Papers by Masaki Matsushima
Earth, Planets and Space, 2022
Wave–particle interactions are fundamental processes in space plasma, and some plasma waves, incl... more Wave–particle interactions are fundamental processes in space plasma, and some plasma waves, including electrostatic solitary waves (ESWs), are recognised as broadband noises (BBNs) in the electric field spectral data. Spacecraft observations in recent decades have detected BBNs around the Moon, but the generation mechanism of the BBNs is not fully understood. Here, we study a wake boundary traversal with BBNs observed by Kaguya, which includes an ESW event previously reported by Hashimoto et al. Geophys Res Lett 37:L19204 10.1029/2010GL044529 (2010). Focusing on the relation between BBNs and electron pitch-angle distribution functions, we show that upward electron beams from the nightside lunar surface are effective for the generation of BBNs, in contrast to the original interpretation by Hashimoto et al. Geophys Res Lett 37:L19204 10.1029/2010GL044529 (2010) that high-energy electrons accelerated by strong ambipolar electric fields excite ESWs in the region far from the Moon. When...
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Earth, Planets and Space, 2003
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Earth, Planets and Space, 2012
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Journal of Geophysical Research: Space Physics, 2012
We have analyzed nongyrotropic electron velocity distribution functions (VDFs) obtained near the ... more We have analyzed nongyrotropic electron velocity distribution functions (VDFs) obtained near the lunar surface. Electron VDFs, measured at ∼10–100 km altitude by Kaguya in both the solar wind and the Earth's magnetosphere, exhibit nongyrotropic empty regions associated with the ‘gyroloss’ effect; i.e., electron absorption by the lunar surface combined with electron gyromotion. Particle‐trace calculations allow us to derive theoretical forbidden regions in the electron VDFs, thereby taking into account the modifications due to nonuniform magnetic fields caused by diamagnetic‐current systems, lunar‐surface charging, and electric fields perpendicular to the magnetic field. Comparison between the observed empty regions with the theoretically derived forbidden regions suggests that various components modify the characteristics of the nongyrotropic electron VDFs depending on the ambient‐plasma conditions. On the lunar nightside in the magnetotail lobes, negative surface potentials sli...
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Japan Geoscience Union, 2015
Applying the latest advanced paleomagnetic technique to the Apollo samples, it is now well establ... more Applying the latest advanced paleomagnetic technique to the Apollo samples, it is now well established that the Moon once had an ancient core dynamo operated from 4.2 to 3.56 billion years ago, or even younger age. Because these results are based on paleointensity retrieved from unoriented samples, any directional information cannot be obtained. Instead, we focus on the magnetic anomalies on the Moon. Since the magnetization of the lunar crust in the magnetic anomalies could be records of an early core dynamo of the Moon, the magnetic anomalies may yield directional information of the lunar paleomagnetic field. Here we present results of our global survey of magnetic anomalies on the lunar surface using magnetometer data acquired by the Lunar Prospector and Kaguya spacecraft. Using an iterative inversion method, we extract magnetization vectors from well-isolated magnetic anomalies and derive the positions of paleomagnetic poles. We find two distinct clusters of the resultant paleom...
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Japan Geoscience Union, 2014
Magnetic fluctuations around the moon are characterized with 2 major categories: (1) large amplit... more Magnetic fluctuations around the moon are characterized with 2 major categories: (1) large amplitude monochromatic waves of 0.01 Hz and (2) monochromatic or non-monochromatic whistler waves, both observed on the dayside surface of the moon or above the terminator. Their generation is associated with (1) the solar wind ions or (2) electrons, respectively, reflected at the surface of the moon or the local crustal magnetic field. The monochromatic whistler waves are found at 1-2 Hz with left-handed polarization due to the Doppler shift caused by the solar wind flow. The frequency range is determined by the group velocity of the whistler waves that can overcome the solar wind speed.
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Tectonophysics, 2020
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Icarus, 2017
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Journal of Geography (Chigaku Zasshi), 2005
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Geophysical Research Letters, 2010
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Earth, Planets and Space, 2010
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Geophysical Research Letters, 2010
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Japan Geoscience Union, Mar 13, 2020
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AGU Fall Meeting 2021, Dec 15, 2021
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Japan Geoscience Union, 2016
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ABSTRACT
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ABSTRACT While plenty of three-dimensional (3-D) seismic tomographic images has been revealed (e.... more ABSTRACT While plenty of three-dimensional (3-D) seismic tomographic images has been revealed (e.g. Zhao et al., 1992; Nakajima et al., 2001), only a few 3-D electrical conductivity distribution model has been proposed in terms of wedge mantle in subduction zones (e.g. Patro et al., 2007). Introducing the state-of-the-art mobile magnetotelluric (MT) observation systems (LEMI-417 and NIMS), we have acquired MT data at Tohoku district, northeastern Japan for the aim of 3-D electrical conductivity distribution in the wedge mantle. Typical observation duration are three months at each site, and MT response functions from 10 to 20000 seconds in period have succesfully collected with fine quality. The site location is arranged with ca. 20 km interval. The MT phase response functions at many sites show over 90 degrees over 5000 seconds and suggest that 3-D distribution beneath this area. Using twenty-three sites' data, we carried out the three-dimensional inversion analysis with WSINV3DMT code (Siripuvaraporn et al., 2005). Although the inversion process is still on the way and the conversion is not enough, the east-west profile (acrsss the Japan Arc) of the preliminary result shows that conductive region appears at about 120 km in depth beneath back-arc region and elongates obliquely towards the volcanic front. The north-south profile (along the Japan Arc) shows the vertical conductive and resistive columns appears alternatively. That basic images are well consisted with the seismic tomographic model (Nakajima, 2001), provided that conductive and low velocity zone should corresponds with each other. Obtained the final 3-D model, our final destination is to estimate the mantle geotherm and fluid distributions in the wedge mantle using seismic tomographic and electrical conductivity images.
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Papers by Masaki Matsushima