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CURATOR
A pinboard by
Lydia Bingley

Graduate Student Researcher, University of California, Los Angeles

PINBOARD SUMMARY

Investigating critical questions in magnetosphere dynamics to improve space weather forecasting.

Space plasma physicists have long sought to answer fundamental questions regarding physical processes that affect space weather and magnetospheric dynamics. This has become a topic of increasing interest as we have evolved into a spacefaring species, sending into orbit an ever increasing number of spacecraft, aircraft, and humans that require protection from high-energy particles and unpredictable space weather storms. Space weather models are currently incomplete, resulting in a lack of predictability of the space environment. Without accurate predictive space weather models to enable warning and mitigation, our space technology assets are vulnerable to the harsh space environment. Understanding the dynamic physical processes that govern this environment is critical to the evolution of our space industry, space exploration and human expansion into space.

An essential step in accurate space weather modeling is understanding the mechanisms responsible for loss of relativistic (“killer”) electrons from Earth’s radiation belts. Direct verification of this mechanism is possible with conjunctions between equatorial spacecraft capturing EMIC waves and equatorial electron distributions, and low-altitude, loss-cone resolving spacecraft measuring relativistic electron precipitation in the ionosphere. Previously, limited conjunctions between ionospheric spacecraft and equatorial spacecraft has made such studies difficult. For the first time due to recent extensive availability to spacecraft data, comprehensive wave and particle measurements from multiple equatorial spacecraft (Van Allen Probes, THEMIS, GOES, MMS) and concurrent precipitation measurements from POES enable us to directly evaluate the role of EMIC waves in relativistic electron losses. The primary objective of this proposed research is to quantify the role of EMIC waves in relativistic electron losses from the Earth’s outer radiation belt.

7 ITEMS PINNED

RAM-SCB simulations of electron transport and plasma wave scattering during the October 2012 "double-dip" storm.

Abstract: Mechanisms for electron injection, trapping, and loss in the near-Earth space environment are investigated during the October 2012 "double-dip" storm using our ring current-atmosphere interactions model with self-consistent magnetic field (RAM-SCB). Pitch angle and energy scattering are included for the first time in RAM-SCB using L and magnetic local time (MLT)-dependent event-specific chorus wave models inferred from NOAA Polar-orbiting Operational Environmental Satellites (POES) and Van Allen Probes Electric and Magnetic Field Instrument Suite and Integrated Science observations. The dynamics of the source (approximately tens of keV) and seed (approximately hundreds of keV) populations of the radiation belts simulated with RAM-SCB is compared with Van Allen Probes Magnetic Electron Ion Spectrometer observations in the morning sector and with measurements from NOAA 15 satellite in the predawn and afternoon MLT sectors. We find that although the low-energy (E< 100 keV) electron fluxes are in good agreement with observations, increasing significantly by magnetospheric convection during both SYM-H dips while decreasing during the intermediate recovery phase, the injection of high-energy electrons is underestimated by this mechanism throughout the storm. Local acceleration by chorus waves intensifies the electron fluxes at E≥50 keV considerably, and RAM-SCB simulations overestimate the observed trapped fluxes by more than an order of magnitude; the precipitating fluxes simulated with RAM-SCB are weaker, and their temporal and spatial evolutions agree well with POES/Medium Energy Proton and Electron Detectors data.

Pub.: 22 Nov '16, Pinned: 29 Jun '17

Rapid local acceleration of relativistic radiation-belt electrons by magnetospheric chorus.

Abstract: Recent analysis of satellite data obtained during the 9 October 2012 geomagnetic storm identified the development of peaks in electron phase space density, which are compelling evidence for local electron acceleration in the heart of the outer radiation belt, but are inconsistent with acceleration by inward radial diffusive transport. However, the precise physical mechanism responsible for the acceleration on 9 October was not identified. Previous modelling has indicated that a magnetospheric electromagnetic emission known as chorus could be a potential candidate for local electron acceleration, but a definitive resolution of the importance of chorus for radiation-belt acceleration was not possible because of limitations in the energy range and resolution of previous electron observations and the lack of a dynamic global wave model. Here we report high-resolution electron observations obtained during the 9 October storm and demonstrate, using a two-dimensional simulation performed with a recently developed time-varying data-driven model, that chorus scattering explains the temporal evolution of both the energy and angular distribution of the observed relativistic electron flux increase. Our detailed modelling demonstrates the remarkable efficiency of wave acceleration in the Earth's outer radiation belt, and the results presented have potential application to Jupiter, Saturn and other magnetized astrophysical objects.

Pub.: 20 Dec '13, Pinned: 29 Jun '17

Simulation of the energy distribution of relativistic electron precipitation caused by quasi-linear interactions with EMIC waves.

Abstract: [1]Previous studies on electromagnetic ion cyclotron (EMIC) waves as a possible cause of relativistic electron precipitation (REP) mainly focus on the time evolution of the trapped electron flux. However, directly measured by balloons and many satellites is the precipitating flux as well as its dependence on both time and energy. Therefore, to better understand whether pitch angle scattering by EMIC waves is an important radiation belt electron loss mechanism and whether quasi-linear theory is a sufficient theoretical treatment, we simulate the quasi-linear wave-particle interactions for a range of parameters and generate energy spectra, laying the foundation for modeling specific events that can be compared with balloon and spacecraft observations. We show that the REP energy spectrum has a peaked structure, with a lower cutoff at the minimum resonant energy. The peak moves with time toward higher energies and the spectrum flattens. The precipitating flux, on the other hand, first rapidly increases and then gradually decreases. We also show that increasing wave frequency can lead to the occurrence of a second peak. In both single- and double-peak cases, increasing wave frequency, cold plasma density or decreasing background magnetic field strength lowers the energies of the peak(s) and causes the precipitation to increase at low energies and decrease at high energies at the start of the precipitation.

Pub.: 01 Dec '13, Pinned: 25 Jun '17

Inferring electromagnetic ion cyclotron wave intensity from low altitude POES proton flux measurements: A detailed case study with conjugate Van Allen Probes observations

Abstract: Electromagnetic ion cyclotron (EMIC) waves play an important role in the magnetospheric particle dynamics and can lead to resonant pitch-angle scattering and ultimate precipitation of ring current protons. Commonly, the statistics of in situ EMIC wave measurements is adopted for quantitative investigation of wave-particle interaction processes, which however becomes questionable for detailed case studies especially during geomagnetic storms and substorms. Here we establish a novel technique to infer EMIC wave amplitudes from low-altitude proton measurements onboard the Polar Operational Environmental Satellites (POES). The detailed procedure is elaborated regarding how to infer the EMIC wave intensity for one specific time point. We then test the technique with a case study comparing the inferred root-mean-square (RMS) EMIC wave amplitude with the conjugate Van Allen Probes EMFISIS wave measurements. Our results suggest that the developed technique can reasonably estimate EMIC wave intensities from low-altitude POES proton flux data, thereby providing a useful tool to construct a data-based, near-real-time, dynamic model of the global distribution of EMIC waves once the proton flux measurements from multiple POES satellites are available for any specific time period.

Pub.: 31 Dec '16, Pinned: 25 Jun '17