James L. Roeder

Ring current activity during the early Bz < 0 phase of the January 1997 magnetic cloud

The passage at Earth of the January 10–11, 1997, magnetic cloud induced a storm of moderate geomagnetic activity with Dst index reaching minimum values of about −83 nT. We study ring current formation during the early Bz negative phase of this magnetic cloud, using energetic particle data from three instruments on the Polar spacecraft and geosynchronous plasma data from the LANL spacecraft. We use our kinetic drift-loss model to simulate the evolution of ring current H+, He+, and O+ ion distributions and associated aeronomical effects during this period. The results from two Volland-Stern type magnetospheric electric field model formulations are compared: (1) Kp-dependent and (2) interplanetary magnetic field (IMF) dependent. We demonstrate that while both electric field models reproduce well the main trends of ring current formation and decay during the storm, the IMF-dependent model reproduces the rapidity of the main storm growth phase and its strength better. Comparing model results during the main phase of the storm with HYDRA, TIMAS, and CAMMICE data we find that the model reproduces very well the ring current distributions near dawn. The formation of the nose event, i.e., the rise of the 10–30 keV energy particles near dusk due to abruptly increased convection is, however, overestimated by the model. We compute plasmaspheric heating through Coulomb collisions as the storm evolves and find that maximum heating occurs initially on the nightside near L∼3.5 and subsequently moves earthward to L∼2.75, in agreement with Millstone Hill radar observations of midlatitude electron temperature enhancement on January 10. However, the magnitude of the energy transferred to plasmaspheric electrons through Coulomb collisions appears to be not sufficient to yield the observed elevated electron temperature at ∼0830 UT, suggesting that additional energy sources should be considered during this event.

Proton ring current pitch angle distributions: Comparison of simulations with CRRES observations

In this study we compare the proton pitch angle distributions (PADs) in the ring current region (L ∼ 3–4) obtained from Combined Release and Radiation Effects Satellite (CRRES) observations during the large magnetic storm (minimum Dst = −170 nT) on August 19, 1991, with results of phase-space mapping simulations in which we trace the bounce-averaged drift of protons during storm-associated enhancements in a model of the convection electric field. We map the phase-space density ƒ according to Liouvilles theorem except for attenuation by charge exchange, which we compute for both an empirical model [Rairden et al., 1986] and a theory-based model [Hodges, 1994] of the neutral H density distribution. We compare simulated pitch angle distributions at 48 keV, 81 keV, and 140 keV at L = 3 and L = 4 directly with the CRRES distributions at the same energies and L values before and during the storm. A steady-state application of our transport model, using the empirical neutral H density model of Rairden et al. [1986], reproduces the absolute intensities well except for E = 140 keV at L = 3 (M = 10 MeV/G) and E = 48 keV at L = 4 (M = 13 MeV/G). The anisotropies (A ∼ 0.2–0.8) of the CRRES and modeled pre-storm pitch angle distributions agree within factors ≲ 2. Time-dependent application of our transport model reproduces measured recovery phase anisotropies (t = 10–12 h after storm onset; A ∼ 0.4–1.2) similarly well at the selected energies and L values, but agreement between modeled and measured absolute intensities is energy-dependent and not consistently good. Our model underpredicts the proton intensities found by CRRES for E > 80 keV at L = 4 in early recovery phase (t = 10–12 h). Perhaps the impulsive stormtime convection electric field was stronger during the main phase than we have assumed here. Comparisons were more difficult in late recovery phase (t = 20 h) because CRRES was too far off the magnetic equator. Proton life-times inferred from the CRRES data during the recovery phase of this storm are considerably shorter than charge-exchange lifetimes for either model, but the empirical neutral H density model of Rairden et al. [1986] leads to smaller discrepancies with the CRRES data at all the selected energies and L values than the theory-based neutral H density model of Hodges [1994] for parameters that most closely represent the seasonal and solar maximum conditions of the August 19, 1991, storm. It appears that charge exchange alone is not enough to explain the observed rapid decay of the ring current proton intensities during the recovery phase of this storm.

A Severe Spacecraft-Charging Event on SCATHA in September 1982,

Abstract : On September 22, 1982, 29 large amplitude electrostatic discharges were detected by the Pulse Analyzer onboard the SCATHA satellite. Seventeen of these pulses exceeded the maximum voltage discrimination level, which was set to 7.4 volts. This was the worst instance of electrostatic discharges encountered to date by the SCATHA satellite. Three different spacecraft anomalies occurred on SCATHA that day, the most serious being a two-minute loss of data. During this same time period, the Surface Potential Monitor experiment aboard the satellite measured the largest differential surface charging observed in the data since the satellites launch in January 1979. Keywords: Electrostatic discharges; Spacecraft anomalies; Spacecraft charging.

The Timescale of Surface-Charging Events

The timescale for creating high potentials on shadowed spacecraft surfaces depends on the conductivity of the surface in question, whether the neighboring surfaces are tied to the spacecraft frame or not, and on the space environment input. It is understood from laboratory and spaceflight measurements that the likelihood of a large surface potential and the timescale over which it might occur depends on these variables, yet the complex interplay between them makes the hazard difficult to assess even in controlled experiments. In this paper, we approach the specific question of the timescale of surface charging using several data sets in several orbit regimes: geostationary orbit (GEO), highly elliptical orbit (HEO), and low-Earth orbit (LEO). The measurements that we will show involve different approaches to the question of surface charging and subsequent electrostatic discharge (ESD) (GEO: surface charge monitors; HEO: direct plasma measurements; LEO: anomalies due to surface charging). However, the main strengths of the data are derived from their long duration covering multiple years and their occasional overlap in time. Here, we report on the timescale of surface-charging events at different locations in the magnetosphere across ~11 years of geomagnetic activity. The results will be relevant for assessments of space system impacts due to surface discharges and ESD, simulations of surface charging, and laboratory testing of flight system designs.

Internal Charging Hazards in Near-Earth Space During Solar Cycle 24 Maximum: Van Allen Probes Measurements

The Van Allen Probes mission provides an unprecedented opportunity to make detailed measurements of electrons and protons in the inner magnetosphere during the weak solar maximum period of cycle 24. The MagEIS suite of sensors measures energy spectra and fluxes of charged particles in the space environment. The calculations show that these fluxes result in electron deposition rates high enough to cause internal charging. We use omnidirectional fluxes of electrons and protons to calculate the dose under varying materials and thicknesses of shielding. We show examples of charge deposition rates during the times of nominal and high levels of penetrating fluxes in the inner magnetosphere covering the period from the beginning of 2013 through mid-2014. These charge deposition rates are related to charging levels quite possibly encountered by shielded dielectrics with different resistivities. Using a simple model, we find temporal profiles for different materials showing the long-term charge deposition rate and estimated charge density levels reaching high levels. These levels are an indicator of internal charging rates that satellites might possibly experience in the inner magnetosphere. The results are compared with charge densities that can induce internal electrostatic discharge.

Extremely Low Frequency Wave Analyzer

Abstract : This report describes the Extremely Low Frequency Wave Analyzer flown as part of the LASSII (Low Altitude Satellite Studies of Ionospheric Irregularities) experiment aboard the CRRES (Chemical Release and Radiation Effects Satellite). This instrument measures electrostatic and electromagnetic waves in the ambient Ionosphere and during the CRRES chemical releases.