Quantifying hiss-driven energetic electron precipitation: A detailed conjunction event analysis

Abstract We analyze a conjunction event between the Van Allen Probes and the low-altitude Polar Orbiting Environmental Satellite (POES) to quantify hiss-driven energetic electron precipitation. A physics-based technique based on quasi-linear diffusion theory is used to estimate the ratio of precipitated and trapped electron fluxes (R), which could be measured by the two-directional POES particle detectors, using wave and plasma parameters observed by the Van Allen Probes. The remarkable agreement between modeling and observations suggests that this technique is applicable for quantifying hiss-driven electron scattering near the bounce loss cone. More importantly, R in the 100-300 keV energy channel measured by multiple POES satellites over a broad L magnetic local time region can potentially provide the spatiotemporal evolution of global hiss wave intensity, which is essential in evaluating radiation belt electron dynamics, but cannot be obtained by in situ equatorial satellites alone. Key Points Measured and calculated hiss Bw from POES electron measurements agree well Electron ratio measured by POES is able to estimate hiss wave intensity This technique can be used to provide global hiss wave distributio

Prompt energization of relativistic and highly relativistic electrons during a substorm interval: Van Allen Probes observations

Abstract On 17 March 2013, a large magnetic storm significantly depleted the multi-MeV radiation belt. We present multi-instrument observations from the Van Allen Probes spacecraft Radiation Belt Storm Probe A and Radiation Belt Storm Probe B at ~6 Re in the midnight sector magnetosphere and from ground-based ionospheric sensors during a substorm dipolarization followed by rapid reenergization of multi-MeV electrons. A 50% increase in magnetic field magnitude occurred simultaneously with dramatic increases in 100 keV electron fluxes and a 100 times increase in VLF wave intensity. The 100 keV electrons and intense VLF waves provide a seed population and energy source for subsequent radiation belt enhancements. Highly relativistic (\u3e2 MeV) electron fluxes increased immediately at L* ~ 4.5 and 4.5 MeV flux increased \u3e90 times at L* = 4 over 5 h. Although plasmasphere expansion brings the enhanced radiation belt multi-MeV fluxes inside the plasmasphere several hours postsubstorm, we localize their prompt reenergization during the event to regions outside the plasmasphere. Key Points Substorm dynamics are important for highly relativistic electron energization Cold plasma preconditioning is significant for rapid relativistic energization Relativistic / highly relativistic electron energization can occur in \u3c 5 hrs

Plasmatrough exohiss waves observed by Van Allen Probes: Evidence for leakage from plasmasphere and resonant scattering of radiation belt electrons

Abstract Exohiss waves are whistler mode hiss observed in the plasmatrough region. We present a case study of exohiss waves and the corresponding background plasma distributions observed by the Van Allen Probes in the dayside low-latitude region. The analysis of wave Poynting fluxes, suprathermal electron fluxes, and cold electron densities supports the scenario that exohiss leaks from the plasmasphere into the plasmatrough. Quasilinear calculations further reveal that exohiss can potentially cause the resonant scattering loss of radiation belt electrons

Nonstorm time dynamics of electron radiation belts observed by the Van Allen Probes

Abstract Storm time electron radiation belt dynamics have been widely investigated for many years. Here we present a rarely reported nonstorm time event of electron radiation belt evolution observed by the Van Allen Probes during 21-24 February 2013. Within 2 days, a new belt centering around L=5.8 formed and gradually merged with the original outer belt, with the enhancement of relativistic electron fluxes by a factor of up to 50. Strong chorus waves (with power spectral density up to 10-4nT2/Hz) occurred in the region L\u3e5. Taking into account the local acceleration driven by these chorus waves, the two-dimensional STEERB can approximately reproduce the observed energy spectrums at the center of the new belt. These results clearly illustrate the complexity of electron radiation belt behaviors and the importance of chorus-driven local acceleration even during the nonstorm times

Jupiter’s low-altitude auroral zones: Fields, particles, plasma waves, and density depletions

The Juno spacecraft's polar orbits have enabled direct sampling of Jupiter's low-altitude auroral field lines. While various data sets have identified unique features over Jupiter's main aurora, they are yet to be analyzed altogether to determine how they can be reconciled and fit into the bigger picture of Jupiter's auroral generation mechanisms. Jupiter's main aurora has been classified into distinct “zones”, based on repeatable signatures found in energetic electron and proton spectra. We combine fields, particles, and plasma wave data sets to analyze Zone-I and Zone-II, which are suggested to carry upward and downward field-aligned currents, respectively. We find Zone-I to have well-defined boundaries across all data sets. H+ and/or H3+ cyclotron waves are commonly observed in Zone-I in the presence of energetic upward H+ beams and downward energetic electron beams. Zone-II, on the other hand, does not have a clear poleward boundary with the polar cap, and its signatures are more sporadic. Large-amplitude solitary waves, which are reminiscent of those ubiquitous in Earth's downward current region, are a key feature of Zone-II. Alfvénic fluctuations are most prominent in the diffuse aurora and are repeatedly found to diminish in Zone-I and Zone-II, likely due to dissipation, at higher altitudes, to energize auroral electrons. Finally, we identify significant electron density depletions, by up to 2 orders of magnitude, in Zone-I, and discuss their important implications for the development of parallel potentials, Alfvénic dissipation, and radio wave generation

JUPITER's AURORAL RADIO SPECTRUM

Juno's first perijove science observations were carried out on 27 August 2016. The 90° orbit inclination and 4163 km periapsis altitude provide the first opportunity to explore Jupiter's polar magnetosphere. A radio and plasma wave instrument on Juno called Waves provided a new view of Jupiter's auroral radio emissions from near 10 kHz to ~30 MHz. This frequency range covers the classically named decametric, hectometric, and broadband kilometric radio emissions, and Juno observations showed much of this entire spectrum to consist of V-shaped emissions in frequency-time space with intensified vertices located very close to the electron cyclotron frequency. The proximity of the radio emissions to the cyclotron frequency along with loss cone features in the energetic electron distribution strongly suggests that Juno passed very close to, if not through, one or more of the cyclotron maser instability sources thought to be responsible for Jupiter's auroral radio emissions

Distortions of Subjective Time Perception Within and Across Senses

Background: The ability to estimate the passage of time is of fundamental importance for perceptual and cognitive processes. One experience of time is the perception of duration, which is not isomorphic to physical duration and can be distorted by a number of factors. Yet, the critical features generating these perceptual shifts in subjective duration are not understood. Methodology/Findings: We used prospective duration judgments within and across sensory modalities to examine the effect of stimulus predictability and feature change on the perception of duration. First, we found robust distortions of perceived duration in auditory, visual and auditory-visual presentations despite the predictability of the feature changes in the stimuli. For example, a looming disc embedded in a series of steady discs led to time dilation, whereas a steady disc embedded in a series of looming discs led to time compression. Second, we addressed whether visual (auditory) inputs could alter the perception of duration of auditory (visual) inputs. When participants were presented with incongruent audio-visual stimuli, the perceived duration of auditory events could be shortened or lengthened by the presence of conflicting visual information; however, the perceived duration of visual events was seldom distorted by the presence of auditory information and was never perceived shorter than their actual durations. Conclusions/Significance: These results support the existence of multisensory interactions in the perception of duration and, importantly, suggest that vision can modify auditory temporal perception in a pure timing task. Insofar as distortions in subjective duration can neither be accounted for by the unpredictability of an auditory, visual or auditory-visual event, we propose that it is the intrinsic features of the stimulus that critically affect subjective time distortions

Response of Jupiter's auroras to conditions in the interplanetary medium as measured by the Hubble Space Telescope and Juno

We present the first comparison of Jupiter's auroral morphology with an extended, continuous and complete set of near-Jupiter interplanetary data, revealing the response of Jupiter's auroras to the interplanetary conditions. We show that for ∼1-3 days following compression region onset the planet's main emission brightened. A duskside poleward region also brightened during compressions, as well as during shallow rarefaction conditions at the start of the program. The power emitted from the noon active region did not exhibit dependence on any interplanetary parameter, though the morphology typically differed between rarefactions and compressions. The auroras equatorward of the main emission brightened over ∼10 days following an interval of increased volcanic activity on Io. These results show that the dependence of Jupiter's magnetosphere and auroras on the interplanetary conditions are more diverse than previously thought

Disappearance of plasmaspheric hiss following interplanetary shock

Abstract Plasmaspheric hiss is one of the important plasma waves controlling radiation belt dynamics. Its spatiotemporal distribution and generation mechanism are presently the object of active research. We here give the first report on the shock-induced disappearance of plasmaspheric hiss observed by the Van Allen Probes on 8 October 2013. This special event exhibits the dramatic variability of plasmaspheric hiss and provides a good opportunity to test its generation mechanisms. The origination of plasmaspheric hiss from plasmatrough chorus is suggested to be an appropriate prerequisite to explain this event. The shock increased the suprathermal electron fluxes, and then the enhanced Landau damping promptly prevented chorus waves from entering the plasmasphere. Subsequently, the shrinking magnetopause removed the source electrons for chorus, contributing significantly to the several-hours-long disappearance of plasmaspheric hiss