Tsuyoshi Thomas Sekiyama

Aerosol data assimilation using data from Himawari-8, a next-generation geostationary meteorological satellite

Himawari-8, a next-generation geostationary meteorological satellite, was launched on 7 October 2014 and became operational on 7 July 2015. The advanced imager on board Himawari-8 is equipped with 16 observational bands (including three visible and three near-infrared bands) that enable retrieval of full-disk aerosol optical properties at 10 min intervals from geostationary (GEO) orbit. Here we show the first application of aerosol optical properties (AOPs) derived from Himawari-8 data to aerosol data assimilation. Validation of the assimilation experiment by comparison with independent observations demonstrated successful modeling of continental pollution that was not predicted by simulation without assimilation and reduced overestimates of dust front concentrations. These promising results suggest that AOPs derived from Himawari-8/9 and other planned GEO satellites will considerably improve forecasts of air quality, inverse modeling of emissions, and aerosol reanalysis through assimilation techniques.

Study of Lower Tropospheric Ozone over Central and Eastern China: Comparison of Satellite Observation with Model Simulation

The lower tropospheric ozone enhancement over Central and Eastern China (CEC) was reported by Hayashida et al. (Atmos Chem Phys 15(17):9865–9881, 2015) using the Ozone Monitoring Instrument (OMI) multiple-layer product retrieved by Liu et al. (Atmos Chem Phys 10(5):2521–2537, 2010), which first showed the lower tropospheric ozone enhancement from ultraviolet and visible (UV-Vis) spectra measurements from space. However, to clarify the enhancement in the concentration of the lowermost ozone using spaceborne measurements, it is necessary to understand the effect of ozone variation in the upper troposphere and lower stratosphere (UT/LS), because of large smoothing errors in the retrieval scheme. In this study, a scheme was developed to eliminate the artificial effect of UT/LS ozone enhancement on lower tropospheric ozone retrieval using OMI. By applying the UT/LS screening scheme for June 2006, we removed the artificial effect of the UT/LS ozone enhancement on the lower tropospheric ozone. Even after UT/LS screening, we were able to show a clear enhancement in the lower tropospheric ozone over CEC in June 2006 and confirmed the conclusion derived by Hayashida et al. (Atmos Chem Phys 15(17):9865–9881, 2015). To clarify the reason for ozone enhancement in June, the effects of emissions from open crop residue burning (OCRB) in the North China Plain on lower tropospheric ozone were also examined using a comparison with model simulations. On the scale of the vertical resolution of OMI observations, the effect of OCRB on ozone enhancement does not seem to be significant, although it may be more significant when focusing on ozone in the planetary boundary layer.

Atmospheric Modeling of 137Cs Plumes From the Fukushima Daiichi Nuclear Power Plant—Evaluation of the Model Intercomparison Data of the Science Council of Japan

Since the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident in March 2011, atmospheric simulation models have improved our understanding of the atmospheric behavior of radionuclides. Model intercomparisons provide valuable and useful information for evaluating the validity and variability of individual model results. In this study, we compared results of seven atmospheric transport models used to simulate 137Cs released from the FDNPP to the atmosphere. All model results used in this analysis had been submitted for a model intercomparison project of the Science Council of Japan (2014, http//www.scj.go.jp/en/report/index.html). Here we assessed model performance by comparing model results with observed hourly atmospheric concentrations of 137Cs, with a particular focus on nine plumes over the Tohoku and Kanto regions. The intercomparison results showed that model performance in reproducing 137Cs concentrations was highly variable among different models and plumes. In general, models better reproduced plumes that passed over many observation stations. The performance among the models was consistent with the simulated wind fields and the source terms used. We also assessed model performance in relation to accumulated 137Cs deposition. Simulated areas of high 137Cs deposition were consistent with the simulated 137Cs plume pathways, though the models that best simulated atmospheric 137Cs concentrations were different from those that best simulated deposition. The ensemble mean of all models consistently reproduced atmospheric 137Cs concentrations and deposition well, suggesting that use of a multimodel ensemble results in more effective and consistent model performance. ©2018. American Geophysical Union. All Rights Reserved.

Mass flux analysis of 137Cs plumes emitted from the Fukushima Daiichi nuclear power plant

Abstract The flow vectors of radioactive cesium-137 (137Cs) plume emitted from the Fukushima Daiichi nuclear power plant in March 2011 were quantitatively depicted by a mass flux analysis in this study. 137Cs plumes were calculated by an Eulerian dispersion model with a 3-km horizontal resolution. The vertically column-integrated mass flux was consistent with the flow approximation based on ground surface 137Cs observations, even though there were some discrepancies that were caused by differences in the wind direction between the ground surface and the dominant plume layer. These discrepancies were explained by combining the use of the ground surface horizontal mass flux with the column-integrated mass flux. The mass flux analysis clearly provided an illustration of 137Cs dominant stream locations, directions, and depositions by reducing high-dimensional model outputs into a lower-dimensional plot. Mass flux (i.e. the product of the mass density and wind velocity) has often been used in dynamic meteorology but has not been used as frequently in atmospheric chemistry or pollutant dispersion studies. However, the concept of mass flux is a robust alternative for conventional validation approaches that only utilize a time series of pollutant concentrations. Mass flux analyses can be used further in atmospheric chemistry as a quantitative visualization tool to track the emission, advection, dispersion, and deposition of atmospheric constituents.

Prediction of health effects of cross-border atmospheric pollutants using an aerosol forecast model

Health effects of cross-border air pollutants and Asian dust are of significant concern in Japan. Currently, models predicting the arrival of aerosols have not investigated the association between arrival predictions and health effects. We investigated the association between subjective health symptoms and unreleased aerosol data from the Model of Aerosol Species in the Global Atmosphere (MASINGAR) acquired from the Japan Meteorological Agency, with the objective of ascertaining if these data could be applied to predicting health effects. Subjective symptom scores were collected via self-administered questionnaires and, along with modeled surface aerosol concentration data, were used to conduct a risk evaluation using generalized estimating equations between October and November 2011. Altogether, 29 individuals provided 1670 responses. Spearmans correlation coefficients were determined for the relationship between the proportion of the participants reporting the maximum score of two or more for each symptom and the surface concentrations for each considered aerosol species calculated using MASINGAR; the coefficients showed significant intermediate correlations between surface sulfate aerosol concentration and respiratory, throat, and fever symptoms (R = 0.557, 0.454, and 0.470, respectively; p < 0.01). In the general estimation equation (logit link) analyses, a significant linear association of surface sulfate aerosol concentration, with an endpoint determined by reported respiratory symptom scores of two or more, was observed (P trend = 0.001, odds ratio [OR] of the highest quartile [Q4] vs. the lowest [Q1] = 5.31, 95% CI = 2.18 to 12.96), with adjustment for potential confounding. The surface sulfate aerosol concentration was also associated with throat and fever symptoms. In conclusion, our findings suggest that modeled data are potentially useful for predicting health risks of cross-border aerosol arrivals.

Study on measurement performance of future space-based Doppler wind lidar in Japan

Wind is fundamental in many atmospheric phenomena. Global wind profile observation is important to improve numerical weather prediction (NWP) and various meteorological studies. Wind profile observations are measured mainly by radiosonde networks. Most of the weather stations are on land, while weather stations on oceans and remote land areas are sparsely distributed. The current global wind observing systems do not satisfy the globally homogeneous wind profile observation. A space-based Doppler wind lidar is one of the candidates for future global wind profile observations. In the paper, we present results from feasibility study of space-based Doppler Wind Lidar.