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  • 1
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    Jupiter's X-ray and EUV auroras monitored by Chandra, XMM-Newton, and Hisaki satellite (2016)
    Wiley
    Details
    Publication Date: 2016-02-06
    Description: Jupiter's X-ray auroral emission in the polar cap region results from particles which have undergone strong field-aligned acceleration into the ionosphere [ Cravens et al. , 2003]. The origin of precipitating ions and electrons and the time variability in the X-ray emission are essential to uncover the driving mechanism for the high energy acceleration. The magnetospheric location of the source field line where the X-ray is generated is likely affected by the solar wind variability. However, these essential characteristics are still unknown because the long-term monitoring of the X-rays and contemporaneous solar wind variability has not been carried out. In Apr 2014, the first long-term multi-wavelength monitoring of Jupiter's X-ray and EUV auroral emissions was made by the Chandra X-ray Observatory, XMM-Newton, and Hisaki satellite. We find that the X-ray count rates are positively correlated with the solar wind velocity and insignificantly with the dynamic pressure. Based on the magnetic field mapping model, a half of the X-ray auroral region was found to be open to the interplanetary space. The other half of the X-ray auroral source region is magnetically connected with the pre-noon to post-dusk sector in the outermost region of the magnetosphere, where the Kelvin-Helmholtz (KH) instability, magnetopause reconnection, and quasi-periodic particle injection potentially take place. We speculate that the high energy auroral acceleration is associated with the KH instability and/or magnetopause reconnection. This association is expected to also occur in many other space plasma environments such as Saturn and other magnetized rotators.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Periodic variations of oxygen EUV dayglow in the upper atmosphere of Venus: Hisaki/EXCEED observations (2015)
    Wiley
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    Publication Date: 2015-10-29
    Description: Using the Extreme Ultraviolet Spectroscope for Exsospheric Dynamics (EXCEED) aboard Hisaki and the Solar Extreme Ultraviolet Monitor (SEM) on the Solar and Heliospheric Observatory (SOHO), we investigate variations of the extreme ultraviolet (EUV) dayglow brightness for OII 83.4 nm, OI 130.4 nm and OI 135.6 nm in the Venusian upper atmosphere observed in Mar-April (period 1), April-May (period 2) and June-July (period 3) in 2014. The result shows that characteristic periodicities exist in the dayglow variations other than the ~ 27-day solar rotational effect of the solar EUV flux: 1.8, 2.8, 3.1, 4.5, and 9.9-day in period 1, 1.1-day in period 2, and 1.0 and 11-day in period 3. Many of these periodicities are consistent with previous observations and theory. We suggest these periodicities are related to density oscillations of oxygen atoms or photoelectrons in the thermosphere. The cause of these periodicities is still uncertain, but planetary-scale waves and/or gravity waves propagating from the middle atmosphere, and/or minor periodic variations of the solar EUV radiation flux may play a role. Effects of the solar wind parameters (velocity, dynamic pressure and interplanetary magnetic field's (IMF) intensity) on the dayglow variations are also investigated using the Analyser of Space Plasma and Energetic Atoms (ASPERA-4) and magnetometer (MAG) aboard Venus Express. Although clear correlation with the dayglow variations is not found, their minor periodicities are similar to the dayglow periodicities. Contribution of the solar wind to the dayglow remains still unknown, but the solar wind parameters might affect the dayglow variations.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
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    Weakening of Jupiter's main auroral emission during January 2014 (2016)
    Wiley
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    Publication Date: 2016-01-29
    Description: In January 2014 Jupiter's FUV main auroral oval decreased its emitted power by 70% and shifted equatorward by ∼1 ∘ . Intense, low latitude features were also detected. The decrease in emitted power is attributed to a decrease in auroral current density rather than electron energy. This could be caused by a decrease in the source electron density, an order of magnitude increase in the source electron thermal energy, or a combination of these. Both can be explained either by expansion of the magnetosphere, or by an increase in the inward transport of hot plasma through the middle magnetosphere and its interchange with cold flux tubes moving outward. In the latter case the hot plasma could have increased the electron temperature in the source region and produced the intense, low latitude features, while the increased cold plasma transport rate produced the shift of the main oval.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
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    Key Role of the Kuroshio Current in the Formation of Frontal Structure of an Extratropical Cyclone Associated with Heavy Precipitation (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract In this study, the authors examined how the Kuroshio Current affected the frontal structure of an extratropical cyclone associated with heavy precipitation. We focused on an extratropical cyclone and related heavy precipitation on Miyake Island, which is situated near the Kuroshio Current, in January 2017. We first investigated the frontal structure and the attendant precipitation using observational data and objective analysis data. As the cyclone grew around the Kuroshio Current, a nonclassic front (outer front) intensified to the north of a warm front. A line‐shaped precipitation band developed along the outer front, contributing to the heavy precipitation on Miyake Island. The outer front lay along a sea surface temperature (SST) front associated with the Kuroshio Current in its early life stage. To clarify the impact of the SST front on the formation of the incipient outer front, we next conducted cloud‐resolving numerical experiments using SST distributions with and without the oceanic frontal structure. In the real SST experiment, sensible heat supply from the Kuroshio Current was large, while the amount from the ocean on the northern side of the warm current was small. This meridional difference in sensible heating caused frontogenesis along the SST front, which created the incipient front. Consequently, the real SST experiment reproduced the formation of the front. In contrast, the SST sensitivity experiments did not simulate such a sensible heating pattern or front formation. Thus, the Kuroshio Current played a key role in forming the incipient outer front and contributed to the heavy precipitation.
    Print ISSN: 2169-897X
    Electronic ISSN: 2169-8996
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
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    Azimuthal Variation in the Io Plasma Torus Observed by the Hisaki Satellite From 2013 to 2016 (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract In the Jovian magnetosphere, sulfur and oxygen ions supplied by the satellite Io are distributed in the so‐called Io plasma torus. The plasma torus is located in the inner area of the magnetosphere and the plasma in the torus corotates with the planet. The density and the temperature of the plasma in the torus have significant azimuthal variations. In this study, data from three‐year observations obtained by the Hisaki satellite, from December 2013 to August 2016, were used to investigate statistically the azimuthal variations and to find out whether the variations were influenced by the increase in neutral particles from Io. The azimuthal variation was obtained from a time series of sulfur ion line ratios, which were sensitive to the electron temperature and the sulfur ion mixing ratio S3+/S+. The major characteristics of the azimuthal variation in the plasma parameters were consistent with the dual hot electron model, proposed to explain previous observations. On the other hand, the Hisaki data showed that the peak System III longitude in the S3+/S+ ratio was located not only around 0°–90°, as in previous observations, but also around 180°–270°. The rotation period, the System IV periodicity, was sometimes close to the Jovian rotation period. Persistent input of energy to electrons in a limited longitude range of the torus is associated with the shortening of the System IV period.
    Print ISSN: 2169-9380
    Electronic ISSN: 2169-9402
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
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    Hot electron component in the Io plasma torus confirmed through EUV spectral analysis (2011)
    Wiley
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    Publication Date: 2011-09-03
    Description: The Io plasma torus is composed mainly of sulfur and oxygen ions and their compounds, together with a background of electrons. In addition to those basic components, several in situ observations have shown that a small percentage of the electrons there have been excited to be as much as 100 times hotter than the background electrons. They have a significant impact on the energy balance in the Jovian inner magnetosphere. However, their generation process has not yet been clarified. One difficulty is that the available data about the hot electrons all come from in situ observations which cannot explore the temporal and spatial distributions explicitly. Therefore, remote sensing which can take a direct picture of the plasma dynamics is necessary in order to clarify the hot electron problem. In this study, a plasma diagnosis method was used for the Io plasma torus EUV spectra taken from the Cassini spacecraft. Agreement with previous observations confirmed the background electron temperature and ion compositions as determined by our model. In addition, the available data are matched even better when the model is run with a hot electron component. This consistent confirmation by remote sensing is a first. Because of the limited temporal resolution and observational coverage, the results could not be used to explain the generation process of the hot electrons. However, we expect that this method will be useful in studying the hot electron generation process when data from future missions with better temporal resolution and more complete coverage become available.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
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    Lifting of xz/yz orbital degeneracy at the structural transition in detwinned FeSe (2014)
    American Physical Society (APS)
    Details
    Publication Date: 2014-09-30
    Description: Author(s): T. Shimojima, Y. Suzuki, T. Sonobe, A. Nakamura, M. Sakano, J. Omachi, K. Yoshioka, M. Kuwata-Gonokami, K. Ono, H. Kumigashira, A. E. Böhmer, F. Hardy, T. Wolf, C. Meingast, H. v. Löhneysen, H. Ikeda, and K. Ishizaka We study superconducting FeSe (Tc=9K) exhibiting the tetragonal-orthorhombic structural transition (Ts∼90K) without any antiferromagnetic ordering, by utilizing angle-resolved photoemission spectroscopy. In the detwinned orthorhombic state, the energy position of the dyz orbital band at the Brilloui... [Phys. Rev. B 90, 121111] Published Mon Sep 29, 2014
    Keywords: Electronic structure and strongly correlated systems
    Print ISSN: 1098-0121
    Electronic ISSN: 1095-3795
    Topics: Physics
    Published by American Physical Society (APS)
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  • 8
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    Impacts of a warming marginal sea on torrential rainfall organized under the Asian summer monsoon (2014)
    Springer Nature
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    Publication Date: 2014-07-19
    Description: Monsoonal airflow from the tropics triggers torrential rainfall over coastal regions of East Asia in summer, bringing flooding situations into areas of growing population and industries. However, impacts of rapid seasonal warming of the shallow East China Sea ECS and its pronounced future warming upon extreme summertime rainfall have not been explored. Here we show through cloudresolving atmospheric model simulations that observational tendency for torrential rainfall events over western Japan to occur most frequently in July cannot be reproduced without the rapid seasonal warming of ECS. The simulations also suggest that the future ECS warming will increase precipitation substantially in such an extreme event as observed in midJuly 2012 and also the likelihood of such an event occurring in June. A need is thus urged for reducing uncertainties in future temperature projections over ECS and other marginal seas for better projections of extreme summertime rainfall in the surrounding areas. Scientific Reports 4 doi: 10.1038/srep05741
    Electronic ISSN: 2045-2322
    Topics: Natural Sciences in General
    Published by Springer Nature
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  • 9
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    Evidence for global electron transportation into the jovian inner magnetosphere (2014)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2014-09-27
    Description: Jupiter's magnetosphere is a strong particle accelerator that contains ultrarelativistic electrons in its inner part. They are thought to be accelerated by whistler-mode waves excited by anisotropic hot electrons (〉10 kiloelectron volts) injected from the outer magnetosphere. However, electron transportation in the inner magnetosphere is not well understood. By analyzing the extreme ultraviolet line emission from the inner magnetosphere, we show evidence for global inward transport of flux tubes containing hot plasma. High-spectral-resolution scanning observations of the Io plasma torus in the inner magnetosphere enable us to generate radial profiles of the hot electron fraction. It gradually decreases with decreasing radial distance, despite the short collisional time scale that should thermalize them rapidly. This indicates a fast and continuous resupply of hot electrons responsible for exciting the whistler-mode waves.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Yoshioka, K -- Murakami, G -- Yamazaki, A -- Tsuchiya, F -- Kimura, T -- Kagitani, M -- Sakanoi, T -- Uemizu, K -- Kasaba, Y -- Yoshikawa, I -- Fujimoto, M -- New York, N.Y. -- Science. 2014 Sep 26;345(6204):1581-4. doi: 10.1126/science.1256259.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA), Sagamihara, Japan. kazuo@stp.isas.jaxa.jp. ; Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA), Sagamihara, Japan. ; Planetary Plasma and Atmospheric Research Center, Tohoku University, Sendai, Japan. ; Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA), Sagamihara, Japan. National Astronomical Observatory of Japan, Mitaka, Japan. ; Department of Geophysics, Tohoku University, Sendai, Japan. ; Department of Earth and Planetary Science, University of Tokyo, Tokyo, Japan. ; Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA), Sagamihara, Japan. Earth-Life Science Institute, Tokyo Institute of Technology, Tokyo, Japan.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25258073" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 10
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    Observation of Excitonic N-Body Bound States: Polyexcitons in Diamond (2013)
    American Physical Society (APS)
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    Publication Date: 2013-07-10
    Description: Author(s): J. Omachi, T. Suzuki, K. Kato, N. Naka, K. Yoshioka, and M. Kuwata-Gonokami We have found a series of resonances associated with the bound state (polyexcitons, PE N s) of N excitons up to N =6 in the emission spectra of diamond under two-photon excitation at around 10 K. Time-resolved spectra show a stepwise formation of PE N s with smaller to larger N , as well as a successive d... [Phys. Rev. Lett. 111, 026402] Published Tue Jul 09, 2013
    Keywords: Condensed Matter: Electronic Properties, etc.
    Print ISSN: 0031-9007
    Electronic ISSN: 1079-7114
    Topics: Physics
    Published by American Physical Society (APS)
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