Meers M. Oppenheim

Ionospheric scintillation driven by plasma irregularities disrupts radio propagation across frequencies from HF to L‐band. While phase‐screen methods dominate scintillation modeling, they can be inadequate in the E‐region where irregularity scales can be comparable to the radio wavelength or Fresnel scale and span orders of magnitude. Here we quantitatively evaluate scintillation with a new full‐wave methodology coupling particle‐in‐cell simulations of the gradient drift (GD) and Farley‐Buneman instabilities with finite‐difference time‐domain electromagnetic propagation. Using a frozen‐in approximation and spatial filtering, we evaluate the contributions of various turbulence scale sizes to HF (6–24 MHz) phase and amplitude scintillation. Long‐wavelength GD waves dominate the modeled amplitude scintillation through diffractive scattering, while Farley‐Buneman turbulence contributes negligibly. Amplitude spectra closely follow irregularities near the Fresnel scale, demonstrating a direct correspondence between scintillation and plasma structuring. These results demonstrate full‐wave scintillation modeling and provide a framework for investigating scintillation across a wide range of spatial scales.

In the coldest regions of the solar atmosphere, lingering discrepancies between models and observations may be caused by the Thermal Farley–Buneman Instability (TFBI). This meter-scale, electrostatic, collisional, multifluid plasma instability converts energy from neutral flows into turbulent motions and heating. In the neutral frame of reference, these neutral flows manifest as an electric field that can drive the TFBI. In this work, we simulate the TFBI across a broad range of solar chromospheric conditions. We find clear proportionality between between TFBI-driven relative temperature increases of charged species ( Δ T s ( turb ) / T s ( 0 ) ) and driving electric field strength relative to the theoretical threshold field required for TFBI growth. We also discover a correlation between relative driving field strength and turbulent motions. Additionally, the TFBI consistently causes average current density to rotate towards the driving field, with the Pedersen/ambipolar component ( J ⋅ E ^ ( 0 ) ) increasing by up to roughly 60% while the Hall component ( J ⋅ E ^ ( 0 ) × B ^ ) decreases in magnitude by up to roughly 80%. Meanwhile, we find TFBI-driven turbulence increases neutral heating rates by (43 ± 7)% on average, with 85% (28/33) of simulations having mean increase more than 29%, and a flat line of best fit suggesting zero correlation with the driving field.

Radar and rocket observations of the terrestrial ionosphere frequently measure turbulent plasma waves, especially during geospace storms. The non‐linear behavior of these waves remains poorly characterized. This paper presents the first fully kinetic 3‐D particle‐in‐cell simulations of Farley–Buneman (FB) turbulence spanning an entire high‐latitude ionospheric column from strongly collisional to nearly collisionless altitudes. These waves initially develop coherent density perturbations spanning kilometers along , having dominant flow angles that increase with altitude. As the FB turbulence saturates, energy cascades to longer wavelengths and spreads in ‐space. These simulations show turbulence‐driven electron heating and anomalous electron transport with a 21% enhancement in height‐integrated conductance for a system driven by an mV/m external field. Simulations like these will improve interpretations of observations and modeling of turbulence‐modified conductivities for space‐weather simulations.

In the coldest regions of the solar atmosphere, models struggle to match observations. Recent work suggests the Thermal Farley–Buneman Instability (TFBI) may play an important role. This meter-scale, electrostatic, collisional, multifluid plasma instability converts energy from neutral flows into turbulent motions and heating. In this work, we improve upon previous methods for solving the linear theory across single-fluid MHD simulation outputs, and present the new tfbi_theory code. We predict much less TFBI growth within a 2D Bifrost plage model than previously suggested. To bypass some limitations of single-fluid MHD models, we also solve TFBI theory across a 5D grid of chromospheric parameters. We find that the TFBI can grow across a wide range of chromospheric densities, temperatures, hydrogen ionization fractions, and magnetic field strengths. We also discover that the minimum ∣ E ∣/∣ B ∣ speed in the neutral reference frame required to drive the TFBI in the chromosphere is less than 3.2 km s ⁻¹ in some regions, but always more than 1 km s ⁻¹ .

The 440 MHz radar at the Millstone Hill Observatory (MHO) collected the first high‐power large‐aperture (HPLA) high latitude meteor data set pointing perpendicular to . In total, it detected 3,345 echoes over 2 nights. This data shows populations that peak at altitudes of km for heads, km for trails, and km for total power. The data set shows nearly identical altitude distributions for head and trail echoes, probably because most meteors were large enough to create both head and trail echoes. These results were compared to head and trail observations from Jicamarca Radio Observatory (JRO) and head observations from the Millstone Zenith Antenna, Arecibo, PFISR, and MU radars. The JRO, Millstone Zenith, and Arecibo head echo altitude distributions have peaks km higher than our MHO data, whilst the PFISR and MU observatories have similar peaks to the MHO data. Also, the JRO trail echo altitude peak matched the MHO peak. This shows that higher‐sensitivity radars (JRO, Zenith, Arecibo) observe weaker meteor head echoes from meteoroids that ablate higher in the atmosphere, while lower‐sensitivity radars generally observe echoes from larger particles that penetrate deeper into the atmosphere (MHO, PFISR, MU). The current MHO data set's lower sensitivity primarily results from pointing at a 13‐degree elevation angle, making measurements at km range, necessary for observing meteors perpendicular to at high latitude. This research improves our understanding of how HPLA radars can detect and characterize meteors.

The ablation of micrometeoroids entering Earth's atmosphere leaves behind a hot, dense column of plasma between 80 and 120 km altitude. Sharp density gradients can drive the plasma unstable, leading to turbulence and waves at the same altitude, which are often observed as coherent radar echoes. These echoes persist for 10s of milliseconds up to several minutes and are known as nonspecular trails. The turbulence from these trails is highly aspect sensitive and typically only observed within a few degrees of perpendicular to the magnetic field. In this letter, we present a new approach to measure the magnetic aspect sensitivity of nonspecular meteor trail echoes using the AMISR‐14 radar system. Using multiple beams, we simultaneously observe each trail at several different angles and directly observe aspect angle effects. Using this approach, we find that at 445 MHz, the observed power decays at 4.58 ± 0.46 dB/degree.

High‐power large‐aperture radar instruments observe numerous meteor head echoes per minute. Head echoes result from reflections of radio waves from plasma surrounding meteoroids as they enter Earth's atmosphere. Knowledge of the spatial distribution of electrons in this plasma is essential to determining the mass loss rate of the meteor as a function of its measured radar cross‐section. Prior work applies theoretical and computational methods to determine the electron density distribution, but assumes the meteoroid emits neutral particles uniformly across its surface. In this paper, a numerical surface ablation model demonstrates that meteoroid mass loss may occur preferentially in the direction facing the oncoming atmosphere. Specifically, meteoroid mass loss becomes proportional to the frontal surface area facing the freestream atmosphere in the limit of high Biot number, but remains isotropic in the limit of low Biot number. Meteoroid rotation has a small effect on the direction of ejected mass, but the effect is insignificant compared to variation in meteoroid properties that affect the Biot number. This result informs our computational meteor plasma model, in which we compare the effect of meteoroid vaporization on the plasma distribution in the limits of low versus high Biot number. The resulting electron density profiles demonstrate order‐of‐magnitude agreement between each other, with peak difference of 70% immediately upstream of the meteoroid. This implies that the directional distribution of vaporizing neutrals likely does not significantly influence head echo observations, lending credence to existing work that assumes isotropic ablation.

Models currently fail to reproduce observations of the coldest regions in the Sun’s atmosphere, though recent work suggests the thermal Farley–Buneman instability (TFBI) may play a critical role. This meter-scale, electrostatic, multifluid plasma instability causes turbulence and heating in the coldest regions of the solar chromosphere. This paper describes how TFBI turbulence and heating varies across multifluid 2D, kinetic 2D, and kinetic 3D simulations. It also presents the first 3D simulations of the TFBI. We find that multifluid and kinetic 2D simulations produce similar results overall, despite using vastly different approaches. Additionally, our kinetic 3D simulations produce a similar or somewhat larger amount of heating compared to 2D, as contributions from the parallel electric field account for only (13 ± 2.5)% of the total turbulent heating in 3D.

Subauroral Ion Drift (SAID) channels and Strong Thermal Emission Velocity Enhancement (STEVE) phenomena are distinct features of ionospheric dynamics that are accompanied by strong electric field forcing that is related to plasma turbulence in the E‐region. This study investigates the role of the Farley‐Buneman Instability (FBI) in modulating SAID and related phenomena, focusing on its impact on the evolution of extreme SAID channels. Using the Geospace Environment Model of Ion‐Neutral Interactions (GEMINI), we incorporate macroscopic effects of FBI‐induced turbulence in the form of anomalous electron heating and non‐linear current density. Results demonstrate that FBI‐induced turbulence produces a significant dampening effect on SAID channel velocity growth by increasing E‐region conductance and density. This effect alters the electric field dynamics and moderates the extreme velocities characteristic of SAID channels. These findings underscore the critical role of including turbulence‐driven processes in predictive models, advancing our understanding of magnetosphere‐ionosphere coupling and space weather phenomena. This work is understood as missing physics that would increase the dampening effect, such as inelastic collisions and excitation of resonant cross‐sections in electron neutral collisions, yet introduces itself as a starting point and an appeal to further improve.

High-power large-aperture radar instruments observe numerous meteor head echoes per minute. Head echoes result from reflections of radio waves from plasma surrounding meteoroids as they enter Earth’s atmosphere. Knowledge of the spatial distribution of electrons in this plasma is essential to determining the mass loss rate of the meteor as a function of its measured radar cross-section. Prior work applies theoretical and computational methods to determine the electron density distribution, but assumes the meteoroid emits neutral particles uniformly across its surface. In this paper, a numerical surface ablation model demonstrates that meteoroid mass loss may occur preferentially in the direction facing the oncoming atmosphere. Specifically, meteoroid mass loss becomes proportional to the frontal surface area facing the freestream atmosphere in the limit of high Biot number, but remains isotropic in the limit of low Biot number. Meteoroid rotation has a small effect on the direction of ejected mass, but the effect is insignificant compared to variation in meteoroid properties that affect the Biot number. This result informs our computational meteor plasma model, in which we compare the effect of meteoroid vaporization on the plasma distribution in the limits of low versus high Biot number. The resulting electron density profiles demonstrate order-of-magnitude agreement between each other, with peak difference of 70\% immediately upstream of the meteoroid. This implies that the directional distribution of vaporizing neutrals likely does not significantly influence head echo observations, lending credence to existing work that assumes isotropic ablation.