Spiegl, T. C.*; Yoden, Shigeo*; Langematz, U.*; Sato, Tatsuhiko; Chhin, R.*; Noda, Satoshi*; Miyake, Fusa*; Kusano, Kanya*; Schaar, K.*; Kunze, M.*
Journal of Geophysical Research; Atmospheres, 127(13), p.e2021JD035658_1 - e2021JD035658_21, 2022/07
The abundance of cosmogenic isotopes in natural archives carries important information about the complex pathways from their source in the upper atmosphere to their deposition via atmospheric transport processes. Here, we use a new modelling framework to (a) estimate the Be production yield for the 774 CE/775 event, (b) evaluate the performance of our model framework by comparing the model results to four ice core records and (c) investigate the atmospheric pathways with a state-of-the-art climate model in detail. The results give new constraints regarding the seasonal timing of the event, underpin the role of the background conditions in the stratosphere, and highlight regional variations in the cosmogenic surface flux.
Nakajima, Toru; Kawakami, Tetsuo*; Iwano, Hideki*; Danhara, Toru*; Sakai, Harutaka*
Journal of Geophysical Research; Solid Earth, 127(5), p.e2021JB023630_1 - e2021JB023630_33, 2022/05
The thermochronological methods were applied to the Higher Himalayan Crystalline (HHC) nappe and the underlying Lesser Himalayan sediments (LHS) to elucidate the denudation process of the middle- and upper-crust of eastern Nepal over the geological time scale. The thermochronological inverse analysis was undertaken for new results of fission-track (FT) age and FT length data of zircon and apatite in order to reconstruct the time-temperature () paths in the temperature range of 60-350 degree. Eight paths obtained along the across-strike section showed that the cooling process of the HHC nappe was characterized by following three aspects: (1) gradual cooling followed by rapid cooling and subsequent gradual cooling, (2) northward-younging of the timing of the rapid cooling, (3) gradual cooling followed by ca. 2 Myr rapid cooling in the frontmost part of the HHC nappe. The observed FT ages and paths were then compared with those predicted by forward thermokinematic modeling. The results of the thermokinematic modeling for the Flat-Ramp-Flat MHT model, in which the HHC and the underlying LHS are denudated accompanied with the movement of the Main Himalayan Thrust (MHT), well reproduced the observed paths and FT ages in eastern Nepal. This suggests that the observed FT ages and paths reflect a denudation process driven by the movement of the MHT showing the flat-ramp-flat geometry, and that the denudation rate and its spatial distribution have roughly been constant in eastern Nepal since ca. 9 Ma.
Kajino, Mizuo*; Adachi, Koji*; Igarashi, Yasuhito*; Satou, Yukihiko; Sawada, Morihiro*; Sekiyama, Tsuyoshi*; Zaizen, Yuji*; Saya, Akane*; Tsuruta, Haruo*; Moriguchi, Yuichi*
Journal of Geophysical Research; Atmospheres, 126(1), 23 Pages, 2021/01
Wada, Yuki*; Enoto, Teruaki*; Nakazawa, Kazuhiro*; Odaka, Hirokazu*; Furuta, Yoshihiro; Tsuchiya, Harufumi
Journal of Geophysical Research; Atmospheres, 125(20), 17 Pages, 2020/10
Usui, Yoichi*; Yamazaki, Toshitsugu*; Oka, Toshitaka; Kumagai Yuho*
Journal of Geophysical Research; Solid Earth, 124(11), p.10672 - 10686, 2019/11
We report the discovery of inverse AMS fabrics from pelagic clay recovered by a 12 m long piston core from the western North Pacific. Rock magnetic data and ferromagnetic resonance spectroscopy indicated that magnetofossils account for most of the mean susceptibility regardless of normal or inverse AMS, suggesting that the inverse AMS fabrics due to magnetofossils may be widespread in pelagic clay.
Uchiyama, Yusuke*; Odani, Sachika*; Kashima, Motohiko*; Kamidaira, Yuki; Mitarai, Satoshi*
Journal of Geophysical Research; Oceans (Internet), 123(12), p.9245 - 9265, 2018/12
no abstracts in English
Akiyoshi, Hideharu*; Kadowaki, Masanao; Nakamura, Haruna*; Sugita, Takafumi*; Hirooka, Toshihiko*; Harada, Yayoi*; Mizuno, Akira*
Journal of Geophysical Research; Atmospheres, 123(22), p.12523 - 12542, 2018/11
A reduction of the total ozone over the southern tip of South America lasting 3 weeks occurred in November 2009. Analyses of the ERA-Interim reanalysis data and the total ozone observed by the Ozone Monitoring Instrument indicate that the total ozone reduction event was caused by a migration of the polar vortex toward the South American continent at the time of the vortex breakup. The vortex migration is associated with an enhanced wave flux from the troposphere at 120-150W and 50-60S to the west of the South American continent to the stratosphere over the southern part of the continent, which led to a large negative geopotential height anomaly in the lower stratosphere. In November, a blocking event was diagnosed from the 500-hPa geopotential height over the west of the South American continent. These results suggest a relation between the long-lasting reduction of the total ozone over the southern tip of South America and the blocking phenomenon in the troposphere of the Southern Hemisphere through wave propagation from the blocking region in 2009. Analysis of the total ozone anomaly for 50-60S and 65-75W over the southern tip of South America in November for 1979-2015 indicates that the negative ozone anomaly in November 2009 was one of the largest anomalies in this 37-year period and was associated with the large negative geopotential height anomaly in the lower stratosphere. Analyses of dynamical fields were also conducted for other years with large geopotential height anomalies.
Sato, Yosuke*; Takigawa, Masayuki*; Sekiyama, Tsuyoshi*; Kajino, Mizuo*; Terada, Hiroaki; Nagai, Haruyasu; Kondo, Hiroaki*; Uchida, Junya*; Goto, Daisuke*; Qulo, D.*; et al.
Journal of Geophysical Research; Atmospheres, 123(20), p.11748 - 11765, 2018/10
A model intercomparison of the atmospheric dispersion of Cs emitted following the Fukushima Daiichi Nuclear Power Plant accident was conducted by 12 models to understand the behavior of Cs in the atmosphere. The same meteorological data, horizontal grid resolution, and an emission inventory were applied to all the models to focus on the model variability originating from the processes included in each model. The multi-model ensemble captured 40% of the observed Cs events, and the figure-of-merit in space for the total deposition of Cs exceeded 80. Our analyses indicated that the meteorological data were most critical for reproducing the Cs events. The results also revealed that the differences among the models were originated from the deposition and diffusion processes when the meteorological field was simulated well. However, the models with strong diffusion tended to overestimate the Cs concentrations.
Kitayama, Kyo*; Morino, Yu*; Takigawa, Masayuki*; Nakajima, Teruyuki*; Hayami, Hiroshi*; Nagai, Haruyasu; Terada, Hiroaki; Saito, Kazuo*; Shimbori, Toshiki*; Kajino, Mizuo*; et al.
Journal of Geophysical Research; Atmospheres, 123(14), p.7754 - 7770, 2018/07
We compared seven atmospheric transport model results for Cs released during the Fukushima Daiichi Nuclear Power Plant accident. All the results had been submitted for a model intercomparison project of the Science Council of Japan in 2014. We assessed model performance by comparing model results with observed hourly atmospheric concentrations of Cs, focusing on nine plumes over the Tohoku and Kanto regions. The results showed that model performance for Cs concentrations was highly variable among models and plumes. We also assessed model performance for accumulated Cs deposition. Simulated areas of high deposition were consistent with the plume pathways, though the models that best simulated Cs concentrations were different from those that best simulated deposition. The ensemble mean of all models consistently reproduced Cs concentrations and deposition well, suggesting that use of a multimodel ensemble results in more effective and consistent model performance.
Kamidaira, Yuki; Uchiyama, Yusuke*; Kawamura, Hideyuki; Kobayashi, Takuya; Furuno, Akiko
Journal of Geophysical Research; Oceans (Internet), 123(4), p.2808 - 2828, 2018/04
We developed a submesoscale eddy-resolving oceanic dispersal modeling system consisting of a double nested oceanic downscaling model and an offline oceanic radionuclides dispersion model to investigate influences of submesoscale coherent structures (SCSs) and associated ageostrophic secondary circulations (ASCs) on the three-dimensional (3D) dispersal and initial dilution of the dissolved radioactive Cs accidentally released from the Fukushima Daiichi Nuclear Power Plant (FNPP1) occurred since March 2011. The extensive model-data comparison demonstrates that the elaborated innermost high-resolution model at a lateral grid resolution of 1 km successfully reproduces transient mesoscale oceanic structures, the Kuroshio path and stratification, and spatiotemporal variations of 3D Cs concentrations. These SCSs and ASCs occurred primarily due to shear instability with baroclinic instability as the secondary mechanism, according to energy conversion and spectral analyses. The vertical Cs flux analysis was performed with decomposition of the variables into the mean, mesoscale, and submesoscale components using frequency and wavenumber filters. The vertical Cs flux analysis explained that 84% of the FNPP1-derived Cs was transported downward below the mixed layer by eddies, with the major contributions from ASCs induced by submesoscale eddies.
Sueoka, Shigeru; Ikeda, Yasutaka*; Kano, Kenichi*; Tsutsumi, Hiroyuki*; Tagami, Takahiro*; Kohn, B. P.*; Hasebe, Noriko*; Tamura, Akihiro*; Arai, Shoji*; Shibata, Kenji*
Journal of Geophysical Research; Solid Earth, 122(8), p.6787 - 6810, 2017/08
no abstracts in English
Sueoka, Shigeru; Shimada, Koji; Ishimaru, Tsuneari; Niwa, Masakazu; Yasue, Kenichi; Umeda, Koji*; Danhara, Toru*; Iwano, Hideki*
Journal of Geophysical Research; Solid Earth, 122(3), p.1848 - 1859, 2017/03
no abstracts in English
Journal of Geophysical Research; Solid Earth, 121(1), p.70 - 91, 2016/01
Macroscopic failure modes (extensional failure or shear failure) in fault damage zones influence hydrogeological properties of fault zones. Based on the Griffith-Coulomb criterion and a simple assumption that the failures are predominantly induced by increasing of differential stresses and/or decreasing of effective normal stresses due to stress concentration along faults, it is implied that extension fractures can exclusively propagate from the faults when the effective mean stress is less than twice the rock tensile strength, whereas shear fractures also can develop when the effective mean stress is more than twice the rock tensile strength, which suppresses the formation of extension fractures. In this study, mechanical tests (the undrained triaxial tests and the unconfined compressive strength tests) using siliceous mudstone specimens given artificial fault(s) were performed under multiple effective confining pressures. Comparison between the damage zone fractures formed at the fault tips by the tests and the loaded effective mean stresses provided results consistent with the above simple model. The similar results are also suggested from the occurrence of natural damage zone fractures observed in the same siliceous mudstone by core logging. Laboratory-measured tensile strengths could be used as the lower threshold strengths considering the strain rate and scale effects and it is implied that hard-linked highly permeable fault zones involving many extension fractures are limited to rock domains which have experienced the effective mean stress less than twice the tensile strength.
Umeda, Koji; Asamori, Koichi; Makuuchi, Ayumu; Kobori, Kazuo; Hama, Yuki*
Journal of Geophysical Research; Solid Earth, 120(4), p.2279 - 2291, 2015/04
Following the Mw 9.0 Tohoku-Oki earthquake, an unusual, shallow normal-faulting swarm sequence occurred near the Pacific coast in the southeast Tohoku district. The observed He/He ratios are significantly lower than the atmospheric value, indicating mantle helium contributed less than 10%. The plausible source of fluids can be attributed to waters released owing to sediment porosity collapse, and smectite-illite and opal-quartz reactions in the subducting sediments, rather than dehydration reactions of the subducting altered basalts and/or hydrated mantle. The aqueous fluids driven off the subducting slab migrate into the fore-arc crust, because of the pressure gradient between lithostatic pore pressure along the plate interface and hydrostatic pore pressure in the overriding crust. The swarm earthquake sequence would have been triggered by stress change associated with the Tohoku-Oki earthquake, enhanced by fluid flow along inherited weakened zones in the crust.
Journal of Geophysical Research; Solid Earth, 120(4), p.2220 - 2241, 2015/04
The author shows a clear correlation with negative power law between transmissivities along fluid-conductive fault zones detected by fluid loggings in boreholes and the effective mean stress normalized a tensile strength of the rock, using data sets from six sites in different conditions. The obtained empirical relation allows to spatially and temporally predicting transmissivities along possible fluid-conductive fault zones in the upper crust using the normalized stress, providing a very useful benchmark for many geoscientific and geotechnical problems relevant to fault zone permeability.
Journal of Geophysical Research; Atmospheres, 119(13), p.8137 - 8159, 2014/07
Recent progress in modeling fogwater (and low cloud water) deposition over terrestrial ecosystems during fogwater droplet interception by vegetative surfaces is reviewed. Several types of models and parameterizations for fogwater deposition are discussed with comparing assumptions, input parameter requirements, and modeled processes. The relationships among deposition velocity of fogwater () in model results, wind speed, and plant species structures associated with literature values were gathered for model evaluation. Quantitative comparisons between model results and observations in forest environments revealed differences as large as two orders of magnitude, which were likely caused by uncertainties in measurement techniques over heterogeneous landscapes. Results from the literature review showed that values ranged from 2.1-8.0 cm s for short vegetation, whereas = 7.7-92 cm s and 0-20 cm s for forests measured by through fall-based methods and the eddy covariance method, respectively. This review also discusses the current understanding of the impacts of fogwater deposition on atmosphere-land interactions and over complex terrain based on results from numerical studies. Lastly, future research priorities in innovative modeling and observational approaches for model evaluation are outlined.
Ota, Masakazu; Nagai, Haruyasu; Koarashi, Jun
Journal of Geophysical Research; Biogeosciences, 118(4), p.1646 - 1659, 2013/12
We investigated the role of root litter input and dissolved organic carbon (DOC) transport in controlling subsurface SOC dynamics by a soil C model. The model involves C turnover by decomposition, interaction between SOC and DOC, and DOC transport along water flows, for three C pools (characterized by turnover times of years, decades and millennia). Model simulations with a range of rooting profiles demonstrated a large proportion (36-78%) of SOC is apportioned to the subsurface (below the first 30 cm) soils and a significant part (39-73%) of the subsurface SOC turns over decadally. DOC transport appeared to be dominant for distributing the C to the deeper horizons. Our results suggest soil C studies focusing on the surface alone significantly underestimate the stock of decadally cycling C and underpredict the responses of soil C to global changes.
Umeda, Koji; Kusano, Tomohiro; Asamori, Koichi; McCrank, G. F.*
Journal of Geophysical Research; Solid Earth, 117(B10), p.B10204_1 - B10204_13, 2012/10
In order to elucidate the geographic distribution of He/He ratios in Southwest Japan, the data from a total of 924 sites were compiled and synthesized. There appears to be good correlation between variations in mantle helium and the geophysical evidence indicating the configuration of the subducting Philippine Sea plate. The helium isotopes observed on the Earth's surface may be efficient geochemical indicators of the configuration of a relatively younger, warm aseismic slab, especially useful in seismically inactive areas.
Koarashi, Jun; Hockaday, W.*; Masiello, C.*; Trumbore, S.*
Journal of Geophysical Research; Biogeosciences, 117, p.G03033_1 - G03033_13, 2012/09
Subsurface horizons contain more than half of the global soil carbon (C), yet the dynamics of this C remains poorly understood. We estimated the amount of decadally-cycling subsurface C from the incorporation of "bomb' radiocarbon (C) using samples taken over 50 years from grassland and forest soils in the Sierra Nevada Mountains, California. The C content of all organic matter fractions increased from the pre- to post-bomb samples, indicating about half of the subsoil C consists of C fixed since 1963. The C content of mineral-associated C increased rapidly from 1992-2009, indicating a significant time lag (20 years) for the arrival of "bomb" C to this fraction. Our results demonstrate that a lagged response of the large subsurface C stores to changes in environmental conditions is possible.
Katata, Genki; Kajino, Mizuo*; Hiraki, Takatoshi*; Aikawa, Masahide*; Kobayashi, Tomiki*; Nagai, Haruyasu
Journal of Geophysical Research, 116(D20), p.D20102_1 - D20102_14, 2011/10
To apply the meteorological model to investigate fog occurrence, acidification, and deposition in mountain forests, the meteorological model WRF was modified to calculate the fog deposition by the simple linear function of fog deposition onto vegetation. The modified version of WRF that includes fog deposition (fog-WRF) was tested in a mountain forest of Mt. Rokko in Japan. The fog-WRF provided a clearly better prediction of liquid water content of fog (LWC) than the original version of WRF. The fog-WRF successfully simulated measured throughfall observations due to fog deposition inside the forest. Using the linear relationship between fog deposition and the altitude given by the fog-WRF calculations and the data from throughfall observations at the certain altitude, vertical distribution of fog deposition can be roughly estimated in mountain forest. The meteorological model that includes the fog deposition is useful for mapping the fog deposition in mountain cloud forests.