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  • 1
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    Asymmetric electrostatic environment around spacecraft in weakly streaming plasmas (2015)
    Wiley
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    Publication Date: 2015-07-17
    Description: The double-probe electric field measurements in drifting plasmas are subject to spurious effects caused by asymmetric electrostatic structure near scientific spacecraft. Some in-situ observations just outside the plasmasphere detected spurious electric fields due to such environmental asymmetry even in subsonic ion flows across the magnetic field line. We have performed three-dimensional particle-in-cell simulations, which allow us to include long and extremely-thin wire booms as well as a spacecraft chassis, and investigated an electrostatic environment that accounts for the observations. The present simulations reveal that even subsonic ion flows can produce an appreciable potential difference between upstream and downstream of the spacecraft, and the potential difference would be detected as a spurious field of a few mV/m The necessary condition for the spurious field is a relatively-high (a few tens of V) spacecraft potential, and also the spacecraft potential hump needs to be expanded by thin wire booms biased at the spacecraft potential. The analysis also reveals that the presence of a heavy ion flow and a field-aligned ion upflow can further enhance the spurious field up to 5 mV/m.
    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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    Unsolved Problems: Meso-Scale Polar Cap Flow Channels’ Structure, Propagation, and effects on Space Weather disturbances (2016)
    Wiley
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    Publication Date: 2016-03-10
    Description: Recent evidence indicates that the magnetosphere-ionosphere system is frequently driven by dynamic meso-scale flow structures that are first seen near the dayside cusps, move across the open-field-line regions of the polar caps, and then enter the plasma sheet where they lead to a large variety of Space Weather disturbances. It will be important to uncover the features of these flow enhancements, including their structure, how they propagate across the polar cap, and what controls their dynamic effects after reaching the nightside plasma sheet.
    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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    Sequence of the Gonium pectorale Mating Locus Reveals a Complex and Dynamic History of Changes in Volvocine Algal Mating Haplotypes (2016)
    Genetics Society of America (GSA)
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    Publication Date: 2016-05-04
    Description: Sex-determining regions (SDRs) or mating-type ( MT ) loci in two sequenced volvocine algal species, Chlamydomonas reinhardtii and Volvox carteri , exhibit major differences in size, structure, gene content, and gametolog differentiation. Understanding the origin of these differences requires investigation of MT loci from related species. Here, we determined the sequences of the minus and plus MT haplotypes of the isogamous 16-celled volvocine alga, Gonium pectorale , which is more closely related to the multicellular V. carteri than to C. reinhardtii . Compared to C. reinhardtii MT , G. pectorale MT is moderately larger in size, and has a less complex structure, with only two major syntenic blocs of collinear gametologs. However, the gametolog content of G. pectorale MT has more overlap with that of V. carteri MT than with C. reinhardtii MT , while the allelic divergence between gametologs in G. pectorale is even lower than that in C. reinhardtii . Three key sex-related genes are conserved in G. pectorale MT : GpMID and GpMTD1 in MT –, and GpFUS1 in MT +. GpFUS1 protein exhibited specific localization at the plus -gametic mating structure, indicating a conserved function in fertilization. Our results suggest that the G. pectorale–V. carteri common ancestral MT experienced at least one major reformation after the split from C. reinhardtii , and that the V. carteri ancestral MT underwent a subsequent expansion and loss of recombination after the divergence from G. pectorale . These data begin to polarize important changes that occurred in volvocine MT loci, and highlight the potential for discontinuous and dynamic evolution in SDRs.
    Electronic ISSN: 2160-1836
    Topics: Biology
    Published by Genetics Society of America (GSA)
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  • 4
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    Stepwise tailward retreat of magnetic reconnection: THEMIS observations of an auroral substorm (2016)
    Wiley
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    Publication Date: 2016-05-03
    Description: Auroral stepwise poleward expansions were clarified by investigating a multiple-onset substorm that occurred on 27 February 2009. Five successive auroral brightenings were identified in all-sky images, occurring at approximately 10 min intervals. The first brightening was a faint precursor. The second brightening had a wide longitude; thus, it represented the Akasofu substorm onset. Other brightenings expanded poleward; thus, they were interpreted to be auroral breakups. These breakups occurred stepwise; that is, later breakups were initiated at higher latitudes. Corresponding reconnection signatures were studied using Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellite observations from between 8 and 24 R E down the magnetotail. The Akasofu substorm onset was not accompanied by a clear reconnection signature in the tail. In contrast, the three subsequent auroral breakups occurred simultaneously (within a few min) with three successive fast flows at 24 R E ; thus, these were interpreted to be associated with impulsive reconnection episodes. These three fast flows consisted of a tailward flow and two subsequent earthward flows. The flow reversal at the second breakup indicated that a tailward retreat of the near-Earth reconnection site occurred during the substorm expansion phase. In addition, the earthward flow at the third breakup was consistent with the classic tailward retreat near the end of the expansion phase; therefore, the tailward retreat is likely to have occurred in a stepwise manner. We interpreted the stepwise characteristics of the tailward retreat and poleward expansion to be potentially associated by a stepwise magnetic flux pile-up.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
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    Self-adjustment and disintegration threshold of Langmuir solitons in inhomogeneous plasmas (2017)
    American Physical Society (APS)
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    Publication Date: 2017-03-21
    Description: Author(s): Y. A. Chen, Y. Nishimura, Y. Nishida, and C. Z. Cheng Dynamics of Langmuir solitons in the presence of a background density gradient is investigated numerically, including cases with steep gradients to the extent the solitons can disintegrate. The disintegration threshold is explained by regarding the electric field part of the soliton as a point mass … [Phys. Rev. E 95, 033205] Published Mon Mar 20, 2017
    Keywords: Plasma Physics
    Print ISSN: 1539-3755
    Electronic ISSN: 1550-2376
    Topics: Physics
    Published by American Physical Society (APS)
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  • 6
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    Mesoscale Convection Structures Associated With Airglow Patches Characterized Using Cluster‐Imager Conjunctions (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract Polar cap ionospheric plasma flow studies often focus on large‐scale averaged properties and neglect the mesoscale component. However, recent studies have shown that mesoscale flows are often found to be collocated with airglow patches. These mesoscale flows are typically a few hundred meters per second faster than the large‐scale background and are associated with major auroral intensifications when they reach the poleward boundary of the nightside auroral oval. Patches often also contain ionospheric signatures of enhanced field‐aligned currents and localized electron flux enhancements, indicating that patches are associated with magnetosphere‐ionosphere coupling on open field lines. However, magnetospheric measurements of this coupling are lacking, and it has not been understood what the magnetospheric signatures of patches on open field lines are. The work presented here explores the magnetospheric counterpart of patches and the role these structures have in plasma transport across the open field‐line region in the magnetosphere. Using red‐line emission measurements from the Resolute Bay Optical Mesosphere Thermosphere Imager, and magnetospheric measurements made by the Cluster spacecraft, conjugate events from 2005 to 2009 show that lobe measurements on field lines connected to patches display (1) electric field enhancements, (2) Region 1 sense field‐aligned currents, (3) field‐aligned enhancements in soft electron flux, (4) downward Poynting fluxes, and (5) in some cases enhancements in ion flux, including ion outflows. These observations indicate that patches highlight a localized fast flow channel system that is driven by the magnetosphere and propagates from the dayside to the nightside, most likely being initiated by enhanced localized dayside reconnection.
    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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  • 7
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    Response of ionospheric electric fields at mid–low latitudes during sudden commencements (2015)
    Wiley
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    Publication Date: 2015-06-05
    Description: Using in situ observations from the ROCSAT-1 spacecraft, we investigated the time response and local time dependence of the ionospheric electric field at mid–low latitudes associated with geomagnetic sudden commencements (SCs) that occurred from 1999 to 2004. We found that the ionospheric electric field variation associated with SCs instantaneously responds to the PI signature on the ground regardless of spacecraft local time. Our statistical analysis also supports the global instant transmission of electric field from the polar region. In contrast, the peak time detected in the ionospheric electric field is earlier than that of the equatorial geomagnetic field (~20 s before in the PI phase). Based on the ground–ionosphere waveguide model, this time lag can be attributed to the latitudinal difference of ionospheric conductivity. However, the local time distribution of the initial excursion of ionospheric electric field shows that dusk-to-dawn ionospheric electric fields develop during the PI phase. Moreover, the westward electric field in the ionosphere, which produces the preliminary reverse impulse of the geomagnetic field on the dayside feature, appears at 18–22 h LT where the ionospheric conductivity beyond the duskside terminator (18 h LT) is lower than on the dayside. The result of a magnetohydrodynamic simulation for an ideal SC shows that the electric potential distribution is asymmetric with respect to the noon–midnight meridian. This produces the local time distribution of ionospheric electric fields similar to the observed result, which can be explained by the divergence of the Hall current under non-uniform ionospheric conductivity.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 8
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    Plasmapause location under quiet geomagnetic conditions (Kp≤ 1): THEMIS observations (2015)
    Wiley
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    Publication Date: 2015-09-13
    Description: We statistically examined the plasmapause location ( L pp ) under quiet geomagnetic conditions ( K p ≤ 1) using the electron density inferred from the THEMIS spacecraft potential for two-year period (2008 and 2009). 543 L pp samples were identified under steady quiet conditions with K p values ≤ 1 during 12 hours prior to the plasmapause crossing. From our large data set, we determined the medians and means of L pp in L and MLT. They are located near geosynchronous orbit and nearly circular. The L pp medians show a slight bulge located in post-dusk sector. Comparing with previous models, our median or mean L pp is extended ∼1-2 L from the earth than the model L pp along the local time from 0800 to 2400 MLT. That is, L pp locations in the previous models are underestimated during quiet geomagnetic conditions.
    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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  • 9
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    Low-energy ion precipitation structures associated with pulsating auroral patches (2015)
    Wiley
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    Publication Date: 2015-06-13
    Description: Pulsating auroras often appear in forms of geo-stable or slowly-convecting " patches" . These patches can maintain their rough shape and size over many sequences of luminosity pulsations, yet slowly drift with ionospheric E×B convection. Because of these characteristics, there has long been speculation that the pulsating auroral patch (PAP) is connected to flux tubes filled with enhanced cold plasma. In this study, we perform a survey on pulsating auroral events when the footprints of low-Earth-orbit satellites traversed the PAPs, with a focus on the low-energy particle signatures associated with the PAPs. As a result, we identified, in a majority (~2/3) of events, the existence of a low-energy ion precipitation structure (LEIPS) that is collocated with the PAP, with core energies ranging from several tens of eV up to a few hundred eV. This result supports the hypothesis that a PAP connects to flux tubes filled with enhanced cold plasma. We further propose that the plasma outflows from the ionosphere are the origin of such cold-plasma flux tubes. We suggest that the PAP is formed by a combination of high-energy electrons of a magnetospheric origin, the low-energy plasma structure of an ionospheric origin, and certain ELF/VLF waves that are intensified and modulated in interactions with both the hot and cold plasma populations.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 10
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    Fast Heating of Imploded Core with Counterbeam Configuration (2016)
    American Physical Society (APS)
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    Publication Date: 2016-07-27
    Description: Author(s): Y. Mori, Y. Nishimura, R. Hanayama, S. Nakayama, K. Ishii, Y. Kitagawa, T. Sekine, N. Sato, T. Kurita, T. Kawashima, H. Kan, O. Komeda, T. Nishi, H. Azuma, T. Hioki, T. Motohiro, A. Sunahara, Y. Sentoku, and E. Miura A tailored-pulse-imploded core with a diameter of 70     μ m is flashed by counterirradiating 110 fs, 7 TW laser pulses. Photon emission ( 〉 40     eV ) from the core exceeds the emission from the imploded core by 6 times, even though the heating pulse energies are only one seventh of the implosion energy.… [Phys. Rev. Lett. 117, 055001] Published Tue Jul 26, 2016
    Keywords: Plasma and Beam Physics
    Print ISSN: 0031-9007
    Electronic ISSN: 1079-7114
    Topics: Physics
    Published by American Physical Society (APS)
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