著者

Tomoaki OSE

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

vol.97, no.5, pp.1041-1053, 2019 (Released:2019-10-09)

参考文献数

22

被引用文献数

4

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In order to investigate the dependence of future projections for summertime East Asian precipitation on their present-day model climatology, the models well reproducing the observed climatology over East Asia are focused on in the analysis of the fifth phase of the Coupled Model Intercomparison Project (CMIP5) future projections for the period from 2075 to 2099 under the Representative Concentration Pathway 8.5 global warming scenario. The future projection by these models indicates that summertime monthly climatological precipitation in future East Asia is more likely systematically decreased in some regions rather than evenly increased in every wet region.  The CMIP5 36-model ensemble mean monthly circulation change at 700hPa is characterized through the future summertime by a cyclonic circulation change to the south of Japan and the associated downward motion changes around Japan. The models showing the above features more clearly tend to simulate stronger westerlies over East Asia and more tropical precipitation in the present-day northern summer climatology. Therefore, an ensemble of the models reproducing the observed westerlies over East Asia, which are stronger than the 36-model ensemble mean, tends to simulate a strong downward motion change regionally in the future East Asian summer so that the possibility of a decrease in monthly precipitation is enhanced there against the “wet-getting-wetter” effect.  The future circulation change over East Asia was considered as part of the western North Pacific circulation change that responds to the future reduction of vertical motion in the vertically stabilized tropics. Large future reduction of the tropical vertical motion necessary for the strong downward motion change in East Asia can be attributed to the present-day climatology of much precipitation and large upward motion in the tropics.

著者

LIU Boqi ZHU Congwen SU Jingzhi MA Shuangmei XU Kang

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.2019-047, (Released:2019-04-19)

被引用文献数

33

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The northward shift of the western North Pacific Subtropical High (WNPSH) in July 2018 broke the historical record since 1958 and resulted in extreme heat waves and casualties across Northeast Asia (NEA). The present work associated this extreme WNPSH anomaly with the anomalies of barotropic anticyclone above NEA originating from the strongest positive tri-pole pattern of sea surface temperature anomaly (SSTA) in the North Atlantic in July. Both data analysis and numerical experiments indicated that the positive tri-pole SSTA pattern could produce an upper-tropospheric wave source over the Europe, which stimulated an eastward propagating wave train along the subpolar westerly jet over the Eurasian continent. When its anticyclonic node reached NEA, the WNPSH started to shift northward. After the cyclonic node in the circulation anomaly encountered the Tibetan Plateau, atmospheric diabatic heating was enhanced over the eastern Tibetan Plateau, initiating another subtropical wave train, which furthered the northward shift of the WNPSH. Therefore, the wave source over Europe was critical for the northward shift of the WNPSH in July, connecting the tri-pole SSTA pattern in the North Atlantic with the WNPSH anomaly and maintaining the downstream effects of thermal forcing over the eastern Tibetan Plateau on the East Asian summer monsoon.

著者

Kei YOSHIMURA Taikan OKI Nobuhito OHTE Shinjiro KANAE

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

vol.82, no.5, pp.1315-1329, 2004 (Released:2004-12-17)

参考文献数

33

被引用文献数

56 85

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This study investigated the dynamic motion of atmospheric water advection by an analytic method called colored moisture analysis (CMA), that allows for the estimation and visualization of atmospheric moisture advection from specific source regions. The CMA water transport model includes balance equations with the upstream scheme and, uses external meteorological forcings. The forcings were obtained from the Global Energy and Water Cycle Experiment (GEWEX) Asian Monsoon Experiments (GAME) reanalysis. A numerical simulation with 79 global sections was run for April to October 1998. The results clearly showed seasonal variations in advection associated with large-scale circulation fields, particularly a difference between rainy and dry seasons associated with the Asian monsoon. The paper also proposes a new definition of southwest Asian monsoon onset and decay, based on the amount of water originating from the Indian Ocean. Earliest onset occurs over southeastern Indochina around 16- 25 May. Subsequent onset occurs in India one month later. These results agree with previous studies on the Asian monsoon onset/end. The CMA provides a clearer, more integrated view of temporal and spatial changes in atmospheric circulation fields, particularly Asian monsoon activities, than previous studies that focused only on one or two distinct circulation features, such as precipitation or wind speed. Furthermore, monsoon transition in a specific year, 1998, first became analyzable, whereas the previous studies used climatologies.

著者

JIN Hao JIN Yi DOYLE James D.

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.2019-011, (Released:2018-11-12)

被引用文献数

2

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Typhoon Nepartak was a category 5 tropical cyclone of 2016 and had significant societal impacts. It went through a rapid intensification (RI), with an increase of maximum wind speed of 51 m s-1 and a decrease of minimum sea level pressure of 74 hPa in 42 h. The real-time forecast from the Coupled Ocean/Atmosphere Mesoscale Prediction System – Tropical Cyclone (COAMPS-TC), starting from 1200 UTC 3 July, predicted the track and intensity reasonably well for Super Typhoon Nepartak and captured the storm’s RI process. Positive interactions among primary and secondary circulations, surface enthalpy fluxes, and mid-level convective heating are demonstrated to be critical for the RI. The storm structure variations seen from the simulated satellite infrared brightness temperature during RI bear considerable resemblance to the Himawari-8 satellite images, although the forecast inner core is too broad, presumably due to the relatively coarse resolution (5 km) used for the real-time forecasts at the time.

著者

SAITO Izumi GOTOH Toshiyuki WATANABE Takeshi

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.2019-049, (Released:2019-05-17)

被引用文献数

17

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To consider the growth of cloud droplets by condensation in turbulence, the Fokker-Planck equation is derived for the droplet size distribution (droplet spectrum). This is an extension of the statistical theory proposed by Chandrakar and coauthors in 2016 for explaining the broadening of the droplet spectrum obtained from the ‘Π-chamber', a laboratory cloud chamber. In this Fokker-Planck equation, the diffusion term represents the broadening effect of the supersaturation fluctuation on the droplet spectrum. The aerosol (curvature and solute) effects are introduced into the Fokker-Planck equation as the zero flux boundary condition at R2=0, where R is the droplet radius, which is mathematically equivalent to the case of Brownian motion in the presence of a wall. The analytical expression for the droplet spectrum in the steady state is obtained and shown to be proportional to Rexp(-cR2), where c is a constant. We conduct direct numerical simulations of cloud droplets in turbulence and show that the results agree closely with the theoretical predictions and, when the computational domain is large enough to be comparable to the Π-chamber, agree with the results from the Π-chamber as well. We also show that the diffusion coefficient in the Fokker-Planck equation should be expressed in terms of the Lagrangian autocorrelation time of the supersaturation fluctuation in turbulent flow.

著者

LEE Meng-Tze LIN Pay-Liam CHANG Wei-Yu SEELA Balaji Kumar JANAPATI Jayalakshmi

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.2019-048, (Released:2019-05-10)

被引用文献数

15

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In the present work, long-term (10 years) raindrop size distribution (RSD) measurements from Joss-Waldvogel Disdrometer (JWD) installed at National Central University (NCU, 24&deg58′6″N 121&deg11′27″E), Taiwan and vertical profile of radar reflectivity were used to analyze the variations in gamma parameters of six seasons (winter, spring, mei-yu, summer, typhoon, and autumn) and types of precipitation. The normalized gamma distribution of RSD revealed that the highest mean Dm (Mass-weighted average diameter) values occurred in summer, whereas the highest mean log10Nw (normalized intercept parameter) values were found in winter. Furthermore, most of the rainfall rate falling at less than 20 mm h-1 occurs in Northern Taiwan. In this study, we used radar reflectivity to differentiate between convective and stratiform systems. It was revealed that the mean Dm values are higher in convective systems, whereas the mean log10Nw values are higher in stratiform systems. The structure of RSD in stratiform systems remains constant in all seasons; however, convection is similar to maritime type. The microphysical characteristics that are responsible for different RSD features in different seasons and types of precipitation are illustrated with the help of contoured frequency by altitude diagrams of radar reflectivity.

著者

SONG Bin ZHI Xiefei PAN Mengting HOU Meiyi HE Chengfei FRAEDRICH Klaus

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.2019-050, (Released:2019-05-24)

被引用文献数

4

---

The turbulent heat flux is the main passageway for air–sea interactions. However, due to lack of long-term observations for the turbulent heat flux, it is difficult to investigate the mechanisms of coupled ocean-atmosphere variabilities, such as the Pacific Decadal Oscillation. We here reconstructed the long-term turbulent heat flux in the North Pacific for the period 1921–2014 based on observations in the International Comprehensive Ocean-Atmosphere Data Set–International Maritime Meteorological Archive. The sea surface temperature, air temperature, wind and humidity were used to reconstruct the turbulent heat flux using the Coupled Ocean–Atmosphere Response Experiment (COARE3.5) algorithm. The modified Fisher–Tippett distribution was employed to calculate the turbulent heat flux at each grid square, and then the missing values were further derived based on data interpolating empirical orthogonal functions (DINEOF). The reconstructed turbulent heat flux was shown to be in accordance with the commonly used short-term heat flux datasets. This reconstruction is further examined by comparison with the long-term data of twentieth century reanalysis from European Center for Medium-range Weather Forecasts twentieth century reanalysis (ERA-20C) and the 20th Century Reanalysis (20CR) dataset from National Oceanic and Atmospheric Administration. It displays a good agreement with the ERA-20C both in spatial and temporal scales, but some differences from the 20CR. By these examinations, the reconstructed turbulent heat flux can well reproduce the main features of the air-sea interaction in the North Pacific, which can be used in studies of the air-sea interaction in the North Pacific on multidecadal timescales.

著者

Suranjith Bandara KORALEGEDARA Chuan-Yao LIN Yang-Fan SHENG

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

vol.97, no.4, pp.821-839, 2019 (Released:2019-08-02)

参考文献数

52

被引用文献数

3

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In this present study, we analyzed the synoptic and mesoscale dynamics and underlying mechanism of an extreme rainfall and flood event that occurred in Sri Lanka between 14-17 May 2016, using the Weather Research and Forecasting Model simulations with a horizontal grid size of 3 km and observational data. This extreme rainfall event was associated with a low-pressure system (LPS) that originated over the Bay of Bengal in the Indian Ocean and passed over Sri Lanka. The observed maximum accumulation of rainfall during the event exceeded 300 mm at several weather stations on 15-16 May and it resulted in severe flooding and landslides, particularly in the western part of the island. The model closely simulated the timing of the initiation of the LPS and its development along the east coast of Sri Lanka. The model could capture the overall rainfall tendency and pattern of this event. Synoptic and mesoscale analyses indicated that this extreme rainfall event occurred as the cumulative effect of a sustained low-level convergence zone, generated by an enhanced westerly monsoon flow and the circulation of the LPS, alongside a continuous supply of high-magnitude moisture, strong vertical motion, and orographic effects of the Central Mountains of Sri Lanka. Model sensitivity experiments indicated that the rainfall over the western slope area of the mountains was enhanced by mountain lifting, whereas western coastal rainfall was reduced because the mountains blocked the northeasterly flow of the LPS.

著者

浅井 富雄

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

vol.48, no.1, pp.18-29, 1970 (Released:2008-05-27)

参考文献数

18

被引用文献数

66 85

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Boussinesq近似にもとづく摂動方程式を差分近似法により数値的に解いて,不安定成層の平面Couette流中で発現する熱対流の性状を調べた.まつ゜流れの安定性を擾乱の水平波長,Richardson数等について示す.一様なシヤーをもつ流れは一般に擾乱の発達を抑制する効果をもち,その効果は波長の短いほど,又流れに直角な方向の波長が平行な方向の波長に比して長い-transverseモード-ほど著しい。一方流れに平行な方向の波長が直角な方向の波長に比して長く-longitudinalモード-なるにつれシヤー流の抑制作用は減じ,,流れに完全に平行なroll状の対流はシヤーの抑制作用を全く受けず増幅率の最も大きい所謂preferredモードとなる.Rayleigh数が大きくなると,基本流の平均速度で伝播する不安定波の他に波長のより短い前者と違った伝播速度をもつ不安定波が現れるが,その増幅率は前者に比して小さい.これらは異る解法により得られたKuo(1963)その他の結論と一致する.以上の予備的調査にもとついて,平均流で移動する波長の長い不安定波(熱対流にとって主要なモード)の構造やそれに伴うエネルギー変換について考察する.対流による熱の鉛直輸送に伴う位置エネルギーから運動エネルギーへの転換の他に,水平運動量の鉛直輸送に伴い基本流と擾乱の間に運動エネルギーの変換が生ずる.特に運動量の鉛直輸送は擾乱の3次元構造に強く依存する.擾乱がtransverseモードの場合,水平運動量は基本流のシヤーに抗して輸送-counter gradient transfer-され,従って擾乱の運動エネルギーから基本流のそれに転換される.この極端な場合が基本流に平行な鉛直面内の2次元対流で,著者(1964)の数値実験はこの結果を裏づけている.他方3次元運動を伴うlongitudinalモードの擾乱はtransverseモードのそれとは逆に運動量を輸送する.即ち基本流から擾乱へ運動エルギーを転換する.そしてシヤー流中ではこのlongitudinalの3次元対流がpreferredモードである.

著者

SEGUCHI Takafumi IWASAKI Suginori KAMOGAWA Masashi USHIYAMA Tomoki OKAMOTO Hajime

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.2019-033, (Released:2019-02-04)

被引用文献数

1

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In the summer of 2016, 14 cases of jumping cirrus (JC) were observed around the Kanto region in Japan by ground-based, visible-light cameras. The cameras were set at the summit of Mt. Fuji and National Defense Academy (Kanagawa, Japan), and 15-second time-lapse photography was continually taken for the period. The location and spatial scale of the JC were calculated by measurements using the photometry of background stars in the nighttime and the geostationary meteorological satellite Himawari-8 infrared imagery. The environmental conditions of the JC were also investigated using radiosonde and Himawari-8 visible and infrared measurements. Comparing our cases to the JC in the United States of America (USA) reproduced by a three-dimensional, non-hydrostatic cloud model from previous studies, their motions, morphology, spatial and temporal scales showed similarities, although the horizontal scale of the JC and the magnitude of the underlying convection was relatively smaller in our cases. The sounding by the radiosonde in the vicinity of the storms showed that 3 of the 14 cases reached the stratosphere. However, the hydration of the lower stratosphere was not supported by an analysis of the brightness temperature difference (BTD) between 6.2 and 10.4 µm measured by Himawari-8. The averaged wind shear across the range of the jumping heights above the anvil was -1.1 ms-1 km-1. The maximum value of the convective available potential energy (CAPE) of the 14 cases was 1384 Jkg-1, which is several times smaller than those of the thunderstorm cases observed in the USA in previous numerical JC studies. This indicates that JC occurs from the cumulonimbus anvil top even if the convection is relatively weak. The motion of JC observed by visible-light cameras shows that it can transport moisture above the tops of the anvils of convective clouds regardless of its altitude as cloud ice appears to be sublimated.

著者

ZHAO Haikun WU Liguang WANG Chao KLOTZBACH Philip J.

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.2019-039, (Released:2019-03-11)

被引用文献数

8

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Most studies have focused on variations of tropical cyclone (TC) frequency, intensity, and track over the western North Pacific (WNP), while variability of WNP TC season onset date (TCSO) has been less studied. Recent research has indicated a close association between WNP TCSO and sea surface temperature (SST) over the tropical Indian Ocean and the tropical central-eastern Pacific. This study finds the relationship between TCSO and SST underwent an interdecadal change in the late 1990s, likely due to a climate shift that occurred around that time. An observed significant correlation between TCSO and SST before the late 1990s and has been insignificant since that time. It was confrimed by the fact that ENSO positively correlates at 0.46 with TCSO from 1965-1999 (significant at the 95 % level), while the correlation becomes insignificant (0.16) during 1998-2016. Further analysis suggests that the close association between TCSO and SST is robust only for major El Niño events, with consistently extreme late TCSO following major El Niños during the satellite era. Accompanying the decay of major El Niños, tropical equatorial easterly anomalies in the WNP are driven by a Matsuno-Gill-type response to the specific SST anomaly pattern over the tropical Indo-Pacific sector. This in turn induces an anomalous anticyclone, anomalous westerly vertical wind shear, reduced mid-level moisture and suppressed convection over the WNP basin – all of which are unfavorable for WNP TCs, resulting in delayed TCSO following major El Niño events. These inter-decadal changes in the inter-annual correlation between TCSO and ENSO are largely due to the changing influence of moderate El Niño events on TCSO before and after the late 1990s. This study improves understanding of the ENSO-TC relationship, which should aid seasonal outlooks of WNP TC activity.

著者

FUJITA Mikiko SATO Tomonori YAMADA Tomohito J. KAWAZOE Sho NAKANO Masuo ITO Kosuke

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.2019-022, (Released:2018-12-17)

被引用文献数

4

---

We investigated extremely heavy precipitation that occurred around the Kinugawa River, Japan, in September 2015, and the probability of extreme precipitation occurrence, using data from a large ensemble forecast more than 1,000 members that were dynamically downscaled to 1.6 km horizontal grid spacing. The observed event was statistically rare among simulated cases and 3-day accumulated precipitation around the target area was equivalent to the 95th percentile among all simulated ensemble members. Our results show that this extreme precipitation event occurred under specific conditions: two coexisting typhoons at close proximity that produces a high atmospheric instability, and water vapor transport from the Pacific Ocean. We also assessed the probability of extreme precipitation in mountainous areas other than the Kinugawa River case. Heavy precipitation also occurred southwest of the Kinugawa River region due to two typhoons, similar to the Kinugawa River case. The tracks of these typhoons shifted marginally; however, there was a difference in the water vapor supplied to the area, causing heavy precipitation. The large-ensemble downscaled data used in this study hence enable us to evaluate the occurrence probability of a torrential rainfall event that was rarely observed, which may contribute to updating a disaster mitigating plan for possible similar disasters in future.

著者

OSE Tomoaki

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.2019-018, (Released:2018-12-07)

被引用文献数

10

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Global warming experiments using three different 60 km-mesh atmospheric global circulation models are studied to characterize ensemble mean future changes in monthly East Asian precipitation for June to August. During the summer, wetting and drying effects due to changes in mean vertical motion play a key role in future precipitation changes, as does the “wet-get-wetter” effect due to increased moisture. The former processes are related adiabatically to the projected modification of 500 hPa horizontal atmospheric circulation, which is characterized by two cyclonic circulation anomalies extending over the eastern Eurasian Continent (C1) and the western North Pacific Ocean (C2) for each month. Over Japan, the western edge of C2 shifts from a region south of the Japanese Islands to northern Japan during June–August, representing a delayed northward movement or southward shift of the westerly jet over the western North Pacific in the future compared with the present-day climatology. Most regions of Japan lie within the northeasterly wind and associated downward motion zones of C2, leading to significant uncertainties in the future precipitation over Japan by the offset against the “wet-get-wetter” effect and possibly even a future decrease in precipitation. A wetter future climate is anticipated under weak subsidence or the upward vertical motion zone of C2, such as western Japan in August away from C2, and the Southwest Islands of Japan in June in the C2 southwesterly wind zone. Over the eastern Eurasian Continent, C1 is distributed mainly over northeastern China in June, central and southern China in July and August respectively. During these months, most of the eastern regions are located within the southwesterly-to-southeasterly wind zone of C1, indicating wet future conditions due to enhanced upward motion. This tendency drives a further increase in precipitation in future wetter East Asian climate via the “wet-get-wetter” effect and the increased evaporation.

著者

YAMAGUCHI Junpei KANNO Yuki CHEN Guixing IWASAKI Toshiki

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.2019-015, (Released:2018-11-24)

被引用文献数

31

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An extreme cold surge event caused record-breaking low temperatures in the East Asia during 20–25 January 2016. The planetary- and synoptic-scale feature of the event is investigated quantitatively using the isentropic cold air mass analysis with the threshold potential temperature of 280 K. Because cold air mass is adiabatically conservative quantity, it is suitable for tracing and examining the extreme cold surges. We further introduce a metric named mean wind of cold air mass, which divides the factor of cold air mass evolution into convergence and advection parts. The new metric allowed us to trace the evolution of the cold air mass with dynamic consistency for a period of more than a week. A thick cold air mass built up over southern Sakha by a convergent cold air mass flow during 16–18 January. It migrated westward and reached Lake Baikal. On 20 January, an intense Siberian High developed with an eastward-moving mid-upper-level ridge, producing a strong surface pressure gradient over coastal regions of the Asian continent. This ridge and a cutoff low to the adjacent east formed a northerly flow in the mid-upper troposphere. The resultant southward flow through the troposphere blew the cold air mass over 480 hPa in thickness to the subtropical region of East Asia, causing strong cold surges there on 24 and 25 January. The abnormality of the event is further quantified using extreme value theory. The cold air mass gradually became rare along the path of the cold air mass from Lake Baikal to eastern China, which experienced as thick a cold air mass as once in 200 years. The cold air mass itself shows little change in thickness. Therefore, the migration of a cold air mass over 540 hPa in thickness from northern Siberia is the major cause of this cold surge extreme.

著者

ZHANG Siqi REN Guoyu REN Yuyu SUN Xiubao

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.2019-004, (Released:2018-10-29)

被引用文献数

5

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This study aimed to improve understanding of the differences in surface air temperature data between observations and reanalysis since the beginning of the 20th century and to address the reanalysis data error. The anomaly correlation, standard deviation, and linear trend of temperature during 1909–2010 in eastern China was analyzed based on homogenized observation data from 16 stations and two sets of 20th century monthly mean surface air temperature reanalysis data (20CR and ERA20C). The results show that the inter-annual and decadal variability were consistent between reanalysis and observations in eastern China after 1979. The reanalysis data exhibited a large fluctuation during the 1960s. The average 20CR temperature was lower than the observations during 1920–1950. The inter-annual and decadal variability for winter and spring were consistent with the observations. The correlation and standard deviation ratio between the reanalysis and observations demonstrated a high consistency of their inter-annual variability and dispersion. The ERA20C data were generally closer to the observations than the 20CR data for the period 1979–2010. The linear trends of surface air temperature showed clear warming in both reanalysis datasets and the observations, but the reanalysis trends were significantly smaller than the observational trends for annual mean temperature and most of the seasonal mean temperatures after the 1950s. Overall, ERA20C was generally closer to the observational temperatures than 20CR during 1909–2010, but this consistency does not necessarily indicate ERA20C’s suitability for climate change research because of the systematic bias referenced to the observational data.

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.

著者

Kazuaki NISHII Takafumi MIYASAKA Yu KOSAKA Hisashi NAKAMURA

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

vol.87, no.3, pp.581-588, 2009 (Released:2009-07-08)

参考文献数

17

被引用文献数

10 11

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A reanalysis dataset is used to establish the relationship between the year-to-year fluctuations in the midwinter storm-track activity over the Far East measured by poleward heat flux associated with subweekly disturbances and the occurrence of the first spring storm with strong southerly winds over Japan (Haru-Ichiban). Our analysis reveals that its early (delayed) occurrence tends to follow the enhanced (suppressed) winter storm-track activity with less (more) apparent minimum in midwinter in the course of the seasonal march. A metric is defined on the basis of the eddy heat flux to measure the reproducibility of the particular seasonal march of the Far East storm-track activity simulated in each of the Coupled Model Intercomparison Project Phase 3 climate models under the present climate. Under a particular global warming scenario, ensemble projection based only on the several models that show the highest reproducibility of the storm-track activity measured with the particular metric indicates that the future enhancement is likely in the midwinter storm-track activity associated with the weakening of the East Asian winter monsoon, implying that Haru-Ichiban is likely to occur earlier in the late 21st century than in the 20th century.

著者

MURATA Hidehiko SAITOH Kotaro SUMIDA Yasuhiko

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.2018-049, (Released:2018-07-13)

被引用文献数

12

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Combination of three visible bands of the Advanced Himawari Imager (AHI) on-board JMA's new-generation Himawari-8 and -9 geostationary meteorological satellites enable production of true color imagery. True color is intuitively understandable to human analysts and beneficial for monitoring surface and atmospheric features. It is especially useful when applied to frequent observation from a geostationary platform. This article reports on an application of a color reproduction approach based on the CIE 1931 XYZ color system to imagery rendering. The approach allows consideration of primary color (RGB) differences among satellite and output devices which in turn cause differences in the colors reproduced. The RGB signals observed by AHI are converted to XYZ tristimulus values, which are independent of devices themselves, and then re-converted to RGB signals for output devices via the application of 3 x 3 conversion matrices. The article also covers an objective technique for the evaluation of XYZ values accuracy. The evaluation indicated that the combination of AHI native RGB bands is sub-optimal for obtaining XYZ values as-is, while a combination in which the green band is replaced by a pseudo band with a central wavelength of around 0.555 µm is optimal. The pseudo band is generated via regression with existing visible and near-infrared bands as predictor variables. The imagery produced using this approach was termed True Color Reproduction (TCR). The approach is applicable to other satellites that have several bands in the visible to near-infrared spectral range, and has the potential for development toward the production of standardized sensor-independent true color imagery.

著者

KAZUMORI Masahiro

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.2018-037, (Released:2018-04-07)

被引用文献数

13

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This article reports on the impacts of Himawari-8 Clear Sky Radiance (CSR) data assimilation in the global and mesoscale numerical weather prediction (NWP) systems of the Japan Meteorological Agency (JMA). Adoption of the Advanced Himawari Imager (AHI) on board JMA’s Himawari-8 and -9 satellites has enhanced observational capabilities in terms of spectral, horizontal, and temporal resolution. Improvements brought by the switchover from the Multi-functional Transport Satellite-2 (MTSAT-2) to the new-generation Himawari-8 satellite include an upgrade to the horizontal resolution of CSR data from 64 to 32 km and an increase in the number of available water vapor bands from one to three. CSR products are obtained every hour and distributed to the NWP community. The improved horizontal and spectral resolution of Himawari-8 CSR data provides new information on horizontal water vapor distribution and vertical profiles in data assimilation. In data assimilation experiments using JMA’s global NWP system, the assimilation of Himawari-8’s three water vapor bands significantly improved the tropospheric humidity field in analysis, especially in the lower troposphere, as compared to assimilation of the single MTSAT-2 water vapor channel. First-guess (FG) departure statistics for microwave humidity sounders indicated an improvement in the water vapor field, especially over Himawari-8 observation areas. Improved forecasting of tropospheric temperature, humidity, and wind fields for Himawari-8 observation areas was also seen. In data assimilation experiments using JMA’s mesoscale NWP system, a disastrous heavy precipitation event that took place in Japan’s Kanto-Tohoku region in 2015 was investigated. A single water vapor band of Himawari-8 CSR corresponding to MTSAT-2 was assimilated, resulting in enhanced contrast of the water vapor field between moist and dry areas, as well as a realistic representation of moist air flows from the ocean in analysis. The changes also improved mesoscale model heavy precipitation forecasts.

著者

KANG Yunhee JEONG Jong-Hoon YOU Cheol-Hwan LEE Dong-In

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.2018-050, (Released:2018-07-13)

被引用文献数

2

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On July 13, 2012, the bow echo was observed over the lee side of the Mt. Halla (1950 m above sea level) on Jeju Island, Korea. Three-dimensional wind-field and surface observation analyses were carried out to understand the structure and evolution of convective system with bow echo on the bell-shaped terrain. The northeastward-moving convective system passed over the approximately bell-shaped, isolated mountain with a mean speed of 17 m s-1. On the windward side of the mountain, the convective system developed by the inflow of unstable warm air from the ocean and terrain-induced upward motion, even with a low CAPE value of 511 J kg-1. When passing the lee side of the mountain, the bow echo was formed in the convective system by the strongest winds behind the bow echo. Behind the leading edge of the bow echo, the strengthened rear-inflow jet (RIJ) descended with relatively dry air along the surface, resulted in enhancing evaporative cooling. The precipitation-induced downdrafts generated a cold pool on the lee side of mountain. The development of an RIJ and cold pool formation both contributed to the evolution of the bow echo. In addition, the isolated bell-shaped terrain had a major indirect influence on the evolution of convective system with bow echo in this event.