Recent ray tracing suggests that plasmaspheric hiss can originate from chorus observed outside of the plasmapause. Although a few individual events have been reported to support this mechanism, the number of reported conjugate events is still very limited. Using coordinated observations between Time History of Events and Macroscale Interactions during Substorms (THEMIS) and Van Allen Probes, we report on an interesting event, where chorus was observed at a large L shell (∼9.8), different from previously reported events at L < 6, but still exhibited a remarkable correlation with hiss observed in the outer plasmasphere (L ∼ 5.5). Ray tracing indicates that a subset of chorus can propagate into the observed location of hiss on a timescale of ∼5-6 s, in excellent agreement with the observed time lag between chorus and hiss. This provides quantitative support that chorus from large L shells, where it was previously considered unable to propagate into the plasmasphere, can in fact be the source of hiss.

Plasmaspheric hiss is known to play an important role in controlling the overall structure and dynamics of radiation belt electrons inside the plasmasphere. Using newly available Van Allen Probes wave data, which provide excellent coverage in the entire inner magnetosphere, we evaluate the global distribution of the hiss wave frequency spectrum and wave intensity for different levels of substorm activity. Our statistical results show that observed hiss peak frequencies are generally lower than the commonly adopted value (~550-Hz), which was in frequent use, and that the hiss wave power frequently extends below 100-Hz, particularly at larger L shells (>-~3) on the dayside during enhanced levels of substorm activity. We also compare electron pitch angle scattering rates caused by hiss using the new statistical frequency spectrum and the previously adopted Gaussian spectrum and find that the differences are up to a factor of ~5 and are dependent on energy and L shell. Moreover, the new statistical hiss wave frequency spectrum including wave power below 100-Hz leads to increased pitch angle scattering rates by a factor of ~1.5 for electrons above ~100-keV at L~5, although their effect is negligible at L-≤-3. Consequently, we suggest that the new realistic hiss wave frequency spectrum should be incorporated into future modeling of radiation belt electron dynamics. Key Points Hiss wave power is activity dependent and frequently extends below 100-Hz Hiss peak frequency is dependent on L and lower than the previous value 550-Hz Difference in hiss diffusion rate is up to 5, and realistic spectra should be used

We investigate the importance of electron scattering by magnetosonic waves in the Earth's inner magnetosphere. A statistical survey of the magnetosonic wave amplitude and wave frequency spectrum, as a function of geomagnetic activity, is performed using the Van Allen Probes wave measurements and is found to be generally consistent with the wave distribution obtained from previous spacecraft missions. Outside the plasmapause the statistical frequency distribution of magnetosonic waves follows the variation of the lower hybrid resonance frequency, but this trend is not observed inside the plasmasphere. Drift and bounce averaged electron diffusion rates due to magnetosonic waves are calculated using a recently developed analytical formula. The resulting timescale of electron energization during disturbed conditions (when AE∗ > 300 nT) is more than 10 days. We perform a 2-D simulation of the electron phase space density evolution due to magnetosonic wave scattering during disturbed conditions. Outside the plasmapause, the waves accelerate electrons with pitch angles between 50° and 70° and form butterfly pitch angle distributions at energies from ∼100 keV to a few MeV over a timescale of several days; whereas inside the plasmapause, the electron acceleration is very weak. Our study suggests that intense magnetosonic waves may cause the butterfly distribution of radiation belt electrons especially outside the plasmapause, but electron acceleration due to magnetosonic waves is generally not as effective as chorus wave acceleration.

Recent ray tracing suggests that plasmaspheric hiss can originate from chorus observed outside of the plasmapause. Although a few individual events have been reported to support this mechanism, the number of reported conjugate events is still very limited. Using coordinated observations between Time History of Events and Macroscale Interactions during Substorms (THEMIS) and Van Allen Probes, we report on an interesting event, where chorus was observed at a large L shell (~9.8), different from previously reported events at L<6, but still exhibited a remarkable correlation with hiss observed in the outer plasmasphere (L~5.5). Ray tracing indicates that a subset of chorus can propagate into the observed location of hiss on a timescale of ~5-6s, in excellent agreement with the observed time lag between chorus and hiss. This provides quantitative support that chorus from large L shells, where it was previously considered unable to propagate into the plasmasphere, can in fact be the source of hiss.

Plasmaspheric hiss plays an important role in controlling the overall structure and dynamics of the Earth's radiation belts. The interaction of plasmaspheric hiss with radiation belt electrons is commonly evaluated using diffusion codes, which rely on statistical models of wave observations that may not accurately reproduce the instantaneous global wave distribution or the limited in situ satellite wave measurements. This paper evaluates the performance and limitations of a novel technique capable of inferring wave amplitudes from low-altitude electron flux observations from the Polar Orbiting Environmental Satellites (POES), which provide extensive coverage in shell and magnetic local time (MLT). We found that, within its limitations, this technique could potentially be used to build a dynamic global model of the plasmaspheric hiss wave intensity. The technique is validated by analyzing the conjunctions between the POES spacecraft and the Van Allen Probes from September 2012 to June 2014. The technique performs well for moderate-to-strong hiss activity (≥30 pT) with sufficiently high electron fluxes. The main source of these limitations is the number of counts of energetic electrons measured by the POES spacecraft capable of resonating with hiss waves. For moderate-to-strong hiss events, the results show that the wave amplitudes from the EMFISIS instruments on board the Van Allen Probes are well reproduced by the POES technique, which provides more consistent estimates than the parameterized statistical hiss wave model based on CRRES data.

©2015. American Geophysical Union. All Rights Reserved. A novel technique capable of inferring wave amplitudes from low-altitude electron measurements from the Polar Operational Environmental Satellites (POES) spacecraft has been previously proposed to construct a global dynamic model of chorus and plasmaspheric hiss waves. In this paper we focus on plasmaspheric hiss, which is an incoherent broadband emission that plays a dominant role in the loss of energetic electrons from the inner magnetosphere. We analyze the sensitivity of the POES technique to different inputs used to infer the hiss wave amplitudes during three conjunction events with the Van Allen Probes. These amplitudes are calculated with different input models of the plasma density, wave frequency spectrum, and electron energy spectrum, and the results are compared to the wave observations from the twin Van Allen Probes. Only one parameter is varied at a time in order to isolate its effect on the output, while the two other inputs are set to the values observed by the Van Allen Probes. The results show that the predicted hiss amplitudes are most sensitive to the adopted frequency spectrum, followed by the plasma density, but they are not very sensitive to the electron energy spectrum. Moreover, the standard Gaussian representation of the wave frequency spectrum (centered at 550-Hz) peaks at frequencies that are much higher than those observed in individual cases as well as in statistical wave distributions, which produces large overestimates of the hiss wave amplitude. For this reason, a realistic statistical model of the wave frequency spectrum should be used in the POES technique to infer the plasmaspheric hiss wave intensity rather than a standard Gaussian distribution, since the former better reproduces the observed plasmaspheric hiss wave amplitudes. Key Points Inferred amplitudes are very sensitive to frequency spectrum and plasma density All estimates remain within a factor of 0.48 to 2.09 of the observed hiss waves Statistical frequency spectra should be used instead of standard Gaussian models

A new 3-D diffusion code is used to investigate the inward intrusion and slow decay of energetic radiation belt electrons (>0.5MeV) observed by the Van Allen Probes during a 10day quiet period on March 2013. During the inward transport, the peak differential electron fluxes decreased by approximately an order of magnitude at various energies. Our 3-D radiation belt simulation including radial diffusion and pitch angle and energy diffusion by plasmaspheric hiss and electromagnetic ion cyclotron (EMIC) waves reproduces the essential features of the observed electron flux evolution. The decay time scales and the pitch angle distributions in our simulation are consistent with the Van Allen Probe observations over multiple energy channels. Our study suggests that the quiet time energetic electron dynamics are effectively controlled by inward radial diffusion and pitch angle scattering due to a combination of plasmaspheric hiss and EMIC waves in the Earth's radiation belts.

A new 3-D diffusion code is used to investigate the inward intrusion and slow decay of energetic radiation belt electrons (>0.5MeV) observed by the Van Allen Probes during a 10day quiet period on March 2013. During the inward transport, the peak differential electron fluxes decreased by approximately an order of magnitude at various energies. Our 3-D radiation belt simulation including radial diffusion and pitch angle and energy diffusion by plasmaspheric hiss and electromagnetic ion cyclotron (EMIC) waves reproduces the essential features of the observed electron flux evolution. The decay time scales and the pitch angle distributions in our simulation are consistent with the Van Allen Probe observations over multiple energy channels. Our study suggests that the quiet time energetic electron dynamics are effectively controlled by inward radial diffusion and pitch angle scattering due to a combination of plasmaspheric hiss and EMIC waves in the Earth's radiation belts.