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  • Articles  (15)
  • 2020-2024  (15)
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  • 1
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    Editorial: the oceanic particle flux and its cycling within the deep water column (2023)
    Frontiers Media
    Details
    Publication Date: 2023-03-11
    Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Conte, M., Pàmies, R., Honda, M., & Herndl, G. Editorial: the oceanic particle flux and its cycling within the deep water column. Frontiers in Earth Science, 10, (2022): 1020065, https://doi.org/10.3389/feart.2022.1020065.
    Description: The oceanic particle flux transfers energy and material from the surface through the water column to the seafloor. (See review by Conte (2019) and references therein). The particle flux fuels life below the sunlit photic zone, exerts a major control on the global cycling of carbon and particle-associated elements, and also plays a major role in long-term carbon sequestration. In this Research Topic we present a collection of articles that provide a broad overview of current research on the interlinked processes controlling the magnitude and composition of the oceanic particle flux, and its cycling and depth attenuation within the deep water column.
    Keywords: Particle flux ; Deep ocean ; Marine particles ; Ocean biogeochemistry ; Carbon cycling ; Marine chemistry
    Repository Name: Woods Hole Open Access Server
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  • 2
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    A new proposed scheme for seamless detection of cutoff lows and preexisting troughs (2023)
    In:  XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)
    Details
    Publication Date: 2023-06-01
    Description: We propose a new scheme based on geopotential height fields to detect cutoff lows starting in the preexisting trough stage. The intensity and scale derived from the proposed scheme will allow for a better understanding of the cutoff low life cycle. These cutoff lows often accompany mesoscale disturbances, causing adverse weather-related events, such as intense torrential rainfall and/or tornadoes. The proposed scheme quantifies the geometric features of a depression from its horizontal height profile. The height slope of a line intersecting the depression bottom and the nearest tangential point (optimal slope) locally indicates the intensity and scale of an isolated depression. The strength of the proposed scheme is that, by removing a local background height slope from a geopotential height field, the cutoff low and its preexisting trough are seamlessly detected as an identical depression. The distribution maps for the detected cutoff lows and preexisting troughs are illustrated along with their intensities, sizes, and local background flows estimated from snapshot height fields. We conducted climatological comparisons of cutoff lows to determine the utility of the proposed scheme.
    Language: English
    Type: info:eu-repo/semantics/conferenceObject
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  • 3
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    Cutoff low approaching routes to the Japan islands (2023)
    In:  XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)
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    Publication Date: 2023-08-30
    Description: Cutoff lows (COLs) are mid-latitude cyclones appear at the upper troposphere. They contain cold air mass derived from the polar region. COLs decrease stability of the lower troposphere (e.g., Hoskins et al. 1985) and often accompany severe weathers (e.g., Mohr et al. 2020), which sometimes causes great damages to mid-latitude regions, such as Japan. Besides, the approaching routes of COLs to the Japan Islands and their seasonal cycles have not been investigated with objective method. In this study, we attempt to elucidate them by utilizing depression detection scheme of Kasuga et al. (2021; K21), which can detect COLs from their early stage (pre-existing trough stage). We have implemented a tracking scheme of COLs by simply searching overlapping of area of COLs. Merge and split of COLs are also recorded to investigate variations of the generation/dissipation of COLs. Generally, COLs approach the Japan Islands from northwest advected by the subpolar jet throughout the seasons. They also approach from southeast in JJA and SON at 200 hPa passing around the North Pacific Subtropical High. These two routes were reported in different studies; we successfully track them with a consistent criterion and confirmed that they have longer durations compared to that of a geopotential minimum detection. Tracks shows different characters at 200 and 500 hPa levels as preceding studies have noted. We have found that strong class of COLs are most frequent in MAM. We are investigating climatological backgrounds of the seasonal variations of COLs and hoping to show the results in the conference.
    Language: English
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  • 4
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    VLBI-GNSS local-tie surveys at the Ishioka Geodetic Observing Station (2023)
    In:  XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)
    Details
    Publication Date: 2023-08-30
    Description: The Geospatial Information Authority of Japan (GSI) has operated two space geodetic techniques, VLBI and GNSS, at the Ishioka Geodetic Observing Station (hereafter Ishioka). We regularly conduct local-tie surveys to determine the local-tie vector connecting those techniques. In 2021, we submitted the results of the surveys to the International Earth Rotation and Reference Systems Service (IERS) to contribute to the construction of the International Terrestrial Reference Frame (ITRF). In ITRF2020, Ishioka was registered as one of the IERS stations for the first time. Reference points of VLBI antennae generally cannot be measured directly and thus need to be estimated in the local-tie survey. In Ishioka, we estimate the position of the reference point of the VLBI antenna by a method called the ‘inside method’, in which targets attached to the inner wall of the azimuth cabin are used for observation. This method is applied only to the specific antenna with an observation pillar constructed in it, but this method is effective to improve efficiency of local-tie survey. We combine the results of the inside-method observation and various other observations using total stations, geodetic leveling and static GNSS, and calculate the local-tie vector with the software called pyaxis. In this report, we will compare the local-tie vector obtained from the surveys with that derived from the ITRF2020 after describing the outline of the local-tie survey technique at Ishioka.
    Language: English
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  • 5
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    Multi-area applicability of machine learning-based immediate tsunami prediction (2023)
    In:  XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)
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    Publication Date: 2023-06-07
    Description: Machine learning is one of the methods employed for the immediate prediction of tsunami occurrence. There have been few studies on error evaluation focusing on the arrival time of the tsunami inundation. In this study, we used machine learning to predict the tsunami arrival times for two areas and evaluated the errors. Tsunamis were calculated for several thousand cases for three different earthquake sizes using the tsunami simulator Q-Wave and assuming a Nankai Trough earthquake. Using these data, we trained a neural network to predict tsunami arrival time on the basis of the initial water level. As the amount of training data increased, the error decreased and the model with the most training data was used to predict the tsunami arrival times for two areas. The errors tended to be particularly large in coastal areas where tsunamis often reach. In some cases, the error was larger in Area B than in Area A, even though the amount of data for Area B was double that of Area A. These errors may be ascribed to variations in the arrival time of tsunamis in the training data due to topographical characteristics. For a magnitude 9.0 earthquake, the standard deviation of the tsunami arrival time in Area B is approximately 1.5 times that of Area A. Therefore, in addition to increasing the number of output variables and the accuracy of tsunami simulation, a more detailed consideration of the effect of area-specific characteristics on the error is needed in the future.
    Language: English
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  • 6
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    Audio-frequency magnetotelluric investigations of the 2018 phreatic eruption site at Mt. Motoshirane, Central Japan (2023)
    In:  XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)
    Details
    Publication Date: 2023-06-27
    Description: Phreatic eruptions are one of the eruption styles that are difficult to forecast and occasionally cause significant damage. Understanding the mechanisms of phreatic eruption is essential for minimizing damage. Mt. Motoshirane, one of the pyroclastic cones of the Kusatsu-Shirane Volcano located in central Japan, experienced a phreatic eruption in 2018 that resulted in casualties. The eruption was abrupt with no precursory phenomena. Mt. Motoshirane has been dormant for the last 1500 years, so it has been poorly monitored and studied. Studies conducted after the eruption suggested that the migration of hydrothermal fluids triggered the eruption, but those studies lacked information on shallow subsurface structure. In this paper, we report on the three-dimensional resistivity structure around the craters of the 2018 eruption, which was estimated from the audio-frequency magnetotelluric data obtained in 2020 and 2022. The inferred resistivity structure basically has a two-layer structure composed of a high-resistivity layer corresponding to the Quaternary lavas near the surface and low resistivities corresponding to the altered Neogene lavas below. Shallow moderately high resistivity regions in the low-resistivity layer are considered fluid reservoirs that have become infiltrated as a result of the eruption. Regions around the crack associated with the eruption showed relatively high resistivity, implying that the low resistivity zone is decoupled beneath the eruption site. We will discuss how the phreatic eruption occurred based on these interpretations in the presentation.
    Language: English
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  • 7
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    Anticyclonic circulation causing extreme snowfall events in the Japan-Sea coast of Japan (2023)
    In:  XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)
    Details
    Publication Date: 2023-06-27
    Description: The northern and central part of Japan facing the Japan Sea are widely snow-covered through winter. There are two types of snowfall distribution: one is the plain-type snowfall dominant in the Japan-Sea coastal plain areas and the other is the mountain-type snowfall dominant along mountain ranges. Although snowfalls are not so heavy in the coastal areas, rare extreme snowfalls are caused by the Japan Sea polar air-mass convergence zone (JPCZ) developed over the southern part of Japan Sea, where the JPCZ tends to appear connecting dents of cyclonic isobars. Further, we found that those extreme snowfalls are often also associated with anticyclonic isobars appeared along the Japan-Sea coast of Japan. Those cyclonic and anticyclonic isobars form “stomach shape pattern over the Japan Sea. In addition, a polar low (PL) tends to appear off the Japan-Sea coast in the northern Japan. Ascending flows with near surface convergence with the JPCZ and PL over the Japan Sea are in conjunction with divergence in the mid troposphere, which causes mid tropospheric convergence in between. This process requires descending flow and causes near surface divergence over the central part of the Japan Sea, which resultantly increases in surface pressure and forms an anticyclonic circulation along the Japan-Sea coast in the northern Japan. Thus convergent snow-cloud band is formed along the coast extending to southwestward, and it encounters the JPCZ oriented to eastward, where extreme snowfall events occur. Further numerical simulations also support robust features.
    Language: English
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  • 8
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    Magnetization structure and its temporal change of Miyakejima volcano, Japan, revealed by uncrewed aerial vehicle aeromagnetic survey (2023)
    In:  XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)
    Details
    Publication Date: 2023-04-20
    Description: Miyakejima volcano experienced its latest eruption in 2000 with the summit subsidence, and the next event is expected in the near future. An aeromagnetic survey in Miyakejima was conducted in March 2021 in order to investigate the current state of its magnetization structure to identify the potential for another eruption and, thus, mitigate volcanic disaster. The survey flight was conducted using an uncrewed aerial vehicle (UAV), a multirotor drone, to deploy a scalar magnetometer. After processing geomagnetic field data from this survey, in combination with data from previous surveys conducted by using another UAV, an uncrewed helicopter, the average magnetization intensity was determined to be 12.4 A/m. Further, the surrounding area of the crater was relatively highly magnetized; however, the crater rim had a low magnetization intensity. Temporal variation was detected between 2014 and 2021 and dominated the central part of the observation area. Decreased magnetization intensity was identified beneath the caldera, which may become recently demagnetized due to heat supply traveling through fractures in the impermeable layer from the deep heat reservoir.
    Language: English
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  • 9
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    Phase locking of the Boreal Summer Intraseasonal Oscillation in the Indian Ocean (2023)
    In:  XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)
    Details
    Publication Date: 2023-07-12
    Description: The Boreal Summer Intraseasonal Oscillation (BSISO), which is characterized by a northeastward move of convective systems at a 30- to 60-day cycle, is the dominant intraseasonal variability in the Indo-Pacific warm pool region during boreal summer. Previous studies have discussed a phase-locking feature of the BSISO with respect to the annual cycle and even suggested its presence in the daily climatological field, referred to as the climatological BSISO (CBSISO). However, there still remains open whether CBSISO is a statistically significant feature, let alone its mechanisms. Here we present strong evidence for the presence of CBSISO based on 42-year records from satellite observations. Even without bandpass filtering, the CBSISO is present in the outgoing longwave radiation and precipitation records for the April-to-December period. Statistically significant spectral peaks are found in both records at about a 40-day period in the tropical Indian Ocean and western Pacific. On the basis of the phase information of individual years, we identified a group of approximately one-fourth of 42 years, which are highly in-phase with the CBSISO. This group of in-phase years have shown an early onset of the dry CBSISO phase in the Indian Ocean in April. There is also a hint that ENSO plays a modulating role in the CBSISO phase. In the presentation, we shall discuss possible mechanisms of the CBSISO.
    Language: English
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  • 10
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    Geodetic measurements and quantitative evaluation for reduced gravitational redshift uncertainty of optical frequency standards (2023)
    In:  XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)
    Details
    Publication Date: 2023-07-19
    Description: The National Institute of Information and Communications Technology (NICT) has developed a Sr optical lattice clock and optical ion clocks employing In+ and Ca+. The centimeter-level uncertainty of site elevation is the cause of 10^(-18)-level frequency uncertainties of optical frequency standards. It is significantly important to understand frequency changes caused by solid-earth tides that often range from 10 to 20 cm in amplitude, by oceanic tidal loading, crustal deformations due to earthquakes, and ground movements with groundwater changes for the stable operation of optical atomic clocks. NICT and partners including the Geospatial Information Authority of Japan (GSI) have been jointly conducting leveling surveys and relative gravimeter observations at NICT’s headquarters in Koganei. These observations reduce the contribution of gravitational redshift to the total uncertainty of the optical lattice clock to the 10^(-19) level. With the support of National Institute of Polar Research (NIPR), absolute gravity measurements were performed in August 2019 and May 2022 to evaluate the effects of the 2011 off the Pacific coast of Tohoku Earthquake on postseismic crustal movement. The obtained absolute gravity change between the two periods was -43.8 μGal, which matches the trend of GNSS vertical movement obtained by GSI. We have introduced a Micro-g LaCoste’s gPhoneX gravimeter for continuous gravity measurements nearby the optical clocks in the end of 2021 and have started to investigate the temporal variation of the ground water level in Koganei. We will present preliminary results of these geodetic measurements.
    Language: English
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