著者

伊藤 耕介 WU Chun-Chieh CHAN Kelvin T. F. TOUMI Ralf DAVIS Chris

出版者

公益社団法人 日本気象学会

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

vol.98, no.1, pp.5-17, 2020

被引用文献数

13

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<p>台風の移動の基礎的な理解はかなり成熟しているが、注目に値する研究の進展が近年も見られる。本論文では、単純化された順圧モデル・精緻な物理モデル・データ解析によって、主に2014年以降に得られた台風の移動に関する新しい概念や既存の概念に関する新たな知見を集約する。これには、台風の移動に関する環境場と台風の相互作用、および、予測可能性の研究を含んでいる。指向流・βジャイア・非断熱加熱といった従来の概念は依然として重要であるが、台風の進路を説明するメカニズムをより正確に理解することは、さらなる進路予報の精度向上に向けて、重要な基礎をなすであろう。</p>

著者

Kenji YOSHIDA Hisanori ITOH

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.90, no.3, pp.377-401, 2012-06-25 (Released:2012-06-30)

参考文献数

46

被引用文献数

12 17

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This study examines the indirect effect of tropical cyclones (TCs) on cases of heavy rainfall during the Baiu season in Kyushu, Japan using data analyses and numerical experiments. A detailed analysis of the heavy rainfall event that occurred on 7 June 1999 (JST) is performed. This event was remotely affected by Typhoon Maggie (9903), which was located approximately 2000 km from Kyushu at the time. As Typhoon Maggie passed close to Taiwan, a high potential vorticity (PV) zone appeared to the north of Taiwan. A low PV region formed simultaneously to the east of Taiwan, corresponding to a northwestward extension of the Pacific high. These dynamical changes induced an enhanced southerly moisture flux between the high PV zone and the low PV region, leading to moisture convergence and heavy rain in the vicinity of Kyushu. During this time, Typhoon Maggie also caused the northward advection of a separate tropical disturbance.The high PV zone to the north of Taiwan was produced by diabatic heating associated with interplay between the circulation of Typhoon Maggie and the topography of Taiwan. In contrast, the low PV region was formed through the advection of low-PV air from low latitudes by Typhoon Maggie. A piecewise PV inversion diagnostic shows that the low PV region was the largest contributor to the southerly moisture flux, although both Typhoon Maggie and the high PV zone also made positive contributions. Numerical experiments reveal that the precipitation in and around Kyushu was enhanced by both the topography of Taiwan and the northward advection of the additional tropical disturbance.This study identifies a new mechanism as an indirect effect of TCs. The core element of this mechanism is a large moisture flux south of Kyushu, which is termed “moisture road,” and the difference from “atmospheric river” is discussed. This mechanism is not unique to Typhoon Maggie, as other cases of heavy rainfall in and around Kyushu are associated with similar situations.

著者

Fumiaki FUJIBE Nobuo YAMAZAKI Kenji KOBAYASHI

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.84, no.6, pp.1033-1046, 2006 (Released:2007-01-22)

参考文献数

26

被引用文献数

43 59

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Long-term changes in the intensity and frequency of heavy precipitation in Japan were analyzed using quality checked daily precipitation data at 51 stations from 1901 to 2004. The analysis is based on ten categories defined from precipitation intensity and frequency, and some indices of heavy precipitation, such as ≥100 mm days, the annual maximum, and the top 100 cases during the 104 years. The result indicates that heavy precipitation based on these indices has increased during the 104 years. The linear trend of precipitation corresponding to the upper 10% is 2.3% per decade, and that of the number of top 100 cases is 2.6% per decade on the average over the stations. The increase is most pronounced in western Japan and in autumn, while weak, but similar signals are found in other regions and seasons as well. However, no increasing trend is found for less intense precipitation, such as ≥50 mm days and the number of top 1000 cases.Analysis was also made for 5, 11, and 31 day precipitations, and some indices of dry weather. It is found that the frequency of dry weather has increased during the 104 years. The number of days with precipitation less than 1 mm has increased in all the seasons and regions, with a trend of 0.4-0.7% per decade on the average, while the lower 1% ofcases of 31-day precipitation have doubled with a trend of 10% per decade.

著者

David J. Karoly Brian J. Hoskins

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.60, no.1, pp.109-123, 1982 (Released:2007-10-19)

参考文献数

34

被引用文献数

84 122

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幾何光学およびゆっくり変化する媒質中の波動伝播論における光路追跡(ray tracing)の考え方を大気中のプラネタリー波伝播の研究に応用した。線形化した球面上の準地衡風ポテンシャル渦度方程式の解法に波動の運動学理論を適用する。子午断面内のプラネタリー波の伝播を支配する指数を定義し,波動活性量(wave activity:エネルギーに類似し,平均流変化のある場合にも保存する量)が,この指数の大きくなる方に向けて屈折されることを示す。

著者

徳山 源次郎

出版者

(公社)日本気象学会

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

vol.2, no.6, pp.184-189, 1924-11-15 (Released:2009-02-05)

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The author picked up 21 case of newly born cyclones in Japan Sea from the end of 1920 to June 1923. They appear mostly in the winter months i.e. Month Oct. Nov. Dec. Jan. Feb. march April June Frequency 1 2 3 4 5 2 1 2 of these cyclones 5 classes may be distinguished with respect to their birth places. He examined the condition prevailing before or at the time of the birth of the cyclones and noticed that a characteristic sudden rises and falls of temperature were always seen. Thus he insists that the cyclones may be the products on the lines of iscontinuity, developing from the horizontal vorticity effected by the orographic conditions as S. Fujiwhara has already has already suggested. The author recommends the hourly observations in order to issue timely warning against the sudden break out of the cyclone of the kind. (S. F.)

著者

Mayuko ODA Hirotada KANEHISA

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.88, no.2, pp.227-238, 2010 (Released:2010-05-22)

参考文献数

12

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On the basis of buoyancy-vorticity (BV) formulation of Harnik et al. (2008), the initial value problem of vertically propagating gravity waves is analytically solved in a zonal-vertical two-dimensional system. The analytical solutions provide an example of the visualization of BV thinking. Further, the analytical solutions enable a qualitative understanding of the growth of gravity waves in a vertically sheared zonal flow (so-called shear instability of gravity waves) by BV thinking. To this end, the basic buoyancy (i.e., basic potential temperature) is assumed to be piecewise uniform in the vertical direction, and the Green function method is employed. The obtained analytical solutions show the following. In a vertically uniform basic zonal flow, the gravity wave, which is initially at the lowest level, propagates vertically upwards, gets reflected from the highest level back to the lowest level and again from the lowest level to the highest level, and so on. In a vertically sheared basic zonal flow, the behavior of the gravity waves depends on the horizontal wave number. This is caused by the dependence of horizontal propagation velocity on the horizontal wave number. Here, horizontal propagation is defined relative to the fluid. If the horizontal propagation and advection by the basic zonal flow are successfully balanced so that the lower and upper phase velocities are nearly equal, then the gravity wave propagates vertically, and the upper and lower disturbances are phase-locked to each other; this results in an effective interaction between them and in growth as an exponential function of time. On the other hand, if the horizontal propagation and advection by the basic zonal flow are out of balance so that the lower and upper phase velocities are different from each other, then the gravity wave hardly propagates vertically, and the upper and lower disturbances horizontally flow away from each other resulting in an absence of interaction between them and in the oscillation (i.e., no growth). At the marginal points between oscillation and growth, the gravity wave grows as a linear function of time. The behavior of analytical solutions can be qualitatively explained by the BV thinking of Harnik et al. (2008).

著者

岩崎 俊樹 中野 尚 杉 正人

出版者

公益社団法人 日本気象学会

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

vol.65, no.4, pp.555-570, 1987

被引用文献数

39

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本論文では新しく開発中の台風進路予報モデルの概要とその予報性能について述べる。この実験モデルは北半球モデルに1-way で接続された局地モデルである。間隔50kmの一様な水平格子と8層の鉛直格子によって構成され,その予報領域は4000km&times;4000kmである。積雲対流スキームには Kuo 方式を採用している。各計算スキームは台風が良く維持されるように調整されている。初期場には適切なモデル台風が客観解析に重ね合わされている。<br>このモデルは1985年に観測された台風の中心示度や移動を精度よく予報した。また,衛星による雲画像と比較すると,台風と梅雨前線の間に強い相互作用があるケースでも,複雑な降水分布の振舞を良く予報できた。<br>インパクトテストによれば,主観解析の精度や北半球モデルの性能は実験モデルの予報精度に大きな影響を及ぼすので,それらにも十分配慮する必要があることが示唆された。

著者

XIN Xiaoge WEI Min LI Qingquan ZHOU Wei LUO Yong ZHAO Zongci

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.2019-043, (Released:2019-04-01)

被引用文献数

3

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Two sets of decadal prediction experiments were performed with Beijing Climate Center climate system model version 1.1 (BCC-CSM1.1) with different initialization strategies. One experiment is relaxing modeled ocean temperature to the Simple Ocean Data Assimilation (SODA) reanalysis data (SODAInit). In the other (EnOI_HadInit) experiment, the modeled ocean temperature were relaxed toward the assimilated ocean data, which were generated by assimilating sea surface temperature (SST) of the Hadley Centre Sea Ice and Sea Surface Temperature (HadISST) data to the ocean model of BCC-CSM1.1 using Ensemble Optimum Interpolation (EnOI) method. Comparisons between EnOI_HadInit and SODAInit hindcasts show that EnOI_HadInit is more skillful in predicting SST over the North Pacific, the southern Indian Ocean, and the North Atlantic. Improved prediction skill is also found for surface air temperature (SAT) over South Europe, North Africa, and Greenland, which is associated with the skillful prediction of the Atlantic multi-decadal oscillation in EnOI_HadInit. EnOI_HadInit and SODAInit are both skillful in predicting East Asian SAT, which is related to their skillful predictions of the tropical western Pacific SST. The result indicates that assimilated data generated by the ocean model of BCC-CSM1.1 with EnOI assimilation provide better initial conditions than SODA reanalysis data for the decadal predictions of BCC-CSM1.1.

著者

LIM Jaechan PARK Hyung-Min

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.2019-041, (Released:2019-03-19)

被引用文献数

1

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In this paper, we propose an H-infinity (H∞) filtering approach for the prediction of bias in post-processing of model outputs and past measurements. This method adopts minimax strategy that is a solution for zero-sum games. The proposed H∞ filtering approach minimizes maximum possible errors whereas a recently common approach that adopts the Kalman filtering (KF) minimizes the mean square errors. The proposed approach does not need the information of noise statistics unlike the method based on the KF, while training process is required. We show that the proposed approach outperforms the method based on the KF in experiments by applying real weather data in Korea.

著者

KUO Tzu-Hsien MURAKAMI Masataka TAJIRI Takuya ORIKASA Narihiro

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.2019-032, (Released:2019-02-02)

被引用文献数

3

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Aluminum oxide (Al2O3) and iron oxide (Fe2O3) particles have been observed not only in industrial areas and their surroundings but also in natural atmospheric environments. These types of aerosols can influence aerosol–cloud interactions. In this study, physico-chemical properties, such as size distribution and ability to act as cloud condensation nuclei (CCN) as well as ice nucleating particles (INPs), of surrogates of ambient Al2O3 and Fe2O3 particles were investigated using a CCN counter, the Meteorological Research Institute’s (MRI’s) cloud simulation chamber, the MRI’s continuous flow diffusion chamber-type ice nucleus counter, and an array of aerosol instruments. The results indicated that their hygroscopicity parameter (κ-value) ranged from 0.01 to 0.03. This range is compatible with that of surrogates of mineral dust particles and is smaller than typical κ-values of atmospheric aerosols. On the other hand, based on their ice nucleation active surface site (INAS) densities, these materials may act as effective INPs via immersion freezing (i.e., ice nucleation triggered by particles immersed in water droplets). In the cloud chamber experiments, Al2O3 and Fe2O3 particles continuously nucleated ice crystals at temperatures < −14°C and < −20°C, respectively. This result indicates that the Al2O3 particles were better INPs than the Fe2O3 particles. Moreover, the INAS density of the Al2O3 particles was comparable to that of natural ambient dust.

著者

TAUVALE Luteru TSUBOKI Kazuhisa

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.2019-042, (Released:2019-04-01)

被引用文献数

7

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Geographic and meteorological characteristics of 479 tropical cyclones (TCs) in a study domain in the Southwest Pacific (defined by 135°E - 120°W and 5°S - 65°S) over the past 48 TC seasons from 1969–1970 to 2016–2017 were examined using the latest Southwest Pacific Enhanced Archive of Tropical Cyclones dataset. Examined metrics include the geographic distributions of TCs, numbers, intensity, length in days (TC days), accumulated cyclone energy (ACE), and power dissipation index (PDI). The results show increasing TC activities in the western, northwestern, northern and central subdomains of the nine subdomains in the study domain. The average latitudes of TC genesis and TC maximum intensity remained almost unchanged. Most of TCs took southward to southeastward paths, and the majority attained their maximum intensities in the western and central parts of the study domain. The annual number of TCs and TC days decreased over the study period, the numbers of stronger TCs slightly increased whereas stronger TC days increased. The highest annual lifetime-maximum intensity and average annual lifetime-maximum intensity also increased. The highest annual maximum intensification rates did not change much over the study period, nor did ACE and PDI. The results show correlations between highest annual lifetime-maximum intensity to the variations of average sea surface temperature (SST) as well as correlations between TC days to the variations of average SST in the region.

著者

HIROSE Hitoshi SHIGE Shoichi YAMAMOTO Munehisa K. HIGUCHI Atsushi

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.2019-040, (Released:2019-03-15)

被引用文献数

23

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We introduce a novel rainfall estimation algorithm with a random-forest machine-learning method only from Infrared (IR) observations. As training data, we use nine-band brightness temperature (BT) observations obtained from IR radiometers on the third-generation geostationary meteorological satellite (GEO) Himawari-8 and precipitation radar observations from the Global Precipitation Measurement core observatory. The Himawari-8 Rainfall estimation Algorithm (HRA) enables us to estimate rain rate with high spatial and temporal resolution (i.e., 0.04° every 10 min), covering the entire Himawari-8 observation area (i.e., 85°E–155°W, 60°S–60°N) based solely on satellite observations. We conducted a case analysis of the Kanto–Tohoku heavy rainfall event to compare rainfall estimation results of HRA and the near-real-time version of the Global Satellite Mapping of Precipitation (GSMaP_NRT), which combines global rainfall estimation products with microwave and IR BT observations obtained from satellites. In this case, HRA could estimate heavy rainfall from warm-type precipitating clouds, although GSMaP_NRT could not estimate heavy rainfall when the microwave satellites were unavailable. Further, a statistical analysis showed that the warm-type heavy rain seen in the Asian monsoon region occurred frequently when the BT differences between the 6.9-μm and 7.3-μm of water vapor (WV) bands (ΔT6.9–7.3) were small. Himawari-8 is the first GEO to include the 6.9-μm band which is sensitive to middle-to-upper tropospheric WV. An analysis for the weighting functions of the WV multibands revealed that ΔT6.9–7.3 became small as WV amount in the middle-to-upper troposphere was small and there were optically thick cloud with the cloud top near the middle troposphere. Statistical analyses during boreal summer (August and September 2015 and July 2016) and boreal winter (December 2015 and January and February 2016) indicate that HRA has higher estimation accuracy for heavy rain from warm-type precipitating clouds than a conventional rain estimation method based on only one IR band.

著者

Akiyoshi WADA Hiroshige TSUGUTI Kozo OKAMOTO Naoko SEINO

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.3, pp.553-575, 2019 (Released:2019-06-05)

参考文献数

62

被引用文献数

4

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The September 2015 Kanto-Tohoku heavy rainfall event occurred in a stationary linear convective system between Typhoons Kilo and Etau. We investigated the influence of sea surface temperature (SST) on the local heavy rainfall event using a regional air-sea strongly coupled data assimilation system based on the local ensemble transform Kalman filter (LETKF) and a nonhydrostatic atmosphere model (NHM) coupled with an ocean-surface wave model and a multilayer ocean model with an Advanced Microwave Scanning Radiometer 2 (AMSR2) level 2 (L2) SST product. From the validation of SST analyzed by the coupled data assimilation system with the Japanese geostationary multi-functional transport satellite 2 hourly SST product and in-situ observations at a moored buoy, we demonstrated that the coupled system with the AMSR2 L2 SST led to an improvement in the SST analysis. Based on the verification using radiosonde observations and radar-rain gauge rainfall analysis, the analysis of the lower-atmospheric components was improved by the air-sea coupled NHM-LETKF. The local torrential rainfall event that occurred around 37°N in the Tochigi prefecture was embedded in a stationary linear convective system. The location of the linear convective system corresponded to the synoptic-scale convergence area between the cyclonic circulation associated with Etau and easterly lower-tropospheric winds. Strong southerly winds associated with Etau caused a periodic enhancement of local convection along the convergence area on the upwind side of the linear convective system and resulted in a wave-like train of the total water content around an altitude of 4-8 km on the leeward side. The improvement of SST analysis could not only change the transition of Etau to the extratropical cyclone but also the lower-tropospheric wind field and thereby the location of the stationary linear convective system with embedded local torrential rain.

著者

新野 宏

出版者

公益社団法人 日本気象学会

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

vol.58, no.1, pp.33-51, 1980

被引用文献数

2

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非圧縮で粘性がなく,密度一様な回転流体中で,回転軸に平行な体積力によって作り出された層流ジェットの振舞を線形論によって調べた。体積力はある有限の領域(以下領Aと呼ぶ)に軸対称に分布している。この力は,ある時刻(t*=0)に急に働き始め,その後の変化として<br>1) 無限に続く場合(連続的な力)<br>2) 時刻t*=T*に止む場合(継続時間T*の力)の2通りを考えるものとする。<br>連続的な力に対しては,流れの場は時間と共に回転軸方向に一様になるが,領域A内ではテイラー&bull;プラウドマンの定理が成り立たない為に圧力と接線速度は軸方向に一様にはならない。特に圧力場には,体積力に逆らうような軸方向の圧力傾度が次第に形成される。この圧力傾度は体積力が働き始めてからt*=10.90/fでほとんど定常になることがわかった。(ここでfはコリオリ係数である。)そして,定常状態では圧力傾度力は軸方向には体積力と,半径方向にはコリオリカとつりあっている。<br>継続時間T*の力に対しては,もしT*が10.90/fよりも大きいならば,力が止んだ後の領域A内の運動はT*によらないことがわかった。このような大きな値のT*に対しては,力が止んでからt*'=3.4/fと6.5/fとの間に領域A内に逆流が生ずる。(ここで,t*'=t*-T*である。)この逆流は,体積力が止むまでそれとつり合っていた逆向きの圧力傾度力によって生ずる。やがて,逆流が弱くなった後は,領域A内に周期約2&pi;/fの減衰振動が残る。この論文のモデルは,回転流体中の乱流ジェットの室内実験で見つかった逆流を説明する為に作られた線形論(新野,1978)をより洗練した形にしたものである。

著者

SHIN Uju LEE Tae-Young PARK Sang-Hun

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.2019-036, (Released:2019-02-19)

被引用文献数

10

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An investigation has been carried out using rainfall observation data, National Centers for Environmental Prediction (NCEP) Climate Forecast System Reanalysis (CFSR) analysis and forecast data to explain the environment and processes that lead to heavy rainfall in the early morning over the Korean peninsula during episodes of cloud clusters (CCs) associated with mesoscale troughs (CCMTs). For this study, nine episodes with maximum hourly rainfall amount in the early morning (i.e., 0300–0900 LST) are selected from seventeen heavy-rainfall episodes associated with CCMTs during 2001–2011. Case studies on two episodes have revealed that, for both episodes, 1) a low-level trough develops over eastern China and its coastal area during the daytime; 2) the strong southwesterly band (SWB; an area with wind speeds > 12.5 m s-1) on the pressure level 925 hPa over the East China Sea, which is located southeast of the trough, strengthens and expands at nighttime toward the southwestern Korean peninsula; 3) the SWB supplies large amount of moisture and increases convective instability over the southwestern Korean peninsula with a convection trigger mechanism (i.e., strong horizontal convergence); and 4) heavy rainfall occurs in the early morning over the southwestern Korean peninsula, where the exit region of the SWB is located. A mechanism for the SWB growth is presented. Furthermore, generality of the major results from the two case studies is verified using the results obtained for the composite fields of the 9 CCMT episodes.

著者

SAUNDERS Peter YU Yafan PU Zhaoxia

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.2019-030, (Released:2019-01-25)

被引用文献数

3

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Hurricane Joaquin, a notable hurricane over the Atlantic Ocean in 2015, is studied with emphasis on its unique hairpin turn that occurred between 2100 UTC 1 October and 0600 UTC 2 October 2015. A series of mesoscale high-resolution numerical simulations is performed with an advanced research version of the Weather Research and Forecasting (WRF) model. The sensitivity of numerical simulations to different cumulus, boundary layer, and microphysical parameterization schemes is examined to investigate the most relevant processes influencing the track evolution of Hurricane Joaquin. It is found that the numerical simulation of Hurricane Joaquin’s track is highly sensitive to the choice of cumulus scheme. Large-scale environmental conditions and hurricane inner-core structures are diagnosed. Results indicate that middle- to upper-level steering flows are crucial in influencing Joaquin’s track. Further investigation of the large-scale environment (e.g., middle- and upper-level trough, blocking high, thermal distribution, etc.) shows that middle-level blocking high plays an important role in Joaquin’s movement. The structure of the hurricane core region, including the vertical extent of diabatic heating, vertical velocity, and relative humidity, could also play an important role. Specifically, the asymmetry and local absolute vorticity tendency over the inner-core region and its vicinity has a strong implication for Joaquin’s hairpin turn.

著者

新田 勍 水野 孝則 高橋 清利

出版者

公益社団法人 日本気象学会

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

vol.70, no.1, pp.447-466, 1992

被引用文献数

43

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1986/87エルニーニョ発生期に起きた、様々な対流活動と流れの場に関する、時間・空間変動の特徴について調べた。この時期、インド洋から太平洋にかけての熱帯域では、季節内変動(ISV)、超雲集団(SCC)、双子低気圧、西風バーストが発生、発達、消滅を繰り返した。<br>多くの季節内変動は、インド洋で発生し、超雲集団、双子低気圧、西風バーストを伴って、西部熱帯太平洋へと伝わって行く。1986年に発生した季節内変動の中で、エルニーニョの発達に重要な役割を果たしたと思われる、(1)5月の双子低気圧、(2)8月に発達したITCZ、(3)本格的なエルニーニョの発達と関係した11月の超雲集団、の3例について詳しい時間変化と水平-垂直構造を調べた。<br>超雲集団が赤道上をインド洋から西部太平洋に東進する過程で、下層の西風バーストが海洋大陸上、特にスマトラの地形によって大きく影響を受けることが明らかになった。

著者

巽 保夫

出版者

公益社団法人 日本気象学会

雑誌

気象集誌. 第2輯

巻号頁・発行日

vol.61, no.2, pp.269-288, 1983

被引用文献数

30

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経済的な時間差分スキームを開発し,プリミティブモデルに使用した。本スキームでは重力波項以外の低周波項はリープフロッグ法で積分し,その時間積分間隔(&Delta;ta)はモデルの最大風速から決まる。振動数の高い重力波に対しては安定な数値解を得るため&Delta;taをM個の短いステップに分割(&Delta;ta/M=&Delta;tb)して時間積分を行う。分割数Mは重力波速の最大値と最大風速の比から決まる。すなわち時間積分は&Delta;tb間隔で計算する重力波項と&Delta;ta間隔で計算する低周波項(リープフロッグ法の時間外挿に当る2&Delta;ta内は一定とみなす)を加えたものを用いて&Delta;tbで積分し,2Mステップで時間積分1サイクルが完了する。本スキームはMarchuk(1965)が提案したsplittingとは全く異なるスキームであり,低周波項に対しては3-levelスキームである特徴を持つ。<br>本スキームの利点は,エクスプリシット法であるためにセミ&bull;インプリシット法と比較してプログラミングが大幅に簡略化される点と,低周波項の時間積分にリープフロッグ法を採用したことにより,2次の差分精度が得られる点である。<br>本スキームを気象庁の1981年のルーチンモデル(4L-NHM)に適用して比較実験を行ない,通常のエクスプリシット積分結果と本質的に差がないことを確認した。本スキームによる計算時間短縮率は Kudoh (1978)が開発したセミ&bull;インプリシットスキームによるものと同等(2.6~3.8)である。本スキームは気象庁の1982年現在のルーチンモデル(8L-NHM及び10L-FLM)に採用され,計算時間の短縮に大いに貢献した。

著者

Hironori FUDEYASU Ryuji YOSHIDA

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.2, pp.439-451, 2019 (Released:2019-04-04)

参考文献数

33

被引用文献数

9

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This study examined the statistical characteristics of tropical cyclones (TCs) for which the cyclogenesis (TCG) process was modulated by upper tropospheric cold lows (UCLs) over the western North Pacific during the 38 years from 1979 to 2016. Among the 965 TCs, 90 TCs (9 %, 2.4 per year) were defined as having TCG influenced by UCLs in the northwest quadrant of the TC region (UL-TCs). Most UL-TCs occurred in the summer, with large variability in the annual occurrence rate of UL-TCs during June to October, ranging from 0 to approximately 30 %. The annual variation was related to the activity of the Tibetan high and the summer temperature anomaly over Japan. The extremely hot summer of 2016 was partly enhanced by the intense Tibetan high, when 4 UL-TCs also occurred. The average location of UL-TCs at the time of TCG and tropical storm formation (TSF) was significantly farther to the north than the average location of TCs not formed under the influence of UCL (N-UL-TCs). Many UL-TCs occurred in lower tropospheric environments associated with the shear line or confluence regions. The UL-TCs tended to move northward, and the occurrence rate of UL-TCs that made landfall in Japan was approximately double that of other countries. The atmospheric environmental parameters around UL-TCs at the time of TCG were more favorable for the development of TCs than those around N-UL-TCs. In contrast, the atmospheric and oceanic environmental parameters around UL-TCs at the time of TSF were less favorable for the development of TCs, such that UL-TCs tended to remain at weak intensity.

著者

Wan-Ru HUANG Po-Han HUANG Ya-Hui CHANG Chao-Tzuen CHENG Huang-Hsiung HSU Chia-Ying TU Akio KITOH

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.2, pp.481-499, 2019 (Released:2019-04-03)

参考文献数

58

被引用文献数

9

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By using the Weather Research and Forecasting (denoted as WRF) model driven by two super-high-resolution global models, High Resolution Atmospheric Model (denoted as HiRAM) and Meteorological Research Institute Atmospheric General Circulation Model (denoted as MRI), this study investigates the dynamical downscaling simulation and projection of extreme precipitation activities (including intensity and frequency) in Taiwan during the Mei-Yu seasons (May and June). The analyses focus on two time period simulations: the present-day (1979-2003, historical run) and the future (2075-2099, RCP8.5 scenario). For the present-day simulation, our results show that the bias of HiRAM and MRI in simulating the extreme precipitation activities over Taiwan can be reduced after dynamical downscaling by using the WRF model. For the future projections, both the dynamical downscaling models (i.e., HiRAM-WRF and MRI-WRF) project that extreme precipitation will become more frequent and more intense over western Taiwan but less frequent and less intense over eastern Taiwan. The east-west contrast in the projected changes in extreme precipitation in Taiwan are found to be a local response to the enhancement of southwesterly monsoonal flow over the coastal regions of South China, which leads to an increase in water vapor convergence over the windward side (i.e., western Taiwan) and a decrease in water vapor convergence over the leeward side (i.e., eastern Taiwan). Further examinations of the significance of the projected changes in extreme precipitation that affect the agriculture regions of Taiwan show that the southwestern agriculture regions will be affected by extreme precipitation events more frequently and more intensely than the other subregions. This finding highlights the importance of examining regional differences in the projected changes in extreme precipitation over the complex terrain of East Asia.