy‐dependent electron dropout indicates EMIC‐wave induced scattering of radiation belt electrons NOAA spacecraft data show relativistic electron precipitation during the dropout event