はやぶさ2プロジェクトチーム

Iku SHINOHARA

  (篠原 育)

Profile Information

Affiliation
Professor, Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency
Degree
Ph.D(The University of Tokyo)

J-GLOBAL ID
200901025081752002
researchmap Member ID
5000018897

Papers

 241
  • Zijin Zhang, Anton Artemyev, Didier Mourenas, Vassilis Angelopoulos, Xiao‐Jia Zhang, S. Kasahara, Y. Miyoshi, A. Matsuoka, Y. Kasahara, T. Mitani, S. Yokota, T. Hori, K. Keika, T. Takashima, M. Teramoto, S. Matsuda, I. Shinohara
    Journal of Geophysical Research: Space Physics, 129(12), Dec 13, 2024  
    Abstract We investigate the dynamics of relativistic electrons in the Earth's outer radiation belt by analyzing the interplay of several key physical processes: electron losses due to pitch angle scattering from electromagnetic ion cyclotron (EMIC) waves and chorus waves, and electron flux increases from chorus wave‐driven acceleration of 100–300 keV seed electrons injected from the plasma sheet. We examine a weak geomagnetic storm on 17 April 2021, using observations from various spacecraft, including GOES, Van Allen Probes, ERG/ARASE, MMS, ELFIN, and POES. Despite strong EMIC‐ and chorus wave‐driven electron precipitation in the outer radiation belt, trapped 0.1–1.5 MeV electron fluxes actually increased. We use theoretical estimates of electron quasi‐linear diffusion rates by chorus and EMIC waves, based on statistics of their wave power distribution, to examine the role of those waves in the observed relativistic electron flux variations. We find that a significant supply of 100–300 keV electrons by plasma sheet injections together with chorus wave‐driven acceleration can overcome the rate of chorus and EMIC wave‐driven electron losses through pitch angle scattering toward the loss cone, explaining the observed net increase in electron fluxes. Our study emphasizes the importance of simultaneously taking into account resonant wave‐particle interactions and modeled local energy gradients of electron phase space density following injections, to accurately forecast the dynamical evolution of trapped electron fluxes.
  • I Made Agus Dwi Suarjaya, Desy Purnami Singgih Putri, Yuji Tanaka, Fajar Purnama, I Putu Agung Bayupati, Linawati, Yoshiya Kasahara, Shoya Matsuda, Yoshizumi Miyoshi, Iku Shinohara
    Remote Sensing, 16(22), Nov 15, 2024  Peer-reviewed
    The plasmasphere within Earth’s magnetosphere plays a crucial role in space physics, with its electron density distribution being pivotal and strongly influenced by solar activity. Very Low Frequency (VLF) waves, including whistlers, provide valuable insights into this distribution, making the study of their propagation through the plasmasphere essential for predicting space weather impacts on various technologies. In this study, we evaluate the performance of different deep learning model sizes for lightning whistler detection using the YOLO (You Only Look Once) architecture. To achieve this, we transformed the entirety of raw data from the Arase (ERG) Satellite for August 2017 into 2736 images, which were then used to train the models. Our approach involves exposing the models to spectrogram diagrams—visual representations of the frequency content of signals—derived from the Arase Satellite’s WFC (WaveForm Capture) subsystem, with a focus on analyzing whistler-mode plasma waves. We experimented with various model sizes, adjusting epochs, and conducted performance analysis using a partial set of labeled data. The testing phase confirmed the effectiveness of the models, with YOLOv5n emerging as the optimal choice due to its compact size (3.7 MB) and impressive detection speed, making it suitable for resource-constrained applications. Despite challenges such as image quality and the detection of smaller whistlers, YOLOv5n demonstrated commendable accuracy in identifying scenarios with simple shapes, thereby contributing to a deeper understanding of whistlers’ impact on Earth’s magnetosphere and fulfilling the core objectives of this study.
  • Weiqin Sun, Xiao‐Jia Zhang, Anton V. Artemyev, Didier Mourenas, Steven K. Morley, Vassilis Angelopoulos, S. Kasahara, Y. Miyoshi, A. Matsuoka, T. Mitani, S. Yokota, T. Hori, K. Keika, T. Takashima, M. Teramoto, I. Shinohara, K. Yamamoto
    Journal of Geophysical Research: Space Physics, 129(11), Oct 28, 2024  
    Abstract Near‐equatorial measurements of energetic electron fluxes, in combination with numerical simulation, are widely used for monitoring of the radiation belt dynamics. However, the long orbital periods of near‐equatorial spacecraft constrain the cadence of observations to once per several hours or greater, that is, much longer than the mesoscale injections and rapid local acceleration and losses of energetic electrons of interest. An alternative approach for radiation belt monitoring is to use measurements of low‐altitude spacecraft, which cover, once per hour or faster, the latitudinal range of the entire radiation belt within a few minutes. Such an approach requires, however, a procedure for mapping the flux from low equatorial pitch angles (near the loss cone) as measured at low altitude, to high equatorial pitch angles (far from the loss cone), as necessitated by equatorial flux models. Here we do this using the high energy resolution ELFIN measurements of energetic electrons. Combining those with GPS measurements we develop a model for the electron anisotropy coefficient, , that describes electron flux dependence on equatorial pitch‐angle, , . We then validate this model by comparing its equatorial predictions from ELFIN with in‐situ near‐equatorial measurements from Arase (ERG) in the outer radiation belt.
  • A. Nagatani, Y. Miyoshi, K. Asamura, L. M. Kistler, S. Nakamura, K. Seki, Y. Ogawa, I. Shinohara
    Geophysical Research Letters, 51(18), Sep 16, 2024  
    Abstract We analyzed time‐of‐flight (TOF) data from the Arase satellite to investigate temporal variations of the molecular ion group (O2+, NO+, and N2+) at 19.2 keV/q in the inner magnetosphere for 6 years from the solar declining to rising phase. The molecular ions counts were estimated by subtracting the background contamination of oxygen counts. While the number of clear molecular ion events was small, the estimated counts exhibited good correlation with the solar wind dynamic pressure and SYM‐H index. Long‐term variations of the molecular ions differed from those of counts of the O+ and N+ group. Additionally, we discuss the importance of the solar wind dynamic pressure in causing variations of molecular ions in the inner magnetosphere.
  • S. Imajo, Y. Miyoshi, Y. Kazama, K. Asamura, I. Shinohara, K. Shiokawa, Y. Kasahara, Y. Kasaba, A. Matsuoka, S.‐Y. Wang, S. W. Y. Tam, T.‐F. Chang, B.‐J. Wang, C.‐W. Jun, M. Teramoto, S. Kurita, F. Tsuchiya, A. Kumamoto, K. Saito, T. Hori
    Journal of Geophysical Research: Space Physics, 129(9), Sep 12, 2024  
    Abstract The Arase satellite observed the precipitation of monoenergetic electrons accelerated from a very high altitude above 32,000 km altitude on 16 September 2017. The event was selected in the period when the high‐angular resolution channel of the electron detector looked at pitch angles within ∼5° from the ambient magnetic field direction, and thereby was the first to examine the detailed distribution of electron flux near the energy‐dependent loss cone at such high altitudes. The potential energy below the satellite estimated from the observed energy‐dependence of the loss cone was consistent with the energy of the upgoing ion beams, indicating that ionospheric ions were accelerated by a lower‐altitude acceleration region. The accelerated electrons inside the loss cone carried a significant net field‐aligned current (FAC) density corresponding to ionospheric‐altitude FAC of up to ∼3μA/m2. Based on the anisotropy of the accelerated electrons, we estimated the height of the upper boundary of the acceleration region to be >∼2 RE above the satellite. The height distribution of the acceleration region below the satellite, estimated from the frequency of auroral kilometric radiation, was ∼4,000–13,000 km altitude, suggesting that the very‐high‐altitude acceleration region was separated from the lower acceleration region. Additionally, we observed time domain structure (TDS) electric fields on a subsecond time scale with a thin FAC indicated by magnetic deflections. Such a TDS may be generated by the formation of double layers in the magnetotail, and its potential drop could significantly contribute (∼40%–60%) to the parallel energization of precipitating auroral electrons.

Misc.

 77

Research Projects

 17