Marc R. Lessard

The Kinetic-scale Energy and momentum Transport eXperiment (KiNET-X) sounding rocket explored the coupling of injected barium ions (Ba+) to the ambient ionospheric plasma at two altitudes by releasing two canisters of barium neutrals, each forming an ionized cloud. KiNET-X had instruments on the main payload and on two small deployed subpayloads (Bobs) to measure the Ba+ density (nBa+). The main payload observed nBa+ at a nearly fixed pitch angle to the local geomagnetic field (B→), whereas the Bobs scanned a range of pitch angles. A simple model based on tracing each cloud's particles agreed with the main payload's observed nBa+ profile from the first release; however, for the second release, non-ideal “skidding” motion was required to capture features of the observed nBa+ profile. This paper is a companion to Moses et al. [Phys. Plasmas 32, 042109 (2025)] that analyzes the Bobs' nBa+ profiles. Comparison between the Bobs' measured and modeled nBa+ profiles indicate that pitch angle scattering occurred in each release. Non-idealized pitch angle distributions may arise in the Ba+ clouds from the presence of electric fields parallel to B→ or wave–particle pitch angle diffusion. Pitch angle scattering processes can be proxied in our model by increasing the field-of-view for the density calculation. These different model configurations capture different portions of the measured subpayloads' density and pitch angle profiles. There is perhaps a combination of skidding and scattering that is not easily represented in our model.

Observations of neutral structuring in the cusp region have been obtained in several satellite and rocket missions. Observations include altitude‐dependent neutral density enhancements (CHAllenging Minisatellite Payload and Gravity Recovery And Climate Experiment satellites) and slight neutral density depletion at lower altitudes (Streak satellite and Rocket Experiment for Neutral Upwelling 2 (RENU2) mission). Soft electron precipitation (< a few hundred eV), ion upwelling, and ion‐neutral momentum exchange are among the processes theorized to drive neutral enhancement. We investigate these processes as they relate to neutral structuring using a high‐resolution ionosphere‐thermosphere numerical model (Alfvén wave scale) that includes inertial ion and neutral terms. A detailed study of a soft electron precipitation event is performed, and the resulting thermospheric response is assessed. Ion‐neutral coupling is found to span vertically for hundreds of kilometers for 15–20 min, enhancing the neutral density at higher altitudes. A slight depletion is found near the F region, driven by divergent ion flow near the region of the most intense electron heating. Temporal effects include an upward traveling compression wave and high‐altitude gravity waves. Thermospheric structuring occurs on a 10‐min time scale.

Electromagnetic ion cyclotron (EMIC) waves are a key driver of particle precipitation and energy redistribution in the magnetosphere. While they have been extensively studied in the inner magnetosphere, their behavior in the outer magnetosphere remains poorly understood. In this study, we utilize ground‐based measurements from the Autonomous Adaptive Low‐Power Instrument Platform (AAL‐PIP) chain to investigate the occurrence and amplitude of H‐band and He‐band EMIC waves under varying AE, SYM‐H, and solar wind dynamic pressure () in Earth's outer magnetosphere ( L > 7). In the outer magnetosphere, both the occurrence rate and amplitude of EMIC waves increase under high AE and enhanced conditions, similar to responses in the inner magnetosphere. However, unlike the inner magnetosphere, where EMIC waves are generally confined near noon, enhanced in the outer magnetosphere drives waves across a broader magnetic local time (MLT) distribution, including the dawn and dusk sectors. Furthermore, during substorm periods, H‐band EMIC waves are absent in the dawn sector—a feature rarely observed in the inner region. SYM‐H shows only a weak correlation with wave amplitude and He‐band wave occurrence, while a stronger correlation is found with H‐band wave activity in both dawn and dusk sectors. Additionally, the radial dependencies also differ: as L increases, the wave occurrence rate decreases for both bands, but H‐band amplitudes increase while He‐band amplitudes decrease. This likely reflects differences in ion composition and wave growth conditions at larger radial distances. This study provides new insights into the global distribution and driving physics of EMIC wave activity in the outer magnetosphere.

The Kinetic-Scale Energy and Momentum Transport Experiment was an ionospheric barium release active plasma experiment designed to investigate the non-ideal momentum coupling between the injected ion cloud and the ambient plasma. It is the first of its kind to feature high-resolution ground-based observations along with multi-point, multi-instrument in situ measurements. We describe a portion of the experimental data and make use of global hybrid and test particle simulations to contextualize and analyze the data. In particular, we seek to measure and understand the non-ideal momentum coupling between an injected ion cloud and the ambient plasma. We find that the simulations and the experiment are in general agreement, and we find substantial evidence of non-ideal physical processes in the in situ data. However, in the optical data, we are not able to distinguish non-ideal momentum coupling from other processes that may delay or slow ionization.

We estimated the altitude of aurora by combining data from all‐sky cameras at multiple places which were obtained during the LAMP sounding rocket experiment in Alaska on 5 March 2022. During the launch window of the rocket, three high‐speed all‐sky cameras were operative at three stations immediately below the trajectory of the rocket: Poker Flat, Venetie and Fort Yukon. The all‐sky cameras captured all‐sky images with a temporal resolution of 100 Hz (80 Hz for the Fort Yukon case). The method of altitude determination is based on analyses of time‐series of the optical intensity obtained from the all‐sky cameras in Venetie and Poker Flat covering the downrange area of the rocket trajectory. The estimated altitude of pulsating aurora during the rocket experiment was found to be consistent with that derived from the in‐situ observation of precipitating electrons with a model of optical emission, which confirms the feasibility of deriving the emission altitude through correlation analyses using time‐series. The estimated altitude of aurora decreased after the expansion onset of the substorm and stayed slightly below 100 km during the interval of pulsating aurora in the recovery phase. In particular, prompt and brief lowering of the auroral emission, well down to around 90 km, was detected during a transition of auroral form from discrete to diffuse which occurred ∼10 min after the onset. This result implies an existence of a process causing harder electron precipitation operative soon after the start of the expansion phase of auroral substorm.

High energy resolution DEMETER satellite observations from the Instrument for the Detection of Particle (IDP) are analyzed during an electromagnetic ion cyclotron (EMIC)‐induced electron precipitation event. Analysis of an Interval Pulsation with Diminishing Periods (IPDP)‐type EMIC wave event, using combined satellite observations to correct for incident proton contamination, detected an energy precipitation spectrum ranging from ∼150 keV to ∼1.5 MeV. While inconsistent with many theoretical predictions of >1 MeV EMIC‐induced electron precipitation, the finding is consistent with an increasing number of experimentally observed events detected using lower resolution integral channel measurements on the POES, FIREBIRD, and ELFIN satellites. Revised and improved DEMETER differential energy fluxes, after correction for incident proton contamination shows that they agree to within 40% in peak flux magnitude, and 85 keV (within 40%) for the energy at which the peak occurred as calculated from POES integral channel electron precipitation measurements. This work shows that a subset of EMIC waves found close to the plasmapause, that is, IPDP‐type rising tone events, can produce electron precipitation with peak energies substantially below 1 MeV. The rising tone features of IPDP EMIC waves, along with the association with the high cold plasma density regime, and the rapidly varying electron density gradients of the plasmapause may be an important factor in the generation of such low energy precipitation, co‐incident with a high energy tail. Our work highlights the importance of undertaking proton contamination correction when using the high‐resolution DEMETER particle measurements to investigate EMIC‐driven electron precipitation.

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.

We have identified for the first time an energy‐time dispersion of precipitating electron flux in a pulsating aurora patch, ranging from 6.7 to 580 keV, through simultaneous in‐situ observations of sub‐relativistic electrons of microburst precipitations and lower‐energy electrons using the Loss through Auroral Microburst Pulsation sounding rocket launched from the Poker Flat Research Range in Alaska. Our observations reveal that precipitating electrons with energies of 180–320 keV were observed first, followed by 250–580 keV electrons 0–30 ms later, and finally, after 500–1,000 ms, 6.7–14.6 keV electrons were observed. The identified energy‐time dispersion is consistent with the theoretical estimation that the relativistic electron microbursts are a high‐energy tail of pulsating aurora electrons, which are caused by chorus waves propagating along the field line.

Foreshock transient (FT) events are frequently observed phenomena that are generated by discontinuities in the solar wind. These transient events are known to trigger global‐scale magnetic field perturbations (e.g., ULF waves). We report a series of FT events observed by the Magnetospheric Multiscale mission in the upstream bow shock region under quiet solar wind conditions. During the event, ground magnetometers observed significant Pc1 wave activity as well as magnetic impulse events in both hemispheres. Ground Pc1 wave observations show ∼8 min time delay (with some time differences) from each FT event which is observed at the bow shock. We also find that the ground Pc1 waves are observed earlier in the northern hemisphere compared to the southern hemisphere. The observation time difference between the hemispheres implies that the source region of the wave is the off‐equatorial region.