著者

Yanru ZHAO Wenqian MAO Kequan ZHANG Yining MA Haifei LI Wenyu ZHANG

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.95, no.3, pp.181-197, 2017 (Released:2017-04-28)

参考文献数

35

被引用文献数

7

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Based on the ERA-20C, climatic variations of the boundary layer height (BLH) over arid and semiarid areas in East Asia and North Africa that span 1900-2010 were analyzed. In East Asia, the BLH exhibited a descending trend from arid region centers to the periphery. Over the past 111 years, the BLH has had a rising trend of 14.0 m decade−1. in the representative region (EA1) of the eastern areas with the 111-year average of 725 m and a decreasing trend of −1.6 m decade−1. in the representative region (EA2) of the western areas with the 111-year average of 792 m. From the mid-1960s to 1970s, EA1's BLH had a sharp rise that caused the average to increase by 93 m after the 1980s. In North Africa, the BLH exhibited a high spatial distribution in the western and southern areas and a relatively low spatial distribution in the eastern and northern areas. Over the past 111 years, the BLH has had a rising trend of 9.7 m decade−1. in the representative region (NA1) of the southwestern region with the 111-year average of 915 m and a decreasing trend of −6.3 m decade−1. in the representative region (NA2) of other regions with the 111-year average of 882 m. In the 1940s and the 1970s, NA1's BLH had two obvious increases that caused the average to increase by 51 m and 22 m, respectively, while NA2's BLH had two obvious declines that caused the average to decrease by 48 m and 7 m, respectively. On the spatial distribution, the BLH, sensible heat flux, latent heat flux, and volumetric soil water had a good corresponding relationship. On the temporal change, the BLH in East Asia had a stronger correlation with thermodynamic factors, whereas the BLH in North Africa had a stronger correlation with dynamic factors. Besides, the upper-level stratification also has some influence on the BLH's change.

出版者

社団法人 日本気象学会

雑誌

氣象集誌. 第1輯 (ISSN:00261165)

巻号頁・発行日

vol.14, no.8, pp.388-394, 1895 (Released:2009-02-05)

著者

Jong-Jin Baik Jong-Su Paek

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.78, no.6, pp.857-869, 2000-12-25 (Released:2009-09-15)

参考文献数

30

被引用文献数

1 31

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バックプロパゲーション型ニューラルネットワークを使って、北西太平洋での熱帯低気圧の強度の変化を12,24,36,48,60,72時間について予測するモデルを開発した。用いたデータは、1983-1996の14年間の北西太平洋の熱帯低気圧に対する、低気圧の位置、強度、NCEP/NCARの再解析、それに海面水温である。ニューラルネットワークの予測因子は重線形回帰モデルの予測因子に基づいて選ばれた。回帰分析により、予測因子の一つ風の鉛直シアーが全ての予測時間に渡って一貫して重要であることを示した。予測因子として気候学的、持続的、総観的因子を用いたニューラルネットワークモデルによる平均予測誤差は、同じ予測因子を用いた重線形回帰モデルに比べて7-16さらに、予測因子として気候学的、持続的因子のみを用いたニューラルネットワークモデルの性能でさえも、総観的因子まで含んだ重線形回帰モデルの性能をわずかに上回った。ニューラルネットワークモデルの性能は14年間の全ての年について回帰モデルを上回るわけではないけれども、ニューラルネットワークモデルの方が良い年の方が逆の年よりもずっと多く、その傾向は短い予測時間の方が顕著である。感度実験により、ニューラルネットワークモデルの平均強度予測誤差は、隠れ層や隠れ層のニューロンの数には敏感ではないことを示した。しかし、熱帯低気圧強度予測のために、より良い隠れ層の構造を用いることにより、回帰モデルに比べてニューラルネットワークモデルをさらに改良する余地がいくらかある。この研究は、予測因子として気候学的、持続的、総観的因子を用いたニューラルネットワークモデルが熱帯低気圧の強度予報において有効な道具として使えることを示唆している。

著者

Yan LI Peilong YE Juan FENG Yao LU Jiahe WANG Zhaoxia PU

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.95, no.2, pp.147-165, 2017 (Released:2017-04-08)

参考文献数

51

被引用文献数

7

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It has been argued that the Coupled Model Intercomparison Project phase 5 (CMIP5) models underestimate the frequency of atmospheric blocking, while projecting a decreasing trend of blocking in the 21st century in the Northern Hemisphere. This average trend may not be true for regional blockings. Focusing on three key regions in Eurasia (the Urals, Baikal, and Okhotsk regions) where blocking significantly influences the weather and climate of East Asia, this study first evaluates the performance of the CMIP5 models by comparing historical simulations with National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis (NNR). Possible changes in the first half of the 21st century are then analyzed using the RCP4.5 and RCP8.5 experiments. It is found that instantaneous blocking frequencies are underestimated in the Urals and Baikal regions for the whole year and in the Okhotsk region in summertime but are overestimated in Okhotsk in wintertime. Blocking episode frequency in the Urals and Baikal regions is underestimated by most of the 13 CMIP5 models, especially the short-duration blocking episodes (4–5 days), and the simulations are better in wintertime than in summertime. However, in the Okhotsk region, the modeled frequency of blocking episodes is close to the value from NNR in summertime but is overestimated in wintertime. Model projections of instantaneous blocking frequency for the first half of the 21st century (2016–2065) show that both RCP4.5 and RCP8.5 runs yield an increasing frequency except during June–August in Eurasia. The multimodel ensemble-mean frequency of blocking episodes clearly decreases in the whole year in the Urals and Baikal regions (especially blocking episodes with short duration) and increases a little in summertime in the Okhotsk region in the first half of the 21st century. The model ensemble-mean frequency of blocking episodes with long duration (more than 9 days) decreases by ~40 % in the Urals region but increases by no more than 5 % in Okhotsk region.

著者

Yoshimi KAWAI Qoosaku MOTEKI Akira KUWANO-YOSHIDA Takeshi ENOMOTO Atsuyoshi MANDA Hisashi NAKAMURA

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.95, no.2, pp.71-90, 2017 (Released:2017-03-17)

参考文献数

31

被引用文献数

6

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The present study investigated how impacts of the inclusion of radiosonde observations conducted locally in the early summer of 2012 over the Kuroshio and Kuroshio Extension (KE) can spread over time across the North Pacific basin to influence the predictability of synoptic and large-scale tropospheric circulation. For that purpose, observing system experiments (OSEs) were performed where each of two extra sets of radiosonde data, one obtained over the East China Sea in mid-May and the other over the KE in early July, was added to an atmospheric ensemble data assimilation system for comparison with the corresponding analyses without those data. The experiments show that the impact of the extra data assimilated propagates eastward mainly due to advection by the subtropical jet (STJ) in May and July. The strong STJ in May allows the upper-tropospheric impact to travel across the basin only within two days. Under the weaker STJ, the corresponding impact in July tends to remain within the western Pacific, until it eventually reaches the eastern portion of the basin. Assimilation of the extra radiosonde data over the Kuroshio or KE can lead to a decrease of pressure over the Gulf of Alaska in both May and July.  Additional forecast experiments based on the OSEs for May revealed that the pressure decrease over the Gulf of Alaska can be traced back to the west of the Alaska Peninsula and to the east of Japan over three days. The impacts that originate on different dates via different paths merge over the central North Pacific, reinforcing the cyclone over the Gulf of Alaska. This study presents examples where the impacts of atmospheric observations over the western boundary current can propagate across the ocean basin through the westerlies to influence the forecast skill in distant regions.

著者

TOCHIMOTO Eigo KAWANO Tetsuya

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

pp.2017-005, (Released:2017-01-13)

被引用文献数

10

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This work investigates development processes of Baiu frontal depressions (BFDs) using a numerical model. To investigate the effects of upper-level disturbances, latent heating, and baroclinicity on the development of BFDs, case-study numerical simulations are performed. In the present study, two typical cases were selected from BFDs that appeared in June and July, 2000-2007: a BFD that developed in the western part of the Baiu frontal zone (W-BFD) from 26 to 27 June 2003 and a BFD that had formed in the eastern part of the Baiu frontal zone (E-BFD) from 1 to 3 July 2003. An available potential energy (APE) diagnosis shows that the effect of latent heating is dominant during the W-BFD development, while baroclinicity as well as latent heating is important to the E-BFD development. A sensitivity experiment excluding upper-level potential vorticity (PV) anomalies shows that upper-level disturbances are important contributors to the development of E-BFDs. The low-level PV and its production associated with latent heating suggest that the W-BFD has a development mechanism driven by latent heating. In the early developmental stage, PV near the W-BFD center is enhanced. This feature is consistent with the nonlinear conditional instability of the second kind mechanism. In the later developmental stage, PV is produced in front of the W-BFD center, in which low-level baroclinicity is large. This process is consistent with a diabatic Rossby vortex. In contrast, the E-BFD develops through a baroclinic instability-like mechanism in the moist atmosphere.

著者

山田 二久次 関根 義彦

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.75, no.5, pp.995-1000, 1997-10-25

被引用文献数

3

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日本東岸における春季(1967〜86年、3〜5月)において、100m水深5℃の等温線緯度で定義される親潮第一分枝南限緯度の年々変化と、北太平洋上の500hPa高度場の関係を解明した。高度場については、北太平洋領域でEOF解析をし、第1・第2成分と親潮南限緯度のラダ相関を解析した。その結果、親潮の南限緯度と500hPa高度のEOF第1成分との間に、3力月遅れ(大気が先行)で有意な相関があることを見いだした。500hPar高度のEOF第1成分の空間パターンはアリューシャン低気圧の南下を示している。なお親潮の南限緯度は、EOF第2成分とは有意な関係はなかった。親潮の南下が著しい年の冬には12月から2月まで、北太平洋の30〜50゜Nでの海水温か負偏差となる。この時海面水温負偏差域の北部では、風の応力ベクトル偏差は西向きで、風の応力が弱まっている。したがって、この温度低下は潜熱・顕熱フラックスやエクマン輸送の増加では説明できず、アリーシャン低気圧の南偏に伴う亜寒帯循環の南下に伴うものであることが示唆された。

著者

Akio KITOH

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.95, no.1, pp.7-33, 2017 (Released:2017-03-01)

参考文献数

220

被引用文献数

69

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This study provides an overview of the Asian monsoon and its change as simulated by atmosphere–ocean coupled general circulation models and high-resolution atmospheric general circulation models, focusing on the seasonal mean circulation and precipitation climatology. After reviewing the drivers of and the elements that affect the monsoon, the ability of those climate models to reproduce the Asian monsoon is assessed. The Asian monsoon is better reproduced in the Coupled Modeling Intercomparison Project phase 5 (CMIP5) models than in the CMIP3 models, although biases remain. Projected future changes in the Asian monsoon at the end of the 21st century are then reviewed. Overall projections are similar for both CMIP3 and CMIP5 models with increases in precipitation, albeit with weakened circulation in the South Asian summer, enhanced circulation and increased precipitation in the East Asian summer, and latitude-dependent changes in the winter monsoon circulation in East Asia. However, differences exist in the projected local changes, leading to uncertainty in projections.

著者

Kunihiko KODERA Nawo EGUCHI Jae N. LEE Yuhji KURODA Seiji YUKIMOTO

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.89, no.3, pp.283-290, 2011-06-25 (Released:2011-06-30)

参考文献数

24

被引用文献数

7 18

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In mid-January 2009, sudden changes in circulation occurred in the tropical troposphere and stratosphere. Convective activity situated over the equatorial Maritime Continent showed an abrupt weakening, whereas that over the South American to African sectors became stronger. Changes also occurred in the latitudinal structure; convective activity in the Northern Hemisphere became weaker, whereas that in the Southern Hemisphere became stronger. The change in convective activity took place in association with a change in tropical circulation, from east–west to north–south type (i.e., from Walker- to Hadley-type circulation). Almost simultaneously with these events in the troposphere, a change in meridional circulation occurred in the stratosphere during a record-breaking stratospheric sudden warming event in January 2009. Stratospheric tropical temperature showed a decrease in response to a strengthening of the hemispherical meridional circulation. In the present study, we show how the stratospheric and tropospheric circulation changes are dynamically coupled.

著者

Hiroaki KAWASE Hidetaka SASAKI Akihiko MURATA Masaya NOSAKA Noriko N. ISHIZAKI

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.93, no.5, pp.571-580, 2015 (Released:2015-11-17)

参考文献数

33

被引用文献数

3 19

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We investigate future changes in winter precipitation around Japan and their uncertainties using the downscalings of a non-hydrostatic regional climate model (NHRCM) with 20-km grid spacing according to global climate projections. The global climate projections were conducted by the atmospheric general circulation model with three patterns of sea surface temperature changes in the Coupled Model Intercomparison Project Phase 5 under the Representative Concentration Pathway 8.5. Moreover, three cumulus convective parameterizations were applied in the present and future climate experiments. The ensemble mean of nine future NHRCM experiments shows decreases in the winter precipitation on the coast of the Sea of Japan and over the Pacific Ocean in the south of the Japanese archipelago. The former decrease in precipitation results from a weakened winter monsoon. The latter corresponds to changes in extratropical cyclone number around Japan, which have a large uncertainty. On the other hand, winter precipitation increases over the northernmost part of Japan (Hokkaido) and the northeastern Asian continent. The strengthened northwesterly around Hokkaido, which results from the reduction of sea ice in the Sea of Okhotsk, causes increased precipitation in the inland area of Hokkaido. In addition, moistening due to global warming relates to increased precipitation in extremely cold regions. These signals are common to most experiments.

著者

Yuhji KURODA

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.85, no.6, pp.889-898, 2007 (Released:2008-03-20)

参考文献数

22

被引用文献数

8 15

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The effect of the Quasi-Biennial Oscillation (QBO) and the El Niño Southern Oscillation (ENSO) on the 11-year solar cycle modulation of the winter-mean North Atlantic Oscillation (NAO) is examined through analysis of observational data from 1958 to 2000. It is found that the solar cycle modulation of the NAO is more strongly enhanced in the westerly phase of the 50-hPa QBO wind and the cold phase of ENSO, although separation of these effects is statistically difficult. On these phases, the signal of the winter-mean NAO extends more to the upper stratosphere and summer-AO reappears more strongly in high solar years, whereas the signal is weaker throughout in low solar years.

著者

Hiroyuki IWASAKI

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.94, no.5, pp.431-442, 2016 (Released:2016-10-31)

参考文献数

25

被引用文献数

7

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Lightning features over the Tibetan Plateau were studied in relation to topography using the World Wide Lightning Location Network (WWLLN) dataset obtained from April 2009 until December 2014. To describe the strength of lightning strokes, lightning strokes with energies above the 90th percentile (7666 J) were defined as strong lightning (S-lightning) strokes, and the ratio of S-lightning strokes to the overall number of lightning (O-lightning) strokes was defined as the strong ratio (S-ratio). O-lightning density over the Tibetan Plateau was found to be high in general, except over the western part of analysis region. Minimum-density zones were observed along the Himalayas approximately 6 km above sea level and in deep valleys within the Tibetan Plateau. The maximum- and minimum-density zones also exhibited maximum and minimum annual rainfall amounts, respectively. S-lightning strokes were also found to frequently occur over the Tibetan Plateau, and most S-ratios in the analysis units exceeded 30 %, which corresponds to three times the global mean. In particular, the S-ratios over the southern part of the Tibetan Plateau, including the Himalayas, were found to be high (50 %) and to correspond with the zone that had the minimum O-lightning density. The maximum O-lightning density was observed to occur during the summer at an elevation approximately 0.2-1.0 km higher than the plateau level. The O-lightning and S-lightning densities around the Nagqu sonde station were negatively correlated with the Showalter stability index (SSI) and the vertical wind shear. The S-ratio and average stroke energy were found to be negatively correlated with the vertical shear but not with the SSI.

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

三角 幸夫

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.77, no.2, pp.615-635, 1999-04-25

参考文献数

28

被引用文献数

10

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1988年から93年のレーダーエコー合成図を解析して日本列島付近の降水の日変化を調べた。この解析は、18のデジタル化レーダーを合成した陸海両方を含む広い領域上で、降水雲の水平規模及び最大降水強度によって、準水平循環によると考えられる大規模降水雲及び対流によると考えられる積雲規模降水雲に分類して日変化を調べた点に特徴がある。小規模で降水強度の強い雲で定義される積雲規模降水雲は、一部の岬を除く日本の4大島の全域・朝鮮半島南部及び沖縄本島で、午後に卓越的な降水最大を持つ。これは疑いなく日射の境界層加熱による。主に大規模降水雲で占められるその他の降水雲はほぼ合成図全域で朝に最大値を持つ日周期を示す。この変動は海陸循環には関係しない。日本上空の西風はこれらの日変化に以下のように影響を与える。東北日本上空の西風は積雲規模降水雲の活動を領域東側で最大にし、さらにそれらの雲を東側近海に運び降水極大を引き起こす。琉球列島周辺では、西風に運ばれる大規模降水雲が5月から7月の間しばしば午後に北東から通過するために、降水量の極大が午後に現れる。

著者

Sushma NAIR Govindrajan SRINIVASAN Ramkrishna NEMANI

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.87, no.6, pp.927-939, 2009 (Released:2010-02-04)

参考文献数

11

被引用文献数

53 109 59

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The Tropical Rainfall Measuring Mission (TRMM) blended rainfall product (3B42-V6 data set) has been used for inter-comparison with observations from a high density rain-gauge network over the western state of Maharashtra, India. The state of Maharashtra was chosen for the inter-comparison exercise primarily because of its diverse rainfall regime. The rain distribution over Maharashtra, characterized by a pronounced longitudinal gradient is closely linked to the north-south oriented orography of the region known as the Western Ghats. The validation exercise was carried out for 7 monsoon seasons from June to September from 1998 to 2004 at various space and time scales. The results are consistent at daily, monthly and seasonal timescales. The comparisons among stations and over geographically similar climatic zones demonstrated that the performance of 3B42-V6 product varies over the different climatic regimes. In terms of spatial reproductivity, the existence of the west-east rainfall gradient along the west coast is captured by the satellite product, but the orographic effect (rainfall maxima is over the Western Ghats as captured by the rain-gauge) is not reflected by 3B42-V6 product. The 3B42V6 product shows rainfall maxima at the coast. The satellite estimates of rainfall amounts over the state were found to be most accurate over regions of moderate rainfall and mainly inaccurate in regions of sharp rainfall gradient. In terms of magnitude of the rainfall amounts, over the windward side of the Western Ghats the 3B42V6 product was unable to resolve the heavy orographic rainfall amounts and over the leeward side the rainfall amounts in the immediate rain-shadow region were overestimated. One of the key results obtained from the daily rainfall intercomparison exercise is the ability of the 3B42-V6 estimates to detect the wet and dry phases of monsoon over most parts of the state (except the leeward side). Though the rainfall amounts estimated by the satellite product were sometimes under/over estimated, the timing of the rain events as estimated by the satellite product was generally coincident with the gauge observations over most of the regions except in the immediate rain-shadow region of the state. The TRMM 3B42-V6 estimates therefore could have tremendous potential to be used for intraseasonal studies over most regions of the state.

著者

平野 烈介

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.4, pp.116-121, 1924-09-15 (Released:2009-02-05)

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From the durations of the preliminary tremors observed at various stations, the author, in his previous paper, located the seismic origin of the Great Kwanto Earthquake at a point to the north of Mt. Fuzi. In the present paper, he found the following two equations representing the relation between the distance of each station from the above point and the time of arrival of the first shock at that station in which Δ is the distance in kilometer and t the time in second measured from its origin assumed at 11h 58m, Sept. 1st, 1923. The first and second equations are well satisfied by the observed values of t and Δ at stations respectively in western and eastern Japan, the greatest discrepancy between the culculated and observed t being 2.7 seconds, while the total value of t ranges between 39-86 seconds. If the above equations are correct, there must be a time difference of 7 seconds for the commencements of the earthquake shocks at the seismic origin for the two waves, one travelling to the east and the other to the west. The author considers a highly strained state of earth crust, in a finite area near the origin, existing before the great earthquake and supposes that the waves actually started from the both sides of the area, whose diameter is about 50km, so that the apparent difference of time is accounted for.

著者

Masakazu TAGUCHI

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.93, no.1, pp.99-115, 2015 (Released:2015-03-18)

参考文献数

36

被引用文献数

2 10

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This study investigates observed interannual changes in the Northern winter stratosphere with El Niño/Southern Oscillation (ENSO) and quasi-biennial oscillation (QBO) using the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data for 56 years. We focus on changes in occurrence of major stratospheric sudden warmings (MSSWs) as well as in seasonal mean states.  Our results reveal complex changes in the MSSW probability with both ENSO and QBO as in the seasonal mean states. However, statistically significant changes at the 90 % confidence level are obtained only for some combinations of ENSO and QBO conditions reflecting the limitation of the data period. When the QBO is in a westerly phase, the MSSW probability increases with the ENSO sea-surface temperature condition in the eastern equatorial Pacific, i.e., from ENSO cold (La Niña), through neutral, to warm (El Niño) years. When the QBO is in an easterly phase, on the other hand, the probability significantly increases for La Niña years than for neutral years, whereas the probability is not significantly different between neutral and El Niño years. A characteristic feature is the high MSSW probability for the La Niña and QBO easterly winters, which is consistent with strengthened stationary wave with zonal wavenumber 1 compared to the climatology.  These results suggest the importance of taking into account both ENSO and QBO factors, when one examines the frequency of MSSWs in the Northern winter stratosphere.

著者

森 一正 石垣 修二 前平 岳男 大矢 正克 竹内 仁

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.77, no.2, pp.459-482, 1999-04-25

参考文献数

37

被引用文献数

1

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1993年8月30日から9月1日まで、(19N, 129E)周辺の北西太平洋上を西進した初期の緩やかな発達期にあった台風Yancy(T9313)が、気象庁観測船啓風丸で観測された。この期間中、Yancyの循環中心は啓風丸の北80kmまで接近した。Ydncy中心部の対流が、船上で得られたレーダー、海上気象、高層気象観測データと最近利用可能になった衛星データを用いて解析された。セルエコー追跡風(CETwinds)が見積もられYancy周辺の下層風データを補うために使用された。初期発達期間中に、雲が1500kmスケールの下層低気圧性循環(LLCC)の南西象限に存在し中心を一にしない構造が、雲システム中心部の円形の厚い上層雲('CDO')の形成を経て同一中心を持つ構造へと遷移した。この同一中心を持つ構造の確立後、Yancyの後期の急激な発達が始まった。Yancy内に様々なメソスケ-ル(100-500km)降水体(MPFs)が次々に組織され時間発展した。このMPFsの形態は台風初期発達過程が4つのサブステージを経て進展するにしたがって変化した。第1サブステージでは大きな(400km)エコーシステム(LES)がLLCCの南西象限に組織され、その上に円形雲システムが出現した。第2サブステージでは、長続きするメソスケールの強い対流域(MICA)がLESの北西端に組織され、それが円形雲システム中の'CDO'のメソスケール降水実体であった。LLCCはMICAの形成後500kmスケールで強化されたようであった。第3サブステージでは、強い低気圧性循環中で、LESと雲システムは500km以上の長さを持つコンマ型スパイラルバンドへと進化した。最終サブステージでは、スパイラルバンドの曲率は増し、より内側のほぼ円形に近いスパイラルバンドが更に強化されたLLCC中に現われた。コンマ型システムの北側頭部はLLCC中心を巻き込みつつあった。MICA周辺に、下層の流れに垂直な線状システムと平行な線状システムが、第1サブステージと第2サブステージに各々形成されていた。LESとMICAは初期発達過程にあるYancyの核構造を構成していた。MICAは、長続きする、エコー頂が高度16kmに達する強い対流にとって3次元的に都合よく組織された構造を持っていた。MICAと500kmスケールのLLCCは互いに強め合っているようであった。MPFsのいくつかの特徴がまとめられ、それらは山岬(1983, 1986)により数値的に再現された、発達中の台風内のメソ対流の特徴とよく対応しているようであった。

著者

Fumio MARUYAMA Kenji KAI Hiroshi MORIMOTO

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.93, no.3, pp.331-341, 2015 (Released:2015-07-10)

参考文献数

23

被引用文献数

1 4

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A climatic regime shift is characterized by an abrupt transition from one quasi-steady climatic state to another. We attempted to explain the change of multifractal behavior of climate indices when a regime shift occurred. We used the wavelet - transform method to analyze the multifractal behaviors of the El Niño/Southern Oscillation (ENSO) index (Niño3.4 index), Pacific Decadal Oscillation (PDO) index, North Pacific Index (NPI), Pacific/North American pattern (PNA) index, and West Pacific pattern (WP) index. We showed the change of multifractality of these climate indices. When the wavelet coherences between the Niño3.4 index and NPI, NPI and PDO index, and Niño3.4 and PDO indices became strong, changes from multifractal to monofractal behavior were observed at climatic regime shifts. It may be possible to explain the background of the change of fractality by regarding climate change as the consequence of mutual interactions of various climatic elements. A fluctuation increase is observed in a coupled chaotic system just before chaos synchronization, which is when fractality and states change. We expect that a similar mechanism possibly exists for a climatic regime shift. When fluctuations became large and multifractality became strong, a climatic regime shift occurred and a change from multifractal to monofractal behavior was observed. The strong interaction of climatic phenomena, such as the ENSO, PDO, and Aleutian Low, caused a climatic regime shift. The fractality change of the PDO index almost corresponded to the regime shifts. In terms of multifractal analysis, we conclude that a climatic regime shift corresponds to a change from multifractality to monofractality of the PDO index.