水の安定同位体比情報を利用した大気と陸面の水循環過程の解明に関する研究

学位の種別: 課程博士審査委員会委員 : （主査）東京大学准教授 芳村 圭, 東京大学教授 須貝 俊彦, 東京大学准教授 今須 良一, 筑波大学准教授 山中 勤, サンディエゴ州立大学准教授 Lai Chun-TaUniversity of Tokyo(東京大学

Quantifying the controls on evapotranspiration partitioning in the highest alpine meadow ecosystem

Quantifying the transpiration fraction of evapotranspiration (T/ET) is crucial for understanding plant functionality in ecosystem water cycles, land‐atmosphere interactions, and the global water budget. However, the controls and mechanisms underlying the temporal change of T/ET remain poorly understood in arid and semiarid areas, especially for remote regions with sparse observations such as the Tibetan Plateau (TP). In this study, we used combined high‐frequency laser spectroscopy and chamber methods to constrain estimates of T/ET for an alpine meadow ecosystem in the central TP. The three isotopic end members in ET (δET), soil evaporation (δE), and plant transpiration (δT) were directly determined by three newly customized chambers. Results showed that the seasonal variations of δET, δE, and δT were strongly affected by the precipitation isotope (R2 = 0.53). The δ18O‐based T/ET agreed with that of δ2H. Isotope‐based T/ET ranged from 0.15 to 0.73 during the periods of observation, with an average of 0.43. This mean result was supported by T/ET derived from a two‐source model and eddy covariance observations. Our overarching finding is that at the seasonal timescale, surface soil water content (θ) dominated the change of T/ET, with leaf area index playing only a secondary role. Our study confirms the critical impact of soil water on the temporal change of T/ET in water‐limited regions such as the TP. This knowledge sheds light on diverse land‐surface processes, global hydrological cycles, and their modeling

Revisiting the contribution of transpiration to global terrestrial evapotranspiration

Even though knowing the contributions of transpiration (T), soil and open water evaporation (E), and interception (I) to terrestrial evapotranspiration (ET=T+E+I) is crucial for understanding the hydrological cycle and its connection to ecological processes, the fraction of T is unattainable by traditional measurement techniques over large scales. Previously reported global mean T/(E+T+I) from multiple independent sources, including satellite-based estimations, reanalysis, land surface models, and isotopic measurements, varies substantially from 24% to 90%. Here we develop a new ET partitioning algorithm, which combines global evapotranspiration estimates and relationships between leaf area index (LAI) and T/(E+T) for different vegetation types, to upscale a wide range of published site-scale measurements. We show that transpiration accounts for about 57.2% (with standard deviation6.8%) of global terrestrial ET. Our approach bridges the scale gap between site measurements and global model simulations,and can be simply implemented into current global climate models to improve biological CO2 flux simulations

A global database of water vapor isotopes measured with high temporal resolution infrared laser spectroscopy

The isotopic composition of water vapour provides integrated perspectives on the hydrological histories of air masses and has been widely used for tracing physical processes in hydrological and climatic studies. Over the last two decades, the infrared laser spectroscopy technique has been used to measure the isotopic composition of water vapour near the Earth's surface. Here, we have assembled a global database of high temporal resolution stable water vapour isotope ratios (delta O-18 and delta D) observed using this measurement technique. As of March 2018, the database includes data collected at 35 sites in 15 Koppen climate zones from the years 2004 to 2017. The key variables in each dataset are hourly values of delta O-18 and delta D in atmospheric water vapour. To support interpretation of the isotopologue data, synchronized time series of standard meteorological variables from in situ observations and ERA5 reanalyses are also provided. This database is intended to serve as a centralized platform allowing researchers to share their vapour isotope datasets, thus facilitating investigations that transcend disciplinary and geographic boundaries

A global database of water vapor isotopes measured with high temporal resolution infrared laser spectroscopy

The isotopic composition of water vapour provides integrated perspectives on the hydrological histories of air masses and has been widely used for tracing physical processes in hydrological and climatic studies. Over the last two decades, the infrared laser spectroscopy technique has been used to measure the isotopic composition of water vapour near the Earth’s surface. Here, we have assembled a global database of high temporal resolution stable water vapour isotope ratios (18O and D) observed using this measurement technique. As of March 2018, the database includes data collected at 35 sites in 15 Köppen climate zones from the years 2004 to 2017. The key variables in each dataset are hourly values of 18O and D in atmospheric water vapour. To support interpretation of the isotopologue data, synchronized time series of standard meteorological variables from in situ observations or MERRA-2 reanalyses are also provided. This database is intended to serve as a centralized platform allowing researchers to share their vapour isotope datasets, thus facilitating investigations that transcend disciplinary and geographic boundaries.

Dataset of "A framework for quantifying hydrologic effects of soil structure across scales"

Dataset Supplementary Data.xlsx contains data used to construct Fig. 2 and Fig. S1 of Bonetti et al., 2021 (A framework for quantifying hydrologic effects of soil structure across scales). These include: - 136 measurements of %clay, %sand, texture based (K0) and structure corrected (Ks) soil saturated hydraulic conductivity from Weynants et al., VZJ (2009). - 976 measurements of %sand, texture based (K0) and structure corrected (Ks) soil saturated hydraulic conductivity from the SWIG database (Rahmati et al., ESSD, 2018). - Soil saturated hydraulic conductivity (Ks) measurements as a function of vegetation biomass (B): 117 xeric sites from Thompson et al., JGR Biogeosciences (2010) and 7 measurements from from a rainfall simulator in Sardinia (Wilson, 2017) - Soil saturated hydraulic conductivity (Ks) measurements as a function of leaf area index (LAI): 15 measurements from Niemeyer et al., VZJ (2014)

Modeling Investigation of Diurnal Variations in Water Flux and Its Components with Stable Isotopic Tracers

The isotopic compositions of water fluxes provide valuable insights into the hydrological cycle and are widely used to quantify biosphere–atmosphere exchange processes. However, the combination of water isotope approaches with water flux components remains challenging. The Iso-SPAC (coupled heat, water with isotopic tracer in soil–plant–atmosphere-continuum) model is a useful framework for simulating the dynamics of water flux and its components, and for coupling with isotopic fractionation and mixing processes. Here, we traced the isotopic fractionation processes with separate soil evaporation (Ev) and transpiration (Tr), as well as their mixing in evapotranspiration (E) for simulating diurnal variations of isotope compositions in E flux (δE). Three sub modules, namely isotopic steady state (ISS), non-steady-state (NSS), and NSS Péclet, were tested to determine the true value for the isotope compositions of plant transpiration (δTr) and δE. In situ measurements of isotopic water vapor with the Keeling-plot approach for δE and robust eddy covariance data for E agreed with the model output (R2 = 0.52 and 0.98, RMSD = 2.72‰, and 39 W m−2), illustrating the robustness of the Iso-SPAC model. The results illustrate that NSS is a better approximation for estimating diurnal variations in δTr and δE, specifically during the alternating periods of day and night. Leaf stomata conductance regulated by solar radiation controlled the diurnal variations in transpiration fraction (Tr/E). The study emphasized that transpiration and evaporation, respectively, acted to increase and decrease the δ18O of water vapor that was affected by the diurnal trade-off between them

An Efficient and Provably Secure Anonymous User Authentication and Key Agreement for Mobile Cloud Computing

Nowadays, due to the rapid development and wide deployment of handheld mobile devices, the mobile users begin to save their resources, access services, and run applications that are stored, deployed, and implemented in cloud computing which has huge storage space and massive computing capability with their mobile devices. However, the wireless channel is insecure and vulnerable to various attacks that pose a great threat to the transmission of sensitive data. Thus, the security mechanism of how the mobile devices and remote cloud server authenticate each other to create a secure session in mobile cloud computing environment has aroused the interest of researchers. In this paper, we propose an efficient and provably secure anonymous two-factor user authentication protocol for the mobile cloud computing environment. The proposed scheme not only provides mutual authentication between mobile devices and cloud computing but also fulfills the known security evaluation criteria. Moreover, utilization of ECC in our scheme reduces the computing cost for mobile devices that are computation capability limited and battery energy limited. In addition, the formal security proof is given to show that the proposed scheme is secure under random oracle model. Security analysis and performance comparisons indicate that the proposed scheme has reasonable computation cost and communication overhead at the mobile client side as well as the server side and is more efficient and more secure than the related competitive works

F2. Evaporation from Lake Kasumigaura: Bulk Coefficients and Spatial Distribution of Latent Heat Flux

Once downloaded, these high definition QuickTime videos may be played using a computer video player with H.264 codec, 1280x720 pixels, millions of colors, AAC audio at 44100Hz and 29.97 frames per second. The data rate is 5Mbps. File sizes are on the order of 600-900 MB. (Other formats may be added later.) Free QuickTime players for Macintosh and Window computers may be located using a Google search on QuickTime. The DVD was produced by J. Robert Cooke.Study of lake evaporation includes various aspects of Dr Brutsaert’s interests such as the exchange processes on water surface, the development of internal boundary layer, estimation of evaporation rate, among others. In the present study, issues on air-water interaction were first revisited. Secondly, horizontal distribution of latent heat fluxes over the lake surface was estimated to study its variability. For these purposes, 10 Hz water vapor, temperature, and wind velocity data have been obtained at the Koshin Observatory located near the center of Lake Kasumigaura, the second largest lake in Japan (220 km2 with mean depth of 4 m) since June of 2007. The corresponding fluxes were determined by applying the eddy correlation method to estimate the bulk coefficients. Agreement and disagreement with previous studies on the bulk transfer coefficients were identified. Also, the influence of lake current, wave, gustiness was investigated. Based on the derived functional form for the bulk coefficient, horizontal distribution of latent heat flux was estimated by first deriving a 100-m grid map of air temperature, wind speed and humidity over the lake area from interpolation of the observed data at meteorological stations in and around Lake Kasumigaura. The bulk method was then applied to each grid to derive latent heat flux every six hours over a year, by assuming the same surface temperature as that at the Koshin Observatory. This was acceptable as the satellite infrared images indicated the presence of quasi-uniform surface water temperature, presumably to reflect well-mixed water body of the shallow lake. The results indicate larger fluxes at the lake center with smaller values near lake shores, mainly to reflect wind speed differences. In comparison, humidity and air temperature is of lessor importance to cause latent heat variability. The mean evaporation over the entire lake surface was found to be 976 (±56) mm/y, while that at the Koshin observatory was 878 mm/y.1_mia0euq