M. J. Starks

Optical ring formation and ionization production in high‐power HF heating experiments at HAARP

[1] Observations of HF-induced artificial optical emissions at the 3.6 MW HAARP facility show unexpected features not seen at the previous 960 kW level. Optical emissions often form a bright rayed ring near the 10% power contour surrounding a central disk with a sharp edge near the 50% power contour. Artificial bottomside layers in ionograms and positive perturbations in total electron content suggest that the bullseye optical patterns are associated with localized enhancements in plasma density below the main F layer. Ray tracing shows transmitter power concentrates in an annular structure consistent with the optical observations. Estimated ionization rates are well within the power available from the transmitter and agree well with the observed intensity of N + 2 427.8 nm emissions. We conclude that the optical bullseye patterns are a refraction phenomenon and an indicator of ionization production within the transmitter beam.

Quasi‐linear simulations of inner radiation belt electron pitch angle and energy distributions

“Peculiar” or “butterfly” electron pitch angle distributions (PADs), with minima near 90°, have recently been observed in the inner radiation belt. These electrons are traditionally treated by pure pitch angle diffusion, driven by plasmaspheric hiss, lightning-generated whistlers, and VLF transmitter signals. Since this leads to monotonic PADs, energy diffusion by magnetosonic waves has been proposed to account for the observations. We show that the observed PADs arise readily from two-dimensional diffusion at L = 2, with or without magnetosonic waves. It is necessary to include cross diffusion, which accounts for the relationship between pitch angle and energy changes. The distribution of flux with energy is also in good agreement with observations between 200 keV and 1 MeV, dropping to very low levels at higher energy. Thus, at this location radial diffusion may be negligible at subrelativistic as well as ultrarelativistic energy.

Intelligent Sampling of Hazardous Particle Populations in Resource‐Constrained Environments

Sampling of anomaly-causing space environment drivers is necessary for both real-time operations and satellite design efforts, and optimizing measurement sampling helps minimize resource demands. Relating these measurements to spacecraft anomalies requires the ability to resolve spatial and temporal variability in the energetic charged particle hazard of interest. Here we describe a method for sampling particle fluxes informed by magnetospheric phenomenology so that, along a given trajectory, the variations from both temporal dynamics and spatial structure are adequately captured while minimizing oversampling. We describe the coordinates, sampling method, and specific regions and parameters employed. We compare resulting sampling cadences with data from spacecraft spanning the regions of interest during a geomagnetically active period, showing that the algorithm retains the gross features necessary to characterize environmental impacts on space systems in diverse orbital regimes while greatly reducing the amount of sampling required. This enables sufficient environmental specification within a resource-constrained context, such as limited telemetry bandwidth, processing requirements, and timeliness.

VLF LH/whistler nonlinear interactions in the topside ionosphere: Simulation study

Summary form only given. Recent observations of the VLF waves with frequencies close to so-called lower hybrid resonance frequency have shown that amplitudes of the observed waves are 20–30 dB smaller than those obtained in VLF propagation models. Nonlinear interactions have been suggested1 to account for the missing mechanism of energy losses in the current propagation models. Our study2 of nonlinear induced scattering in electrostatic limit based on a novel 3D code which includes so-called vector nonlinearity pinned the above nonlinear mechanism as a very likely source of this discrepancy. The results virtually reproduce the Demeter satellite observations of intense broadband lower hybrid (LH) electrostatic waves generated by whistler-mode waves from the VLF transmitter NWC. Here we present the results of the extension of the numerical model to electromagnetic (whistler) limit and discuss possible ways of doing the modeling in realistic geometry, essential for obtaining the correct spatial distribution of attenuation of the pump wave emitted from spacecraft through various latitude/longitude as well as altitude regions of the ionosphere.