Y. Tohjima - Academia.edu (original) (raw)

Papers by Y. Tohjima

Radiocarbon, 2019

ABSTRACTSurface radiocarbon (Δ14C) in the North Pacific has been monitored using a commercial vol... more ABSTRACTSurface radiocarbon (Δ14C) in the North Pacific has been monitored using a commercial volunteer observation ship since the early 2000s. Here we report the temporal and spatial variations in Δ14C in the summer surface water when the surface ocean is vertically stratified over a 13-yr period, 2004–2016. The long-term Δ14C decreasing trend after the late 1970s in the subtropical region has continued to the present and the rate of decrease of the Kuroshio and Kuroshio Extension, North Pacific and California current areas is calculated to be –3.3, –5.2 and –3.3 ‰/yr, respectively. After 2012 the Δ14C of the Kuroshio and Kuroshio Extension area, however, has remained at an approximately constant value of around 50‰. The result may indicate that subtropical surface Δ14C in the western North Pacific has reached an equilibrium with atmospheric Δ14CO2. The Δ14C in the subarctic region is markedly lower than values in the subtropical region and it seems that the decreasing tendency of ...

Temporal and spatial variations of atmospheric molecular hydrogen (H2) are observed using aircraf... more Temporal and spatial variations of atmospheric molecular hydrogen (H2) are observed using aircrafts over Novosibirsk (55° N, 83° E), West Siberia, Yakutsk (62° N, 130° E), East Siberia and Sagami-bay (35° N, 139° E), Japan since 1997. H2 mixing ratios in air samples collected in Pylex flasks are measured using a gas chromatograph (HP5890, Agilent Technologies) equipped with Reduction Gas Detector (RGD-2, Trace Analytical). Primary standard gases with their mixing ratios of 400, 500, 600 and 700 ppb were prepared by gravimetric method. Four working standard gases, ranging from 420 to 630 ppb, are calibrated by primary standard approximately once per year. Atmospheric H2 mixing ratios observed in this study show clear seasonal variation with their maximum in spring or summer and minimum in late autumn or early winter. The phase of the seasonal change in lower troposphere is 1-3 months earlier than that in upper troposphere. Peak-to-peak amplitude at 1km over Novosibirsk is 40 ppb, whi...

Journal of Geophysical Research, 2002

In situ measurements of atmospheric methane (CH 4) from the monitoring stations at Cape Ochi-ishi... more In situ measurements of atmospheric methane (CH 4) from the monitoring stations at Cape Ochi-ishi (latitude 43°10 0 N, longitude 145°30 0 E) during the period from July 1995 to July 2000 and at Hateruma Island (latitude 24°03 0 N, longitude 123°48 0 E) during the period from January 1996 to January 2000 are presented. At each station a fully automated gas chromatograph equipped with a flame ionization detector measures the CH 4 mixing ratios at a frequency of more than 82 air samples per day. Over the above observation periods, average growth rates of CH 4 mixing ratios were 4.5 parts per billion (ppb) yr À1 for Ochi-ishi and 4.7 ppb yr À1 for Hateruma, but there were considerable fluctuations in the instantaneous growth rate. The peak-to-peak amplitudes in the seasonal cycles determined from the smooth curve fits were 71 ppb for Ochi-ishi and 94 ppb for Hateruma. These seasonal amplitudes are larger than those at the sampling network sites of the National Oceanic and Atmospheric Administration Climate Monitoring and Diagnostics Laboratory. Analysis of the back trajectories indicated that the air masses at both sites are transported from continental Asia in winter and from the Pacific Ocean in summer. Because there are strong CH 4 sources in continental Asia but no strong sources in the Pacific Ocean, the seasonality of airflow patterns can explain the enhancement of the seasonal cycles. The significantly large seasonality, especially at Hateruma, is a result of air masses originating from a wide range of latitudes, the clear seasonality of airflows, and the steep latitudinal gradient of the CH 4 mixing ratio.

Geophysical Research Letters, 2006

Detection of regional scale sea-to-air oxygen emission related to spring bloom near Japan by usin... more Detection of regional scale sea-to-air oxygen emission related to spring bloom near Japan by using in-situ measurements of the atmospheric oxygen/nitrogen ratio

1 TransCom N2O model inter-comparison Part II: Atmospheric 1 inversion estimates of N2O emissions... more 1 TransCom N2O model inter-comparison Part II: Atmospheric 1 inversion estimates of N2O emissions 2 3 R. L. Thompson, K. Ishijima, E. Saikawa, M. Corazza, U. Karstens, P. K. Patra, 4 P. Bergamaschi, F. Chevallier, E. Dlugokencky, R. G. Prinn, R. F. Weiss, S. O’Doherty, 5 P. J. Fraser, L. P. Steele, P. B. Krummel, A. Vermeulen, Y. Tohjima, A. Jordan, 6 L. Haszpra, M. Steinbacher, S. Van der Laan, T. Aalto, F. Meinhardt, 7 M. E. Popa, J. Moncrieff, and P. Bousquet 8 9 1. Norwegian Institute for Air Research, Kjeller, Norway 10 2. Laboratoire des Sciences du Climat et l'Environnement, Gif sur Yvette, France 11 3. Research Institute for Global Change, JAMSTEC, Yokohama, Japan 12 4. Center for Global Change Science, MIT, Cambridge, MA, USA 13 5. Emory University, Atlanta, GA, USA 14 6. Institute for Environment and Sustainability, JRC, Ispra, Italy 15 7. Max Planck Institute for Biogeochemistry, Jena, Germany 16 8. NOAA Earth System Research Laboratory, Global Monitoring Division, Bo...

C. Minejima, M. Kubo, Y. Tohjima, H. Yamagishi, Y. Koyama, S. Maksyutov, K. Kita, and H. Mukai Na... more C. Minejima, M. Kubo, Y. Tohjima, H. Yamagishi, Y. Koyama, S. Maksyutov, K. Kita, and H. Mukai National Institute for Environmental Studies, Tsukuba 305-8506, Japan Graduate School of Science and Engineering, Ibaraki University, Mito, Ibaraki 310-8512, Japan Faculty of Science, Ibaraki University, Mito, Ibaraki 310-8512, Japan now at: Department of Chemical Engineering, Tokyo University of Aguriculture and Technology 184-8588, Japan

Earth System Science Data Discussions, 2016

The global methane (CH 4) budget is becoming an increasingly important component for managing rea... more The global methane (CH 4) budget is becoming an increasingly important component for managing realistic pathways to mitigate climate change. This relevance, due to a shorter atmospheric lifetime and a stronger warming potential than carbon dioxide, is challenged by the still unexplained changes of atmospheric CH 4 over the past decade. Emissions and concentrations of CH 4 are continuing to increase making CH 4 the second most important human-induced greenhouse gas after carbon dioxide. Two major difficulties in reducing uncertainties come from the large variety of diffusive CH 4 sources that overlap geographically, and from the destruction of CH 4 by the very short-lived hydroxyl radical (OH). To address these difficulties, we have established a consortium of multidisciplinary scientists under the umbrella of the Global Carbon Project to synthesize and stimulate research on the methane cycle, and producing regular (~biennial) updates of the global methane

Atmospheric Chemistry and Physics Discussions, 2008

Simultaneous ground-based measurements of ozone (O 3) and carbon monoxide (CO) were conducted in ... more Simultaneous ground-based measurements of ozone (O 3) and carbon monoxide (CO) were conducted in March 2005 as part of the East Asian Regional Experiment (EAREX) 2005 under the umbrella of the Atmospheric Brown Clouds (ABC) project. Multiple air quality monitoring networks were integrated by performing intercomparison of individual calibration standards and measurement techniques to ensure comparability of ambient measurements, along with providing consistently high time-resolution measurements of O 3 and CO at the surface sites in East Asia. Ambient data collected from eight surface stations were compared with simulation results obtained by a regional chemical transport model to infer recent changes in CO emissions from East Asia. Our inverse estimates of the CO emissions from China up to 2005 suggested an increase of 16% since 2001, in good agreement with the recent MOPITT satellite observations and the bottom-up estimates up to 2006. The O 3 enhancement relative to CO in continental pollution plumes traversed in the boundary layer were examined as a function of transport time from the Asian continent to the western Pacific Ocean. Comparison of the observed ∆O 3 /∆ CO ratios and their modeled spatial distributions suggests an increase in the ∆ O 3 /∆ CO ratio due likely to en-route photochemical O 3 formation during eastward transport, confirming that East Asia is an important O 3 source region during spring.

Atmospheric Chemistry and Physics Discussions, 2015

Extremely high levels of column-averaged dry-air mole fractions of atmospheric methane (XCH<su... more Extremely high levels of column-averaged dry-air mole fractions of atmospheric methane (XCH<sub>4</sub>) were detected in August and September 2013 over Northeast Asia (~ 20 ppb above the averaged summertime XCH<sub>4</sub> over 2009–2012, after removing a long-term trend), as being retrieved from the Short-Wavelength InfraRed (SWIR) spectral data observed with the Thermal And Near-infrared Sensor for carbon Observation-Fourier Transform Spectrometer (TANSO-FTS) onboard Greenhouse Gases Observing Satellite (GOSAT). Similar enhancements of…

Atmospheric Chemistry and Physics Discussions, 2013

N 2 O surface fluxes were estimated for 1999 to 2009 using a time-dependent Bayesian inversion te... more N 2 O surface fluxes were estimated for 1999 to 2009 using a time-dependent Bayesian inversion technique. Observations were drawn from 5 different networks, incorporating 59 surface sites and a number of ship-based measurement series. To avoid biases in the inverted fluxes, the data were adjusted to a common scale and scale offsets were included in the optimization problem. The fluxes were calculated at the same resolution as the transport model (3.75 • longitude × 2.5 • latitude) and at monthly time resolution. Over the 11 yr period, the global total N 2 O source varied from 17.5 to 20.1 Tg a −1 N. Tropical and subtropical land regions were found to consistently have the highest N 2 O emissions, in particular, in South Asia (20 % of global total), South America (13 %) and Africa (19 %), while emissions from temperate regions were smaller, Europe (6 %) and North America (7 %). A significant multi-annual trend in N 2 O emissions (0.045 Tg a −2 N) from South Asia was found and confirms inventory estimates of this trend. Considerable inter-annual variability in the global N 2 O source was observed (0.8 Tg a −1 N, 1 standard deviation, SD) and was largely driven by variability in tropical and subtropical soil fluxes, in particular in South America (0.3 Tg a −1 N, 1 SD) and to a lesser extent in Africa (0.3 Tg a −1 N, 1 SD). Notable variability was also found for N 2 O fluxes in the tropical and southern oceans (0.15 and 0.2 Tg a −1 N, 1 SD, respectively). Inter-annual variability in the N 2 O source correlates strongly with ENSO, where El Niño conditions are associated with lower N 2 O fluxes from soils and from the ocean and vice-versa for La Niña conditions.

Radiation protection dosimetry, Jan 22, 2015

In this study, the (222)Rn flux density distribution at surface was estimated in East Asia with t... more In this study, the (222)Rn flux density distribution at surface was estimated in East Asia with the Bayesian synthesis inversion using measurement data and a long-range atmospheric (222)Rn transport model. Surface atmospheric (222)Rn concentrations measured at Hateruma Island in January 2008 were used. The estimated (222)Rn flux densities were generally higher than the prior ones. The area-weighted mean (222)Rn flux density for East Asia in January 2008 was estimated to be 44.0 mBq m(-2) s(-1). The use of the estimated (222)Rn flux density improved the discrepancy of the model-calculated concentrations with the measurements at Hateruma Island.

Journal of Geophysical Research: Atmospheres, 2015

We present methane (CH4) emissions for East Asia from a Bayesian inversion of CH4 mole fraction a... more We present methane (CH4) emissions for East Asia from a Bayesian inversion of CH4 mole fraction and stable isotope (δ13C‐CH4) measurements. Emissions were estimated at monthly resolution from 2000 to 2011. A posteriori, the total emission for East Asia increased from 43 ± 4 to 59 ± 4 Tg yr−1 between 2000 and 2011, owing largely to the increase in emissions from China, from 39 ± 4 to 54 ± 4 Tg yr−1, while emissions in other East Asian countries remained relatively stable. For China, South Korea, and Japan, the total emissions were smaller than the prior estimates (i.e., Emission Database for Global Atmospheric Research 4.2 FT2010 for anthropogenic emissions) by an average of 29%, 20%, and 23%, respectively. For Mongolia, Taiwan, and North Korea, the total emission was less than 2 Tg yr−1 and was not significantly different from the prior. The largest reductions in emissions, compared to the prior, occurred in summer in regions important for rice agriculture suggesting that this sourc...

Atmospheric Chemistry and Physics Discussions, 2013

We present a comprehensive estimate of nitrous oxide (N 2 O) emissions using observations and mod... more We present a comprehensive estimate of nitrous oxide (N 2 O) emissions using observations and models from 1995 to 2008. High-frequency records of tropospheric N 2 O are available from measurements at Cape Grim,

ABSTRACT Our study focuses on evaluating the merit of using the Lagrangian particle dispersion mo... more ABSTRACT Our study focuses on evaluating the merit of using the Lagrangian particle dispersion models for resolving the atmospheric composition variability at time scale of several hours and spatial scales of tenth of kilometers, which is necessary in analysis of continuous ground based monitoring and upcoming space based observation data. Using LPDM is an attractive way to increase the horizontal resolution of fluxes, and has been tested on atmospheric chemistry studies. The backward plume transport approach is more efficient for precalculation of transport matrixes for limited number of observations. Once backward plume transport is calculated, one can carry out forward calculation for any neutral tracer. As part of the effort, we simulate daytime CO2 concentration variations with FLEXPART model at five West-Siberian stations for year 2005 and 3-hourly CO2 and CH4 concentration variations at Hateruma, Japan, from year 2000 to year 2006. Concentration variations calculated by FLEXPART are compared with those calculated by NIES global atmospheric tracer transport model, and with observations. In West-Siberia, seasonal CO2 variations are reproduced in both model results, but FLEXPART shows better agreement with observations than NIES model at synoptic scale, especially in autumn to spring period, when the PBL height is shallower. However, several peaks in observations are not reproduced by both models. Summer time simulations show good resemblance between both models and observations, with LPDM showing better time resolution. In simulation of Hateruma data, we focus attention on CO2 and CH4 concentration variations during winter (late December to early April). Contrary to simulations over Siberia in summer, the observed short-term (synoptic scale) CO2/CH4 concentrations variations appear much stronger in observation than in the NIES model simulation. On the other hand synoptic scale variations of CO2 and CH4 are fairly well reproduced in LPDM simulation, while still there are numerous problems with timing and amplitude of spikes. Nevertheless the results demonstrated feasibility of using LPDM for analyzing continuous observations and showed advantage over using the Eulerian-type models.

Atmospheric Chemistry and Physics Discussions, 2014

This study examines N 2 O emission estimates from five different atmospheric inversion frameworks... more This study examines N 2 O emission estimates from five different atmospheric inversion frameworks based on chemistry transport models (CTMs). The five frameworks differ in the choice of CTM, meteorological data, prior uncertainties and inversion method but use the same prior emissions and observation data set. The posterior modelled atmospheric N 2 O mole fractions are compared to observations to assess the performance of the inversions and to help diagnose problems in the modelled transport. Additionally, the mean emissions for 2006 to 2008 are compared in terms of the spatial distribution and seasonality. Overall, there is a good agreement among the inversions for the mean global total emission, which ranges from 16.1 to 18.7 TgN yr −1 and is consistent with previous estimates. Ocean emissions Published by Copernicus Publications on behalf of the European Geosciences Union. 6178 R. L. Thompson et al.: TransCom N 2 O model inter-comparison-Part 2 represent between 31 and 38 % of the global total compared to widely varying previous estimates of 24 to 38 %. Emissions from the northern mid-to high latitudes are likely to be more important, with a consistent shift in emissions from the tropics and subtropics to the mid-to high latitudes in the Northern Hemisphere; the emission ratio for 0-30 • N to 30-90 • N ranges from 1.5 to 1.9 compared with 2.9 to 3.0 in previous estimates. The largest discrepancies across inversions are seen for the regions of South and East Asia and for tropical and South America owing to the poor observational constraint for these areas and to considerable differences in the modelled transport, especially inter-hemispheric exchange rates and tropical convective mixing. Estimates of the seasonal cycle in N 2 O emissions are also sensitive to errors in modelled stratosphere-to-troposphere transport in the tropics and southern extratropics. Overall, the results show a convergence in the global and regional emissions compared to previous independent studies.

Radiocarbon, 2019

Journal of Geophysical Research, 2002

Geophysical Research Letters, 2006

Earth System Science Data Discussions, 2016

Atmospheric Chemistry and Physics Discussions, 2008

Atmospheric Chemistry and Physics Discussions, 2015

Atmospheric Chemistry and Physics Discussions, 2013

Radiation protection dosimetry, Jan 22, 2015

Journal of Geophysical Research: Atmospheres, 2015

Atmospheric Chemistry and Physics Discussions, 2013

Atmospheric Chemistry and Physics Discussions, 2014