TY - JOUR
T1 - Dependence of Generation of Whistler Mode Chorus Emissions on the Temperature Anisotropy and Density of Energetic Electrons in the Earth's Inner Magnetosphere
AU - Katoh, Y.
AU - Omura, Y.
AU - Miyake, Y.
AU - Usui, H.
AU - Nakashima, H.
N1 - Funding Information:
The computer simulation was performed on the KDK computer system at the Research Institute for Sustainable Humanosphere, Kyoto University, and the computational resources of the HPCI system provided by the Research Institute for Information Technology, Kyushu University; the Information Technology Center, Nagoya University; and the Cyberscience Center, Tohoku University through the HPCI System Research Project (Project IDs: hp160131 and hp170064). This study is supported by Grants-in-Aid for Scientific Research (26287120, 15H05747, 15H05815, 15H03730, 17K18798, and 17H06140) of Japan Society for the Promotion of Science. This research is also supported by “Advanced Computational Scientific Program” of Research Institute for Information Technology, Kyushu University, by “Joint Usage/Research Center for Interdisciplinary Large-scale Information Infrastructures” in Japan (Project ID: jh170005-NAH), by MEXT as “Exploratory Challenge on Post-K computer” (Elucidation of the Birth of Exoplanets (Second Earth) and the Environmental Variations of Planets in the Solar System), and by “Computational Joint Research Program (Collaborative Research Project on Computer Science with High-Performance Computing)” at the Institute for Space-Earth Environmental Research, Nagoya University. We thank D. Summers for useful discussions. The simulation data supporting this paper are available upon request to the cor responding author.
Publisher Copyright:
©2018. American Geophysical Union. All Rights Reserved.
PY - 2018/2
Y1 - 2018/2
N2 - We carry out a series of self-consistent electron hybrid code simulations for the dependence of chorus generation process on the temperature anisotropy and density of energetic electrons in the Earth's inner magnetosphere. We use the same magnetic field gradient in the simulation system and different temperature anisotropy AT for the initial distribution of energetic electrons at the magnetic equator. We conduct 6 sets of simulations for different AT from 4 to 9, changing the initial number density Nh of energetic electrons at the equator in each set of simulations. By analyzing the spectra obtained in the simulation results, we identify chorus elements with rising tones in the results for higher Nh but no distinct chorus in smaller Nh. We compare the simulation results with estimations of the threshold and optimum amplitude proposed by the nonlinear wave growth theory. We find that the chorus generation processes reproduced in the simulation results are consistently explained by the theoretical estimates. We also compare the simulation results with linear growth rates for all simulation runs. We find clear disagreement between the spectral characteristics of reproduced chorus and the predictions by the linear theory. The present study clarifies that the spectra of chorus are essentially different from those predicted by the linear theory and are determined fully by nonlinear processes of wave-particle interactions in the chorus generation region.
AB - We carry out a series of self-consistent electron hybrid code simulations for the dependence of chorus generation process on the temperature anisotropy and density of energetic electrons in the Earth's inner magnetosphere. We use the same magnetic field gradient in the simulation system and different temperature anisotropy AT for the initial distribution of energetic electrons at the magnetic equator. We conduct 6 sets of simulations for different AT from 4 to 9, changing the initial number density Nh of energetic electrons at the equator in each set of simulations. By analyzing the spectra obtained in the simulation results, we identify chorus elements with rising tones in the results for higher Nh but no distinct chorus in smaller Nh. We compare the simulation results with estimations of the threshold and optimum amplitude proposed by the nonlinear wave growth theory. We find that the chorus generation processes reproduced in the simulation results are consistently explained by the theoretical estimates. We also compare the simulation results with linear growth rates for all simulation runs. We find clear disagreement between the spectral characteristics of reproduced chorus and the predictions by the linear theory. The present study clarifies that the spectra of chorus are essentially different from those predicted by the linear theory and are determined fully by nonlinear processes of wave-particle interactions in the chorus generation region.
KW - numerical experiments
KW - wave-particle interaction
KW - whistler mode chorus
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U2 - 10.1002/2017JA024801
DO - 10.1002/2017JA024801
M3 - Article
AN - SCOPUS:85041483155
VL - 123
SP - 1165
EP - 1177
JO - Journal of Geophysical Research: Space Physics
JF - Journal of Geophysical Research: Space Physics
SN - 2169-9380
IS - 2
ER -