Bottom-up emission inventories can provide valuable information for understanding emission status and are needed as input datasets to drive chemical transport models. However, this type of inventory ...has the disadvantage of taking several years to be compiled because it relies on a statistical dataset. Top-down approaches use satellite data as a constraint and overcome this disadvantage. We have developed an immediate inversion system to estimate anthropogenic NOx emissions with NO2 column density constrained by satellite observations. The proposed method allows quick emission updates and considers model and observation errors by applying linear unbiased optimum estimations. We used this inversion system to estimate the variation of anthropogenic NOx emissions from China and India from 2005 to 2016. On the one hand, NOx emissions from China increased, reaching a peak in 2011 with 29.5 Tg yr−1, and subsequently decreased to 25.2 Tg yr−1 in 2016. On the other hand, NOx emissions from India showed a continuous increase from 2005 to 2016, reaching 13.9 Tg yr−1 in 2016. These opposing trends from 2011 to 2016 were −0.83 and +0.76 Tg yr−1 over China and India, respectively, and correspond to strictly regulated and unregulated future scenarios. Assuming these trends continue after 2016, we expect NOx emissions from China and India will be similar in 2023, with India becoming the world's largest NOx emissions source in 2024.
Robust estimates of CO2 budget, CO2 exchanged between the atmosphere and terrestrial biosphere, are necessary to better understand the role of the terrestrial biosphere in mitigating anthropogenic ...CO2 emissions. Over the past decade, this field of research has advanced through understanding of the differences and similarities of two fundamentally different approaches: “top‐down” atmospheric inversions and “bottom‐up” biosphere models. Since the first studies were undertaken, these approaches have shown an increasing level of agreement, but disagreements in some regions still persist, in part because they do not estimate the same quantity of atmosphere–biosphere CO2 exchange. Here, we conducted a thorough comparison of CO2 budgets at multiple scales and from multiple methods to assess the current state of the science in estimating CO2 budgets. Our set of atmospheric inversions and biosphere models, which were adjusted for a consistent flux definition, showed a high level of agreement for global and hemispheric CO2 budgets in the 2000s. Regionally, improved agreement in CO2 budgets was notable for North America and Southeast Asia. However, large gaps between the two methods remained in East Asia and South America. In other regions, Europe, boreal Asia, Africa, South Asia, and Oceania, it was difficult to determine whether those regions act as a net sink or source because of the large spread in estimates from atmospheric inversions. These results highlight two research directions to improve the robustness of CO2 budgets: (a) to increase representation of processes in biosphere models that could contribute to fill the budget gaps, such as forest regrowth and forest degradation; and (b) to reduce sink–source compensation between regions (dipoles) in atmospheric inversion so that their estimates become more comparable. Advancements on both research areas will increase the level of agreement between the top‐down and bottom‐up approaches and yield more robust knowledge of regional CO2 budgets.
The model performance of a regional-scale meteorology-chemistry model (NHM-Chem) has been evaluated for the consistent predictions of the chemical, physical, and optical properties of aerosols. These ...properties are essentially important for the accurate assessment of air quality and health hazards, contamination of land and ocean ecosystems, and regional climate changes due to aerosol-cloud-radiation interaction processes. Currently, three optional methods are available: the five-category non-equilibrium method, the three-category non-equilibrium method, and the bulk equilibrium method. These three methods are suitable for the predictions of regional climate, air quality, and operational forecasts, respectively. In this paper, the simulated aerosol chemical, physical, and optical properties and their consistency were evaluated using various observation data in East Asia. The simulated mass, size, and deposition of SO42− and NH4+ agreed well with the observations, whereas those of NO3−, sea salt, and dust needed improvement. The simulated surface mass concentration (PM10 and PM2.5) and spherical extinction coefficient agreed well with the observations. The simulated aerosol optical thickness (AOT) and dust extinction coefficient were significantly underestimated.
An experiment study was conducted on the operational characteristics of the JEST-type loop thermosyphon when an initial liquid level of a working fluid was lowered. This thermosyphon was invented in ...2012 by one of the authors with a jet explosion stream technology (JEST) for cooling high-heat-generation and high-heat-flux CPUs. The present experiment aims at lowering the height of the thermosyphon for rack-level thermal management in a datacenter. Hydrofluoroether (HFE)-7000 was used as the working fluid. In experiment, an evaporator section of the thermosyphon was heated with a heating block while a condenser section was water-cooled using a thermostatic bath. Temporal changes in temperatures of the thermosyphon were obtained with thermocouples. Moreover, the circulation flow rate of the working fluid in the thermosyphon was obtained with a simple measurement method. The initial liquid level of the working fluid was changed as 166, 268, 368 mm while the height of the thermosyphon was 1200 mm. Experimental results are shown regarding the effect of the initial liquid level on the circulation flow rates of the vapor and liquid phases of the working fluid as well as the heat transfer coefficient at the evaporator section. An additional experiment was also conducted when the height of the thermosyphon was lowered from 1200 mm to 480 mm. It was confirmed that the thermal performance of the thermosyphon decreased when the initial liquid level was lowered; however, the thermal performance was recovered by lowering the height of the thermosyphon. Therefore, the JEST-type loop thermosyphon can be applied to the rack-level thermal management in a datacenter.
East Asia (China, Japan, Koreas, and Mongolia) has been the world's economic engine over at least the past two decades, exhibiting a rapid increase in fossil fuel emissions of greenhouse gases (GHGs) ...and has expressed the recent ambition to achieve climate neutrality by mid‐century. However, the GHG balance of its terrestrial ecosystems remains poorly constrained. Here, we present a synthesis of the three most important long‐lived greenhouse gases (CO2, CH4, and N2O) budgets over East Asia during the decades of 2000s and 2010s, following a dual constraint approach. We estimate that terrestrial ecosystems in East Asia is close to neutrality of GHGs, with a magnitude of between −46.3 ± 505.9 Tg CO2eq yr−1 (the top‐down approach) and −36.1 ± 207.1 Tg CO2eq yr−1 (the bottom‐up approach) during 2000–2019. This net GHG sink includes a large land CO2 sink (−1229.3 ± 430.9 Tg CO2 yr−1 based on the top‐down approach and −1353.8 ± 158.5 Tg CO2 yr−1 based on the bottom‐up approach) being offset by biogenic CH4 and N2O emissions, predominantly coming from the agricultural sectors. Emerging data sources and modeling capacities have helped achieve agreement between the top‐down and bottom‐up approaches, but sizable uncertainties remain in several flux terms. For example, the reported CO2 flux from land use and land cover change varies from a net source of more than 300 Tg CO2 yr−1 to a net sink of ∼−700 Tg CO2 yr−1. Although terrestrial ecosystems over East Asia is close to GHG neutral currently, curbing agricultural GHG emissions and additional afforestation and forest managements have the potential to transform the terrestrial ecosystems into a net GHG sink, which would help in realizing East Asian countries' ambitions to achieve climate neutrality.
Plain Language Summary
East Asia (China, Japan, Koreas and Mongolia) is not only the hotspot of anthropogenic greenhouse gas (GHG, including CO2, CH4 and N2O) emissions, but also a region with large CO2 sink. However, the greenhouse gas balance of greenhouse gases over the region is poorly understood. In this study, we performed a synthesis for over 40 flux terms to provide the first‐of‐its‐kind GHG budget assessment over the decades of 2000s and 2010s. We find terrestrial ecosystems in East Asia is close to neutrality of GHGs. The bottom‐up approach summing up component fluxes estimated a net balance of −36.1 ± 207.1 Tg CO2eq yr−1, while the top‐down approach based on atmospheric inversions estimated a net balance of −46.3 ± 505.9 Tg CO2eq yr−1. This results from compensation of the large CO2 sink by CH4 and N2O emissions, and from compensation of net GHG sink over natural ecosystems by net GHG source over agricultural ecosystems. Thus, curbing agricultural GHG emissions has the potential to realizing the ambitious goal of achieving climate neutrality over East Asia.
Key Points
A comprehensive greenhouse gas (CO2, CH4 and N2O) accounting including about 40 flux terms over East Asia is reported
Terrestrial ecosystems in East Asia are close to greenhouse gas neutral
Natural ecosystems is a net greenhouse gas sink, compensated by a net source from agricultural ecosystems
The Japan Meteorological Agency (JMA) launched a next-generation geostationary meteorological satellite (GMS), Himawari-8, on October 7, 2014, which began its operation on July 7, 2015. The Advanced ...Himawari Imager (AHI) onboard Himawari-8 has 16 observational bands that enable the retrieval of full-disk maps of aerosol optical properties (AOPs), including aerosol optical thickness (AOT) and the Ångström exponent (AE), with unprecedented spatial and temporal resolutions. In this study, we combined an aerosol transport model with the Himawari-8 AOT using the data assimilation method and performed aerosol assimilation and forecasting experiments on smoke from an intensive wildfire that occurred over Siberia between May 15 and 18, 2016. To effectively utilize the high observational frequency of Himawari-8, we assimilated 1-h merged AOTs generated through the combination of six AOT snapshots taken over 10-min intervals, three times per day. The heavy smoke originating from the wildfire was transported eastward behind a low-pressure trough and covered northern Japan from May 19 to 20. The southern part of the smoke plume then traveled westward, in a clockwise flow associated with high pressure. The forecast without assimilation reproduced the transport of the smoke to northern Japan; however, it underestimated AOT and the extinction coefficient compared with observed values mainly because of errors in the emission inventory. Data assimilation with the Himawari-8 AOT compensated for the underestimation and successfully forecasted the unique C-shaped distribution of the smoke. In particular, the assimilation of the Himawari-8 AOT in May 18 greatly improved the forecast of the southern part of the smoke flow. Our results indicate that the inheritance of assimilation cycles and the assimilation of more recent observations led to better forecasting in this case of a continental smoke outflow.
An integrated understanding of the biogeochemical consequences of climate extremes and land use changes is needed to constrain land-surface feedbacks to atmospheric CO
from associated climate change. ...Past assessments of the global carbon balance have shown particularly high uncertainty in Southeast Asia. Here, we use a combination of model ensembles to show that intensified land use change made Southeast Asia a strong source of CO
from the 1980s to 1990s, whereas the region was close to carbon neutral in the 2000s due to an enhanced CO
fertilization effect and absence of moderate-to-strong El Niño events. Our findings suggest that despite ongoing deforestation, CO
emissions were substantially decreased during the 2000s, largely owing to milder climate that restores photosynthetic capacity and suppresses peat and deforestation fire emissions. The occurrence of strong El Niño events after 2009 suggests that the region has returned to conditions of increased vulnerability of carbon stocks.
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.
This study constructs a merged total column ozone (TCO) dataset using 20 available satellite Level 2 TCO (L2SAT) datasets over 40 years from 1978 to 2017. The individual 20 datasets and the merged ...TCO dataset are corrected against ground-based Dobson and Brewer spectrophotometer TCO (GD) measurements. Two bias correction methods are used: simple linear regression (SLR) as a function of time and multiple linear regression (MLR) as a function of time, solar zenith angle, and effective ozone temperature. All of the satellite datasets are consistent with GD within ±2–3 %, except for some degraded data from the Total Ozone Mapping Spectrometer/Earth Probe during a period of degraded calibration and from the Ozone Mapping and Profiling Suite (OMPS) provided from NOAA at an early stage of measurements. OMPS data provided from NASA show fairly stable L2SAT–GD differences. The Global Ozone Monitoring Experiment/MetOp-A and -B datasets show abrupt changes of approximately 8 DU coincident with the change of retrieval algorithm. For the TCO merged datasets created by averaging all coincident data located within a grid cell from the 20 satellite-borne TCO datasets, the differences between corrected and uncorrected TCOs by MLR are generally positive at lower latitudes where the bias correction increases TCO because of low effective ozone temperature. In the trend analysis, the difference between corrected and uncorrected TCO trends by MLR shows clear seasonal and latitudinal dependency, whereas such seasonal and latitudinal dependency is lost by SLR. The root mean square difference of L2SAT–GD for the uncorrected merged datasets, 8.6 DU, is reduced to 8.4 DU after correction using SLR and MLR. Therefore, the empirically corrected merged TCO datasets that are converted into time-series homogenization with high temporal-resolution are suitable as a data source for trend analyses as well as assimilation for long-term reanalysis.
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