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Temporal variations of atmospheric radon-222 (222Rn) observed at four Japan Meteorological Agency stations in Japan by the Meteorological Research Institute were analyzed using an online Global Spectral Atmosphere Model-Transport Model (GSAM-TM). Monthly and diurnal variations and a series of synoptic high-222Rn events were extracted from 5 years to 12 years of 222Rn observations during 2007 - 2019. Observed seasonal patterns of winter maxima and summer minima, driven mainly by monsoons, were well reproduced by the GSAM-TM based on existing 222Rn emission inventories, but their absolute values were generally underestimated, indicating that our understanding of 222Rn emission processes in East Asia is lacking. The high-resolution model (~ 60 km mesh) demonstrated that observed consecutive high-222Rn peaks at several-hour timescales were caused by two 222Rn streams from different regions and were not well resolved by the low-resolution model (~ 200 km mesh). GSAM TM simulations indicate that such cold-front-driven events are sometimes accompanied by complicated threedimensional atmospheric structures such as stratospheric intrusion over the front, significantly affecting distributions of atmospheric components. A new calculation approach using hourly 222Rn values normalized to daily means was used to analyze the diurnal 222Rn cycle, allowing diurnal cycles in winter to be extracted from 222Rn data that are highly variable due to sporadic continental 222Rn outflows, which tend to obscure the diurnal variations. Normalized diurnal cycles of 222Rn in winter are consistent between observations and model simulations, and seem to be driven mainly by diurnal variations of planetary boundary layer height (PBLH). These results indicate that 222Rn in the near-surface atmosphere, transported from remote source regions, could vary diurnally by up to 10 % of the daily mean mainly owing to local PBLH variations, even without significant local 222Rn emissions. [ABSTRACT FROM AUTHOR]

Atmospheric radon-222 (222Rn) variability is analyzed and compared with model simulations made by the Nonhydrostatic Icosahedral Atmospheric Model (NICAM), with three horizontal resolutions (223, 56, and 14 km), in order to understand high 222Rn events predominantly caused by frontal activities. Seasonal variations of event frequency are well reproduced by the model, with correlation coefficients of 0.79 (223 km) to 0.99 (14 km). The three horizontal resolutions can reproduce general features of the observed peak shapes of events in winter, which dominantly reflect the passage of cold fronts that trap dense amounts of 222Rn. Peak height and width are well reproduced by the 56 km and 14 km resolution models, while the 223 km resolution model shows much lower and broader peaks due to insufficient resolution. We also find that simulations of 222Rn and equivalent potential temperature gradient (|∇θe|) during the events show similar horizontal distributions around the 222Rn observation station, suggesting |∇θe| is a useful tool to understand the variability of atmospheric components around fronts. Consequently, model with horizontal resolution of 56 km and 14 km can well simulate spatiotemporal variations of atmospheric components driven by frontal activities, while 223 km resolution is not enough to reproduce them. [ABSTRACT FROM AUTHOR]

Satellite observations are expected to play an important role in studying carbon fluxes. However, it is necessary to properly remove spatiotemporal bias from these observations. In this study, we estimated the spatiotemporal bias in satellite XCO2 data by making an inversion of in-situ observations. Compared to the GOSAT XCO2 (NIES Ver. 2.97-8) concentrations derived from this analysis, the global average difference is -1.26 ppm, with a difference of -0.76 ppm over the land and -1.54 ppm over the ocean. We then developed a method to correct the bias between the satellite XCO2 and the in-situ inversed XCO2 data. Using this bias correction method, we performed an inverse analysis using in-situ and satellite observations and found that the error relative to the independent observations decreased mainly in the middle and upper troposphere compared to the in-situ inversion. Compared to previous studies, the introduction of satellite observations also suppressed large variations in the regional CO2 flux, except in regions with few observations. After correction using the proposed method, the estimated CO2 flux can be used to provide improved estimates of regional CO2 fluxes; however, the results also show a need for increasing the CO2 observation sites and improving the analysis system. [ABSTRACT FROM AUTHOR]

We analyzed temporal variations of carbon monoxide (CO) in the upper troposphere from 30°N to 30°S observed using instruments aboard commercial airliner flights between Japan and Australia over the period 1993-2016. Here we focused on the CO variations in the Southern Hemisphere (SH) that showed a unique seasonal cycle with an increased CO around October-November every year. The seasonal CO peaks in the SH showed significant interannual variability (IAV), and are notably enhanced in strong El Niño years, especially 1997. The CO enhancements are proportionally associated with CO emissions from Indonesian fires, when compared to the Global Fire Emissions Database (GFED). The IAV of the CO peak anomalies relative to the mean seasonal cycle was assessed by a statistical regression model that uses a combination of multiple climate indices and their interaction terms. We found that over 80% of the CO IAV observed in the upper troposphere could be explained by the model. The largest anomaly in 1997 showed a different CO-climate relationship than the other periods, which could be due to amplification during synchronized climate modes, or include additional influence from other factors such as human activities. [ABSTRACT FROM AUTHOR]

The accuracy of chemical tracer simulations by atmospheric general circulation model (AGCM)-based chemistry-transport models (ACTMs) depends on the quality of AGCM transport properties, even when the meteorology is nudged towards the reanalysis fields. Here we show that significant improvements in tracer distribution are achieved when hybrid vertical coordinate is implemented in MIROC4.0 AGCM, compared to its predecessors AGCM5.7b based on sigma coordinate. Only explicitly resolved gravity waves are propagated into the stratosphere in MIROC4- ACTM. The MIROC4-ACTM produces "age-of-air" up to about 5 years in the tropical upper stratosphere (~1 hPa) and about 6 years in the polar middle stratosphere (~10 hPa), in agreement with observational estimates. Comparisons of MIROC4-ACTM simulation with observed sulphur hexafluoride (SF6) in the troposphere also show remarkable improvements over the AGCM57b-ACTM simulation. MIROC4-ACTM is characterized by weaker convective mass flux and thus older age of air in the tropical troposphere, relative to AGCM57b-ACTM. The role of convective transport on tracer simulations is depicted using vertical cross-sections of 222Rn (radon) distributions. Both the ACTM versions show similar results when compared with 222Rn measurements at remote sites. All aspects of tracer transport in MIROC4-ACTM is promising for inverse modelling of greenhouse gases sources and sinks at reduced bias. [ABSTRACT FROM AUTHOR]

Methane (CH4) plays important roles in atmospheric chemistry and short-term forcing of climate. A clear understanding of atmospheric CHCH4's budget of emissions and losses is required to aid sustainable management of Earth's future environment. We used an atmospheric chemistry-transport model (JAMSTEC's ACTM) for simulating atmospheric CHCH4. A global inverse modeling system has been developed for estimating CHCH4 emissions from 53 land regions for 2002-2012 using measurements at 39 sites. An ensemble of 7 inversions is performed by varying a priori emissions. Global net CHCH4 emissions varied between 505-509 and 524-545 Tg yr-1 during 2002-2006 and 2008-2012, respectively (ranges based on 7 inversion cases), with a step like increase in 2007 in agreement with atmospheric measurements. The inversion system did not account for interannual variations in OH radicals reacting with CHCH4 in the atmosphere. Our results suggest that the recent update of the EDGAR inventory (version 4.2FT2010) overestimated the global total emissions by at least 25 Tg yr-1 in 2010. The increase in CHCH4 emission since 2004 originated in the tropical and southern hemisphere regions, coinciding with an increase in non-dairy cattle stocks by ~10 % from 2002 (with 1056 million heads) to 2012, leading to ~10 Tg yr-1 increase in emissions from enteric fermentation. All 7 ensemble cases robustly estimated the interannual variations in emissions, but poorly constrained the seasonal cycle amplitude or phase consistently for all regions due to the sparse observational network. Forward simulation results using both a priori and a posteriori emissions are compared with independent aircraft measurements for validation. Based on the results of the comparison, we reject the upper limit (545 Tg yr-1) of global total emissions as 14 Tg yr-1 too high during 2008-2012, which allows us to further conclude that the increase in CH4 emissions over the East Asia (mainly China) region was 7-8 Tg yrv-1 between the 2002-006 and 2008-2012 periods, contrary to 1-17 Tg yr-1 in the a priori emissions. [ABSTRACT FROM AUTHOR]