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Nakamura S.,Kyoto University | Omura Y.,Kyoto University | Shoji M.,Solar Terrestrial Environment Laboratory | Nose M.,Kyoto University | And 3 more authors.
Journal of Geophysical Research A: Space Physics | Year: 2015

We report subpacket structures found in electromagnetic ion cyclotron (EMIC) rising tone emissions observed by the Time History of Events and Macroscale Interactions during Substorms (THEMIS) probes. We investigate three typical cases in detail. The first case shows a continuous single rising tone with four obvious subpackets, and the second case is characterized by a patchy emission with multiple subpackets triggered in a broadband frequency. The third case looks like a smooth rising tone without any obvious subpacket in the fast Fourier transform spectrum, while its amplitude contains small peaks with increasing frequencies. The degree of polarization of each subpacket is generally higher than 0.8 with a left-handed polarization, and the wave direction of the subpackets is typically field aligned. We show that the time evolution of the observed frequency and amplitude can be reproduced consistently by nonlinear growth theory. We also compare the observed time span of each subpacket structure with the theoretical trapping time for second-order cyclotron resonance. They are consistent, indicating that an individual subpacket is generated through a nonlinear wave growth process which excites an element in accordance with the theoretically predicted optimum amplitude. ©2015. American Geophysical Union. All Rights Reserved. Source


Shoji M.,Solar Terrestrial Environment Laboratory | Shoji M.,Japan Aerospace Exploration Agency | Omura Y.,Kyoto University
Journal of Geophysical Research: Space Physics | Year: 2014

We perform parametric analyses of electromagnetic ion cyclotron (EMIC) triggered emissions with a gradient of the nonuniform ambient magnetic field using a hybrid simulation. According to nonlinear wave growth theory, as the gradient of the ambient magnetic field becomes larger, the theoretical threshold of the wave amplitude becomes larger, although the optimum wave amplitude for nonlinear wave growth does not change. With a larger magnetic field gradient, we obtain coherent rising-tone spectra because the triggering process of the EMIC triggered emission takes place only under a limited condition on the wave amplitude. On the other hand, with a smaller magnetic field gradient, triggering of the emissions can be caused with various wave amplitudes, and then the subpackets are generated at various locations at the same time. The concurrent triggering of emissions results in incoherent waves, observed as "broadband" EMIC bursts. Broadband emissions induce rapid precipitation of energetic protons into the loss cone since the scattering by the concurrent triggering takes place faster than that of the coherent emissions. The coherent triggered emission causes efficient proton acceleration around the equator because of the stable particle trapping by the coherent rising-tone emission. Key Points A small magnetic field gradient induces concurrent EMIC triggered emissions Concurrent emissions result in incoherent waves and rapid proton precipitation A coherent rising tone causes efficient proton acceleration near the equator ©2014. American Geophysical Union. All Rights Reserved. Source


Itow Y.,Solar Terrestrial Environment Laboratory | Itow Y.,Kobayashi Maskawa Institute for Origin of Particles and Universe
EPJ Web of Conferences | Year: 2015

Observations of ultra high energy cosmic rays by extensive air showers rely on correct modeling of hadronic interaction in the forward region at very high energy. Recent new data from the LHC, especially for forward particle production, are important for a precise understanding of air shower development. In this article recent forward production data from p-p, p-Pb, and Pb-Pb collisions at LHC are reviewed. © Owned by the authors, published by EDP Sciences, 2015. Source


Xing J.-H.,Kyoto University | Takahashi K.,Kyoto University | Yabushita A.,Kyoto University | Kinugawa T.,Kyoto University | And 9 more authors.
Aerosol Science and Technology | Year: 2011

Particle mass spectrometers of two types - a time-of-flight aerosol mass spectrometer (AMS) of Aerodyne Research Inc. and a laser desorption/ionization single particle aerosol mass spectrometer (LISPA-MS) developed at Nagoya University - were deployed to characterize aerosol particles in the Tokyo metropolitan area during the summer of 2008. Based on the ensemble measurements by AMS, equivalent mass concentration of organic aerosol, traced by mass-to-charge ratio (m/z) 44, showed a closer correlation with particulate nitrate and gas-phase odd oxygen, [O3+NO2], whereas equivalent mass concentration of organic aerosol, traced by m/z 57, did not. On a particle-by-particle basis, the relative signal peak area of various target species in the LISPA-MS spectra, which was calculated as the ion-signal fraction of the species relative to the total signal peak area summed over all the ion peaks in each spectrum, was used as a measure of the relative amount of the species. A rough qualitative agreement was obtained between the temporal variation observed in the LISPA-MS RCOO- signal and that in the AMS m/z 44, but not the AMS m/z 57, in which the LISPA-MS RCOO- signal was defined as the sum of the relative signal peak areas of 17 different negative-ion mass peaks used as markers of oxygenated organics. Analysis of the LISPA-MS spectra also showed that approximately 95% of the oxygen-containing organic particles contained nitrate, which is expected to be responsible in part for the correlation between AMS m/z 44 and AMS nitrate. Copyright © American Association for Aerosol Research. Source


Inoue S.,Kyung Hee University | Magara T.,Kyung Hee University | Pandey V.S.,National Institute of Technology Tiruchirappalli | Shiota D.,Solar Terrestrial Environment Laboratory | And 5 more authors.
Astrophysical Journal | Year: 2014

We develop a nonlinear force-free field (NLFFF) extrapolation code based on the magnetohydrodynamic (MHD) relaxation method. We extend the classical MHD relaxation method in two important ways. First, we introduce an algorithm initially proposed by Dedner et al. to effectively clean the numerical errors associated with ∇ · B . Second, the multigrid type method is implemented in our NLFFF to perform direct analysis of the high-resolution magnetogram data. As a result of these two implementations, we successfully extrapolated the high resolution force-free field introduced by Low & Lou with better accuracy in a drastically shorter time. We also applied our extrapolation method to the MHD solution obtained from the flux-emergence simulation by Magara. We found that NLFFF extrapolation may be less effective for reproducing areas higher than a half-domain, where some magnetic loops are found in a state of continuous upward expansion. However, an inverse S-shaped structure consisting of the sheared and twisted loops formed in the lower region can be captured well through our NLFFF extrapolation method. We further discuss how well these sheared and twisted fields are reconstructed by estimating the magnetic topology and twist quantitatively. © 2014. The American Astronomical Society. All rights reserved.. Source

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