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Filters: Author is Hwang, Junga  [Clear All Filters]
Authors: Yoon Peter H., Hwang Junga, Kim Hyangpyo, and Seough Jungjoon
Title: Quasi Thermal Noise Spectroscopy for Van Allen Probes
Abstract: Quasi thermal fluctuations in the Langmuir/upper‐hybrid frequency range are pervasively observed in space plasmas including the radiation belt and the ring current region of inner magnetosphere as well as the solar wind. The quasi thermal noise spectroscopy may be employed in order to determine the electron density and temperature as well as to diagnose the properties of energetic electrons when direct measurements are not available. However, when employing the technique, one must carefully take the spacecraft orientation into account. The present paper takes the upper‐hybrid and multiple harmonic—or (n + 1/2)fce—emissions measured by the Van Allen Probes as an example in order to illustrate how the spacecraft antenna geometrical factor can be incorporated into the theoretical . . .
Date: 04/2019 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2019JA026460 Available at:
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Authors: Hwang Junga, and Yoon Peter H.
Title: High-frequency thermal fluctuations and instabilities in the radiation belt environment
Abstract: This paper overviews the electrostatic and electromagnetic theories of spontaneous emission in magnetized plasma as they relate to measured electric and magnetic field fluctuations in quiet time radiation belt and ring current region. The pervasively detected high‐frequency fluctuations in the upper‐hybrid frequency range as well as the background low‐frequency range spectral profile in the whistler mode range are explained within the context of the spontaneous emission theory. The quasilinear calculation of loss‐cone instability is also carried out in order to validate the assumption of spontaneous emission model. It is shown that the saturated wave amplitudes associated with the upper‐hybrid and multiple‐harmonic cyclotron instability are quite low, indicating that the theore. . .
Date: 10/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2018JA025643 Available at:
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Authors: Bin Kang Suk-, Min Kyoung-Wook, Fok Mei-Ching, Hwang Junga, and Choi Cheong-Rim
Title: Estimation of pitch angle diffusion rates and precipitation time scales of electrons due to EMIC waves in a realistic field model
Abstract: Electromagnetic ion cyclotron (EMIC) waves are closely related to precipitating loss of relativistic electrons in the radiation belts, and thereby, a model of the radiation belts requires inclusion of the pitch angle diffusion caused by EMIC waves. We estimated the pitch angle diffusion rates and the corresponding precipitation time scales caused by H and He band EMIC waves using the Tsyganenko 04 (T04) magnetic field model at their probable regions in terms of geomagnetic conditions. The results correspond to enhanced pitch angle diffusion rates and reduced precipitation time scales compared to those based on the dipole model, up to several orders of magnitude for storm times. While both the plasma density and the magnetic field strength varied in these calculations, the reduction of the . . .
Date: 10/2015 Publisher: Journal of Geophysical Research: Space Physics Pages: 8529 - 8546 DOI: 10.1002/2014JA020644 Available at:
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