• 천문학회보
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• 제38권2호
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• pp.94.1-94.1
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• 2013

Whistler mode chorus waves, which are observed outside the plasmasphere of the Earth's magnetosphere, play a major role in accelerating and scattering energetic electrons in the radiation belts. In this study we developed a predicting scheme of the global distribution of chorus by using the Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellite data. First, we determined global spatial distributions of chorus activity, and identified fit functions that best represent chorus intensities in specific L-MLT zones. Second, we determined the specific dependence of average chorus intensity on preceding solar wind conditions (e.g., solar wind speed, IMF Bz, energy coupling degree) as well as preceding geomagnetic states (as represented by AE, for example). Finally, we combined these two results to develop the predicting functions for the global distribution and intensity of chorus. Implementing these results in the radiation belt models should improve the local acceleration effect by chorus waves.

• Journal of Astronomy and Space Sciences
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• 제31권4호
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• pp.295-301
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• 2014

Whistler mode chorus wave is considered to play a critical role in accelerating and precipitating the electrons in the outer radiation belt. In this paper we test a conventional scenario of triggering chorus using THEMIS satellite observations of waves and particles. Specifically, we test if the chorus onset is consistent with development of anisotropy in the electron phase space density (PSD). After analyzing electron PSD for 73 chorus events, we find that, for ~80 % of them, their onsets are indeed associated with development of the positive anisotropy in PSD where the pitch angle distribution of electron velocity peaks at 90 degrees. This PSD anisotropy is prominent mainly at the electron energy range of ${\leq}$ ~20 keV. Interestingly, we further find that there is sometimes a time delay among energies in the increases of the anisotropy: A development of the positive anisotropy occurs earlier by several minutes for lower energy than for an adjacent higher energy.

• 천문학회보
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• 제32권2호
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• pp.37.1-37.1
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• 2007

• Journal of Astronomy and Space Sciences
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• 제26권4호
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• pp.439-450
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• 2009

2006년 상반기동안 GOES 10에 의해 관측된 > 2MeV의 전자에너지 채널에서 반복되는 상대론적 전자 증가 이벤트(GREE, Geosynchronous Relativistic Electron Event)가 4회 있었다. 이 현상들은 모두 코로나 구멍(Coronal hole)에서부터 나온 고속 태양풍(HSS, High Speed Solar Wind Stream)과 관련된 것으로 여겨진다. 약 27일 주기를 갖는 이 4회의 전자 증가 현상은 플럭스가 점점 증가하는 형태를 보인다. 현재까지 알려진 상대론적 전자 증가 현상의 주요 원인으로는 다음의 요소들이 언급되어 왔다: (1) 코로나 구멍과 관련된 태양풍 속도, (2) Pc5 ULF 파동, (3) 행성간 자기장(IMF, Interplanetary Magnetic Field) Bz의 남쪽 성 분, (4) 자기 부폭풍(substorm)의 발생, (5) 증가된 휘슬러 모드 코러스 파동(whistler mode chorus wave)과 (6)동압력(dynamic pressure). 따라서 이 논문에서는 2006년 상반기 동안 앞에서 언급한 6가지 현상 들을 분석하여 어느 요소가 상대론적 전자 증가 현상의 플럭스와 가장 가까운 연관성이 있는지 알아보고자 한다.

• Journal of Astronomy and Space Sciences
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• 제32권4호
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• pp.317-325
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• 2015

Energy spectra of electron microbursts from 170 keV to 340 keV have been measured by the solid-state detectors aboard the low-altitude (680 km) polar-orbiting Korean STSAT-1 (Science and Technology SATellite). These measurements have revealed two important characteristics unique to the microbursts: (1) They are produced by a fast-loss cone-filling process in which the interaction time for pitch-angle scattering is less than 50 ms and (2) The e-folding energy of the perpendicular component is larger than that of the parallel component, and the loss cone is not completely filled by electrons. To understand how wave-particle interactions could generate microbursts, we performed a test particle simulation and investigated how the waves scattered electron pitch angles within the timescale required for microburst precipitation. The application of rising-frequency whistler-mode waves to electrons of different energies moving in a dipole magnetic field showed that chorus magnetic wave fields, rather than electric fields, were the main cause of microburst events, which implied that microbursts could be produced by a quasi-adiabatic process. In addition, the simulation results showed that high-energy electrons could resonate with chorus waves at high magnetic latitudes where the loss cone was larger, which might explain the decreased e-folding energy of precipitated microbursts compared to that of trapped electrons.

• 천문학회보
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• 제37권1호
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• pp.90.1-90.1
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• 2012

Understanding the dynamics of relativistic electron acceleration, loss, and transport in the Earth's radiation belt during magnetic storms is a challenging task. The U.S. National Science Foundation's Geospace Environment Modeling (GEM) has identified five magnetic storms for in-depth study that occurred during the second half of the Combined Release and Radiation Effects Satellite (CRRES) mission in the year 1991. In this study, we show the responses of relativistic radiation belt electrons to the magnetic storms by comparing the time-dependent 3-D Versatile Electron Radiation Belt (VERB) simulations with the CRRES MEA 1 MeV electron observations in order to investigate the relative roles of the competing effects of previously proposed scattering mechanisms at different storm phases, as well as to examine the extent to which the simulations can reproduce observations. The major scattering processes in our model are radial transport due to Ultra Low Frequency (ULF) electromagnetic fluctuations, pitch-angle and energy diffusion including mixed diffusion by whistler mode chorus waves outside the plasmasphere, and pitch-angle scattering by plasmaspheric hiss inside the plasmasphere. We provide a detailed description of simulations for each of the GEM storm events.

• 천문학회보
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• 제37권2호
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• pp.132.1-132.1
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• 2012

Radiation Belt Environment (RBE) model has developed to understand radiation belt dynamics as it considers whistler mode hiss and chorus waves which is responsible for relativistic electron acceleration and precipitation. Recently, many studies on electron loss by pitch-angle scattering have reported that elctromagnetic ion cyclotron (EMIC) wave is also responsible for main loss mechanism in dusk and equatorial regeion. Here, we attempt to incorporate EMIC into RBE model simulation code to understand more detailed physical dynamics in Radiation belt environemnt. We compare this developed model to data during storm events where both of electron loss and EMIC waves were detected.