Simultaneous ground-based and satellite observations of natural VLF waves in Antarctica: A case study of downward ionospheric penetration of whistler-mode waves

AbstractTo investigate downward ionospheric-penetration characteristics of VLF (several hundred Hz to 17.8 kHz) whistler-mode waves, we conducted simultaneous observations (in 2006) of natural VLF waves using both ground stations in Antarctica and the Japanese Akebono satellite. The ground-based and satellite observations included an interesting event for which both observed similar VLF waves. In this study, we theoretically calculate down-going whistler-mode wave propagation based on ground-satellite observations using the full-wave analysis. In a case study, the observed wave-normal angles were approximately 140–160 degrees for a dayside chorus event on 15 March 2006. The theoretical calculation showed that the wave-normal angles for ionospheric penetration should be around 155.6 degrees, with its angular width of approximately 2 degrees. Moreover, the wave-energy loss due to ionospheric penetration is estimated at 20.4 dB based on our theoretical calculation, in accordance with the observed 17–19 dB

The pulsating aurora and natural VLF emissions observed at Syowa Station

第2回極域科学シンポジウム/第35回極域宙空圏シンポジウム 11月16日（水） 統計数理研究所 3階リフレッシュフロ

Magnetic conjugacy of Pc1 waves and isolated proton precipitation at subauroral latitudes: Importance of ionosphere as intensity modulation region

Pc1 geomagnetic pulsations, equivalent to electromagnetic ion cyclotron waves in the magnetosphere, display a specific amplitude modulation, though the region of the modulation remains an open issue. To classify whether the amplitude modulation has a magnetospheric or ionospheric origin, an isolated proton aurora (IPA), which is a proxy of Pc1 wave–particle interactions, is compared with the associated Pc1 waves for a geomagnetic conjugate pair, Halley Research Base in Antarctica and Nain in Canada. The temporal variation of an IPA shows a higher correlation coefficient (0.88) with Pc1 waves in the same hemisphere than that in the opposite hemisphere. This conjugate observation reveals that the classic cyclotron resonance is insufficient to determine the amplitude modulation. We suggest that direct wave radiation from the ionospheric current by IPA should also contribute to the amplitude modulation

Investigating Mercury's Environment with the Two-Spacecraft BepiColombo Mission

The ESA-JAXA BepiColombo mission will provide simultaneous measurements from two spacecraft, offering an unprecedented opportunity to investigate magnetospheric and exospheric dynamics at Mercury as well as their interactions with the solar wind, radiation, and interplanetary dust. Many scientific instruments onboard the two spacecraft will be completely, or partially devoted to study the near-space environment of Mercury as well as the complex processes that govern it. Many issues remain unsolved even after the MESSENGER mission that ended in 2015. The specific orbits of the two spacecraft, MPO and Mio, and the comprehensive scientific payload allow a wider range of scientific questions to be addressed than those that could be achieved by the individual instruments acting alone, or by previous missions. These joint observations are of key importance because many phenomena in Mercury's environment are highly temporally and spatially variable. Examples of possible coordinated observations are described in this article, analysing the required geometrical conditions, pointing, resolutions and operation timing of different BepiColombo instruments sensors.Peer reviewe

Investigating Mercury's Environment with the Two-Spacecraft BepiColombo Mission

The ESA-JAXA BepiColombo mission will provide simultaneous measurements from two spacecraft, offering an unprecedented opportunity to investigate magnetospheric and exospheric dynamics at Mercury as well as their interactions with the solar wind, radiation, and interplanetary dust. Many scientific instruments onboard the two spacecraft will be completely, or partially devoted to study the near-space environment of Mercury as well as the complex processes that govern it. Many issues remain unsolved even after the MESSENGER mission that ended in 2015. The specific orbits of the two spacecraft, MPO and Mio, and the comprehensive scientific payload allow a wider range of scientific questions to be addressed than those that could be achieved by the individual instruments acting alone, or by previous missions. These joint observations are of key importance because many phenomena in Mercury's environment are highly temporally and spatially variable. Examples of possible coordinated observations are described in this article, analysing the required geometrical conditions, pointing, resolutions and operation timing of different BepiColombo instruments sensors

Simultaneous ground and satellite observations of EMIC waves and high energy ions at magnetic conjugate points

第3回極域科学シンポジウム/第36回極域宙空圏シンポジウム 11月26日（月）、27日（火） 国立極地研究所 2階ラウン

Coherent nonlinear scattering of energetic electrons in the process of whistler mode chorus generation

Cyclotron resonant wave-particle interaction of whistler mode chorus emissions drives pitch angle scatterings of a wide range of energetic electrons in the magnetosphere. We study a coherent scattering process associated with generation of the whistler mode rising chorus emissions near the geomagnetic equator in a self-consistent electromagnetic full-particle simulation. The simulation shows that coherent whistler mode rising chorus emissions scatter energetic electrons very effectively through formation of an electromagnetic electron hole. The nonlinear interaction induces acceleration of resonant electrons trapped by the wave and deceleration of untrapped resonant electrons. When the frequency of a rising chorus element continuously increases in time from lower frequencies to higher frequencies, the parallel resonant velocity continuously decreases toward lower-velocity ranges resulting in significant scattering of resonant electrons. The lower limit of resonant parallel velocity is determined by the upper frequency limit of the rising chorus element. The unscattered electrons with low parallel velocities and the accelerated resonant electrons trapped by the wave result in the distribution clearly peaked at 90°. Successive generation of rising chorus elements can scatter resonant electrons in the same resonance velocity range. The repeated scatterings make the distribution much sharper at 90°, leading to formation of a pancake distribution function as observed in the inner magnetosphere