著者

LIANG Jianyu TERASAKI Koji MIYOSHI Takemasa

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

pp.2023-005, (Released:2022-11-01)

被引用文献数

3

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The observation operator (OO) is essential in data assimilation (DA) to derive the model equivalent of observations from the model variables. In the satellite DA, the OO for satellite microwave brightness temperature (BT) is usually based on the radiative transfer model (RTM) with a bias correction procedure. To explore the possibility to obtain OO without using physically based RTM, this study applied machine learning (ML) as OO (ML-OO) to assimilate BT from Advanced Microwave Sounding Unit-A (AMSU-A) channels 6 and 7 over oceans and channel 8 over both land and oceans under clear-sky conditions. We used a reference system, consisting of the nonhydrostatic icosahedral atmospheric model (NICAM) and the local ensemble transform Kalman filter (LETKF). The radiative transfer for TOVS (RTTOV) was implemented in the system as OO, combined with a separate bias correction procedure (RTTOV-OO). The DA experiment was performed for one month to assimilate conventional observations and BT using the reference system. Model forecasts from the experiment were paired with observations for training the ML models to obtain ML-OO. In addition, three DA experiments were conducted, which revealed that DA of the conventional observations and BT using ML-OO was slightly inferior, compared to that of RTTOV-OO, but it was better than the assimilation based on only conventional observations. Moreover, ML-OO treated bias internally, thereby simplifying the overall system framework. The proposed ML-OO has limitations due to (1) the inability to treat bias realistically when a significant change is present in the satellite characteristics, (2) inapplicability for many channels, (3) deteriorated performance, compared with that of RTTOV-OO in terms of accuracy and computational speed, and (4) physically based RTM is still used to train the ML-OO. Future studies can alleviate these drawbacks, thereby improving the proposed ML-OO.

著者

Han LI Xuyang GE Melinda PENG Lu LI

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.5, pp.729-749, 2022 (Released:2022-09-24)

参考文献数

45

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In this study, the effect of the zonally-elongating monsoon trough (MT) on the interaction of binary tropical cyclones (BTCs) is investigated by using data analysis and idealized simulations. The interaction of BTCs is found to be sensitive to the relative orientation of the two tropical cyclones (TCs) embedded in the MT. When the two cyclones are lined up in a northeast–southwest (NE–SW) orientation, the MT steers the two cyclones to approach each other and promotes the Fujiwhara effect. In contrast, when the initial cyclones are oriented in the northwest–southeast direction of the MT, they will move away from each other under the large-scale steering flows.Idealized simulations are conducted to understand how the MT and the β-effect influence the BTC interactions, focusing on NE–SW oriented pairs. The steering flows at different stages are examined by partitioning them into the one from the MT and the other cyclone in the pair. The analysis shows that the binary TCs' motions are mainly controlled by the large-scale steering flows in the initial stage. In the case of BTCs with a NE–SW orientation, the MT can promote two TCs to approach each other, thus increasing the possibility of binary interactions.The sensitivity of the interaction of BTCs to their intensities, the strength of the MT, and the β-effect are examined. The stronger the MT, the stronger its large-scale steering flows will be, thus making the two NE–SW oriented TCs merge faster. Furthermore, the binary interaction is stronger on the β-plane compared with that on the f-plane. It is likely due to the β-induced Rossby wave energy dispersion. As the MT evolves into a monsoon gyre (MG)-like pattern, a pronounced southwesterly flow emanates in the southeast quadrant of MG. This southwesterly flow acts as a steering flow to help the western TC move northeastward, accelerating to reach the critical distance.

著者

斎藤 錬一

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.26, no.8, pp.208-215, 1948 (Released:2009-02-05)

参考文献数

3

被引用文献数

1 1

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In a medium which consists of numerous small particles of transparent substance, like snow, fog and cloud, the intensity of radiation, passing through it, decreases. However, there is a question, if the rate of decrease obeys an exponential law, as was expected by many investigators. In this regard, Dietzius, in 1922, obtained equations: solving Schuster's equations and tried to discuss the decrease of brightness in fog. In the above equation, A0 means intensity of incident radiation at x=0 and A intensity of radiation advancing to x direction at the point x and B that of radiation returning backwards by the effect of diffuse reflexion of the part of the medium ahead. And, 2_??_ means a coefficient of diffuse reflexion of the medium, h its thickness, and μ the albedo at the base (x=h).The present writer investigated the value of γ and β, when the medium is not homogeneous, that is, (1) when(2) when the medium consists of two layers, whose coefficients are _??_ and _??_ respectively.In the case (1), the decrease of the radiation is no more linear, but parabolic.In the case (2), we can show that the relationshold, where A', B' are the proceeding and backing radiation in the second medium, whose coefficient is _??_; A'h'_??_ advancing radiation at the boundary of two layers; h' the thickness of the first medium; and the other notations are same as before. The above equations contain only _??_, and independent of _??_, so they fit _??_or computation of _??_ from experimental data. After we have got _??_ by use of _??_e above relation, then we can use the following relations for the first medium, where μ* meansThe relations (4) may enable us to calculate the value of _??_ This method will be also applied to the medium which consists of more than two layers and will be extended further to the medium whose coefficient changes continuously, if we divide the whole layer into many thin strata and carry out the above procedure for each stratum.Returning to the case of the uniform medium, the radiation, which reaches the base, is obtained, put ng x=hin the equation (1), viz.This means, _??_h depends on μ extraordinarily, and in the extreme case, μ=1, _??_h becomes 1. In the other words, if we place a mirror at the base of a fog stratum, the incident ray at the top, after passing through it, reaches the mirror without any drop in its strength. This is far beyond our imagination based upon experience. Such a misleading conclusions may come from the unnatural assumption of no absorptive power in the medium.Let us take absorption into account, and put From this equation we get, under the same boundary condition for the uniform medium, where At x=0, we have and at x=h, we haveWhen _??_ is large enough, we have for smaller value of x, that is, at the portion near the surface; for the value of x not considerably different from h that is, at the portion near the base plane.These equations (11), (12) teach us the-following facts in the case of fog, for example. If the fog layer is sufficiently thick, the decrease at the top portion obeys exponential law, while at the base (that is at the ground), the intensity changes linearly.From the equation (11), we getWe must take special care in treating with the surface condition, as will be shown in another article. However, we may think that β0 is an approximate value of albedo of the fog (and also, of the cloud). As we see, β0 and accordingly the albedo does not depend on absolute values of k and _??_, but on, their ratio k/_??_ Also, we have to remark, that β0 has no dependence upon μ the albedo of the base, against Dietzius' solution (1).It is also interesting to consider about the condition at the base.

著者

山中 大学 田中 浩

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.62, no.1, pp.1-17, 1984 (Released:2007-10-19)

参考文献数

32

被引用文献数

22 25

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中層大気中に存在する薄い乱流層の成因の一つという観点から, 対流圏起源の慣性内部重力波の臨界高度砕波を理論的に吟味してみた。Coriolis力による慣性効果は長周期または長波長の内部重力波については無視できないものである。基本場の鉛直シアーと Coriolis因子を一定とした慣用の非粘性線形方程式系から慣性内部重力波を表わす厳密解が導かれ, さらに Olver(1974)が拡張した Liouville-Green 法を用いて臨界高度近傍での正しい局所分散関係式を得た。この関係式から慣性内部重力波の重要な特徴として, Jones臨界高度の「弁効果」, および, 上下の臨界高度の内側の一対の「転移高度」の存在, の二つが見出された。類似の特徴は, 無限小シアーと水平方向の異方性とを仮定する系について過去に指摘されているが (Grimshaw, 1975, 1980), それらの仮定は弁効果と転移高度の存否に関する限り本質的なものではないと言元る。弁効果と転移高度との複合作用の結果として慣性内部重力波は Jones臨界高度近傍で波面の走向に依存した吸収また反射を受ける。すなわち吸収率および吸収に伴う砕波乱流層の厚さは波面の走向が東西に向うほど増大し, 一方波面が南北に沿うような波は実質的に反射される。基本場の Richardson 数が大きいと転移高度はそれぞれ臨界高度に近接するため, 両臨界高度の内側の乱流層は外側のそれよりもずっと薄くなる。以上のすべての特性は Jones 臨界高度近傍のある領域内でのみ起こり, その外部ではよく知られた非慣性内部重力波と本質的に同じ特性が得られる。この領域はCoriolis 因数に比例した厚さを持ち, 非慣性内部重力波では完全に消失してしまう。現実の成層圏乱流層との比較さらに中間圏以高まで達する重力波の定量的情報としての活用を考え, 慣性内部重力波とその砕波乱流層の厚さとの関係を表わす式を具体的に導いた。メソスケール領域の水平波長を仮定する場合, 慣性内部重力波のつくる乱流層は非慣性波のそれに比べて薄くなる。

著者

高村 民雄 田中 正之 中島 映至

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.62, no.3, pp.573-582, 1984 (Released:2007-10-19)

参考文献数

16

被引用文献数

16 17

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エアロソルによる散乱光強度の角度分布の情報から,エアロソルの複素屈折率及び粒径分布が,Inversionlibrary法を用いて,求められてきた。ここでは,1978年2月から11月に至る,仙台•青葉山での250の観測例から,これらの粒子の光学的性質の湿度依存性についてまとめた。この期間のデータを一定の湿度範囲毎に分類してみると,エアロソルの光学的性質に,湿度に対する顕著な依存性のあることが明らかとなった。この依存性を説明する為に,Hänelの理論を適用した。この時,粒子の乾燥状態での複素屈折率を1.58-0.04iとし,質量増加係数を屈折率の観測値から推定した。この値は,これまでの他の結果と比較して,妥当なものである。これらの結果を確認する為に,実際の大気を用いて,数例の加湿実験を行なった。その結果は,2月から11月までの観測から得られた傾向を支持するものであった。

著者

KUSUNOKI Kenji UENO Kenichi

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

pp.2022-047, (Released:2022-08-25)

被引用文献数

3

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Nocturnal temperature inversion (NTI) is an important factor characterizing the local climate in mountainous areas. In central Japan, most of the mountain slopes are covered by forests, but the effects of their leaf expansion/fall on the NTI variations in basins have not been clarified. According to a three-year leaf area index (LAI) observation in the mixed forest of the Sugadaira Highland (1320 m a.s.l.), Nagano Prefecture, Japan, we identified weakening of the NTI associated with leaf expansion and strengthening after leaf fall in a small basin. Using digital elevation and land-cover data, we defined the distribution of the deciduous and mixed forests in the catchment area of nocturnal cold air drainage. The estimated timings of leaf expansion/fall at the catchment scale based on the effective cumulative temperature almost coincided with the NTI changes. Micrometeorology observations showed that NTI at the forest floor and downslope winds at the adjacent grassland strengthened during the dormant (leafless) season in the nighttime when the radiative cooling is strong. Calm and clear nights were chosen during the spring dormant season and the summer growing season for 22 and 30 nights, respectively. The heat loss during the cold-air pool development was estimated, and converted to storage heat flux in the forest areas. The storage heat flux was 3.8 W m−2 more on average in the growing season than the dormant season, and it was less than that of forests estimated in previous studies (several 10 W m−2), indicating that an increase in storage heat flux of the forests with leaf expansion could cancel nocturnal radiative cooling and weaken gravity currents at the forest floor.

著者

Yayoi HARADA Hirotaka KAMAHORI Chiaki KOBAYASHI Hirokazu ENDO Shinya KOBAYASHI Yukinari OTA Hirokatsu ONODA Kazutoshi ONOGI Kengo MIYAOKA Kiyotoshi 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.94, no.3, pp.269-302, 2016 (Released:2016-07-02)

参考文献数

54

被引用文献数

261 329

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This study investigates the quality of the Japanese 55-year Reanalysis (JRA-55), which is the second global reanalysis constructed by the Japan Meteorological Agency (JMA), by comparing it with other reanalyses and observational datasets. Improvements were found in the representation of atmospheric circulation on an isentropic surface and in the consistency of momentum budget based on the mass-weighted isentropic zonal mean method. The representation of climate variability in several regions was also examined. In the tropics, the frequencies of high spatial correlations with precipitation, which were estimated using the Tropical Rainfall Measuring Mission Multisatellite Precipitation Analysis, are clearly higher in JRA-55 than in JRA-25. The results indicate that JRA-55 generally improved the representations of phenomena on a wide range of space-time scales, such as equatorial waves, and transient eddies in the storm track regions, compared with JRA-25 during the satellite era. Moreover, JRA-55 improved the temporal consistency compared with the older reanalyses throughout the reanalysis period. In the stratosphere, we found larger discrepancies between reanalyses for the extra-tropical stratosphere during the Southern Hemisphere (SH) winter. Comparisons with radiosonde temperature revealed that JRA-55 has a smaller bias in temperature than the other reanalyses in the extra-tropical SH winter before 1979. Some issues in JRA-55 were also identified. The amplitude of equatorial waves and Madden-Julian oscillation in JRA-55 are weaker than in the other reanalyses. JRA-55 shows unrealistic strong cooling in South America and Australia, although the spatial distribution of the long-term temperature trends in JRA-55 is the closest to an observational dataset of global historical surface temperature.

著者

山田 広幸 伊藤 耕介 坪木 和久 篠田 太郎 大東 忠保 山口 宗彦 中澤 哲夫 長浜 則夫 清水 健作

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.1297-1327, 2021 (Released:2021-10-31)

参考文献数

97

被引用文献数

11

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2017年台風第21号(ラン)対する上部対流圏の航空機観測を、新たに開発したドロップゾンデシステムを備えた民間ジェット機を用いて行った。これは、日本の研究グループがドロップゾンデを用いて非常に強い台風の内部コアを観測した初めての事例である。本論文では、目の暖気核構造と、それに関連するアイウォールの熱力学的および運動学的特徴について記述する。この台風は観測の2日間において、鉛直シアーが強まる環境で最大の強度を維持した。ドロップゾンデにより、この期間に対流圏中層と上層に温位偏差の極大をもつ二重暖気核構造が維持されたことが捉えられた。この2つの暖気核は相当温位が10 K以上異なり、起源が異なることが示唆された。飽和点分析により、上部暖気核の空気はアイウォールから流入したことが示唆された。鉛直シアーベクトルの左半円側におけるアイウォール上昇気流は、台風の中心側で相当温位が高く絶対角運動量が低い2層の構造を持っていた。飽和点とパーセル法の分析から、この中心側の上昇気流で相当温位が370Kを超える暖かい空気が目の境界層から流入し、最終的に上部暖気核に輸送されることが示唆された。これらの結果から、目の境界層を起源とする高い相当温位の空気の鉛直輸送が、鉛直シアーによる台風強度への負の影響に対抗して、上部対流圏の目の継続的な昇温に寄与するという仮説が導かれた。この研究は、相当温位の計算に必要な温度と湿度の測定が、ドロップゾンデのような消耗型の機器でしか行えない現状において、アイウォール貫通型の上部対流圏航空機観測が暖気核構造の監視に重要であることを示している。

著者

TSUYUKI Tadashi TAMURA Ryosuke

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.2022-027, (Released:2022-02-22)

被引用文献数

4

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Recent progress in the particle filter has made it possible to use it for nonlinear or non-Gaussian data assimilation in high-dimensional systems, but a relatively large ensemble is still needed to outperform the ensemble Kalman filter (EnKF) in terms of accuracy. An alternative ensemble data assimilation method based on deep learning is presented, in which deep neural networks are locally embedded in the EnKF. This method is named the deep learning-ensemble Kalman filter (DL-EnKF). The DL-EnKF analysis ensemble is generated from the DL-EnKF analysis and the EnKF analysis deviation ensemble. The performance of the DL-EnKF is investigated through data assimilation experiments in both perfect and imperfect model scenarios using three versions of the Lorenz 96 model and a deterministic EnKF with an ensemble size of 10. Nonlinearity in data assimilation is controlled by changing the time interval between observations. Results demonstrate that despite such a small ensemble the DL-EnKF is superior to the EnKF in terms of accuracy in strongly nonlinear regimes and that the DL-EnKF analysis is more accurate than the output of deep learning due to positive feedback in assimilation cycles. Even if the target of training is an EnKF analysis with a large ensemble or a simulation by an imperfect model, the improvement introduced by the DL-EnKF is not very different from the case where the target of training is the true state.

著者

Boqi LIU Congwen ZHU Jingzhi SU Shuangmei MA Kang XU

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.4, pp.913-925, 2019 (Released:2019-08-02)

参考文献数

50

被引用文献数

16 33

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The northward shift of the Western North Pacific Subtropical High (WNPSH) in July 2018 broke the historical record since 1958 and resulted in extreme heat waves and casualties across Northeast Asia (NEA). In the present work, we associated this extreme WNPSH anomaly with the anomalies of barotropic anticyclone above NEA originating from the strongest positive tripole pattern of sea surface temperature anomaly (SSTA) in the North Atlantic in July. Both data analysis and numerical experiments indicated that the positive tripole SSTA pattern could produce an upper-tropospheric wave source over Europe, which stimulated an eastward propagating wave train along the subpolar westerly jet over the Eurasian Continent. When its anticyclonic node reached NEA, the WNPSH started to shift northward. After the cyclonic node in the circulation anomaly encountered the Tibetan Plateau (TP), atmospheric diabatic heating was enhanced over the eastern TP, initiating another subtropical wave train, which furthered the northward shift of the WNPSH. Therefore, the wave source over Europe was critical for the northward shift of the WNPSH in July, connecting the tripole SSTA pattern in the North Atlantic with the WNPSH anomaly and maintaining the downstream effects of thermal forcing over the eastern TP on the East Asian summer monsoon.

著者

菊地 勝弘 遊馬 芳雄 谷口 恭 菅野 正人 田中 正之 早坂 忠裕 武田 喬男 藤吉 康志

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.71, no.6, pp.715-731, 1993-12-25 (Released:2009-09-15)

参考文献数

7

被引用文献数

1 2

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冬季の海上の層積雲の雲頂の構造と反射率の関係を調べるために、航空機によるステレオ写真観測法を使った観測が1989年1月から1991年1月にわたって、日本海の若狭湾沖および奄美諸島周辺の太平洋上で行われた。最初に、雲頂高度と反射率との間の関係が調べられ、両者の間にはかなりよい相関が認められた。特に奄美諸島周辺での観測では高い相関が認められた。次にCloud area ratio(雲の領域率)と雲頂の反射率との関係が調べられた。その結果、低い反射率の雲域では雲頂高度が比較的低くて雲層が薄く、また、その高度差は大きく、雲頂の形状は鋸の歯のように鋭かった。一方、高い反射率の雲域では雲頂高度が高くて雲層が厚く、そして一様で形状は平で台形のような形をしていた。しかし、奄美諸島北部の例では、雲頂高度が他の2例に比して低く、しかも最高雲頂高度と最低雲頂高度との高度差が400m以上もある層積雲であったにもかかわらず、その反射率は比較的高かった。この反射率の違いはliquid water pathの差によるものと推定される。

著者

JIA Li REN Fumin DING Chenchen JIA Zuo WANG Mingyang CHEN Yuxu FENG Tian

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.2022-029, (Released:2022-03-10)

被引用文献数

7

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The Dynamical–Statistical–Analog Ensemble Forecast model for landfalling typhoon precipitation (the DSAEF_LTP model) identifies tropical cyclones (TCs) from history data that are similar to a target TC, and then assembles the precipitation amounts and distributions of those identified to obtain those of the target TC. Two original ensemble methods in the DSAEF_LTP model, mean and maximum, tend to under- and over-forecast TC precipitation, respectively. In addition, these two methods are unable to forecast precipitation at stations beyond their maxima. To overcome the shortcomings and improve the forecast performance of the DSAEF_LTP model, the following five new ensemble methods are incorporated: optimal percentile, fuse, probability matching mean, equal difference-weighted mean, and TSAI (Tropical cyclone track Similarity Area Index)-weighted mean. Then, model experiments for landfalling TCs over China in 2018 are conducted to evaluate the forecast performance of the DSAEF_LTP model with the new ensemble methods. Results show that the overall performance of the optimal percentile (the 90th percentile) ensemble method is superior, with the false alarm rate lower than that of the original ensemble methods. As compared to five operational numerical weather prediction models, the improved DSAEF_LTP model shows advantages in predicting accumulated rainfall, especially with the rainfall of over 250 mm. When implementing the experiments, above results, however, it is found that the model forecast performance varies, depending on the type of TC tracks. That is, the accumulated rainfall forecast for westbound TCs is significantly better than that of northbound TCs. To address this issue, different schemes are used to forecast the accumulated rainfall of TCs with the two different track types. The precipitation forecast performance for westbound and northbound TCs, using the 90th percentile and the probability-matched ensemble mean ensemble method, respectively, is much better than that using a single ensemble method for all the TCs.

著者

筆保 弘徳 吉田 龍二 山口 宗彦 永戸 久喜 室井 ちあし 西村 修司 別所 康太郎 及川 義教 小出 直久

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.1, pp.61-72, 2020 (Released:2020-03-26)

参考文献数

36

被引用文献数

1 5

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本研究は、2009年から2017年にかけて北西太平洋で発生した熱帯低気圧(TC)において、トロピカルストームの強度に発達する前に減衰した熱帯低気圧(TD)の特性と環境場の条件を調査した。特に、大規模な流れパターンと関連させて、トロピカルストームの強度まで発達した熱帯低気圧(TS)と比較した。流れパターンは以下の5つに分類した。シアライン(SL)、東西風合流域(CR)、モンスーンジャイア(GY)、偏東風波動(EW)、および既存のTCからのロスビー波応答で発生したパターン(PTC)である。ベストトラックデータと早期ドボラックデータを用いて、476例のTC事例のうち、263例のTDが検出された。CRまたはPTC(EW)のパターンで発生したTCは、他のパターンと比較してトロピカルストームの強度に達する(達しない)割合が多い。夏と秋のCR、GY、およびEW(PTC)のTDの平均位置は、同じパターンのTSよりも西(東および北)に偏っていた。TDの周囲の環境場パラメータはTSよりも発達に不向きな傾向があり、CR、EW、PTC(SL、GY、PTC)で大気(海洋)の環境場パラメータに有意な差がある。流れパターンで分類したトロピカルストームの強度に達するための環境場条件は以下のようにまとめられる。SLとGYはより高いtropical cyclone heat potential、CRはより弱い鉛直シア、EWはより湿潤な場、そしてPTCはより高い海面温度と先行のTCが強いことである。

著者

田中 博 野原 大輔 横井 みずほ

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.78, no.5, pp.611-630, 2000-10-25

被引用文献数

5

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本研究では、韓国のIce Valleyと福島県の中山風穴の現地観測結果を基に、0次元モデル、流路に沿った1次元モデル、鉛直断面としての2次元モデルを開発して、風穴循環の一連の数値シミュレーションを行なった。これらの風穴は、周辺の稀少な高山植物の生育により国の特別天然記念物に指定されているが、近年氷の減少傾向が見られ、その原因究明が急務となっている。現地観測および数値実験の結果として、以下のことが明らかになった。(1)風穴循環の主な駆動力は、外気と崖錘内部の気温差による水平圧傾度力である。(2)崖錘内部の空気の滞留時間は約2日であり、平均的な風穴循環は、約1mm/sと推定される。(3)春から夏にかけてのカタバ風としての冷風穴循環は、秋から冬にかけてのアナバ風としての温風穴循環と入れ替わる。(4)崖錘表面に植生が殆どないIce Valleyの場合、夏季の安定したカタバ流とは対照的に冬季には不安定による対流混合が発生し、このような風穴循環の夏冬非対称性が、崖錘内部の平均温度を下げる熱フィルターの役割を果たす。外気が暑ければ暑いほど、崖錘内部のカタバ風が強くなることは注目に値する。Ice Valleyや中山風穴における夏期氷結の謎は、部分的ではあるが、この風穴循環のメカニズムによって説明することができる。

著者

ブランド サムソン

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.50, no.4, pp.332-341, 1972

被引用文献数

37

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24年間(1945-1968)に亘る資料を用い,台風並みの強さをもつ巨大及び微少熱帯低気圧の地理的及び季節的変動をしらべた.<br>これらじょう乱の性質については,何れも,地理的及び,季節的傾向があることが,はっきりと認められた.

著者

HUANG Huei-Ping RAGHUNATHAN Girish Nigamanth

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.2022-012, (Released:2021-11-02)

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Retrograde long waves in the higher latitudes of Northern Hemisphere can episodically attain large amplitudes and sustain coherent phase propagation for 2-3 weeks. The potential influence of such waves on extended-range weather forecast has been conjectured but not systematically quantified. Using a set of ensemble reforecast data, this study examines the predictability associated with an extraordinary retrograde-wave episode in the 1979-80 winter. Quantified by the anomaly correlation of 500 hPa geopotential height in the 40°N-70°N latitudinal band, increased week-2 predictability is found within the sub-period with the presence of coherent retrograde waves. Some individual forecasts made within the retrograde-wave event exhibit the behavior of “return of skills”. The results suggest a future investigation into the relation between the uptick of anomaly correlation in week-2 and detailed dynamics of the retrograde waves.

著者

CHANG Yi MA Qianrong GUO Lijun DUAN Jing LI Jun ZHANG Xiaopeng GUO Xueliang LOU Xiaofeng CHEN Baojun

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.2022-003, (Released:2021-09-30)

被引用文献数

5

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Meiyu front precipitation makes the region prone to frequent floods, mudslides, landslides, and other disasters, and has been the focus of ongoing and challenging meteorological research. Raindrop size distribution (RSD) is a fundamental method for exploring the characteristics and physical processes of rainfall. This study investigated the precipitation characteristics in Lushan mountainous areas during the Meiyu season using laser disdrometer observed RSD data from 2016 to 2019. For the average spectra of five rain rate classes, the concentrations of large raindrops (> 0.5 mm) increased with rain rate (R), while the concentrations of small raindrops (< 0.5 mm) increased only under rain rates higher than 10 mm h−1. The gamma distribution parameters of N0 and Λ increased/decreased with rain rate, and μ exhibited negative values in different rain rate classes. The distribution pattern features were N (D) = 721D−1.79e−1.20D. Distributions of the frequency for mass-weighted mean diameter (Dm) and the logarithm of the generalized intercept parameter (log10Nw) both showed a unique bimodal type, and an exceptionally high Nw (log10Nw > 4.5) subset with small Dm was determined. The stratiform and convective rain of RSD were also investigated. Dm − R and Nw − R showed similar variations in two types of precipitation. The lower μ values resulted in higher primary and constant coefficients in the quadratic polynomial fitting for the μ − Λ relationship (Λ = 0.0347μ2 + 1.180μ + 2.495). The Z − R relationship in stratiform precipitation characteristics was Z = 203R1.59. Further investigations showed that high Nw values usually occurred in persistent precipitation. The RSD can be characterized as high concentrations of the first two diameter classes with narrow spectrum width (< 1 mm), which were captured during in-cloud rain with a low but continuous rain rate (< 5 mm h−1). The mountainous topography plays an important role in reshaping the characteristics of RSD and the physical processes of precipitation.

著者

中井 専人 山下 克也 本吉 弘岐 熊倉 俊郎 村上 茂樹 勝島 隆史

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.45-56, 2022 (Released:2022-02-23)

参考文献数

34

被引用文献数

2

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Xバンド水平偏波レーダー反射因子(Zh)と降雪強度水当量(R)の関係式を6種類の固形降水粒子種(クラス)について示す。これらの関係式は、日本の新潟県における同時観測によって得られたZh、R、及び降水粒子種を比較することによって求められた。式の形はZh = B R1.67を仮定し、Bを観測により決定される係数とした。Rの値と降水粒子種は、それぞれ、風よけネット内に設置された高分解能降水強度計と光学式ディスドロメーターを用いて求められた。平均Zhは地上観測点風上側に位置する約100 km2の解析領域について求められた。3冬季にわたる48事例について、卓越する降水粒子種、代表的な粒径と落下速度、Zh、R、Bの平均値が得られた。濃密雲粒付雪片のBの平均値は雲粒付雪片の値より小さかった。最も大きなBの値は雲粒無し樹枝状結晶の雪片(unrimed-Dクラス)の事例について、最も小さいBの値は雲粒無し低温型結晶の雪片(unrimed-Cクラス)が降っていた事例について得られた。霰事例のBの平均値は、雲粒付及び濃密雲粒付雪片の値に対して大まかに2倍程度であり、unrimed-Dクラスの値よりも小さかった。Xバンドにおいては、雪片の単位降水強度あたりの後方散乱が霰よりも強いか弱いかは、ライミングの程度と構成雪結晶の種類に依存していた。

著者

SHIBATA Kiyotaka NAOE Hiroaki

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.2022-001, (Released:2021-09-30)

被引用文献数

1

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Decadal variations of the quasi-biennial oscillation (QBO) in the equatorial stratosphere are investigated, using the Singapore data and reanalysis data from 1950s to 2019/2020. It is found that the QBO is decadally modulated in the amplitude as well as in the period. These two decadal variations are positively correlated with each other after 1980s, while they show approximately negative correlation before 1980s. In the time series of the QBO amplitude from 1950s to 2014, there are four maxima (QBOmax) around 1967, 1983, 1995, and 2005, and three minima (QBOmin) around 1973, 1988, and 2000. Composite analyses of QBOmax and QBOmin based on these extrema reveal that the decadal amplitude variations have maximum amplitude of about 3 m s−1 at 20 hPa in the vertical. In the horizontal structure there appear off-equator extrema of about 3.5 m s−1 around 5°N at 20 hPa, while at 50 hPa extrema of about 1.8 m s−1 are situated around 5°S. The decadal amplitude variations of the QBO are closely and positively correlated with the decadal components of Niño 3.4 sea surface temperature anomalies (SSTa) and Pacific decadal oscillation (PDO) index, suggesting that the tropical SSTa in the central Pacific substantially influences the QBO in the decadal time-scales.

著者

STEPPELER Jürgen LI Jinxi FANG Fangxin ZHU Jiang

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.2021-077, (Released:2021-09-09)

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The spectral element (SE) and local Galerkin (LG) methods may be regarded as variants and generalizations of the classic Galerkin approach. In this study, the second-order spectral element (SE2) method is compared with the alternative LG scheme referred to as o2o3 that combines a second-order field representation (o2) with a third-order representation of the flux (o3). The full name of o2o3 is o2o3C0C1, where the continuous basis functions in C0-space are used for the field representation and the piecewise third-order differentiable basis functions in C1-space are used for the flux approximation. The flux in o2o3 is approximated by a piecewise polynomial function that is both continuous and differentiable, in contrast to many Galerkin and LG schemes that use either continuous or discontinuous basis functions for flux approximations. We show that o2o3 not only has some advantages of SE schemes but also possesses third-order accuracy similar to o3o3 and SE3, while SE2 possesses second-order accuracy and does not show superconvergence. SE3 has an approximation order greater than or equal to three and uses the irregular Gauss-Lobatto collocation grid, while SE2 and o2o3 have a regular collocation grid; this constitutes an advantage for physical parameterizations and follow-up models, such as chemistry or solid-earth models. Furthermore, o2o3 has the technical simplicity of SE2. The common features (accuracy, convergence and numerical dispersion relations) and differences between these schemes are described in detail for one-dimensional homogeneous advection tests. A two-dimensional test for cut cells indicates the suitability of o2o3 for realistic applications.