Bibliography

Analyzing EMIC Waves in the Inner Magnetosphere Using Long-Term Van Allen Probes Observations

With 64-month magnetic data from Van Allen Probes, we have studied not only the global distribution, wave normal angle (θ), and ellipticity (ε) of electromagnetic ion cyclotron (EMIC) waves, but also the dependence of their occurrence rates and magnetic amplitudes on the AE* index (the mean value of AE index over previous 1 hr). Our results show that H+ band waves are preferentially detected at 5 <= L <= 6.5, in the noon sector. They typically have small θ (<30\textdegree) and weakly left-hand polarization but become more oblique and linearly polarized at larger magnetic latitudes or L-shells. With the increase of AE* index, their occurrence rate significantly increases in the noon sector, and their source region extends to dusk sector. He+ band waves usually occur in the predawn and morning sectors at 3 <= L <= 4.5. They generally have moderate θ (30 \textdegree - 40\textdegree) and left-hand polarization and also become more oblique and linearly polarized at larger latitudes or L-shells. There is a clear enhancement of occurrence rate and amplitude during active geomagnetic periods, especially in the dusk and evening sectors. O+ band waves mainly occur at 3 <= L <= 4 in the predawn sector. They have either very small θ (<20\textdegree) or very large θ (>50\textdegree), and typically linear or weakly right-hand polarization. During active periods, they mostly occur at the midnight sector and L < 3.5. As a valuable supplement to previous statistical studies, our result provides not only a more compresentive EMIC wave model for evaluating their effects on the radiation belt, but also detailed observational constraints on generation mechanisms of EMIC waves.

Chen, Huayue; Gao, Xinliang; Lu, Quanming; Wang, Shui;

Published by: Journal of Geophysical Research: Space Physics      Published on: 08/2019

YEAR: 2019     DOI: 10.1029/2019JA026965

A long-term statistical work; EMIC wave; inner magnetosphere; spatial distribution; Van Allen Probes; Van Allen Probes observation; Wave fundamental characters

Properties of intense field-aligned lower-band chorus waves: Implications for nonlinear wave-particle interactions

Resonant interactions between electrons and chorus waves are responsible for a wide range of phenomena in near-Earth space (e.g., diffuse aurora, acceleration of MeV electrons, etc.). Although quasi-linear diffusion is believed to be the primary paradigm for describing such interactions, an increasing number of investigations suggest that nonlinear effects are also important in controlling the rapid dynamics of electrons. However, present models of nonlinear wave-particle interactions, which have been successfully used to describe individual short-term events, are not directly applicable for a statistical evaluation of nonlinear effects and the long-term dynamics of the outer radiation belt, because they lack information on the properties of intense (nonlinearly resonating with electrons) chorus waves. In this paper, we use the THEMIS and Van Allen Probes datasets of field-aligned chorus waveforms to study two key characteristics of these waves: effective amplitude w (nonlinear interaction can occur when w > 2) and wave-packet length β (the number of wave periods within it). While as many as 10 - 15\% of chorus wave-packets are sufficiently intense (w > 2 - 3) to interact nonlinearly with relativistic electrons, most of them are short (β < 10) reducing the efficacy of such interactions. Revised models of non-linear interactions are thus needed to account for the long-term effects of these common, intense but short chorus wave packets. We also discuss the dependence of w, β on location (MLT, L-shell) and on the properties of the suprathermal electron population.

Zhang, X.-J.; Thorne, R.; Artemyev, A.; Mourenas, D.; Angelopoulos, V.; Bortnik, J.; Kletzing, C.; Kurth, W.; Hospodarsky, G.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 06/2018

YEAR: 2018     DOI: 10.1029/2018JA025390

chorus waves; Effective amplitude; nonlinear wave-particle interaction; spatial distribution; statistics; Van Allen Probes; Wave-packet length

The occurrence and wave properties of H ⁺ -, He ⁺ -, and O ⁺ -band EMIC waves observed by the Van Allen Probes

We perform a statistical study of electromagnetic ion cyclotron (EMIC) waves detected by the Van Allen Probes mission to investigate the spatial distribution of their occurrence, wave power, ellipticity, and normal angle. The Van Allen Probes have been used which allow us to explore the inner magnetosphere (1.1 to 5.8 Re). Magnetic field measurements from the Electric and Magnetic Field Instrument Suite and Integrated Science onboard the Van Allen Probes are used to identify EMIC wave events for the first 22 months of the mission operation (8 September 2012 \textendash 30 June 2014). EMIC waves are examined in H+-, He+-, and O+-bands. Over 700 EMIC wave events have been identified over the three different wave bands (265 H+-band events, 438 He+-band events, and 68 O+-band events). EMIC wave events are observed between L = 2 \textendash 8, with over 140 EMIC wave events observed below L = 4. Results show that H+-band EMIC waves have two peak MLT occurrence regions: pre-noon (0900 < MLT <= 1200) and afternoon (1500 < MLT <= 1700) sectors. He+-band EMIC waves feature an overall stronger dayside occurrence. O+-band EMIC waves have one peak region located in the morning sector at lower L-shells (L < 4). He+-band EMIC waves average the highest wave power overall (>0.1 nT2/Hz), especially in the afternoon sector. Ellipticity observations reveal that linearly polarized EMIC wave dominate in lower L-shells.

Saikin, A.; Zhang, J.-C.; Allen, R.C.; Smith, C.; Kistler, L.; Spence, H.; Torbert, R.; Kletzing, C.; Jordanova, V.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 09/2015

YEAR: 2015     DOI: 10.1002/2015JA021358

EMIC waves; Fast Fourier Transform; spatial distribution; Van Allen Probes