著者

YUMIMOTO Keiya TANAKA Taichu Y. YOSHIDA Mayumi KIKUCHI Maki NAGAO Takashi M. MURAKAMI Hiroshi MAKI Takashi

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2018-035, (Released:2018-04-08)

被引用文献数

21

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The Japan Meteorological Agency (JMA) launched a next-generation geostationary meteorological satellite (GMS), Himawari-8, on October 7, 2014 and 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 resolution. 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 due to 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 during 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.

著者

ISHIJIMA Kentaro TSUBOI Kazuhiro MATSUEDA Hidekazu TANAKA Taichu Yasumichi MAKI Takashi NAKAMURA Takashi NIWA Yosuke HIRAO Shigekazu

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2022-017, (Released:2021-12-10)

被引用文献数

2

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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 on-line Global Spectral Atmosphere Model–Transport Model (GSAM-TM). Monthly and diurnal variations, and a series of synoptic high-222Rn events were extracted from 5-12 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 three-dimensional 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 owing mainly to local PBLH variations, even without significant local 222Rn emissions.

著者

NAOE Hiroaki MATSUMOTO Takanori UENO Keisuke MAKI Takashi DEUSHI Makoto TAKEUCHI Ayako

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2020-019, (Released:2020-02-03)

被引用文献数

1

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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.

著者

WU Jing KUROSAKI Yasunori SEKIYAMA Tsuyoshi Thomas MAKI Takashi

出版者

公益社団法人 日本気象学会

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2023-004, (Released:2022-10-27)

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In drylands, the dry vegetation coverage affects dust occurrence by modulating threshold friction velocity (or wind speed) for dust emission. However, there has been little research into quantifying the effect of dry vegetation coverage on dust occurrence. This study investigated spatial and temporal variations of dust occurrence and three definitions of strong wind frequency over the Gobi Desert and surrounding regions in March and April, months when dust occurrence is frequent, during 2001-2021. We evaluated the effects of variations in dry vegetation on dust occurrence by using the threat scores of forecasted dust occurrences for each strong wind definition. Our results indicate that dry vegetation, which was derived from the MODIS Soil Tillage Index, affects dust occurrence more remarkably in April than in March. In March, land surface parameters such as soil freeze-thaw and snow cover, in addition to dry vegetation coverage, should be considered to explain dust variations in that month. However, use of the threshold wind speed estimated from dry vegetation coverage improved the prediction accuracy of dust occurrence in April. Therefore, we propose that the dry vegetation coverage is a key factor controlling dust occurrence variations in April. The findings imply that estimation of dry vegetation coverage should be applied to dust models.

著者

KAJINO Mizuo DEUSHI Makoto SEKIYAMA Tsuyoshi Thomas OSHIMA Naga YUMIMOTO Keiya TANAKA Taichu Yasumichi CHING Joseph HASHIMOTO Akihiro YAMAMOTO Tetsuya IKEGAMI Masaaki KAMADA Akane MIYASHITA Makoto INOMATA Yayoi SHIMA Shin-ichiro TAKAMI Akinori SHIMIZU Atsushi HATAKEYAMA Shiro SADANAGA Yasuhiro IRIE Hitoshi ADACHI Kouji ZAIZEN Yuji IGARASHI Yasuhito UEDA Hiromasa MAKI Takashi MIKAMI Masao

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2019-020, (Released:2018-12-09)

被引用文献数

36

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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 5-category non-equilibrium, 3-category non-equilibrium, and bulk equilibrium methods. 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 by 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 and dust extinction coefficient were significantly underestimated.