著者

柳井 連雄

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.39, no.5, pp.282-309, 1961-12-28 (Released:2007-10-19)

参考文献数

98

被引用文献数

17 33

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台風の発生機構を力学的に説明することを試みた。台風の発生とは,既存の大規模な低緯度擾乱が激しい自由対流に転化することであると考える。第一章で大気中に起る種々の自由対流,強制対流について一般的考察を行なつた。特に堰形渦中の自由子午面須環の発達速度を不安定成層,安定成層の各々の場合につき摂動の水平スケールの関数として論じた。台風のような大きいスケールを持つ擾乱の発達を説明し得るものは安定成層中の傾圧性(すなわちradialな温度差)による力学的不安定であつて,これはFultzやHideによつて行なわれたdishpan実験中にみられ,Kuoによつて理論的に説明されている激しいHadley型対流の機構と本質的に同じである。第二章では実際の台風発生過程を三段階に分け,各々のstageにおいて支配的な機構を説明した。第一は偏東風波に伴う力学的強制上昇流の維持,第二はその強化と,その中での積雲対流の誘発,潜熱放出による中心部の温暖化,第三が形成された水平温度差が臨界値を越したときの激しいHadley型自由対流への転化である。要するに凝結熱は発生期においても台風の一次的垂直循環の直接的原因ではなく,それはwarm coreの形成,維持を通して重要なのである。

著者

KHATRI Pradeep HAYASAKA Tadahiro IWABUCHI Hironobu TAKAMURA Tamio IRIE Hitoshi NAKAJIMA Takashi Y.

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.2018-036, (Released:2018-04-09)

被引用文献数

9

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The present study implements long-term surface observed radiation data (pyranometer observed global flux and sky radiometer observed spectral zenith transmittance data) of multiple SKYNET sites to validate water cloud optical properties (cloud optical depth COD and effective radius Re) observed from space by MODIS onboard TERRA and AQUA satellites and AHI onboard Himawari-8 satellite. Despite some degrees of differences in COD and Re between MODIS and AHI, they both showed common features when validated using surface based global flux data as well as cloud properties retrieved from sky radiometer observed zenith transmittance data. In general, CODs from both satellite sensors are found to overestimated when clouds are optically thin. Among a number of factors (spatial and temporal variations of cloud, sensor and solar zenith angles), the solar zenith angle (SZA) is found to have an impact on COD difference between reflectance based satellite sensor and transmittance based sky radiometer. The Re values from the sky radiometer and satellite sensor are generally poorly correlated. The difference in Re between the sky radiometer and satellite sensor is negatively correlated with COD difference between them, which is likely due to the inherent influence of Re retrieval precision on COD retrieval and vice versa in transmittance based sky radiometer.

著者

OKUYAMA Arata TAKAHASHI Masaya DATE Kenji HOSAKA Keita MURATA Hidehiko TABATA Tasuku YOSHINO Ryoko

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.2018-033, (Released:2018-03-30)

被引用文献数

23

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The new geostationary meteorological satellite of the Japan Meteorological Agency (JMA), Himawari-8, entered operation on 7 July 2015. Himawari-8 features the new 16-band Advanced Himawari Imager (AHI), whose spatial resolution and observation frequency are improved over those of its predecessor MTSAT-series satellites. These improvements will bring unprecedented levels of performance in nowcasting services and short-range weather forecasting systems. In view of the essential nature of navigation and radiometric calibration in fully leveraging the imager’s potential, this study reports on the current status of calibration for the AHI. Image navigation is accurate to within 1 km, and band-to-band co-registration has also been validated. Infrared-band calibration is accurate to within 0.2 K with no significant diurnal variation, and is being validated using an approach developed under the GSICS framework. Validation approaches are currently being tested for the visible and near-infrared bands. Two such approaches were compared and found to produce largely consistent results.

著者

Kang Sung-Dae 木村 富士男

出版者

公益社団法人 日本気象学会

雑誌

Journal of the Meteorological Society of Japan. Ser. II (ISSN:00261165)

巻号頁・発行日

vol.75, no.5, pp.955-968, 1997-10-25

参考文献数

25

被引用文献数

3 11

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寒気が暖かい海面に移流してくるときには、しばしば筋状雲が観測される。これらの中で、海岸近くにある山の風下において特に太く長い筋状雲が見られることがある。一般の細い筋状雲の生成にはシアーと成層不安定が重要とされている。しかし、山岳風下の太い筋状雲の生成には成層不安定の他に重要なメカニズムが存在すると考えられる。上記の筋状雲の生成に係わっているであろう2つの要素、成層不安定と地形による力学的擾乱、を高分解能に設定したコロラド州立大学のメソモデルであるRAMS(Regional Atmospheric Modelling System)を使って調べた。数値実験では、基本場として一様な大気安定度と風速の低Froude数の流れを考え、これを風上境界に与えた。上記2つの効果を見るため数値実験は、主として海上の不安定成層の強さを決めている海面温度と、陸上の山岳の有無を変えて数値実験を行った。その結果、海面からの顕熱輸送が大きく、山岳を仮定したときには、モデルによって安定した形状の筋状雲が再現された。筋状雲は高度約1kmで一対の対流性ロールの間に形成される。以下の5つの性質が明らかになった。1)安定した形状の筋状雲が形成されるためには不安定層と地形性の力学擾乱の両方が必要である。2)海面からの顕熱が対流性ロールと筋状雲を維持する主な原因であり、雲の中の凝結による潜熱の解放による効果は無視できる。3)一対の対流性ロールはそれぞれ2つのサブ・ロールの複合体である。サブ・ロールの一つは、大きな半径をもつ弱いロール、もう一つは小さな半径の強いロールである。前者(外部サブ・ロール)は水蒸気を広い範囲から集め、後者(内部サブ・ロール)はロール対の間にある強い上昇流によって水蒸気を上層へ輸送する役割を担っている。内部サブ・ロールの存在が筋状雲の形状を細い状態に保っている。5)静力学平衡の仮定を置いても置かなくても筋状雲の再現は可能である。これは大気の鉛直方向の慣性が本質的には重要な役割をしていないことを意味し、また必ずしも地形の水平規模の大きさによって、筋状雲の生成が制約されるものではないことも示唆している。

著者

Hongli WANG Linjing QIU Xiaoning XIE Zhiyuan WANG Xiaodong LIU

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.96, no.4, pp.391-403, 2018 (Released:2018-08-02)

参考文献数

27

被引用文献数

2

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The climate variability in monsoon and arid regions attributable to dynamic vegetation is investigated using NCAR's Community Earth System Model with the Dynamic Global Vegetation Model. Two present climate simulations, one using dynamics and the other using fixed vegetation cover, are carried out. A comparative analysis of the two simulations reveals that the climate in monsoon and arid regions exhibits different responses to dynamic vegetation. On the hemispheric scale, precipitation mainly increases in the Northern Hemisphere and decreases in the Southern Hemisphere in response to dynamic vegetation, while the surface temperature exhibits a consistent decrease. On the regional scale, precipitation decreases caused by dynamic vegetation are the main trend in monsoon regions except for the Asian monsoon region, while precipitation responses to vegetation change are weak in arid regions relative to monsoon regions. The surface temperature increases significantly because of dynamic vegetation only in the boreal winter Asian monsoon region, while the rest of the monsoon and arid regions mainly exhibit reduced surface temperatures. Therefore, the climate variability in the Asian monsoon region is clearly different from the other regions. Further analysis shows that dynamic vegetation can modulate variations in the east–west sea-level pressure gradient and lower-level meridional winds in East Asia, and it can strengthen (weaken) the East Asian summer (winter) monsoon. Mechanistic analysis reveals that the difference in hemispheric and regional climate variations may be due to changes in the dynamic vegetation-induced moisture flux and net surface radiative forcing.

著者

ZHUGE Xiaoyong ZOU Xiaolei

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.2018-041, (Released:2018-04-13)

被引用文献数

19

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Convective initiation (CI) nowcasting often has a low probability of detection (POD) and a high false-alarm ratio (FAR) at sub-tropical regions where the warm-rain processes often occur. Using the high spatial- and temporal-resolution and multi-spectral data from the Advanced Himawari Imager (AHI) on board Japanese new-generation geostationary satellite Himawari-8, a stand-alone CI nowcasting algorithm is developed in this study. The AHI-based CI algorithm utilizes the reflectance observations from channels 1 (0.47 μm) and 7 (3.9 μm), brightness temperature observations from infrared window channel 13 (10.4 μm), the dual-spectral differences between channels 10 (7.3 μm) and 13, 13 and 15 (12.4 μm), as well as a tri-spectral combination of channels 11, 15 and 13, as CI predictors without relying on any dynamic ancillary data (e.g., cloud type and atmospheric motion vector products). The proposed AHI-based algorithm is applied to CI cases over Fujian province in the Southeastern China. When validated by S-band radar observations, the CI algorithm produced a POD as high as 93.33 %, and a FAR as low as 33.33 % for a CI case day that occurred on 1 August 2015 over Northern Fujian. For over 216 CI events that occurred in a three-month period from July to September 2015, the CI nowcasting lead time has a mean value of ~64 minutes, with a longest lead time over 120 minutes. It is suggested that false-alarm nowcasts that occur in the presence of capping inversion require further investigation and algorithm enhancements.

著者

播磨屋 敏生

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.46, no.4, pp.272-279, 1968 (Released:2008-05-27)

参考文献数

13

被引用文献数

2 5

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かぎ状絹雲をmother-cloudからの降水のtrai1によるものと考えて,その特異な形を決める因子を観測値に基づいた温度,湿度,風速の垂直分布のもとで数値計算により調べた.計算の結果から次の事が結論される.かぎ状絹雲の形は,降水粒子の質量および風の垂直シャーに非常に依存する.また軸比が非常に大きい針状結晶を除いては,降水粒子の形にはあまり依存しない.

著者

Xi CAO Renguang WU

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.96, no.4, pp.317-336, 2018 (Released:2018-07-27)

参考文献数

43

被引用文献数

7

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The present study compares contributions of different environmental factors to the tropical cyclone (TC) genesis over the western North Pacific (WNP) during 2015 and 2016. A local instantaneous view of conditions for the TC genesis is adopted in the present study, which is distinct from the previous view of large-scale temporal averaged conditions. The present study also distinguishes the contributions of three time scale variations (synoptic, intraseasonal, and interannual) of a number of factors. Common to 2015 and 2016, the positive contribution of lower-level vorticity and upward motion to the TC genesis is mainly from the intraseasonal and synoptic components; the contribution of the barotropic energy conversion to the development of synoptic disturbances is larger from climatological mean winds and intraseasonal wind variations than from interannual wind variations; all three time scale variations of mid-level specific humidity contribute positively to the TC genesis; the barotropic energy conversion from climatological mean winds is due to the terms in relation to the meridional shear and zonal convergence of zonal wind. In comparison, the positive contribution of lower-level vorticity and mid-level specific humidity is larger in 2015 than in 2016 on all the three time scales; the contribution of the barotropic energy conversion in relation to the meridional shear of interannual variations of zonal wind and the zonal convergence of intraseasonal variations of zonal wind are larger in 2015 than in 2016; the vertical wind shear on all the three time scales and the sea surface temperature on the interannual time scale have a larger positive contribution to the TC genesis in 2016 than in 2015.

著者

Kayo Ide Philippe Courtier Michael Ghil Andrew C. Lorenc

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.75, no.1B, pp.181-189, 1997-03-25 (Released:2008-01-31)

参考文献数

32

被引用文献数

286 622

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The need for unified notation in atmospheric and oceanic data assimilation arises from the field's rapid theoretical expansion and the desire to translate it into practical applications. Self-consistent notation is proposed that bridges sequential and variational methods, on the one hand, and operational usage, on the other. Over various other mottoes for this risky endeavor, the authors selected: "When I use a word, " Humpty Dumpty said, in rather a scornful voice tone, "it means just what I choose it to mean - neither more more less. "Lewis Carroll, 1871.

著者

Yoshimitsu CHIKAMOTO Masahide KIMOTO Masayoshi ISHII Masahiro WATANABE Toru NOZAWA Takashi MOCHIZUKI Hiroaki TATEBE Takashi T. SAKAMOTO Yoshiki KOMURO Hideo SHIOGAMA Masato MORI Sayaka YASUNAKA Yukiko IMADA Hiroshi KOYAMA Masato NOZU Fei-fei JIN

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.90A, pp.1-21, 2012 (Released:2012-06-07)

参考文献数

52

被引用文献数

14 24

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Sea surface temperature (SST) predictability in the Pacific on decadal timescales is examined in hindcast experiments using the coupled atmosphere-ocean model MIROC with low, medium, and high resolutions. In these hindcast experiments, initial conditions are obtained from an anomaly assimilation procedure using the observed oceanic temperature and salinity while prescribing natural and anthropogenic forcing based on the IPCC concentration scenarios. Our hindcast experiments show the predictability of SST in the western subtropical Pacific, the Indian Ocean, and the tropics to the North Atlantic. Previous studies have examined the SST predictability in the Indian Ocean and the Atlantic, but SST predictability in the western subtropical Pacific has not been evaluated. In the western Pacific, the observed SST anomalies in the subtropics of both hemispheres increased rapidly from the early 1990s to the early 2000s. While this SST warming in the western subtropical Pacific is partly explained by global warming signals, the predictions of our model initialized in 1995 or 1996 tend to simulate the pattern of the SST increase and the associated precipitation changes. This large climate change around the late 1990s may be related to phenomena such as the recent increase in the typhoon frequency in Taiwan and the weakened East Asian monsoon reported by recent studies.

著者

吉野 正敏

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.38, no.1, pp.27-46, 1960-12-26 (Released:2007-10-19)

参考文献数

31

被引用文献数

4 3

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According to official observation, the maximum rainfall recorded in Japan is 55.9mm in 10 minutes, 87.9mm in 30 minutes, 157.0mm in 1 hour, 415.3mm in 6 hours, 844.5mm in 10 hours, 1, 109mm in 24 hours, 3, 462mm in 1 month and 10, 21.6mm in 1 year, Comparing these amounts with the world records reported by Jennings (1950), it is noticed that maximum rainfall in Japan is comparable only to world figures in the 1∼0 to 24 hour duration. This is thought to be because polar fronts or tropical cyclones in Japan and adjacent areas are stronger in that time period, while convectional rain, such as thunderstorms of short duration, or continuous rain, such as orographic rainfall under monsoonal conditions, are weaker than in another parts of the world. In addition, distribution maps of observed maximum rainfall within 10 minutes, 1 hour, 6 hours and 24 hours were drawn, and the distribution patterns were considered in connection with their causes.The constants, k and n, for an experimental equation of the depth-duration curve, R=ktn, where t is time (in minutes) and R, rainfall amount (in mm), were then calculated. As for the rainfall amount, R, the mean values obtained from the 1 st to the 5 th ranking in the official records of the Japan Meteorological Agency from 1941 to 1950, as observed every 10, 20 and 30 minutes and every 1, 3, 6, 18, 24, and 36 hours for each of the 109 stations in Japan, were used. Separating the time periods into those between 10 minutes and 1 hour and those between 6 and 36 hours, it was shown that the k and n values exhibited a wide range according to geographical regions and the above-mentioned time periods. These facts are shown in the accompanying figures and tables.Finally, the constants, b, k, and n, for an experimental equation for the intensityduration curve, i=k/(t+b)n, where t is time (in minutes) and i, the rainfall intensity (in mm per minute) were obtained by calculating the intensity values by the same method as is described above for the mean rainfall values. The distribution of b, k, and n values revealed marked localization as is shown in the figures attached. The values decrease with distance from the sea coast in central Japan, and are generally smaller on mountain tops than at the bottoms.

著者

秋山 孝子

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.53, no.5, pp.304-316, 1975 (Released:2007-10-19)

参考文献数

6

被引用文献数

31 48

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豪雨期間を含む1972年6月29日から7月14日に至る16日間について,日本列島近傍の水蒸気流束分布•水蒸気収束の状況を解析した.その結果は下記のごとくに要約される.(1)豪雨域の下層(700mb∼地上)で,強い水蒸気流束の収束がみられる.この収束は,下層の水蒸気sink(負のδq/δt,つまり降水)をもたらすと同時に.上向きのωqを通して,上層でのsinkをひきおこす.(2)稠密な雨量観測点から求めた面積平均雨量と,収支計算から求めた降水量は,よい一致を示している.(3)降水量の多寡によって,解析期間を"light","heavy"および"extremely heavy"rainfall periodに分類すると,その各々について,極めて特徴的な水蒸気流束分布が得られた.(4)heavy rainfall periodでは,南西諸島海域からSW-風によって,日本列島上のcloud zoneに流入する水蒸気流束の収束が特徴的である.またこのSW-水蒸気流束は,南西諸島海域で,太平洋上からの湿潤なSE-風によって強化されたものである.(5)extremely heavy rainfall periodでは, cloud zoneによる水蒸気の輸送量は減少し,日本列島の南方から,直接豪雨帯に向うSE-風による, transversalな水蒸気流束がいちじるしく増大し,その収束が,豪雨域内の主な水蒸気sinkとなる.(6)豪雨期間,降雨の水蒸気sourceは,太平洋高気圧によっておおわれている,雲のない亜熱帯海域であることが結論される.

著者

村上 多喜雄 松本 淳

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.72, no.5, pp.719-745, 1994-10-25 (Released:2008-01-31)

参考文献数

38

被引用文献数

151 267

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西部北太平洋における夏のモンスーン(WNPM)は、8月中ごろの最盛期には、東南アジアモンスーン(SEAM)と同程度かそれ以上に活発になる。これら2つの夏のモンスーン地域の境界は、OLRが190Wm-2以下になる両モンスーンの上昇域の間にあって、OLRが230Wm-2以上と比較的高く、相対的な好天域である南シナ海にある。主要な下降域は中部北太平洋にあり、そこでは太平洋高気圧の発散域の上層に、熱帯上部対流圏トラフの収束域が位置している。すなわち、29℃を超える世界でもっとも高い海水温域にあるWNPMの中心地域(北緯10-20度、東経130-150度)では、活発な対流活動が生じ、東経110度付近の南シナ海と、西経140度付近の中部北太平洋との間に、顕著な東西循環が起こっている。この東西循環の鉛直構造は、北緯10-20度付近ではバロクリニックで、東経150度以東では下層が偏東風、上層が偏西風となっており、以西ではこの逆となる。WNPMは、北緯10度から20度付近における海水温の東西コントラストと、北緯20-30度付近における、大陸-海洋間の東西の熱的コントラストの複合作用の結果として生じていると考えられる。WNPM域の極側には大きな大陸がないため、南北の熱的コントラストの影響は、二義的なものとなる。一方SEAMは、主に南北の海陸熱的コントラストによって駆動される、南北循環によって生じている。SEAMは10月初め以前に後退するのに対し、WNPMは29℃を超える高海水温が維持されているため、11月初めまで持続する。

著者

Augusto José PEREIRA FILHO Felipe VEMADO Kazuo SAITO Hiromu SEKO José Luis FLORES ROJAS Hugo Abi KARAM

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.96A, pp.247-263, 2018 (Released:2018-05-17)

参考文献数

54

被引用文献数

5

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The Tokyo Metropolitan Area Convection Study (TOMACS) for extreme-weather-resilient cities is a research and development project (RDP) of the World Weather Research Programme (WWRP). TOMACS provided a multiplatform and high spatiotemporal resolution dataset for the present research on three episodes of deep convection in the Tokyo Metropolitan Area (TMA) under its heat island effect and sea breeze circulations. Heavy rainfall episodes of August 26, 2011, and July 23 and August 12, 2013, were simulated with (and without) the tropical town energy budget (T-TEB) model coupled with the advanced regional prediction system (ARPS). The T-TEB/ARPS system used initial and boundary conditions from the Japan Meteorological Agency (JMA) mesoscale analysis data for 24-hour integration runs at 5-km resolution over Japan and at 1-km resolution over TOMACS area. The 1-km resolution hourly rainfall field simulations were verified against the respective automated meteorological data acquisition system (AMeDAS) rain gauge network measurements. Statistics of the Contingency tables were obtained to estimate the critical success index (CSI), probability of detection (POD), and false alarm rate (FAR) as well as the root mean square error (RMSE). The T-TEB/ARPS simulations improved the south and east sea breeze circulations of TMA and its urban heat island effect. The time evolution of CSI scores improved within the advective time scale, whereas dissipation (phase) errors on precipitation RMSE increased with the integration time and were larger than the dispersion (amplitude) errors. The initial and boundary conditions of JMA greatly improved the simulations as compared to the previous ones performed with the outputs of NCEP's global forecast system as indicated by the TOMACS datasets. Thus, the results represent the temporal and spatial evolutions of the atmospheric conditions leading to the development of a deep convection within TOMACS region. Furthermore, TMA is a good testbed to evaluate the urban surface schemes, such as T-TEB in this study.

著者

川村 隆一 村上 多喜雄

出版者

社団法人日本気象学会

雑誌

Journal of the Meteorological Society of Japan. Ser. II (ISSN:00261165)

巻号頁・発行日

vol.76, no.4, pp.619-639, 1998-08-25

参考文献数

30

被引用文献数

10

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赤外輝度温度、850hPa高度、風、気温、比湿データに調和解析を適用し、季節変化の長周期成分(第1から第3調和関数までの和)をLモード、残りの調和関数で表現される短周期成分をSモードと定義した。初夏の期間、Lモードはカムチャッカ半島-オホーツク海上のリッジと、中国北部(大陸の熱的低気圧の中心)から日本、さらに東方へ延びるトラフのブロッキング型循環パターンを示す。オホーツク海上の局所的なLモード高気圧セルの発達により、アリューシャン諸島付近から北日本へかけての下層東風偏差が強まる。この東風偏差と大陸の熱的低気圧の南東縁に沿った南西風偏差によって、日本付近で水蒸気収束を伴う強い低気圧性シアーが形成される。初夏にみられる東アジアと西部北太平洋との間の東西温度勾配の強化と関連した、Lモード下層トラフの発達は梅雨システムの形成に必要である。大陸スケールの熱的低気圧の発達に起因する、中国東岸に沿うLモード南西風は、モンスーン西風と中緯度偏西風をつなぐブリッジとなり、結果として南シナ海から中部北太平洋へ延びる対流圏下層の西風ダクトを生み出す。6月中旬の梅雨オンセット期には、対流起源のSモードonset cycloneが南シナ海上で発達し、ほぼ同時にSモードonset anticycloneがonset cycloneの北東側に組織化される。下層西風ダクト周辺のSモード擾乱の増幅が熱帯から日本南部へ、湿潤で温暖な空気の北向き移流をもたらしている。7月中旬までに、アジア大陸の熱的低気圧はそのピークに達し、関連して東南アジアの夏季モンスーンも最盛期が訪れる。7月下旬の梅雨明け頃は、大陸の熱的低気圧は地表面冷却により衰退し始めるが、Lモード太平洋高気圧は依然として北へ発達し、8月初めに最盛期を迎える。海陸間の東西温度勾配の弱化に伴い、日本付近のLモード下層トラフが消失し、一方では西太平洋モンスーン(WNPM)トラフが発達する。また、梅雨オンセットと同様に梅雨明け時にもSモード擾乱の発達がみられる。このように、大陸-海洋の熱的コントラストに関係する、Lモード循環の季節進行が、下層西風ダクト内および周辺のSモード擾乱の活動を強く規制している。そのメカニズムとして、西風ダクトがSモード擾乱の順圧ロスビー波の分散に対するwave guideとして働いている可能性や、水平シアーをもったLモード平均流の存在が、二つのモード間の順圧相互作用を通してSモード擾乱の発達と持続に重要な働きをしている可能性があげられる。いずれにしても、Lモード循環とSモード擾乱の複合効果が、梅雨オンセットや梅雨明けのようなローカルな気候学的イベントを非常に急速かつ劇的な変化にしていることに変わりはない。

著者

KUJI Makoto MURASAKI Atsumi HORI Masahiro SHIOBARA Masataka

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.2018-025, (Released:2018-02-05)

被引用文献数

9

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Cloud fractions were observed during research cruises onboard the research vessel (R/V) Shirase between Japan and Antarctica using a whole-sky camera and a ceilometer. The cruises, Japanese Antarctic Research Expeditions (JARE) 55 and 56, took place from November 2013 to April 2014 and November 2014 to April 2015, respectively. Cloud fractions were estimated from the whole-sky camera based on the sky brightness and spectral characteristics, while the ceilometer recorded the cloud occurrence frequency. According to the comparison of daily-averaged cloud fractions from the whole-sky camera with the ceilometer observations over the open ocean between Japan and Antarctica, the correlation coefficients were 0.87 and 0.93 for JARE 55 and 56, respectively. Overall, the results from both observation methods were consistent over the open ocean. Nevertheless, it was necessary to take surface conditions into consideration, particularly for the estimated cloud fractions from the whole-sky camera, because the contrast in brightness and spectral properties between cloudy and clear skies was lower over the sea ice region, owing to the higher surface albedo. Hence, the classification parameter was expressed as a function of sun elevation over the sea ice region in this study. This parameter was determined from part of the data over the sea ice region during JARE 55 and then applied to JARE 56 as well as to remaining data from JARE 55. As a result, the daily-averaged cloud fractions over the sea ice region were approximately 84% and 57% from JARE 55 and 56, respectively. The daily-averaged cloud fractions estimated from the whole-sky camera were also consistent with the ceilometer observations where the correlation coefficients with the sea ice region were 0.93 and 0.96 for JARE 55 and 56, respectively.

著者

Jing XU Yuqing WANG

出版者

Meteorological Society of Japan

雑誌

Journal of the Meteorological Society of Japan. Ser. II (ISSN:00261165)

巻号頁・発行日

pp.2018-014, (Released:2017-12-26)

被引用文献数

29

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The dependence of intensification rate (IR) of a tropical cyclone (TC) on its initial structure, including the radius of maximum wind (RMW) and the radial decay rate of tangential wind outside the RMW, is examined based on ensemble of simulations using a nonhydrostatic axisymmetric cloud-resolving model. It is shown that the initial spinup period is shorter and the subsequent IR is larger for the storm with the initially smaller RMW or with the initially more rapid radial decay of tangential wind outside the RMW. The results show that the longevity of the initial spinup period is determined by how quickly the inner-core region becomes nearly saturated in the middle and lower troposphere and thus deep convection near the RMW is initiated and organized. Because of the larger volume and weaker Ekman pumping, the inner-core of the initially larger vortex takes longer time to become saturated and thus experiences a longer initial spinup period. The vortex initially with the larger RMW (with the slower radial decay of tangential wind outside the RMW) has lower inertial stability inside the RMW (higher inertial stability outside the RMW) develops more active convection in the outer-core region and weaker boundary-layer inflow in the inner-core region and thus experiences lower IR during the primary intensification stage.

著者

Guanghua CHEN Ke WANG

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.96, no.2, pp.97-110, 2018 (Released:2018-03-23)

参考文献数

38

被引用文献数

8

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Although both the tropical cyclone (TC) peak seasons in 2016 and 1998 are in the decaying stage of a super El Niño, TC activities over the western North Pacific (WNP) exhibit vast differences. The TCs in 2016 were greater in number and intensity and had distinct monthly variations in TC activity in contrast to those in 1998. The detailed comparison shows that the warm sea surface temperature anomaly over the WNP in 2016 had higher magnitude and a more eastward extension than that in 1998. In August, coincident with the enhanced Madden–Julian oscillation westerly phase, more TCs clustered within the eastward-extending convective belt caused by the southwesterly surge. The mean longitude of TC genesis in 2016 shifted more eastward, which is favorable for the longer lifetime and greater intensity of the TCs. In terms of the extratropical influences, the cyclonic circulation anomaly associated with the Silk Road Pattern from the middle latitude penetrated southward and split the WNP subtropical high (WNPSH) into two components in August of 2016, thus causing deep-tropospheric southerly steering flows in between and TC northward-prone tracks. During the boreal autumn in 2016, the WNPSH strengthened and stretched westward, producing the robust easterly steering flows that led to successive TCs affecting the coastal areas of East Asia.

著者

Yuhei YAMAMOTO Hirohiko ISHIKAWA Yuichiro OKU Zeyong HU

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.96B, pp.59-76, 2018 (Released:2018-03-16)

参考文献数

53

被引用文献数

28

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This paper presents a method for estimating the land surface temperature (LST) from Himawari-8 data. The Advanced Himawari Imager onboard Himawari-8 has three thermal infrared bands in the spectral range of 10-12.5 μm. We developed a nonlinear three-band algorithm (NTB) that makes the best use of these bands to estimate the LST. The formula of the algorithm includes 10 coefficients. The optimum values of these coefficients were derived using a statistical regression method from the simulated data, as obtained by a radiative transfer model. The simulated data sets correspond to a variety of values of LST, as well as surface emissivity, type and season of temperature and water vapor profiles. Viewing zenith angles (VZAs) from 0° to 60° were considered. For the coefficients obtained in this way, we verified the root-mean-square error (RMSE) in terms of the VZA, LST and precipitable water dependence. We showed that the NTB can accurately estimate the LST with an RMSE less than 0.9 K compared with the nonlinear split-window algorithm developed by Sobrino and Romaguera (2004). Moreover, we evaluated the sensitivities of the LST algorithms to the uncertainties in input data by using the dataset independent of the dataset used to obtain coefficients. Consequently, we showed that the NTB has the highest robustness against the uncertainties in input data. Finally, the stepwise LST retrieval method was constructed. This method includes a simple cloud mask procedure and the land surface emissivity estimation. The LST product was evaluated using in-situ data over the Tibetan Plateau, and the validity was confirmed.

著者

Yuhei YAMAMOTO Hirohiko ISHIKAWA

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.96B, pp.43-58, 2018 (Released:2018-03-16)

参考文献数

32

被引用文献数

20

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Land surface emissivity (LSE) in the thermal infrared (TIR) is an essential parameter in the retrieving land surface temperature (LST) from space. This paper describes the LSE maps in three TIR bands (centered at 10.4, 11.2 and 12.4 μm) used for retrieving the LST from Himawari-8. Himawari-8, a next-generation geostationary satellite has high spatial and temporal resolutions compared to previous geostationary satellites. Because of these improvements, the Himawari-8 LST product is expected to contribute to the observation of small-scale environments in high-frequency. In this study, the LSE is estimated by a semi-empirical method, which is a combination of the classification based method and the normalized difference vegetation index (NDVI) thresholds method. The land cover classification information is taken from the Global Land Cover by National Mapping Organizations version3 (GLCNMO 2013). Material emissivities of soil, vegetation and others are taken from the MODIS UCSB emissivity library and the ASTER spectral library. This method basically follows the semi-empirical methods developed by the previous studies, but advanced considerations are added. These considerations are the phenology of vegetation, flooding of paddy fields, snow/ice coverage, and internal reflections (cavity effect) in urban areas. The average cavity effect on LSE in urban canopies is approximately 0.01, but it reaches 0.02 in built-up areas. The sensitivity analysis shows that the total LSE errors for the three bands are less than 0.02. The LSE estimation is especially stable at the vegetation area, where the error is less than 0.01.