著者

Prashant KUMAR Rakesh GAIROLA 久保田 拓志 Chandra KISHTAWAL

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.3, pp.741-763, 2021 (Released:2021-06-14)

参考文献数

69

被引用文献数

9

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インド夏季モンスーン(ISM)期間中の正確な降雨量推定はインド亜大陸およびその周辺で最も重要な活動の一つである。宇宙航空研究開発機構(JAXA)は、Global Satellite Mapping of Precipitation(GSMaP)降雨プロダクトとして、全球客観解析データ等を補助データとして用いて計算した衛星プロダクトであるGSMaP_MVKや全球地上雨量計データで調整したGSMaP_Gaugeを提供している。本研究では、2016~2018年のISM期間で、インド南西部の州の1つであるカルナータカ州における高密度地上雨量計ネットワークを基準として、GSMaP降雨プロダクト(バージョン7)の日降雨量を検証する。さらに、本研究の主目的として、これらの高密度地上雨量計観測を、ハイブリッド同化法を用いてGSMaP降雨量に同化することで、最終的な降雨推定を改善する。ここで、ハイブリッド同化法は二次元変分(2D-Var)法とKalmanフィルタの組合せであり、2D-Var法を用いて地上雨量計観測を統合し、Kalmanフィルタを用いて2D-Var法の背景誤差を更新する。準備としての検証結果は、GSMaP_Gauge降雨量が北部内陸カルナータカ州(NIK)と南部内陸カルナータカ州(SIK)地域で十分な精度を持ち、西ガーツ山脈の地形性豪雨領域で大きな誤差を持つことを示唆する。これらの誤差はGSMaP_MVK降雨量の地形性豪雨領域でより大きかった。ランダムに選択した地上雨量計観測を用いたハイブリッド同化結果は、独立した地上雨量計観測と比較して、GSMaP_GaugeとGSMaP_MVK降雨量の精度を改善した。これらの日雨量における改善は地形性豪雨領域でより顕著である。GSMaP_MVK降雨プロダクトは、JAXAの運用処理において地上雨量計による調整が含まれていないので、より大きな改善を示した。また本研究は、Cressman法や最適内挿法と比較して、用いられた雨量計の数のインパクトに対するハイブリット同化法の優位性を示す。

著者

NAKAMURA Kenji

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.2021-035, (Released:2021-03-12)

被引用文献数

11

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The Tropical Rainfall Measuring Mission (TRMM) satellite was launched in 1997 and the observations continued for more than 17 years. The features of TRMM observation were as follows: (a) it followed a non-sun synchronized orbit that enabled diurnal variation of precipitation to be investigated, (b) it carried a precipitation radar and microwave and infrared radiometers, along with two instruments of opportunity in the form of a lighting sensor and a radiation budget sensor, and (c) it worked as a standard reference for precipitation measurements for other spaceborne microwave radiometers, which enabled global rain maps to be developed. For science, TRMM provided precise and accurate rain distributions over tropical and subtropical regions. The rainfall results are primarily important for the study of the precipitation climatologies, while the three-dimensional images of precipitation systems enabled the study of the global characteristics of precipitation systems. Technologically, the spaceborne rain radar onboard TRMM demonstrated the effectiveness of radars in space, while the combination with other rain observation instruments showed its effectiveness as a calibration source. Multi-satellite rain maps in which TRMM was the reference standard have been developed, and they became prototypes of the multi-satellite Earth observation systems. Based on the great success of TRMM, the Global Precipitation Measurement (GPM) was designed to expand TRMM's coverage to higher latitudes. The core satellite of GPM is equipped with a dual frequency precipitation radar (DPR) and a microwave radiometer. DPR consists of a Ku-band radar (KuPR) and a Ka-band radar (KaPR) and has a capability to discriminate solid from liquid precipitation. The period of the precipitation measurement with spaceborne radars extended to more than 23 years which may make it possible to detect the change of precipitation climatology related to change in the global environment. While TRMM's and GPM's accomplishments are very broad, this paper tries to highlight Japan's contributions to the science of these missions.

著者

YAMAJI Moeka KUBOTA Takuji YAMAMOTO Munehisa K.

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.2021-033, (Released:2021-02-17)

被引用文献数

8

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Reliability information of satellite precipitation products is required for various applications. This study describes and evaluates a reliability flag of the Global Satellite Mapping of Precipitation Near-Real-Time precipitation product (GSMaP_NRT). This flag was developed to characterize the reliability of GSMaP_NRT data simply and qualitatively by considering its algorithm characteristics. The reliability at each pixel is represented by any one of ten levels (10 being the best and 1 the worst) by considering three major factors: 1) “surface type reliability”—which takes into account that estimation of rainfall using passive microwave sensors is better over the oceans than over land and coastal areas; 2) “low-temperature reliability”—which takes into account the lower reliability due to surface snow cover in low-temperature conditions; and 3) “Moving Vector with Kalman Filter (MVK) propagation reliability”—which means that the reliability gets worse with the increase in time since the last overpass of the passive microwave sensor. To evaluate the utility of the reliability flag, statistical indices are calculated for each reliability level using gauge-calibrated ground radar data around Japan. It is found that the reliability flag represents the differences in GSMaP accuracy: the accuracy worsens as the reliability decreases. The GSMaP errors exhibit seasonal changes that are well represented by the ten levels of the reliability flag, indicating that the reliability flag can be used to catch seasonal variations in GSMaP accuracy due to changes in environmental factors. This study also raises the possibility of improving the reliability flag by using information related to heavy orographic rainfall. It is shown how the error features of heavy orographic rainfall differ from those of the total rainfall, and it is suggested that heavy orographic rainfall information can be utilized to further improve the reliability flag.

著者

CHENG Chiu Tung SUZUKI Kentaroh

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.2021-031, (Released:2021-02-18)

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The transport and removal processes of aerosol particles, as well as their potential impacts on clouds and climate, are strongly dependent on the particle sizes. Recent advances in computational capabilities enable us to develop sectional aerosol schemes for general circulation models and chemical transport models. The sectional aerosol modeling framework provides a capacity to explicitly simulate the variations in size distributions due to microphysical processes such as nucleation and coagulation, based on the mechanisms suggested from laboratory studies and field observations. Here, we develop a two-moment sectional aerosol scheme for Spectral Radiation-Transport Model for Aerosol Species (SPRINTARS-bin) for use in NICAM (Nonhydrostatic ICosahedral Atmospheric Model) as an alternative to the original mass-based (single-moment) SPRINTARS-orig aerosol module. NICAM-SPRINTARS is a seamless multiscale model that has been used for regional-to-global simulations of different resolutions based on the same model framework. In this study, we performed global simulations with NICAM-SPRINTARS-bin at typical climate model resolution (Δx ∼ 230 km) with nudging to a meteorological re-analysis. We compared our results with equivalent simulations for the original model (NICAM-SPRINTARS-orig) and observations including 500 nm aerosol optical depth and 440-870 nm Angstrom Exponent in AErosol RObotic NETwork (AERONET) measurements, particle number concentrations measured at Global Atmospheric Watch (GAW) sites and size-resolved number concentrations measured at European Supersites for Atmospheric Aerosol Research (EUSAAR) and German Ultrafine Aerosol Network (GUAN) sites. We found that compared to NICAM-SPRINTARS-orig, NICAM-SPRINTARS-bin demonstrates the long-range transport of ultra-fine particles to high latitudes and predicts higher Angstrom Exponent and total number concentrations that better agrees with observations. The latter underscores the importance of resolving the microphysical processes that determine concentrations of ultra-fine aerosol particles and explicitly represent size-dependent deposition in predicting these properties. However, number concentrations of coarse particles are still underestimated by both the original mass-based and the new microphysical schemes. Further efforts are needed to understand the reasons for the differences with the observed size distributions, including testing different emission and secondary organic aerosol production schemes, incorporating inter-species coagulation and black carbon aging, as well as performing simulations with higher spatial resolutions.

著者

Takumi Honda Takemasa Miyoshi

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.17, pp.113-119, 2021 (Released:2021-06-01)

参考文献数

38

被引用文献数

1

---

In July 2018, record-breaking heavy precipitation caused catastrophic disasters in west Japan. This study investigated the predictability of this precipitation event using a regional ensemble data assimilation system. A series of daily ensemble forecast experiments showed that the forecast ensemble spread during the heavy precipitation event increased in the forecasts initialized on 1 July and 3 July. The first peak of the forecast ensemble spread was associated with the uncertain track forecast of Typhoon Prapiroon. Namely, about a half of the ensemble members predicted eastward recurvature of the typhoon, whereas the other members predicted that the typhoon stayed near China. The later peak was associated with the southern convective disturbances near the Ryukyu Islands. Composite analysis and ensemble-based correlations showed that more active convective activities corresponded to a stronger cyclonic circulation and pushed the main precipitation band northward. The results implied that Prapiroon and the southern convective disturbances played important roles in the July 2018 heavy rain event and largely contributed to its predictability.

著者

Masaki Katsumata Kyoko Taniguchi Tomoaki Nishizawa

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2021-022, (Released:2021-05-21)

---

This article is a correction to SOLA Vol.16A (2020) pp. 6-11.

著者

Biao Geng Ryuichi Shirooka

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.17, pp.81-87, 2021 (Released:2021-05-07)

参考文献数

34

---

The internal structure and evolution of a monsoon trough (MT) and associated mesoscale convective systems (MCSs) in the western North Pacific were investigated, based mainly on radiosonde and a Doppler radar observations in Palau. The MT was observed on 15-16 June 2013, with the pre-existing disturbance of Typhoon Leepi (2013) being embedded in it. The large-scale circulation around the MT featured a pattern representing an active MT. Deep convection developed ahead and at the leading edge of the downward-sloping monsoonal flow, where intense low-level convergence was observed. Stratiform precipitation broadened rearward over the MT axis. A deep and wide layer of warm and moist air over the MT axis was undercut by a layer of cold air sloping downward from the trailing stratiform region to the leading convective region. An intense low-pressure zone formed in the interface between the warm layer above and cold layer below, with the westerly monsoonal and easterly trade flows being enhanced on its west and east sides, respectively, from the low to middle troposphere. The results suggest that a strengthening of the large-scale cyclonic circulation in response to the internal processes of the MCSs triggered by the MT is important for typhoon genesis.

著者

Kazuyo Murazaki Hirotaka Kamahori Chiaki Kobayashi Seiji Yukimoto

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.17, pp.88-95, 2021 (Released:2021-05-07)

参考文献数

32

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This study evaluated the effects of sea surface temperature (SST) resolution on dynamically downscaled daily surface air temperature (Tsrf) in the Kanto region during early summer. Two downscaling experiments and one additional experiment were conducted using different SST datasets for the months of June and July over a 10-year period. The results demonstrated that the Tsrf difference in the Kanto region between the high-resolution SST experiment (Run-H) and the low-resolution SST experiment (Run-C) correlates positively with the difference in surrounding SST. The impact of SST difference depends on the wind direction and speed. By comparing the results with observations at meteorological stations, the number of days with warm Tsrf bias in Run-C significantly reduces in Run-H, but the number of days with cold Tsrf bias still remains. These results suggest that SST resolution influences the downscaled Tsrf reproducibility over land, and it is worthwhile to pay attention to coastal SST.

著者

Paula Maldonado Juan Ruiz Celeste Saulo

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.17, pp.96-102, 2021 (Released:2021-05-19)

参考文献数

34

被引用文献数

4

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This study investigates the impact of applying different types of initial and boundary perturbations for convective-scale ensemble data assimilation systems. Several observing system simulation experiments (OSSEs) were performed with a 2-km horizontal resolution, considering a realistic environment, taking model error into account, and combining different perturbations' types with warm/cold start initialization. Initial perturbations produce a long-lasting impact on the analysis's quality, particularly for variables not directly linked to radar observations. Warm-started experiments provide the most accurate analysis and forecasts and a more consistent ensemble spread across the different spatial scales. Random small-scale perturbations exhibit similar results, although a longer convergence time is required to up-and-downscale the initial perturbations to obtain a similar error reduction. Adding random large-scale perturbations reduce the error in the first assimilation cycles but produce a slightly detrimental effect afterward.

著者

Kazuto Takemura Hitoshi Mukougawa Shuhei Maeda

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2021-021, (Released:2021-05-18)

被引用文献数

2

---

Rossby waves propagating along the Asian jet frequently cause the breaking near the jet exit region. This study examines characteristics of oceanographic condition and atmospheric circulation associated with interdecadal variability of Rossby wave breaking frequency near Japan in August. Sea surface temperature during a period of the higher Rossby wave breaking frequency is cooler over the central part of the tropical North Pacific, compared with that during a period of the lower frequency. Convective activities are suppressed over the region consistent with the cooler sea surface temperature, contributing to an enhanced and southwestward extended mid-Pacific trough. Deceleration and diffluence of the Asian jet are stronger during the period of the higher frequency than that during the period of the lower one. The enhanced deceleration and diffluence of the jet are associated with the enhanced and southwestward extended mid-Pacific trough. The abovementioned dynamical influence is also shown by a numerical simulation using an atmospheric linear baroclinic model. These results indicate that the interdecadal variability of sea surface temperature over the central part of the tropical North Pacific has an impact on that of the Rossby wave breaking frequency near Japan, through the modulated convective activities and mid-Pacific trough.

著者

前田 修平 竹村 和人 小林 ちあき

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.2, pp.449-458, 2021 (Released:2021-04-14)

参考文献数

17

被引用文献数

3

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本研究では、ユーラシアパターン―ユーラシア北部において冬季に卓越するテレコネクションパターン―に関連する惑星波の変調を、JRA-55を使用した合成図分析により解析し、波―平均流相互作用を含むユーラシアパターンの力学的メカニズムを明らかにする。 平年偏差の点からは、ユーラシアパターンは、北ヨーロッパ、中西部シベリア、および日本に作用中心を持つ、等価順圧な鉛直構造をした定常ロスビー波型のテレコネクションとして知られている。一方、帯状平均からのずれの観点では、ユーラシアパターンは、東アジアの冬季モンスーンに関連する惑星波の活動度を変調する。 強化された東アジア冬季モンスーンに対応するユーラシアパターンの正位相では、対流圏のユーラシア中部から北太平洋において東方・上方に伝播する惑星波が平年より強まる。この惑星波の強化には、東アジアにおける帯状平均から擾乱への傾圧エネルギー変換が寄与する。強化され東方・上方に伝播した惑星波は、上部対流圏で収束し、それにより中高緯度の直接循環偏差と、中緯度下部対流圏への寒気流出を引き起こす。これらの結果は、ユーラシアパターンは主に惑星波の活動に関係する全球的な力学モードの1つであることを示す。

著者

Peter VOELGER Peter DALIN

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.2, pp.497-504, 2021 (Released:2021-04-26)

参考文献数

24

被引用文献数

2

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A case study of the occurrence of polar stratospheric clouds (PSCs) on February 13th, 2017, in northern Sweden is reported in this paper. For the first time, a quasistationary edge of a bright and extended PSC layer (∼ 600-km long) on the eastern side of the Scandinavian mountain range was photographed and registered using lidar observations. Both lidar measurements and model simulations demonstrated that atmospheric conditions were fairly unchanged for several hours during the presence of the PSC. Strong winds across the Scandinavian mountain range were responsible for triggering the formation of mountain lee waves in the Kiruna area, which induced the formation of the quasistationary long and straight edge of the PSCs.

著者

JAIN Shipra CHHIN Rattana DOHERTY Ruth M. MISHRA Saroj K. YODEN Shigeo

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.2021-021, (Released:2021-01-13)

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Equilibrium climate sensitivity (ECS) is defined as the change in global-mean surface air temperature due to the doubling or quadrupling of CO2 in a climate model simulation. This metric is used to determine the uncertainty in future climate projections, and therefore the impact of model changes on ECS is of large interest to the climate modeling community. In this paper, we propose a new graphical method, which is an extension of the Gregory's linear regression method, to represent the impact of model changes on ECS, climate forcing and climate feedbacks in a single diagram. Using this visualization method, one can quantify (a) whether the model- or process-change amplifies, reduces, or has no impact on global warming, and evaluate (b) the percentage changes in ECS, climate forcing and climate feedbacks and (c) ranges of the uncertainties in the estimated changes. We demonstrate this method using an example of climate sensitivity simulations with and without interactive chemistry. This method can be useful for multi-model assessments where the response of multiple models for the same model experiment (e.g., usage of interactive chemistry as compared to the prescribed chemistry as shown here) can be assessed simultaneously, which is otherwise difficult to compare and comprehend. We also demonstrate how this method can be used to examine the spread in ECS, climate forcing and climate feedbacks with respect to the multi-model mean (or one benchmark model) for multi-model frameworks like Coupled Model Intercomparison Project Phase 5 or for different ensemble members in a large ensemble of simulations carried out using a single model.

著者

JIAN Hong-Wen CHEN Wei-Ting CHEN Peng-Jen WU Chien-Ming RASMUSSEN Kristen L.

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.2021-013, (Released:2020-12-02)

被引用文献数

5

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This study investigates the synoptic scale flows associated with extreme rainfall systems over the Asian-Australian monsoon region (90-160°E and 12°S-27°N). Based on statistics of the 17-year Precipitation Radar observations from Tropical Rainfall Measurement Mission, a total of 916 extreme systems with both the horizontal size and maximum rainfall intensity exceeding the 99.9th percentiles of the tropical rainfall systems are identified over this region. The synoptic wind pattern and rainfall distribution surrounding each system are classified into four major types: Vortex, Coastal, Coastal with Vortex, and None of above, with each accounting for 44 %, 29 %, 7 %, and 20 %, respectively. The vortex type occurs mainly over the off-equatorial areas in boreal summer. The coast-related types show significant seasonal variations in their occurrence, with high frequency in the Bay of Bengal in boreal summer and on the west side of Borneo and Sumatra in boreal winter. The None-of-the-above type occurs mostly over the open ocean, and in boreal winter these events are mainly associated with the cold surge events. The environment analysis shows that coast-related extremes in the warm season are found within the areas where high total water vapor and low-level vertical wind shear occur frequently. Despite the different synoptic environments, these extremes show a similar internal structure, with broad stratiform and wide convective core rain. Furthermore, the maximum rain rate locates mostly over convective area, near convective-stratiform boundary in the system. Our results highlight the critical role of the strength and direction of synoptic flows in the generation of extreme rainfall systems near coastal areas. With the enhancement of the low-level vertical wind shear and moisture by the synoptic flow, the coastal convection triggered diurnally has a higher chance to organize into mesoscale convective systems and hence a higher probability to produce extreme rainfall.

著者

清木 達也

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.2, pp.379-402, 2021 (Released:2021-04-12)

参考文献数

61

被引用文献数

7

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本研究では全球降水観測計画主衛星(GPM)に搭載された二周波降水レーダー(DPR)を利用して雹の三次元分布を全球規模で検出する手法を提案した。雹の検出にはKu帯におけるレーダー反射因子(ZKu)に加え、Ku帯とKa帯のレーダー反射因子の比率(DFR)、そして再解析データから得られる気温分布を利用した。検証には地上レーダーの粒子種判別プロダクトを利用した。本研究では、雹粒子が雨との衝突によって急速に成長する事に着目し、二粒子衝突モデルによって雹の成長を特徴づけられると仮定した。ここで、本研究で取り扱う雹はKu帯とKa帯の散乱特性に基づいて定義されており、一般的に定義される雹の他に高密度の霰や小さい凍結雨滴を含んでいる事が考えられる。 まず初めに、降雹の一事例を基にZKuとDFRの散布図の特徴を抽出したところ、二粒子衝突モデルに則った成長曲線は雹の分布をよく捉えられることが分かった。気温に依存して雹の密度が変化する事から、本研究では五つの温度帯で雹を検出するためのZKuとDFRの閾値を定義した。この閾値を用いて地上レーダーとGPM-DPRがマッチングする74の雹事例を抽出し、雹の検出精度を検証した。この検証を通じて、本研究では雹の誤検出を低減する融解雪除去フィルター及び雨除去フィルターを提案した。これら雹閾値と誤検出除去フィルターを準全球観測データに適用したところ、雹は陸上と海上の収束帯に広く存在することが分かった。特に海洋上の雹は凍結高度付近に薄く(厚さ1500m以下)広く存在しており、その存在は従来の地上レーダー網では見逃されていたことが示唆された。最後に、凍結高度付近の薄い雹層を除去するフィルターを追加したところ、特に陸上の雹を伴う深い対流を選択的に捉えられた。

著者

Paula Maldonado Juan Ruiz Celeste Saulo

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2021-015, (Released:2021-04-14)

被引用文献数

4

---

This study investigates the impact of applying different types of initial and boundary perturbations for convective-scale ensemble data assimilation systems. Several OSSEs were performed with a 2-km horizontal resolution, considering a realistic environment, taking model error into account, and combining different perturbations' types with warm/cold start initialization. Initial perturbations produce a long-lasting impact on the analysis's quality, particularly for variables not directly linked to radar observations. Warm-started experiments provide the most accurate analysis and forecasts and a more consistent ensemble spread across the different spatial scales. Random small-scale perturbations exhibit similar results, although a longer convergence time is required to up-and-downscale the initial perturbations to obtain a similar error reduction. Adding random large-scale perturbations reduce the error in the first assimilation cycles but produce a slightly detrimental effect afterward.

著者

Kazuyo Murazaki Hirotaka Kamahori Chiaki Kobayashi Yukimoto Seiji

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2021-014, (Released:2021-03-31)

---

This study evaluated the effects of sea surface temperature (SST) resolution on dynamically downscaled daily surface air temperature (Tsrf) in the Kanto region during early summer. Two downscaling experiments and one additional experiment were conducted using different SST datasets for the months of June and July over a 10-year period. The results demonstrated that the Tsrf difference in the Kanto region between the high-resolution SST experiment (Run-H) and the low-resolution SST experiment (Run-C) correlated positively with the difference in surrounding SST. The impact of SST difference depended on the wind direction and speed. By comparing the results with observations at meteorological stations, the number of days with warm Tsrf bias in Run-C significantly reduced in Run-H, but the number of days with cold Tsrf bias remained steady. These results suggest that SST resolution influences the downscaled Tsrf reproducibility over land, and it is worthwhile to pay attention to coastal SST.

著者

James Taylor Arata Amemiya Takumi Honda Yasumitsu Maejima Takemasa Miyoshi

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.17, pp.48-56, 2021 (Released:2021-03-23)

参考文献数

28

被引用文献数

6

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The predictability of the July 2020 heavy rainfall event that saw record-breaking rainfall over Western Japan in July 2020 is examined with the near real-time SCALE-LETKF numerical modelling system in a low resolution 18-km configuration setting. Ensemble-mean 5-day rainfall total forecasts showed close agreement with Japanese Meteorological Agency 1-km precipitation analyses in relation to the large-scale distribution of rainfall and to location of heaviest rainfall over Kyushu. Onset and duration of rainfall at specific sites across Kyushu were also well predicted by the forecasts. However, the precise prediction of heavy rainfall, including over the worst-hit Kumamoto and Kagoshima prefectures, was severely underestimated. Examination of the atmospheric conditions at the time of the heavy rainfall from reanalysis datasets and ensemble member forecasts showed very high humidity over central Kyushu with strong transport of moisture from the southwest to central regions. In addition, strong low-level convergence was observed to the west of Kyushu in both reanalysis and best performing member forecasts during the time of heavy rainfall, suggesting a potential contributing factor to the record-breaking rainfall.

著者

Biao Geng Ryuichi Shirooka

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2021-013, (Released:2021-03-18)

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The internal structure and evolution of a monsoon trough (MT) and associated mesoscale convective systems (MCSs) in the western North Pacific were investigated, based mainly on radiosonde and a Doppler radar observations in Palau. The MT was observed on June 15-16, 2013, with the pre-existing disturbance of Typhoon Leepi (2013) being embedded in it. The large-scale circulation around the MT featured a pattern representing an active MT. Deep convection developed ahead and at the leading edge of the downward-sloping monsoonal flow, where intense low-level convergence was observed. Stratiform precipitation broadened rearward over the MT axis. A deep and wide layer of warm and moist air over the MT axis was undercut by a layer of cold air sloping downward from the trailing stratiform region to the leading convective region. An intense low-pressure zone formed in the interface between the warm layer above and cold layer below, with the westerly monsoonal and easterly trade flows being enhanced on its west and east sides, respectively, from the low to middle troposphere. The results suggest that a strengthening of the large-scale cyclonic circulation in response to the internal processes of the MCSs triggered by the MT is important for typhoon genesis.

著者

Akiyoshi Wada Johnny C. L. Chan

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.17A, no.Special_Edition, pp.29-32, 2021 (Released:2021-03-18)

参考文献数

18

被引用文献数

9

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In the 2019 tropical cyclone season in the western North Pacific, Typhoons FAXAI and HAGIBIS made landfall in Japan while keeping the intensity, resulting in serious disasters. This study addresses the influences of an increasing trend and variations in the upper ocean heat content above 26°C (tropical cyclone heat potential: TCHP) from January 1982 to June 2020 on FAXAI and HAGIBIS. TCHP underneath FAXAI and HAGIBIS in 2019 was higher than the climatological mean except for a part of mature phase of HAGIBIS due to HAGIBIS-induced sea surface cooling. TCHP significantly increased with the interannual oceanic variations (IOVs) in the subtropical (15°N-20°N, 140°E-150°E) and midlatitude (30°N-35°N, 130°E-140°E) areas where FAXAI and HAGIBIS intensified or kept the intensity. From an empirical orthogonal function (EOF) analysis of TCHP, we demonstrate that the leading three EOF modes of TCHP explain approximately 76.8% of total variance, but the increase in TCHP along the tracks of FAXAI and HAGIBIS particularly in the early intensification of HAGIBIS cannot be explained only by the IOVs included in the leading three EOF modes but rather by the warming trend irrespective of the IOVs.