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

Joseph Q. Basconcillo Ger Anne W. Duran Aaron A. Francisco Rusy G. Abastillas Flaviana D. Hilario Edna L. Juanillo Ana Liza S. Solis Anthony Joseph R. Lucero Shalou-Lea A. Maratas

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.13, pp.114-119, 2017 (Released:2017-06-28)

参考文献数

21

被引用文献数

4 9

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To overcome the limitation of low network density and sparse distribution of meteorological stations, spatial interpolation is being performed for estimating meteorological variables that are not geographically covered by existing observation network. While there are several readily available spatial interpolation techniques, it is still difficult to determine which one best estimates actual observation. Considering the stimulus for disaster risk reduction, hydrological, agricultural, and other applications of interpolated data, this study compared six interpolation techniques (Inverse Distance Weighted (IDW), Completely Regularized Spline (CRS), Tension Spline (TS), Ordinary Kriging (OK), Universal Kriging (UK), and ANUSPLIN) that have been recommended in tropical maritime region. Validation results comparing historical monthly and interpolated rainfall data from 1981-2010 in 65 stations in the Philippines show that OK has the best performance among the aforementioned techniques followed by ANUSPLIN and TS. Ultimately, this study is a contribution to the existing inadequate literatures that have documented and evaluated interpolation techniques that can be used in archipelagic regions with prominent climate variability.

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 35

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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

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.

著者

和田 章義

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

vol.99, no.6, pp.1453-1482, 2021 (Released:2021-12-16)

参考文献数

81

被引用文献数

5

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2018年、日本に上陸した台風チャーミーは進路転向後に急衰弱した後、数日間その強さを維持した。続いて台風コンレイはチャーミーによって冷やされた海域を急衰弱しつつ通過した。これら2つの台風が急衰弱した海域は、海洋中規模渦が豊富な海域である。これら2つの台風の強度変化における冷水渦の役割とその類似点及び相違点を理解するため、2km水平解像度非静力学大気モデルと大気波浪海洋結合により数値シミュレーションを実施した。また冷水渦の強度を観測により確証できないため、チャーミーの弱化に有意に寄与する規模を仮定した人工冷水渦を埋め込んだ海洋初期値及び日付の異なる海洋初期値を用いた感度実験を実施した。コンレイに対しては、日付の異なる海洋初期値の代わりに、9つの大気初期値に対するアンサンブルシミュレーションを実施した。2つのシミュレートされた台風の急衰弱における海洋場の役割は、どちらも台風通過時の海水温低下による海洋貯熱量の低下と関係していた。チャーミーとコンレイに対するシミュレーション結果のほとんどは、成熟期または衰退期の期間、過剰発達傾向を示した。チャーミーの過発達は不十分な海面水温低下により生じており、人工冷水渦は海水温低下の促進を助長した。一方でコンレイの過発達は台風進路シミュレーションの失敗に関連していた。コンレイの進路が適切にシミュレートされることにより、コンレイはより多くの時間、海水温低下域上を移動することとなり、鉛直シア上流側における地表面付近及びインフロー境界層、台風中心への内部コア域における水蒸気輸送の減少を通じて、弱化を強めることとなった。2つの台風に見られた共通点として、中心における下降流と関連する断熱加熱の減少が台風弱化と密接にかかわっていた。

著者

IKUTA Yasutaka FUJITA Tadashi OTA Yukinari HONDA Yuki

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.2021-076, (Released:2021-09-14)

被引用文献数

11

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The regional data assimilation system at the Japan Meteorological Agency employs a variational data assimilation system on the basis of the non-hydrostatic model ASUCA (named ASUCA-Var). This paper reviews configurations and the current status of ASUCA-Var. To consider the consistency of analysis and prognostic variables, the control variables of ASUCA-Var include soil variables and basic atmospheric variables. The background-errors based on the control variables are calculated every three hours for land and sea grid points to better reflect the representative error covariance structure, taking into account daily variations and differences in structure on land and sea. Although the cost function is designed to be a perfect quadratic form, the basic field update method in the optimization process allows the nonlinearity of the observation operator and numerical weather prediction model to be incorporated into the solution of optimization problem in the incremental four-dimensional variational (4D-Var) method. The outer/inner models used in the incremental 4D-Var method are based on ASUCA, with suitable configurations according to each resolution and applied linearization. Observation operators are implemented for various kinds of observations used, with unified interfaces encapsulating external simulators. Variational quality control and variational bias correction are also introduced for advanced observation handling within the variational system. Parallelization is introduced to enhance computational efficiency, including adjoint calculations. To assess the impact of assimilated observations, degrees of freedom for signal are also available. In addition, as a system for operational use, ASUCA-Var is designed for sustainable development. The meso-scale analysis and local analysis workflows are presented as operational implementations of ASUCA-Var. ASUCA-Var improves forecasting in a wide range of validation indices. The major future improvements of ASUCA-Var include the introduction of the flow-dependent background-error and the extension of the control variable to hydrometeors, which are expected to enhance the prediction accuracy of the operational regional model.

著者

TAKAMURA Tamio KHATRI Pradeep

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.2021-075, (Released:2021-09-06)

被引用文献数

1

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A rotating shadow-band spectro-radiometer system is a powerful tool for surveying light in the environment. It can provide the following spectral components of the solar irradiance without using any traditional solar tracking tool: direct normal irradiance (spDNI), diffuse horizontal irradiance (spDHI), and global horizontal irradiance (spGHI). Both irradiances, spDNI and spDHI, are derived from the combination of spGHI observations at different shadow-band positions. The shadow-band system induces basic errors caused by the imperfect corrections of the diffuse irradiance shadowed by band. To restrict the basic errors to within 2 %, the band slant-angle should be within 72 deg for a usual operating condition of the MS-700 spectro-radiometer manufactured by EKO Instruments Co., Ltd. with the MB-20 shadow-band system for MS-700. The errors in the spDNI and spDHI estimation are evaluated quantitatively by using realistic models that consider instrumental and atmospheric conditions. Estimates of spDNI can result in optical depth errors. The relative error in this estimation is described by using a correction coefficient Cfwd defined by the ratio of the true diffuse irradiance simulated by the shadowed irradiance to the approximate value observed. The value of Cfwd depends on the magnitude of the aerosol optical depth as well as the aerosol type. This error analysis should help to improve the accuracy of this system of measurements.

著者

YANG Wen-Ting FU Shen-Ming SUN Jian-Hua ZHENG Fei WEI Jie MA Zheng

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.2021-074, (Released:2021-09-09)

被引用文献数

7

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At present, satellite-derived precipitation estimates have been widely used as a supplement for the real precipitation observation. Detailed evaluations of a satellite precipitation estimate are the prerequisite for using it effectively. Based on the daily precipitation observation from 91 rain gauges throughout Thailand during a 15-yr period, this study evaluated the performances of daily precipitation data of CMORPH and TRMM (3B42 version 7) in an interpolating-grid-points-into-stations manner. This filled in the deficiencies of the current evaluations of TRMM-3B42v7's performances over Thailand, made the first evaluation of CMORPH in this region, and showed the first report of relative performances of two datasets. For the entire Thailand, a total of 35 factors (including precipitation intensity, spatial distribution pattern, duration/interval) was used in the evaluation. It is found that only 12 of them (including annual and monthly variations of precipitation, conditional rain rate in rainy season, rainfall interval in entire year, non-precipitation days, etc.) were reproduced credibly (i.e., relative error was less than 20 %) by the two datasets. Both TRMM-3B42v7 and CMORPH displayed similarly poor performances in representing intensity and spatial distribution of extreme precipitation. Comparisons based on the 35 factors indicate that TRMM-3B42v7 displayed a better overall performance than CMORPH for the entire Thailand.  For each region of Thailand, CMORPH/TRMM-3B42v7 showed different performances in different regions (a total of 19 factors was used). The CMORPH/TRMM-3B42v7 data made credible estimates over all five regions of Thailand in terms of daily precipitation intensity and monthly variation of precipitation, whereas, in terms of precipitation day fraction, conditional rain rate during dry season, and interval/duration of rainfall events during the rainy season, it showed notable errors in all regions. Overall, TRMM-3B42v7 exhibited superior performances to CMORPH for the North, Northeast, East, and South of Thailand, whereas, CMORPH and TRMM-3B42v7 displayed similar performances for the Central Thailand.

著者

ARIAS Ivan CHANDRASEKAR V.

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.2021-069, (Released:2021-08-12)

被引用文献数

3

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The cross-validation of radars in a network is important in making consistent retrievals across the domain and assuring the product quality. During the RELAMPAGO field campaign, two C-band radars, namely the Colorado State University C-band Hydrological Instrument for Volumetric Observations (CSU-CHIVO) and the C-band Scanning ARM Precipitation Radar (CSAPR-2), were deployed near the Sierras de Cordoba in Argentina, a region known for having some of the most intense severe weather in the world. In addition to these two radars, the operational radar of the Cordoba City, the Radar Meteorologico Argentino 1 (RMA-1), adds another instrument to the RELAMPAGO network. This study presents an intercomparison between the RELAMPAGO C-band radars using the GPM spaceborne radar as a common reference. A method to bring ground-based radars into better agreement is also proposed. Moreover, the attenuation correction for the C-band radar is studied in the context of intercomparing two radars. The attenuation coefficients are computed for the RELAMPAGO domain using the local disdrometers deployed during the campaign. After the attenuation correction, CSU-CHIVO, CSAPR-2, and RMA-1 compare well with GPM-DPR with a high correlation and bias less than 1 dB.

著者

Chao WANG Liguang WU Haikun ZHAO Qingyuan LIU Ji WANG

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

vol.99, no.6, pp.1413-1422, 2021 (Released:2021-12-16)

参考文献数

46

被引用文献数

2

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Translation speed is an important factor determining locally accumulated disasters induced by tropical cyclones (TCs). We found that the basin wide TC translation speed over the western North Pacific (WNP) in the late season (October–December) experienced an abrupt decrease in the early 1980s. However, this slowdown cannot be explained by the previously proposed deceleration in large-scale steering. In this study, we demonstrated that this slowdown results from the decreased proportion of subtropical TC track frequency in the early 1980s. Because late-season large-scale steering flow in the subtropical WNP is much greater than that in the tropical WNP, TCs influencing the subtropical WNP generally hold greater translation speed than that of TCs staying in the tropical WNP. Thus, a decrease in the ratio of subtropical TC track frequency can lead to a notable decrease in the basin wide TC translation speed. The decreased ratio of subtropical TC track frequency results from the strengthened southwestward steering and the reduced ratio of TC genesis in the tropical eastern WNP, which is linked to a WNP anticyclonic circulation that appears to be driven by the Atlantic Multi-decadal Oscillation. The result introduces the crucial role of TC track shift in the basin wide TC translation speed and has important implications for understanding the effects of climate change on TC translation speed.

著者

S. Manabe

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.34, no.6, pp.308-320, 1956-12-25 (Released:2007-10-19)

参考文献数

15

被引用文献数

17 20

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whether does the heat released by condensation actualy affect the large scale pattern or not? In order to answer this question, we examined the conservation of the potential vorticity and potential temperature in rainly regions for 12 hr period. At the same time, computing the 3-dimensional distribution of 12 hourly condensation by using the continuity relation of water vapour, we estimated the expected amount of the individual change of potential vorticity, and compared it with the observed one. As an example, a case of medium intensity of rainfall was taken, and it was found that the change of potential vorticity in the condensation region was small and hardly detectable. However, for the second case, when the extremely intense and large scale precipitation occurred, considerably large change of potential vorticity which has the same sense with the expected one is observed. Finally, the quantitative discussions about these two cases are performed.

著者

Yuji KITAMURA Akihiro HORI Toshimasa YAGI

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.91, no.5, pp.655-666, 2013 (Released:2013-11-29)

参考文献数

26

被引用文献数

5 9

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Wind tunnel experiments and large-eddy simulations for stable stratification are performed to specify flux Richardson number Rf and turbulent Prandtl number Pr as a function of gradient Richardson number Ri. We attempted to avoid self-correlation by using independent samples for the variables commonly contained in these nondimensional numbers and confirmed the dependence of Rf and Pr on Ri for 10−3 < Ri < 5. We found that Rf could exceed unity in a stable boundary layer under a developing stage, while the assumption of local energy balance violates for Rf > 1, which corresponds to negative production of turbulent kinetic energy. Nevertheless, the analysis of the TKE budget shows that the third-order term in the prognostic equation of TKE, which plays a role in the TKE transfer, can contribute to increase TKE despite negative TKE production. Therefore, TKE cannot be determined locally and the effects of TKE transfer must be taken into account in the region satisfying Rf > 1.