著者

Shiori Sugimoto Rui Ito Koji Dairaku Hiroaki Kawase Hidetaka Sasaki Shingo Watanabe Yasuko Okada Sho Kawazoe Takeshi Yamazaki Takahiro Sasai

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.14, pp.46-51, 2018 (Released:2018-04-01)

参考文献数

32

被引用文献数

7

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To evaluate the influence of spatial resolution in numerical simulations on the duration of consecutive dry days (CDDs) and near-surface temperature over the central mountains in Japan, a regional climate model was used to conduct two experiments with horizontal resolutions of 5 and 20 km. Compared with observations, the spatial and temporal features of the CDDs were simulated well in the 5 km experiment, whereas in the 20 km simulation they were overestimated over the mountains and underestimated in the surrounding regions. The accuracy in the simulated CDDs affected the near-surface temperature in the model. In years with a difference of more than five days in the CDDs between the 5 and 20 km experiments, near-surface temperatures over the mountains were 0.2-0.3 K lower in the 5 km simulation compared with the 20 km simulation. This was due to the lower number of CDDs in 5 km simulation causing active cloud convection and reduced net radiation at the ground, resulting from a large decrease in the solar radiation at the ground. In addition, a land surface wetness controls a spatial heterogeneity of temperature difference between two experiments.

著者

Chung-Chuan YANG Chun-Chieh WU Kevin K. W. CHEUNG

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.2018-009, (Released:2017-12-15)

被引用文献数

1

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The steering flow analysis based on potential vorticity (PV) diagnosis is used to examine the reasons why the National Centers for Environmental Prediction Global Forecast System (NCEP-GFS) model showed large track forecast errors with over-recurving movement in Typhoon Fengshen (2008). In particular, two forecasts initialized at 0000 UTC 19 and 20 June 2008 are demonstrated in this study. The deep-layer-mean (DLM) steering flow between 925 and 300 hPa with tropical cyclone components filtered out is directed to the west or northwest in the analysis field, which can account for the continuous westward and northwestward movement in the best track. However, the DLM steering flow is shown more toward the north in the forecast fields. Four distinct PV features associated with the corresponding subtropical high, monsoon trough, continental high, and midlatitude trough are identified to diagnose their balanced steering flows around the storm. The result based on PV analysis indicates that the reduced westward steering flow in the forecast field is mainly attributed to the subtropical high which is over-predicted to extend southwestward, as well as the continental high with underestimated coverage, as characterized by the geopotential height at 500 hPa. The steering flow associated with the monsoon trough plays an essential role while Typhoon Fengshen (2008) experiences northward recurvature in both analysis and forecast fields. Therefore the associated reduced westward steering flow in the NCEP-GFS model leads to the over-recurvature of Fengshen.

著者

Teruyuki KATO

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.2018-008, (Released:2017-12-08)

被引用文献数

19

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This study investigated the representative height of low-level water vapor field that can be used to examine the occurrence possibility of heavy rainfall in East Asia. First, cloud base heights (CBHs) of moist convection were statistically examined by performing simulations with a 1-km-resolution numerical model during April–August 2008, with a focus on Kyushu and Shikoku Islands, western Japan. CBHs of moist convection with strong updrafts were simulated mainly around 500 and 300 m heights above sea level over land and over the ocean, respectively. This result indicates that low-level humid air below a height of 500 m is very important for the initiation of strong moist convection. Moreover, the equivalent potential temperature θe at the CBHs was examined to clarify θe values of lifted air parcels initiating cumulonimbus development. This result showed that below the CBHs, θe was usually around 355 K. Next, given these results for the CBHs, θe at 500 m height from 10-km-resolution objective analysis data was statistically compared with θe at various heights and pressure levels over the ocean south of 35 °N in East Asia during June–September 2008. These comparisons showed that analyses at the 850-hPa level could not represent the low-level water vapor field, while the θe field at 850 hPa in the Baiu season was strongly influenced by convective activity over the Baiu frontal zone. The θ e field at 925 hPa also could not adequately represent the low-level water vapor field, but the difference in θ e between heights of 250 and 500 m was very small. Because high θ e layers must have some thickness, data at 500 m height can be considered representative of the low-level water vapor field in analyses examining the initiation of moist convection leading to heavy rainfall.

著者

Hironori IWAI Shoken ISHII Seiji KAWAMURA Eiichi SATO Kenichi KUSUNOKI

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.3-23, 2018 (Released:2018-02-19)

参考文献数

61

被引用文献数

4

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During the Tokyo Metropolitan Area Convection Study for Extreme Weather Resilient Cities (TOMACS), many isolated convective storms developed in the southern Kanto Plain on August 17, 2012. The aim of this study was to clarify the dynamics leading to the convection initiation of one of them using different remote sensing instruments. Before the convection initiation, a southeasterly flow transported water vapor inland from Tokyo Bay and the well-mixed and a cumulus-cloud-topped convective boundary layer developed. A convergence line in the form of a sea breeze front (SBF) also moved inland from Tokyo Bay. A near-surface air parcel was lifted to its lifting condensation level (LCL) by an updraft in a convergence zone with a 3 km horizontal scale, which formed the west edge of the convergence line. The saturated air parcel at the LCL was then lifted to its level of free convection (LFC) by the updrafts associated with thermals below the cumulus cloud base. A Ku-band radar detected the first echo of hydrometeors about 6 minutes after the air parcel reached its LFC, then the convective cell developed rapidly. When an SBF arriving from Sagami Bay passed under the cell, the updraft over the nose of the SBF triggered a new precipitation cell, but no intensification of the preexisting cell was observed.

著者

Yoshihito SETO Hitoshi YOKOYAMA Tsuyoshi NAKATANI Haruo ANDO Nobumitsu TSUNEMATSU Yoshinori SHOJI Kenichi KUSUNOKI Masaya NAKAYAMA Yuto SAITOH Hideo TAKAHASHI

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.35-49, 2018 (Released:2018-02-19)

参考文献数

16

被引用文献数

4

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The relationships between the occurrence of intense rainfall and the convergence of surface winds and water vapor concentration for typical heavy-rainfall cases were examined using data from July to August in 2011-2013, obtained from high-density meteorological observations in Tokyo, Japan. Additionally, the temporal variations in wind convergence and water vapor between days with and without heavy rainfall events were compared. Corresponding to heavy-rainfall areas, the convergence of surface winds tended to increase for several tens of minutes prior to the heavy rainfall. The peak of convergence was observed 10-30 min before the heavy-rainfall occurrence, and convergence continued to increase for approximately 30 min until the convergence peak time. Around the heavy-rainfall area, the increase in the water vapor concentration index coincided with the increase in convergence. From these results, by monitoring the temporal variations and distributions of these parameters using a high-density observation network, it should be possible to predict the occurrence of heavy rainfall rapidly and accurately.

著者

Shin-ichi SUZUKI Takeshi MAESAKA Koyuru IWANAMI Shingo SHIMIZU Kaori KIEDA

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.25-33, 2018 (Released:2018-02-19)

参考文献数

20

被引用文献数

4

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X-band dual-polarization (multi-parameter) radars were used to observe a supercell storm that generated an F3 tornado in Ibaraki Prefecture, Japan on 6 May 2012. The observed data collected for this storm clearly exhibited the typical polarimetric features of a supercell storm, such as the ZDR (differential reflectivity) arc, ZDR column, and the KDP (specific differential phase) column, as well as their time evolution. The ZDR arc emerged at 10 to 15 min before the tornadogenesis. The ZDR column appeared approximately 1 h before the formation of the ZDR arc and was intermittent until tornadogenesis. As the ZDR arc appeared, the column became tall and stable and lasted until the dissipation of the tornado. These ZDR signatures of the supercell storm persisted for approximately half an hour.

著者

Shusuke NISHIMOTO 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.96, no.1, pp.5-24, 2018 (Released:2018-02-08)

参考文献数

17

被引用文献数

1

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We analytically solve a forced linear problem of vortex Rossby waves (VRWs) associated with the vortex resiliency of tropical cyclones. We consider VRWs on a basic barotropic axisymmetric vortex. VRWs, which are initially absent, are successively forced by a vertically sheared unidirectional environmental flow. The problem is formulated in the quasigeostrophic equations, linearized about the basic vortex. The basic potential vorticity (PV) is assumed to be piecewise constant in the radial direction so that the problem can be analytically solved. The obtained solutions show the following. When the vertical interaction (VI) between the VRWs is weak, a stationary mode (called the pseudo mode) is selectively forced and grows linearly in time, and the vortex is eventually destroyed by the environmental vertical shear. When the VI is moderate, an almost form-preserving quasi-mode (simply called the quasi mode) of the VRWs appears and precesses about a downshear-left tilt equilibrium (DSLTE). The precession does not grow and the vortex maintains vertical coherence. In particular, in the presence of the inward radial gradient of the basic PV at the critical radius, the precession damps and the quasi mode eventually approaches the DSLTE. When the VI is strong, the VRWs are simply advected by the basic angular velocity at each radius to be axisymmetrized to some extent about the DSLTE, and the vortex maintains vertical coherence. To examine the diabatic effect near the eyewall, the solution with the basic buoyancy frequency being small in the central region and large in the outer region is also obtained. The small and large buoyancy frequencies imply strong and weak VIs, respectively. The central VRWs are simply advected by the basic vortex flow. While, the outer VRWs precess about the DSLTE just like a quasi mode, and the vortex maintains vertical coherence.

著者

ドエル ノルペルド

出版者

METEOROLOGICAL SOCIETY OF JAPAN

雑誌

氣象集誌. 第1輯 (ISSN:00261165)

巻号頁・発行日

vol.33, no.5, pp.254-256, 1914

著者

Peiming Wu Dodi Ardiansyah Satoru Yokoi Shuichi Mori Fadli Syamsudin Kunio Yoneyama

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.13, pp.36-40, 2017 (Released:2017-03-24)

参考文献数

17

被引用文献数

9 16

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This study examined the impact of an active phase of the Madden–Julian Oscillation (MJO) on a torrential rain event that occurred on the western coast of Sumatra Island on 12 December 2015, using surface meteorological observations, meteorological radar observations, and balloon sounding data obtained from the pre-Years of the Maritime Continent field campaign. Strong MJO activity took place in mid-December 2015 into January 2016. Radar observations revealed that a convergence and convective cloud merger of mesoscale convective systems from an eastward propagating MJO and westward moving diurnal convection over the western coast of the island was the immediate cause of the torrential rain. An investigation of the occurrence of convection over the island showed that both westward moving diurnal convection from the mountains and eastward propagating convection from the Indian Ocean occurred on 12 December, because the westerly winds in the lower troposphere associated with the MJO were only just initiated and were weak on the day. The results suggest that the leading edge of the MJO westerly wind bursts provided favorable conditions for an active phase of the MJO to work with the westward moving diurnal convection and cause torrential rain on the western coast of Sumatra Island.

著者

井上 長太郎

出版者

METEOROLOGICAL SOCIETY OF JAPAN

雑誌

氣象集誌. 第1輯 (ISSN:00261165)

巻号頁・発行日

vol.16, no.4, pp.154-174, 1897

著者

馬塲 信倫

出版者

METEOROLOGICAL SOCIETY OF JAPAN

雑誌

氣象集誌. 第1輯 (ISSN:00261165)

巻号頁・発行日

vol.10, no.10, pp.505-516, 1891

著者

Esperanza O. CAYANAN Tsing-Chang CHEN Josefina C. ARGETE Ming-Cheng YEN Prisco D. NILO

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.89A, pp.123-139, 2011 (Released:2011-05-05)

参考文献数

14

被引用文献数

37 42

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Intense southwest monsoon (SWM) rainfall events causing massive landslides and flash floods along the western sections of the Philippines were studied. These rainfall events, are not directly coming from the tropical cyclones (TCs) for they are situated far north to northeast of Luzon Island. The heavy rainfall is hypothesized as caused by the interaction of strong westerlies with the mountain ranges along the west coast of Luzon that produces strong vertical motion and consequently generates heavy rainfall. Four of heavy SWM rainfall cases were examined to determine how the presence and position of tropical cyclones in the Philippine vicinity affect these SWM rainfall events; three cases with TC of varying positions within the Philippine area of responsibility (PAR) and the fourth case without TC. Using a spatial Fourier decomposition approach, the total streamfunction is decomposed into two flow regimes: monsoon basic flow (Waves 0-1) and tropical cyclone perturbation flow (Waves 2-23) over a domain of (20°E-140°W, 5°S-35°N). The purpose of this flow decomposition is to determine the latter’s effect on or contribution to the monsoon activity. The analysis utilized the NCEP Final (FNL) data with 1° long. × 1° lat. resolution. Results show that the tropical cyclones over the Pacific Ocean located northeast of Luzon generate strong southwesterly winds over the west coast of Luzon. These in addition to the southwesterlies from the basic flow strengthened the southwest winds that interact with the high Cordillera Mountain ranges

著者

Le DUC Yohei SAWADA

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.102, no.1, pp.35-47, 2024 (Released:2023-12-12)

参考文献数

31

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It is well-known in rainfall ensemble forecasts that ensemble means suffer substantially from the diffusion effect resulting from the averaging operator. Therefore, ensemble means are rarely used in practice. The use of the arithmetic average to compute ensemble means is equivalent to the definition of ensemble means as centers of mass or barycenters of all ensemble members where each ensemble member is considered as a point in a high-dimensional Euclidean space. This study uses the limitation of ensemble means as evidence to support the viewpoint that the geometry of rainfall distributions is not the familiar Euclidean space, but a different space. The rigorously mathematical theory underlying this space has already been developed in the theory of optimal transport (OT) with various applications in data science.In the theory of OT, all distributions are required to have the same total mass. This requirement is rarely satisfied in rainfall ensemble forecasts. We, therefore, develop the geometry of rainfall distributions from an extension of OT called unbalanced OT. This geometry is associated with the Gaussian-Hellinger (GH) distance, defined as the optimal cost to push a source distribution to a destination distribution with penalties on the mass discrepancy between mass transportation and original mass distributions. Applications of the new geometry of rainfall distributions in practice are enabled by the fast and scalable Sinkhorn-Knopp algorithms, in which GH distances or GH barycenters can be approximated in real-time. In the new geometry, ensemble means are identified with GH barycenters, and the diffusion effect, as in the case of arithmetic means, is avoided. New ensemble means being placed side-by-side with deterministic forecasts provide useful information for forecasters in decision-making.

著者

新野 宏

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.5, pp.1001-1023, 1982 (Released:2007-10-19)

参考文献数

39

被引用文献数

12 11

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密度一様の回転流体中の非発散の水平シア流の安定性を弱非線形理論によって調べた。考えたシア流はyを流れる横切る方向の座標とするとき,U(y)=tank y と U(y)=sech2y の2通りである。コリオリ係数の緯度変化の効果(ベータ効果)及び底面でのエクスマン摩擦の効果を考慮してある。不安定波の振幅の時間及び空間変調を記述する一般化されたランダウ方程式の係数を様々なβ(≅dy/dy)の値に対して求めた。この論文で考えた範囲のβの値に対しては,どちらのシア流の不安定も超臨界型であることがわかった。従って,臨界値より大きなレイノルズ数に対しては,有限振幅の不安定波が変形された基本流との間に平衡状態を形成することが予測される。有限振幅の定常波の side-band 波に対する安定性も調べた。超臨界のレイノルズ数に対して,波数κ0の有限振幅波は,もしκ0がS(κ1-κc)<κ0-κc<S(κ2-κc)をみたすならば安定である。ここで,kcは臨界波数,k1とk2(k<k2)はそのレイノルズ数に対する2つの中立波の波数であり,Sは定数である。U(y)=tanh y に対しては,β=0のときSは1/√3に等しい。Sはβの絶対値が増すと共に減少する。従って,有限振幅波が安定な波数領域はβの絶対値が大きくなるにつれて減少する。U(y)=sech2 yに対しては,βの絶対値が小さいときには(無次元のβでβ=-1.9~0.5)Sの値は0に等しく,有限振幅波は不安定である。βがこの範囲外のときには,Sはβの絶対値が増すと共に大きくなるが,1/√3より大きくなることはない。

著者

Kyohei Yamada Tadahiro Hayasaka Hironobu Iwabuchi

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.8, pp.94-97, 2012 (Released:2012-08-21)

参考文献数

20

被引用文献数

4 4

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To estimate contributions of water vapor (WV), carbon dioxide (CO2), and clouds to longwave radiation, surface downward longwave irradiance (DLI) was evaluated by comparing observations with values calculated using data from vertical profiles of WV and clouds obtained from radiosonde observations at five Baseline Surface Radiation Network (BSRN) sites. The observed DLI was reproduced by calculation with an accuracy of 3.9 ± 4.4 W m-2 for clear-sky conditions at all sites, but the accuracy was -7.7 ± 8.6 W m-2 for overcast conditions. The individual contributions of WV, CO2, and clouds to DLI were evaluated by removing these factors one by one from the normal condition including all of the factors (removal method) and by removing all factors except for one particular factor (addition method). The results indicate that the contributions of WV and clouds are relatively large, whereas the contribution of CO2 is relatively small.

著者

Karumuri ASHOK Zhaoyong GUAN Toshio YAMAGATA

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.81, no.1, pp.41-56, 2003 (Released:2003-03-18)

参考文献数

31

被引用文献数

187 214

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Using observed sea surface temperature data from 1871-1998, and observed wind data from 1958-1998, it is confirmed that the recently discovered Indian Ocean Dipole (IOD) is a physical entity. Many IOD events are shown to occur independently of the El Niño. By estimating the contribution from an appropriate El Niño index based on sea surface temperature anomaly in the eastern Pacific, it is shown that the major fraction of the IOD Mode Index is due to the regional processes within the Indian Ocean. Our circulation analysis shows that the Walker circulation during the pure IOD events over the Indian/ Pacific Ocean is distinctly different from that during the El Niño events. Our power spectrum analysis, and wavelet power spectrum analysis show that the periodicities of El Niño and IOD events are different. The results from the wavelet coherence analysis show that, during the periods when strong and frequent IOD events occurred, the Indian Ocean Dipole Mode Index is significantly coherent with the equatorial zonal winds in the central Indian Ocean, suggesting that these events are well coupled. During the periods when there seems to be some relationship between the equatorial zonal winds in the central Indian Ocean and ENSO index, no significant coherence is seen between the Indian Ocean Dipole Mode Index and the equatorial zonal winds in the central Indian Ocean, except after 1995, suggesting that most of the IOD events are not related to ENSO.

著者

竹村 和人 向川 均

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.101, no.1, pp.5-19, 2023 (Released:2023-02-07)

参考文献数

45

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本研究では、夏季アジアジェット出口付近でロスビー波の砕波を伴うシルクロードパターンが、太平洋・日本(PJ)パターンを引き起こす割合を調査した。ここで、シルクロードパターン事例は、ユーラシア大陸上での対流圏上層の南北風の主成分分析に基づき、黄海及び日本付近が高気圧性偏差となるパターンで特徴づけられる第1、2主成分を用いて抽出した。さらに、抽出した事例を、砕波を伴う事例と伴わない事例に分類した。 砕波を伴うシルクロードパターン事例では、アジアジェット出口付近の上層での高気圧性偏差は、砕波を伴わない事例と比べて東西により広がった形状を持ち、振幅も大きい。この事例の合成図では、シルクロードパターンに伴う波列パターンがユーラシア大陸上に存在し、アジアジェット出口付近で砕波を伴っていた。砕波の発生は、砕波域でのアジアジェットの強い減速及び分流と関連する。また砕波は、上層の高渦位気塊の進入を通して、砕波域の南側で活発な対流活動を促し、PJパターンを形成する。合成図において出現する明瞭なPJパターンは、南側で低気圧性偏差、北側で高気圧性偏差を持つ双極子構造を示す。そして、砕波を伴うシルクロードパターン事例の約60~70%が、PJパターンを伴っていた。 一方、砕波を伴わないシルクロードパターン事例の合成図では、ユーラシア大陸上で波列パターンは存在するが、砕波域の南側で活発化した対流活動及びPJパターンは存在しない。そして、砕波を伴わないシルクロードパターン事例の約40~50%がPJパターンを伴っていた。したがって、砕波によって正のPJパターンの出現頻度は1.2~1.7倍に増加し、砕波はPJパターンの励起に重要な役割を果たしていることが明らかになった。

著者

Brant Liebmann Harry H. Hendon John D. Glick

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.3, pp.401-412, 1994-06-25 (Released:2009-09-15)

参考文献数

18

被引用文献数

372 402

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当論文においては、西太平洋及びインド洋における熱帯低気圧とMadden-Julian振動(MJO)との関連を記述する。熱帯低気圧は振動の積雲対流活動活発期に生じ易いし、雲塊は下層の低気圧性渦度の周辺に存在し、発散場はMJOに伴う積雲対流活動の西方極側に現れる。熱帯低気圧や台風の絶対数は振動の積雲対流活動活発期に増大するが、弱い熱帯低気圧から転化する熱帯低気圧と台風の比率は、積雲対流活動活発期と乾燥期において同一である。積雲対流活動活発期においてより多くの熱帯低気圧や台風が存在するのは、当時期により多くの弱い熱帯低気圧が存在することによる。当研究の第三の結果は、積雲対流活動活発期の熱帯低気圧の活動度がMJOの活動度に限定されていない点である。事実、我々はMJOと独立かつ無作為に選ばれた積雲対流活動活発期において熱帯低気圧の活動度が同等に増大することを見いだした。結論として、MJOは熱帯低気圧に影響を及ぼす独自の機構を持つと言うより、むしろそれに伴う熱帯の変動度が大きな割合を占めるという点で重要である。

著者

竹村 和人 向川 均

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.100, no.1, pp.115-139, 2022 (Released:2022-02-22)

参考文献数

48

被引用文献数

5

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太平洋・日本(Pacific–Japan; PJ)パターンの形成に及ぼす日本の東海上で生ずるロスビー波砕波の寄与の重要性を、熱帯大気海洋変動の寄与と比較しながら定量的に調べた。まず、正及び負の位相を持つPJパターンのそれぞれの事例を、砕波が発生した事例と発生しなかった事例に分類した。その結果、砕波によって引き起こされた正位相のPJパターン事例数は、正位相全事例の約20%を占めることが分かった。また、砕波を伴う正位相のPJパターン事例数は、砕波を伴う正負両位相事例の約80%を占めていた。次に、砕波を伴う正位相のPJパターン事例について、ラグ合成図を用いたQベクトルに基づく診断を行った。その結果、日本の東海上での砕波が、北西太平洋亜熱帯域へ向かう南西方向への高渦位大気の進入と、それによって北西太平洋亜熱帯域で力学的に惹起される強い対流活動を通して、PJパターンの形成を促進することが示された。このPJパターンの形成メカニズムは先行研究で示されたものと一致する。一方、砕波を伴う負位相のPJパターン事例を対象とする合成図解析によって、砕波と関連する対流圏上層での東西方向に延伸した大気循環場偏差、及びインド洋全体での正の海面水温偏差が北西太平洋亜熱帯域での対流活動を弱化させたために、砕波の発生にも拘わらず、負位相のPJパターンが形成されたことが示された。最後に、砕波を伴わない正負両位相のPJパターン事例では、北西太平洋亜熱帯域での対流活動域が、時間とともに北西進してPJパターンの形成を促すことが合成図解析の結果より示された。砕波を伴わないPJパターンは、熱帯での海面水温偏差や北半球夏季季節内振動の位相と密接に関連し、「純粋な」熱帯の影響によって形成されることが明らかとなった。

著者

Hirokazu Endo

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.7, pp.5-8, 2011 (Released:2011-01-07)

参考文献数

21

被引用文献数

18 18

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This study investigates long-term changes in Baiu rainfall in Eastern and Western Japan using daily precipitation records at 37 stations for the years 1901 through 2009, focusing on its seasonal progress. This period is much longer than various data analyzed in previous observational studies. In the early Baiu season (early to mid June), significant long-term decreasing trends are observed in Eastern and Western Japan, accompanying large inter-decadal variation in the former half of the 20th century. In the late Baiu season (mid to late July), in contrast, significant long-term increasing trends are observed on the Japan Sea side of Eastern and Western Japan. No significant trends are recognized either in the mid Baiu season (late June to early July) or in the entire Baiu season (June to July) over all regions. It is interesting to note that the observed tendency of delayed Baiu withdrawal in the last 109 years, when global warming has been in progress, is similar to its future changes projected by climate models.