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  • English  (4)
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  • 1
    Monograph available for loan
    Monograph available for loan
    Global warming - the research challenges : a report of Japan's global warming initiative (2004)
    Dordrecht : Springer
    Details Availability
    Call number: AWI A1-18-91447
    Type of Medium: Monograph available for loan
    Pages: XIII, 161 S , Ill., graph. Darst., Kt , 25 cm
    ISBN: 1402029403
    Uniform Title: Chikyū-ondanka-kenkyū-no-saizensen 〈engl.〉
    URL: http://www.loc.gov/catdir/enhancements/fy0823/2005298846-d.html
    URL: http://www.gbv.de/dms/goettingen/478056125.pdf
    Language: English
    Note: Translated from the Japanese
    Location: AWI Reading room
    Branch Library: AWI Library
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  • 2
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    Evaluation of calculation method to estimate soil moisture in SiBUC land surface model (2023)
    In:  XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)
    Details
    Publication Date: 2023-05-22
    Description: Soil moisture is a key state variable for estimating water and energy budgets in land surface model. In SiBUC, soil moisture is calculated using Richards’ equation. Due to strong nonlinearity of the RE, fine discretization is necessary to calculate infiltration, particularly in near-surface soil with significant hydraulic gradients. SiBUC discretizes soil into three layers and solves the Richards’s equation using explicit-midpoint method. This study evaluated the calculation method to solve the Richards equation in SiBUC by comparing it to a reference model HYDRUS 1-D. Soil in SiBUC was partitioned into 5 cm, 200 cm, and 500 cm deep from the top, while that in HYDRUS was uniformly 1 cm deep. To improve the accuracy of soil moisture by SiBUC, four layers were added between the first and second layers, with thickness of 10 cm, 20 cm, 50 cm, 100 cm from the top. The default SiBUC overestimates soil-water flux drawdown on the near surface after rainfall events, resulting in lower soil moisture than HYDRUS. Interpolation calculations with significant difference in soil thickness contributed to the numerical error. The revised SiBUC demonstrates that increasing the vertical resolution between the first and second layers can alleviate this problem. However, there is still a gap between the two models due to the discrepancy in soil-water flux attributed to their different numerical methods. Preliminary analysis shows that applying an implicit method without iterative technique can improve the accuracy of soil moisture without excessive computing cost.
    Language: English
    Type: info:eu-repo/semantics/conferenceObject
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  • 3
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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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  • 4
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    Vertical quasi-two-dimensional modeling for hillslope surface-subsurface flow (2023)
    In:  XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)
    Details
    Publication Date: 2023-09-12
    Description: Rainfall-runoff models have been developed to predict runoff in response to rainfall. However, practical models do not adequately represent the rainfall-runoff processes and their applicability may decrease under specific conditions. Model parameter optimization is often required to obtain sufficient accuracy, but calibrated parameters do not always reflect watershed characteristics. Alternatively, models based on Richards’ equation are more precise and can directly use observed parameter values but are impractical due to their huge computational costs. In this study, we propose a vertical quasi-two-dimensional model for hillslope surface-subsurface flow (quasi-2D model), aiming at both appropriate representation of waterflow mechanism and reduction of computational cost. Subsurface flow is described by Richards’ equation, wherein the hydraulic gradient in the downward direction is approximated by the slope gradient. Surface flow is modeled using the kinematic wave model, which is computed separately from subsurface flow computation. This method can consider vertical soil moisture distribution and simplify the modeling of the runoff process. Rainfall-runoff simulations were conducted on a single slope using the quasi-2D model and compared with the results computed by a detailed model solving the two-dimensional Richards’ equation (2D model). For both subsurface and surface flows, the quasi-2D model reproduced the results of the 2D model well (NSE 〉 0.99). Furthermore, the computation time of the quasi-2D model was reduced to less than 1/10 of that of the 2D model. These results indicate that our quasi-two-dimensional modeling enables saturated-unsaturated flow simulations at lower computational costs, and is expected to be applied to basin-scale simulations.
    Language: English
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