著者

Bjorn STEVENS Masaki SATOH

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.99, no.6, pp.1393-1394, 2021 (Released:2021-12-24)

参考文献数

10

著者

MURAKAMI 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.2019-009, (Released:2018-11-05)

被引用文献数

4

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A large amount of snowfall caused by snow clouds over the Sea of Japan sometimes severely affects social and economic activities in Japan. Therefore, snow clouds, which form and develop mainly over the ocean and bring heavy snowfall to populated coastal plains, have long been intensively studied from the perspective of disaster prediction and prevention. Most studies have analyzed data acquired by aerological, meteorological satellite, and radar observations, or have conducted numerical simulations. Because of the difficulties involved in accessing cloud systems over the ocean, however, few in situ observation data have been available, and up until the middle 1990s, many problems remained unsolved or their analysis and simulation results remained unvalidated. Here, knowledge gained from instrumented aircraft observations made from the middle 1990s through the early 2000s is reviewed, in particular with regard to the development of a convectively mixed boundary layer and the inner structures of longitudinal-mode cloud bands, Japan-Sea polar-air mass convergence zone cloud bands, and a polar low. Unsolved problems relating to the inner structures and precipitation mechanisms of snow clouds and the expected contributions of aircraft observations to further progress in these areas of atmospheric science are also briefly discussed.

著者

Falko JUDT Daniel KLOCKE Rosimar RIOS-BERRIOS Benoit VANNIERE Florian ZIEMEN Ludovic AUGER Joachim BIERCAMP Christopher BRETHERTON Xi CHEN Peter DÜBEN Cathy HOHENEGGER Marat KHAIROUTDINOV 小玉 知央 Luis KORNBLUEH Shian-Jiann LIN 中野 満寿男 Philipp NEUMANN William PUTMAN Niklas RÖBER Malcolm ROBERTS 佐藤 正樹 澁谷 亮輔 Bjorn STEVENS Pier Luigi VIDALE Nils WEDI Linjiong ZHOU

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.99, no.3, pp.579-602, 2021 (Released:2021-06-10)

参考文献数

68

被引用文献数

26

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近年のコンピューターとモデル開発の進歩により、全球ストーム解像モデルの時代が始まり、それに伴って気象や気候予測が一変する可能性を秘めている。本研究では、この新しいクラスのモデルを検証するという一般的なテーマの中で、9つの全球ストーム解像モデルについて、熱帯低気圧(TC)をシミュレートする能力を評価した。その結果、大まかにいえば、これらのモデルは現実的な熱帯低気圧を再現し、熱帯低気圧の強度の正確なシミュレーションを可能とするなど、全球モデルの長年の課題が解消されていることが示された。一方、TCはモデルの設計に強く影響され、全てのモデルはTCの数、強度、大きさ、構造に関して独自のバイアスを持っている。いくつかのモデルは他のモデルよりも優れたTCをシミュレートするが、全ての点で優れたモデルが存在するわけではなかった。全体的な結果は、全球ストーム解像モデルがTC予測の新時代を切り拓くことが可能であることを示しているが、その可能性を最大限に引き出すためには改良が必要である。

著者

宇田 智紀 坂上 貴之 稲津 將 古賀 一基

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.99, no.5, pp.1169-1183, 2021 (Released:2021-10-27)

参考文献数

21

被引用文献数

3

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本論文では500hPaの等高線が作るトポロジー構造を抽出して大気ブロッキング現象の同定を実現するアルゴリズムを提案する。このアルゴリズムは,構造安定な2次元のハミルトンベクトル場の作る流線パターンのトポロジーによる分類理論に基づいて、この流線構造に部分順序根付き木(partially cyclically ordered rooted tree=COT)表現とそれに付随するレーブグラフ(Reeb graph)という木構造を一意に割り当て、それを用いてブロッキング同定を可能にする。この方法は,従来手法に比べて気象学的なパラメータをほとんど利用せずに簡便かつ効果的に大気ブロッキング現象を抽出できる。加えて、従来手法では困難であったオメガ(Ω)型や双極子型といった大気ブロッキングのタイプ(型)を区別することもできる。このアルゴリズムで同定された大気ブロッキングイベントの期間やそのタイプは現業予報で行われている主観的な判断とよく一致する。

著者

TAKATA Kumiko HANASAKI Naota

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.2021-034, (Released:2021-02-22)

被引用文献数

2

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The Minimal Advanced Treatments of Surface Interaction and RunOff (MATSIRO), which has been used as a land-surface scheme in the global climate model, the Model for Interdisciplinary Research On Climate (MIROC), calculates Dunne runoff and base runoff using the TOPography-based MODEL (TOPMODEL). In past experiments that used MATSIRO, the runoff and its response to precipitation were too low compared to observation. We conjectured that those biases could be attributed to the water table's excessive depth. Its depth was diagnosed based on grid-mean soil moisture, using a saturation threshold that was originally set to almost equal the porosity. In this study, sensitivity experiments, in which the threshold was decreased to 75 %, 50 %, 25 %, and less than 13 % of the porosity, were conducted, and the subsequent effects on river flow were investigated in the Chao Phraya River basin, Thailand, as a case study. As a result, both Dunne and base runoff increased along with the response of river flow to precipitation. The simulated river flow matched observations most closely with the threshold of 50 % saturation. In addition, soil moisture and the Bowen ratio also changed significantly with the runoff changes induced by the threshold changes. These results suggested the importance of the relationship between grid-mean soil moisture and groundwater level for TOPMODEL. Preliminary global experiments indicate that the runoff sensitivity might be dependent on climate zone.

著者

SATO Takuto KUSAKA Hiroyuki

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.2021-047, (Released:2021-04-14)

被引用文献数

1

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In this study, we compare the accuracy of five representative similarity metrics in extracting sea level pressure (SLP) patterns for accurate weather chart classification: correlation coefficient, Euclidean distance (EUC), S1-score (S1), structural similarity (SSIM), and average hash. We use a large amount of teacher data to statistically evaluate the accuracy of each metric. The evaluation results reveal that S1 and SSIM have the highest accuracy in terms of both average and maximum scores. Their accuracy does not change even when non-ideal data are used as the teacher data. In addition, S1 and SSIM can reproduce the subjective resemblance between two maps better than EUC. However, EUC reproduces the central position of the signal in a sample case. This study can serve as a reference for identifying the most useful similarity metric for the classification of SLP patterns, especially when using non-ideal teacher data.

著者

Takeshi ENOMOTO Shozo YAMANE Wataru OHFUCHI

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.93, no.2, pp.199-213, 2015 (Released:2015-05-14)

参考文献数

31

被引用文献数

8 10

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Simple methods are formulated using an ensemble forecast to identify the sensitive initial perturbations that grow in a specified region at the verification time. These methods do not require the tangent-linear or adjoint models, but use an ensemble forecast to obtain approximated solutions. Input to the sensitivity calculation can be any ensemble forecast integrated from initial conditions perturbed with the bred vector, singular vector, or ensemble Kalman filter methods. Two formulations are presented here to approximate the adjoint and singular vector methods using an ensemble forecast. The ensemble singular vector sensitivity, which has already been applied in previous studies, is obtained with a single eigenvector calculation. The ensemble adjoint sensitivity only requires an even simpler matrix-vector multiplication. To validate the formulations, ensemble-based sensitivity analysis has been conducted in a few cases. First, the two methods were applied to identify the sensitive initial perturbations that grow in the verification region over Japan in January and August 2003. The first singular vector mode indeed achieves the largest amplitude at the verification time, but that is not necessarily true after the verification time. Both methods can identify the sensitive regions more specifically than the regions with large ensemble spread in cases with a mid-latitude cyclone and with a tropical cyclone. The monthly-mean sensitivity in January 2003 indicates the effect of Rossby waves and synoptic disturbances in upstream sensitive regions over Siberia, Tibet, and a downstream sensitive region in the north-western Pacific; the sensitivity in August 2003 suggests the influence of the Asian summer monsoon. Next, for an August 2002 storm case in Europe, global 20-km resolution simulations were conducted from the initial conditions perturbed by the ensemble singular vector method to compare with the unperturbed simulation. In the perturbed simulation, the cyclone is deeper by a few hPa in its north-east sector with more precipitation north of the Alps more consistently with observations. These results indicate that reasonable sensitive regions can be identified with our methods.

著者

WU Ying-Jhang LIOU Yu-Chieng LO Yi-Chuan TAI Sheng-Lun CHANG Shao-Fan SUN Juanzhen

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.2021-049, (Released:2021-04-20)

被引用文献数

1

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The evolution of a heavy rainfall event occurred on 19 August 2014 in northern Taiwan is investigated with observed data and analyses from a newly-developed system named IBM_VDRAS, which is based on a four-dimensional Variational Doppler Radar Assimilation System (VDRAS) with the capability to assimilate radar observations and surface station data over a complex terrain by adopting the Immersed Boundary Method (IBM). This event possesses different precipitating processes and track from those frequently observed in that region. From the surface observations and the high spatiotemporal resolution analysis fields generated by IBM_VDRAS, it is found that the rainfall process started with the initiation of two individual convective cells triggered through the interaction between land-sea breeze and terrain in two different cities (Taoyuan and Taipei). The outflow of one of the convective cells developed in Taoyuan City at an earlier time merged with another convective system which grew in Taipei Basin, and provided favorable conditions to intensify the latter. The enhanced major convective cell moved into the Taipei City metropolitan area and produced 80 mm of precipitation within approximately 2.5 h. The kinematic, thermodynamic, and microphysical fields of the convective cells are analyzed in details to explain the mechanisms which helped to maintain the structure of the rainfall system. Sensitivity experiments of quantitative precipitation forecast (QPF) show that the terrains prevent the location of major rainfall from shifting outside of Taipei Basin. By assimilating surface data, the model can better predict the position of the rainfall.

著者

SHIBATA Kiyotaka SAI Ayano

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.2021-019, (Released:2021-01-13)

被引用文献数

2

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The surface meteorological data in Japan, beginning around the 1880s, archived by the Japan Meteorological Agency are analyzed focusing on the long–term trends and variations in humidity and temperature. It is found that the annual–mean temperature trend exhibits statistically significant warming of 1.0-2.5°C century−1 for most stations, while the annual–mean relative humidity shows significantly decreasing trend of −2 % to −12 % century−1 for most stations with small seasonality. On the other hand, the annual–mean mixing ratio trend displays a different spatial distribution compared to the temperature or relative humidity trend. In this study, three types of trends exist: significantly positive and negative values, and virtually zero. Significantly negative trends of about −0.2 to −0.3 g kg−1 century−1 are located approximately in the Pacific side of Honshu from the middle Tohoku through Shikoku to the eastern Kyushu. Significantly positive trends of about 0.2 to 0.4 g kg−1 century−1 are observed over Hokkaido, the western Japan along Sea of Japan, the western Kyushu, and the remote islands including Okinawa. The overall pattern is similar for other seasons except for most of the remote islands in winter. Empirical orthogonal function (EOF) analysis indicates that the linear trends in the annual–mean temperature and relative humidity can be almost explained by the nearly uniform persistent warming and drying of EOF–1 components. On the other hand, for the annual–mean mixing ratio, EOF–2 is almost identical with the linear trend component, although the fraction of EOF–2 (14 %) is much smaller than that of EOF–1 (49 %). In recent years from 1960 to 2018 the mixing ratio and temperature trends are very different from those in the longer period from the 1880s. The mixing ratio trend and the temperature trend increase on average from 0.0 to 0.5 g kg−1 century−1 and from 1.5°C to 2.5°C century−1, respectively.

著者

FENG Lujia ZHANG Tengfei KOH Tieh-Yong HILL Emma M.

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.2021-026, (Released:2021-01-15)

被引用文献数

3

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Using data from the Sumatran GPS Array in Indonesia–a hero network in tectonic and earthquake studies–we study the summer intra-seasonal variability of precipitable water vapor (PWV) over Sumatra in years without strong inter-annual variability. Unlike most other studies that use external meteorological data to derive PWV from GPS (Global Positioning System) signal delays, we use the zenith wet delay (ZWD) time series estimated from a regular geodetic-quality processing routine as a proxy for PWV variations without using auxiliary meteorological data. We decompose the ZWD space-time field into modes of variability using rotated Empirical Orthogonal Function (EOF) analysis, and investigate the mechanisms behind the two most important modes using linear regression analysis both with and without lags. We show that the summer intra-seasonal variability of daily ZWD over Sumatra in 2008, 2016, and 2017 is dominated by the South Asian Summer Monsoon, and further influenced by dry-air intrusions associated with Rossby waves propagating in the Southern Hemisphere midlatitudes. Both active South Asian monsoons and dry-air intrusions contribute to the dryness over Sumatra during northern summer. Our results indicate an intra-seasonal connection between the South Asian and western North Pacific Summer Monsoons: when the South Asian monsoon is strong, it pumps atmospheric water vapor over the eastern Indian Ocean to feed into the western North Pacific monsoon. We also show a tropical-extratropical teleconnection where PWV over the southern Maritime Continent can be modulated by the activity of eastward-traveling Rossby waves in the southern midlatitudes. Our case study demonstrates the use of regional continuously operating GPS (cGPS) networks for investigating atmospheric processes that govern intra-seasonal variability in atmospheric water vapor.

著者

水野 量

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.70, no.1, pp.115-121, 1992 (Released:2007-10-19)

参考文献数

37

被引用文献数

13 13

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日本列島の150地点における地上気象観測データを用いて、あられ降水の統計的特徴を調べた。1971-1986年の全国150地点の地上気象観測によると、あられ日数は冬期の東北•北陸地方の日本海沿岸で卓越している。また、1982-1986年のデータから、この地域の1月のあられによる降水量は少なくとも月降水量の1/4~1/3であると推定された。以上のあられ降水の統計分析から、日本列島におけるシーディングポテンシャルが議論された。

著者

大泉 伝 斉藤 和雄 Le DUC 伊藤 純至

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.98, no.6, pp.1163-1182, 2020 (Released:2020-12-17)

参考文献数

34

被引用文献数

5

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数値気象予測モデルの要素が豪雨のシミュレーションに与える影響を調べるため、広い領域を対象とした超高解像度実験を2014年8月の広島の豪雨事例で行った。本研究はPart 1 の2013年10月伊豆大島での研究に続くものであり同様の実験を行った。これらの研究から豪雨のシミュレーションにおいて広い領域で高解像度モデル(解像度500m以下)を用いる有用性を示した。 広島の事例では降水帯の位置や強度はモデルの解像度に影響を受けることがわかった。解像度2kmの実験では降水帯は再現されたがその位置は北東にずれていた。解像度500mと250mの実験ではこの降水帯の位置ずれは軽減された。最も降水帯の位置と強度をよく再現したのは解像度250mの実験であった。降水帯に対する境界層スキームの影響は小さく、この点は伊豆大島の事例と異なっていた。 本研究では対流コア数のモデル解像度依存性についても調査した。モデルの解像度に対する対流コア数の変化率は解像度500mで小さくなる事がわかった。この結果は、対流コア数は解像度500mより高解像度になると収束する可能性を示す。

著者

NAYAK Sridhara TAKEMI Tetsuya

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.2019-003, (Released:2018-10-29)

被引用文献数

13 27

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Typhoons are considered as one of the most powerful disaster-spawning weather phenomena. Recent studies have revealed that typhoons will be stronger and more powerful in a future warmer climate and be a threat to lives and properties. In this study, we conduct downscaling experiments of an extreme rain-producing typhoon, Typhoon Lionrock (2016) in order to assess the impacts of climate change on resulting hazards by assuming pseudo global warming (PGW) conditions. The downscaled precipitations over the landfall region in the present climate condition agree well with the Radar- Automated Meteorological Data Acquisition System (Radar-AMeDAS) observations. A typhoon track in the future climate similar to that in the present climate is successfully reproduced, with a stronger wind speed (by ~20 knots) and lower central pressure (by ~20 hPa) under the PGW condition. The changes in precipitation amounts associated with the typhoon under PGW condition are analyzed over 7 individual prefectures in the northern part of Japan. The typhoon in the warming climate produces more precipitation over all prefectures. Iwate, Aomori, Akita, Miyagi and Hokkaido are projected to have relatively more precipitation associated with the typhoon in the warming climate. The overall analysis suggests that Typhoon Lionrock under PGW may increase the risk of flooding, damages to infrastructures, and lives staying along the typhoon track.

著者

Sridhara NAYAK 竹見 哲也

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.98, no.6, pp.1147-1162, 2020 (Released:2020-12-12)

参考文献数

59

被引用文献数

12

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極端降水の振る舞いを説明する上でのクラウジウス-クラペイロン(CC)スケーリングの有用性について、現在気候および疑似地球温暖化(PGW)条件で調べた。日本で発生した最近の2つの極端降水イベント、すなわち2017年7月5~6日の九州北部での豪雨および2018年7月5~8日の四国での豪雨を対象として、格子解像度1 kmでの領域気象シミュレーションにより解析した。数値シミュレーションにはWeather Research and Forecasting(WRF)モデルを用い、モデルデータは1時間間隔で格子点毎の値として出力し、解析に用いた。極端に強い降水の発生頻度とその強度は、時間雨量強度で評価すると、2つのイベントともに、PGW条件下で増大する。極端に強い降水(> 50 mm h-1)は、現在気候条件では気温22℃に上がるまでCCスケーリングにしたがい、PGW条件では24℃の気温に上がるまでCCスケーリングにしたがう。降水と気温の関係において、極端降水のピーク強度は、現在気候条件では25℃で約140 mm h-1であり、一方、PGW条件では 27℃で約160 mm h-1となる。極端降水の気温に対する増加率は、現在気候条件では約3% ℃-1であり、PGW条件では約3.5% ℃-1であることが分かった。将来の温暖化気候におけるピーク降水強度の増加と気温に対する降水量の増加率は、気温減率の減少にもかかわらず、大気中の水蒸気および不安定エネルギーが増加することに起因する。著者の知る限りでは、本研究の結果は、事例解析ではあるものの、極端降水に対するCCスケーリングについて定量的に調べた最初の取り組みであると言える。

著者

HARADA Yayoi ENDO Hirokazu TAKEMURA Kazuto

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.2020-062, (Released:2020-08-12)

被引用文献数

5

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To explore large-scale atmospheric factors causing heavy rainfall events that occurred widely in western Japan, a composite analysis of atmospheric fields during the past heavy rainfall events in the region is performed using the Japanese 55-year Reanalysis. During heavy rainfall events, atmospheric fields are characterized by an upper-tropospheric trough over the Korean Peninsula (KP), an upper-tropospheric ridge to the east of Japan, a surface high-pressure system to the southeast of Japan, and southwesterly moisture flux. The composite analysis indicates that a clear wave train due to quasi-stationary Rossby wave-packet propagation (RWPP) along the polar front jet (PFJ) over Siberia tends to occur just before extreme events. Further analysis considering various time-scale variabilities in the atmosphere reveals that surface high-pressure anomalies to the southeast of Japan are dominated by variability with a 25–90-day period, whereas variability with an 8–25-day period dominates lower-pressure anomalies over the East China Sea (ECS) in relation to the development of the upper-tropospheric trough around the KP. We also investigate atmospheric fields during an extreme heavy rainfall event that occurred in early July 2018 (HR18). Atmospheric features during HR18 are generally similar to those of the other heavy rainfall events. However, a remarkable RWPP occurred along the sub-tropical jet (STJ) in late June 2018 and intensified a surface high-pressure system to the southeast of Japan. In addition, a low-pressure system with an 8–25-day period to the south of Japan developed in association with wave breaking induced by the remarkable RWPP along the STJ and propagated northwestward toward the ECS and then to Japan. The simultaneous development of high- and low-pressure systems contributed to the extreme southerly moisture flux into western Japan. HR18 is also characterized by a sharp upper-tropospheric trough over the KP that is dominated by high-frequency variability with a period < 8 days.

著者

SUZUKI Kento IWASAKI Toshiki YAMAZAKI 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.2021-002, (Released:2020-10-21)

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Local fronts formed near the coast of the Kanto Plain mainly in a cold season, so-called “coastal fronts”, tend to be forecast on the inland side of their actual positions by the operational mesoscale Numerical Weather Prediction (NWP with a horizontal grid spacing of 5 km) model at Japan Meteorological Agency (JMA). In this study, we confirm a systematic NWP error through statistical validations of coastal fronts that occurred with southerly onshore winds during 2015-2018. Using a nonhydrostatic numerical model (JMA-NHM), we explore the relevant physical mechanisms through sensitivity experiments involving different horizontal resolution, envelope orography, and physics parameterization schemes for three cases with typical errors. The operational NWP model is shown to have a systematic error, with local fronts being consistently shifted to the inland side of their actual positions when the forecast period exceeds 5 hours, regardless of precipitation. The sensitivity experiments suggest that the systematic error associated with coastal fronts may be primarily caused by an underestimation of the mountain barrier surrounding the Kanto Plain in the model. The northwestward distance error of coastal fronts, averaged over the three illustrative cases, can be reduced by 27 % and 37 % by increasing the horizontal resolution from 5 km to 2 km and 1 km, respectively, and can be almost entirely eliminated by using the envelope orography. Moreover, the evaporative cooling of precipitation shifts coastal fronts to the seaward. Most coastal fronts are thought to take the form of cold air trapped on the southeastern slope of the mountains surrounding the Kanto Plain, where the elevation angle of the frontal surface is roughly controlled dynamically. The local front shifts to the seaward when the ridgelines of the mountains become higher, and shifts to the seaward through the reduction of the elevation angle when the trapped air becomes colder.

著者

西井 和晃 田口 文明 中村 尚

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.98, no.4, pp.801-820, 2020 (Released:2020-08-26)

参考文献数

32

被引用文献数

8

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2018年7月に日本において2つの極端現象が発生した。本研究では大気大循環モデル(AGCM)のアンサンブル実験にもとづき、これらをもたらした大気大循環偏差に対する海面水温偏差の潜在的影響を評価した。一つ目の極端現象は、7月上旬での西日本を中心とする豪雨であり、日本の南西にあった低気圧性偏差と日本の東にあった高気圧性偏差による顕著な水蒸気輸送がこの主要因である。全球で観測された海面水温を与えたAGCM実験は日本の東の高気圧性偏差を再現できず、このため水蒸気輸送と豪雨を再現できなかった。もう一つの極端現象は7月中下旬に日本で全国的に観測された猛暑であり、これは日本を覆う顕著な高気圧性偏差によるものである。この高気圧性偏差はAGCM実験によって高温偏差とともによく再現された。さらなる実験により、熱帯と中緯度北太平洋のそれぞれの海面水温偏差が、猛暑をもたらした北西太平洋上の大気循環の主要モードを強制していた可能性が示された。また、6月から7月にかけて持続した北西太平洋での亜熱帯ジェットの北偏傾向、及び、北半球中緯度対流圏での高温偏差傾向も、これらの海面水温偏差がそれぞれ強制していた可能性を示した。

著者

KAWANO Tetsuya KAWAMURA Ryuichi

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.2020-033, (Released:2020-05-12)

被引用文献数

21

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A quasi-stationary convective band that persisted for approximately ten hours caused precipitation in the northern part of Kyushu Island, Japan on 5 July 2017. The extreme amount of rainfall produced by this convective band caused a number of landslides and flash floods and resulted in a severe disaster. The Weather and Research and Forecasting (WRF) model was used to perform numerical simulations and to clarify the genesis and maintenance processes of the convective band. A full-physics WRF simulation successfully reproduced the observed features of the convective band and extreme precipitation. It is shown that a quasi-stationary convergence zone in the low level played a crucial role in generating and maintaining the convective band. Trajectory and frontogenesis analyses showed that low-level confluent flows due to the blocking effects of a high pressure system located over the Sea of Japan were responsible for the formation, intensification, and sustenance of the convergence zone. Furthermore, the frontal structure of the convergence zone was intensified due to the land-sea thermal contrast between Kyushu Island and the Tsushima Strait. Two additional experiments, namely a simulation with flattened topography of Kyushu Island and a simulation without considering raindrop evaporation also reproduced the observed band well. These results indicate that topography and a cold pool due to raindrop evaporation played only minor roles in the genesis and maintenance of the convective band.

著者

TAKAMURA Nao WADA Akiyoshi

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.2020-035, (Released:2020-05-26)

被引用文献数

3

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In August 2016, a total of eight typhoons formed in the western North Pacific, and four of which landed on northern and eastern Japan. These typhoons were associated with heavy rainfall and strong winds and caused massive damages in the Japanese archipelago. Moreover, five of the eight typhoons underwent extratropical transition (ET), which was more frequent than an average of 2.1 typhoons per year during August. To clarify the characteristics of the typhoon tracks that caused such unusual landfall and frequent ET in August 2016, we conducted k-means cluster and cyclone phase space (CPS) analyses for typhoons that occurred in August and September. Composite analysis and case study were also conducted to clarify the synoptic environments around the typhoons. To examine the unusual characteristics in August 2016, we compared the results of the analyses for this period with those in August from 2001 to 2015 and those in September 2016. The k-means cluster analysis showed that the direction of the typhoon tracks in August 2016 were more northward than that of the typhoons in August from 2001 to 2015 and those in September 2016. Moreover, the CPS analysis revealed that ET in August 2016 was characterized by a more indistinct structural change from a warm-core structure to a cold-core structure with a shorter duration than ET in August from 2001 to 2015. The synoptic environments around the typhoons in August 2016 were characterized by enhanced undulations of the upper-tropospheric jet stream, increased amplitudes of the mid-tropospheric trough, and relatively warm air around the typhoons in the lower troposphere. These synoptic environments explained the unusual landfall of typhoons with a more northward track and the more frequent ET and more indistinct structural evolution of ET in August 2016.

著者

YAMAJI Moeka TAKAHASHI Hiroshi G. KUBOTA Takuji OKI Riko HAMADA Atsushi TAKAYABU Yukari N.

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.2020-038, (Released:2020-05-27)

被引用文献数

18

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This study investigates the global drop size distribution (DSD) of rainfall and its relationship to large-scale precipitation characteristics using the Dual-frequency Precipitation Radar (DPR) onboard the Global Precipitation Measurement (GPM) Core Observatory. This study focuses on seasonal variations in the dominant precipitation systems regarding variations in DSD. A mass-weighted mean diameter (Dm), which is estimated based on the dual-frequency information derived from the GPM/DPR, is statistically analyzed as a typical parameter of the DSD. Values of the annual mean Dm, in general, are larger over land than over the oceans, and the relationship between Dm and precipitation rate (R) is not a simple one-to-one relationship. Furthermore, Dm exhibits statistically significant seasonal variations, specifically over the northwest Pacific Ocean, whereas R shows insignificant variations, indicating the variations in R cannot explain the distinct seasonal changes in Dm. Focusing on the seasonal variation in Dm over the northwest Pacific Ocean, the results indicate that the variation in Dm is related to the seasonal change in the dominant precipitation systems. In the summer over the northwest Pacific Ocean, Dm is related to the organized precipitation systems associated with the Baiu front over the mid-latitudes and tropical disturbances over the subtropical region, with relatively higher precipitation top heights, composed of both stratiform and convective precipitations. Contrary to the summer, larger Dm over the mid-latitudes in winter is related to extratropical frontal systems with ice particles in the upper layers, which consists of more stratiform precipitation in the storm track region. The smaller Dm over the subtropical northwest Pacific Ocean in winter is associated with shallow convective precipitation systems with trade-wind cumulus clouds and cumulus congestus under the subtropical high.