著者

Shimizu Shingo

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.19A, no.Special_Edition, pp.i-iii, 2023 (Released:2023-10-24)

参考文献数

11

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Catastrophic disasters triggered by mesoscale convective systems occur annually in East Asia, with a notable increase in casualties and extensive damages between 2019 and 2021 due to record-breaking rainfall in Japan. There is an urgent need for a comprehensive understanding of the physical processes and dynamic mechanisms behind these extreme rainfall events. This requires the integration of various research approaches, including observational analysis, statistical data analysis, and weather forecasting with data assimilation. Additionally, we must consider the impact of large-scale atmospheric circulation on extreme weather in East Asia. In this special edition, jointly coordinated with Journal of the Meteorological Society of Japan, we have published nine articles covering extreme events in East Asia from 2017 to 2022. Here, we provide an overview of these papers. From a large-scale view perspective, Horinouchi et al. (2021) and Ueda et al. (2021) examined the influence of synoptic-scale moisture conditions and sea surface temperatures on severe rainfall events in Kyushu, Japan during the summer of 2020. Additionally, Takemura et al. (2022) investigated the large-scale atmospheric factors contributing to the record-breaking early onset of Baiu season in most parts of western Japan in 2021. Furthermore, Kuramochi et al. (2021) conducted a study on the causes of the anomalous warm conditions in winter 2019 and 2020 over East Asia, utilizing large-scale atmospheric analysis and global simulations. Three papers focused on the statistical features of environmental conditions suitable for the occurrence of “senjo-kousuitai” (Kato 2020). Goto and Satoh (2022) applied a similar definition of senjo-kousuitai as proposed by Kato 2020 to a satellite-based precipitation dataset covering 20 years from 2000 to 2019. They confirmed a high occurrence frequency in Kyushu, the Nansei Islands (South of Kyushu), and the East China sea. Based on analysis using reanalysis datasets, it was determined that low-level water vapor flux and vertical wind shear are essential for the development of senjo-kousuitai. Sato and Hosotani (2023) also confirmed the importance of these two factors based on reanalysis data spanning the past 20 years. Additionally, Naka and Takemi (2023) proposed the significance of moist absolutely unstable layers (MAULs) in enhancing heavy rainfall in the preceding hours. Numerical simulations were also employed in research efforts. Tochimoto et al. (2022) conducted sensitivity experiments to investigate the impact of the upper-level trough on the heavy rainfall. In another study, Terasaki and Miyoshi (2022) demonstrated the high predictability of heavy rainfall by utilizing data assimilation with 1024-ensemble members. Doyle et al. (2023) indicated the importance of a mesoscale convective system, orographic ascent, and equatorial wave components in contributing to the extreme flood that occurred in southwestern Sulawesi, Indonesia in January 2019 by conducting adjoint model simulations and the sensitivity analysis. To mitigate the damages caused by various extreme weather events, it is essential to consolidate our research achievements and further enhance the predictability of these events.

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

vol.17, pp.125-129, 2021 (Released:2021-06-26)

参考文献数

18

被引用文献数

2

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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

竹村 和人 向川 均 前田 修平

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.4, pp.879-897, 2021 (Released:2021-08-20)

参考文献数

47

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現在気候及び将来気候を対象とする大気大循環モデルによる大規模アンサンブルシミュレーションの結果を用いて、8月の北太平洋中央部におけるロスビー波の砕波頻度の将来変化、及びそれに関連する大気循環場の特徴を調べた。現在気候実験における北太平洋中央部での砕波頻度は、再解析データと同様に、エルニーニョ・南方振動と関連することが相関解析より示された。将来気候実験における北太平洋中央部での砕波頻度は、現在気候実験と比べて顕著に減少することが分かった。将来気候実験では、アジアモンスーン循環が顕著に弱化し、その結果としてアジアジェット気流が南偏する傾向が見られた。このアジアジェット気流の将来変化に伴って、北太平洋中央部ではジェット気流の分流・減速が弱化し、それは砕波頻度の減少と関連していた。また将来気候実験では、ユーラシア大陸及び北太平洋の中緯度でロスビー波の波束伝播が弱化する傾向が明瞭であり、このことは砕波頻度の減少と整合的である。相関解析及び頻度分布の解析より、将来気候実験における砕波頻度の減少は、フィリピンの東海上での積雲対流活動の弱化と関連することが示された。さらに、ω方程式を用いた診断より、砕波頻度の減少は、中部太平洋トラフの弱化及びそれに伴う力学的上昇流の弱化を通して、フィリピンの東海上での積雲対流活動の弱化に影響を及ぼすことが示された。

著者

Hidehiko MURATA Kotaro SAITOH Yasuhiko SUMIDA

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.96B, pp.211-238, 2018 (Released:2018-11-15)

参考文献数

22

被引用文献数

10 12

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The combination of three visible bands of the Advanced Himawari Imager (AHI) aboard Japan Meteorological Agency's (JMA) new-generation Himawari-8 and Himawari-9 geostationary meteorological satellites enables the production of true color imagery. True color is intuitively understandable to human analysts and beneficial for monitoring surface and atmospheric features. It is particularly useful when applied to frequent observations from a geostationary platform. In this article, we report on an application of a color reproduction approach based on the International Commission on Illumination (CIE) 1931 XYZ color system to imagery rendering. This approach allows the consideration of primary color (RGB) differences among satellite and output devices, which in turn cause differences in the colors reproduced. The RGB signals observed by the AHI are converted to XYZ tristimulus values, which are independent of the devices themselves, and then reconverted to RGB signals for output devices via the application of 3 × 3 conversion matrices. This article also covers an objective technique for the evaluation of the accuracy of XYZ values. The evaluation indicated that the combination of AHI native RGB bands is suboptimal for obtaining XYZ values as is, whereas a combination in which the green band is replaced by a pseudo band with a central wavelength of around 0.555 μm is optimal. The pseudo band is generated via regression with existing visible and near-infrared bands as predictor variables. The imagery produced using this approach was termed True Color Reproduction (TCR). This approach is applicable to other satellites that have several bands in the visible to near-infrared spectral range, and it has the potential for development toward the production of standardized sensor-independent true color imagery.

著者

WANG Chung-Chieh CHEN George Tai-Jen NGAI Chi-Hong TSUBOKI Kazuhisa

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.2018-051, (Released:2018-07-31)

被引用文献数

5

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There exists a minor, secondary early-morning peak in mei-yu rainfall climatology along the western coast of Taiwan, and this work investigates one such event on 8 June 2012 in southwestern Taiwan under weak synoptic conditions through both observational analysis and numerical modeling, with the main focus on the triggering mechanism of the convection. Observations show that the convection developed offshore around midnight near the leading edge of a moderate low-level southwesterly wind surge of 15-20 kts, and intensified and moved onshore to produce rainfall. The cold outflow from precipitation also led to new cell development at the backside, and the rain thus lasted for several hours till about 0700 LST. Numerical simulation using a cloud-resolving model at a grid size of 0.5 km successfully reproduced the event development with close agreement with the observations, once a time delay in the arrival of the southwesterly wind surge in initial/boundary conditions (from global analyses) is corrected. Aided by two sensitivity tests, the model results indicate that the convection breaks out between two advancing boundaries, one from the onshore surge of the prevailing southwesterly wind and the other from the offshore land/mountain breeze, when they move to about 40 km from each other. Also, both boundaries are required, as either one alone does not provide sufficient forcing to initiate deep convection in the model. These findings on the initiation of offshore convection in the mei-yu season, interestingly, are qualitatively similar to some cases in Florida with two approaching sea breeze fronts (in daytime over land).

著者

Hisaki EITO Teruyuki KATO Masanori YOSHIZAKI Ahoro ADACHI

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.83, no.4, pp.551-576, 2005 (Released:2005-10-07)

参考文献数

32

被引用文献数

23 26

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On 16 January 2001 during the field experiment named WMO-01, a meso-β-scale snowband extending eastward from Toyama Bay was observed in the coastal area of eastern Hokuriku district, middle part of Japan. This snowband stagnated for about half a day and brought a snowfall of about 50 cm in this region.Numerical simulations of this snowband are performed using a nonhydrostatic cloud resolving model (NHM), with a horizontal grid size of 1 km. The NHM well reproduces many characteristics of the observed snowband. The snowband forms over the convergence zone between a cold southerly land breeze and a northwesterly winter monsoon, to which heat and moisture is supplied from relatively warm sea surface. Convective snow cells with the horizontal scale of a few km successively form at the northern part of the snowband and propagate east-southeastward. Meso-γ-scale convective snow systems are organized, consisting of developed snow cells in the snowband. A cold pool forms under the snowband. The diabatic cooling due to the sublimation of snow is responsible for the formation of the cold pool. After the land breeze became weak, the cold pool contributes to the maintenance of the horizontal convergence with the northwesterly winter monsoon at the northern edge of the snowband by compensating for the weakened land breeze. Therefore, the formation of the cold pool is significant for the maintenance of thesnowband.

著者

ISHIOKA Keiichi YAMAMOTO Naoto FUJITA Masato

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.2022-022, (Released:2021-12-28)

被引用文献数

1

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In the discretization of the primitive equations for numerical calculations, a formulation of a three-dimensional spectral model is proposed that uses the spectral method not only in the horizontal direction but also in the vertical direction. In this formulation, the Legendre polynomial expansion is used for the vertical discretization. It is shown that semi-implicit time integration can be efficiently done under this formulation. Then, a numerical model based on this formulation is developed and several benchmark numerical calculations proposed in previous studies are performed to show that this implementation of the primitive equations can give accurate numerical solutions with a relatively small degrees of freedom in the vertical discretization. It is also shown that, by performing several calculations with different vertical degrees of freedom, a characteristic property of the spectral method is observed in which the error of the numerical solution decreases rapidly when the number of vertical degrees of freedom is increased. It is also noted that an alternative to the sponge layer can be devised to suppress the reflected waves under this formulation, and that a “toy” model can be derived as an application of this formulation, in which the vertical degrees of freedom are reduced to the minimum.

著者

TOHJIMA Yasunori NIWA Yosuke TSUBOI Kazuhiro SAITO Kazuyuki

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.2022-021, (Released:2021-12-28)

被引用文献数

2

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Synoptic-scale variabilities of atmospheric CO2 and CH4 observed at Yonagunijima (Yonaguni Island, YON, 24.47°N, 123.01°E) during winter (from January to March) in 1998-2020 were examined. The monthly mean variability ratios (ΔCO2/ΔCH4) based on correlation slopes within 24-hour time windows showed a clear increasing trend, which is mainly attributed to the unprecedented increase in the fossil fuel-derived CO2 (FFCO2) emissions from China. A similar increasing trend of the ΔCO2/ΔCH4 ratio had been reported for the observation at Hateruma Island (HAT, 24.06°N, 123.81°E), located at about 100 km east of YON. However, the absolute values for YON were 34 % larger than those for HAT. In addition, the monthly average in February 2020 for YON showed no marked change, while that for HAT showed an abrupt considerable decrease associated with the FFCO2 emission decrease in China presumably caused by the COVID-19 lockdown. Investigating the diurnal variations, we found that the local influences were larger at YON, especially during daytime, than at HAT. Using nighttime data (20-6 LST) and a longer time window (84-hour), we succeeded in reducing the local influences and the resulting monthly mean ΔCO2/ΔCH4 ratio showed considerable similarity to that observed at HAT including the abrupt decrease in February 2020. These results convinced us that the ΔCO2/ΔCH4 ratio could be successfully used to investigate the relative emission strength in the upwind region.

著者

Adam H. Sobel 堀之内 武

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.78, no.2, pp.167-173, 2000-04-25 (Released:2009-09-15)

参考文献数

29

被引用文献数

11 12

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ITCZやモンスーントラフ域で観測される回転性の総観規模風速擾乱の幾つかの側面は、大きなメソスケール対流システムに特徴的な振幅や時・空間スケールを持つパルス的加熱に対する、乾燥・静止大気の線形応答を考えることで理解できることを議論する。その鍵は、短波長のロスビー波の平均流から見た群速度、位相速度は小さいことと、加熱が赤道上よりも赤道から少し離れた位置にあるほうがロスビーモードの応答は遥かに大きなエネルギーを持つことである。故に、観測される擾乱に似た特徴を持つ総観規模ロスビー波は、大きなメソスケール積雲システムが発達する赤道を少し離れた領域に存在するということになる。

著者

SISWANTO Siswanto SCHRIER Gerard van der HURK Bart van den

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.2022-023, (Released:2022-02-08)

被引用文献数

4

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Sub-daily extreme precipitation in Jakarta exhibits trends related to local temperature, seasonal tropical monsoon circulations, and other environmental drivers. Analysis of 81 years of hourly rainfall between 1900-2010 shows a significant increase of about doubling the number of short-duration rainfall events in the wet season. In recent decades, rainfall is found to be higher in intensity and shorter in duration relative to preceding decades. These short-duration rain showers develop typically between afternoon and late night or during early morning hours. Changing short-duration rainfall characteristics throughout the last century are partly attributed to changes in the surface environment of urban Jakarta. A recent temperature increase and land surface drying in the city, in combination with a small increase of the atmospheric moisture content, promote intensified atmospheric convection. A combination of rain gauge data with upper-air observations collected during 2002-2016 reveals that surface warming in the urbanized city accompanied by enhanced availability of moisture results in an increase of convective available potential energy (CAPE), which contributes to enhanced intense precipitation. Super Clausius-Clapeyron scaling (CC) of high-intensity rainfall is attributed to high near-surface temperature and atmospheric moisture content in the morning. This super CC scaling is present in a relatively small range of surface temperature values. Results of this study are in agreement with earlier findings exploring the intensification of extreme morning precipitation and a temporal shift of the diurnal convective maximum from late afternoon to late night/early morning in response to local warming. For a delta city such as Jakarta with abundant convection and heavy precipitation, a well-maintained rainfall database is crucial to assist urban flood early warning.

著者

増山 元三郎

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.15, no.6, pp.215-223, 1937-06-05 (Released:2009-02-05)

参考文献数

8

被引用文献数

1 1

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Je suppose que les postulates fondamentaux en hydrodynamique sont K. I.....K. 10 (§ 1), qui soot été employés par nombreux auteurs explicitement on implicitement pour deduire l'équation de NAVIER-STOKES (1.17).Il y a en § 2 quelques critiques pour les postulates K. I.....K. 10, et on obtient un nonvel terme turbulent fr (2.3). Il faut en conséquence développer le tenseur de viscosité Zrs en série des gradients de vitesse vr, s comme (2.5). Dans le cas du médium isotrope le coefficient de viscosité _??_rsmn n'est pas nécessairement symétrique, et on a un nouvel terme kr (2.7) additivement à côté droit de l'équation (2.11). Si on l'écrit vectoriellement, on obtient (2.9) pour kr comme l'expression vectorielle. J.y donne de plus une nouvelle expression (2.12), qui peut être employée au lieu de relation “Austausch” de Prandtl.On a quelques explications à phenomènes hydrodynamiques biers connues mais non expliqués jusqu'ici (§ 3). Enfin j'étudie sur la fondation d'équation (3.2) quand tourbillon se mouvoit le long de son axe, et explique géométriquement sa condition nécessaire et suffisante.

著者

伊藤 耕介

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.2, pp.321-341, 2022 (Released:2022-04-13)

参考文献数

46

被引用文献数

4

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気象庁の全球日別海面水温解析の準リアルタイム版(以下、R-MGD)では、解析時間の前に得られた観測データに短時間スケールの変動を落とすようなフィルタを適用している。そのため、台風の通過に伴う急激な海面水温の変化がバイアスを生むと考えられる。本研究では、R-MGDの現場観測に対するバイアスを、北西太平洋における台風の通過に沿って定量化した。初めに、2020年8月~9月にかけて立て続けに接近した3つの台風に関し、事例解析を行った。R-MGDは3つの台風の通過直後では2℃以上もの正バイアスを生じており、最後の台風が通過して1週間以上経過したのち負バイアスが観測された。R-MGDと係留ブイの比較を行ったところ、短時間スケールを落とすフィルタリングと解析時間の前に得られたデータを用いていることで、バイアスが説明できた。次に、2015年5月から2020年10月の期間でコンポジット解析を行ったところ、台風最接近の1日前から4日後までに統計的に有意な正バイアス、台風最接近の7日後から14日後までに統計的に有意な負バイアスが、台風から500 kmの範囲内で検出された。正バイアスは、冷たい亜表層の水と激しい台風の通過に伴って生じやすく、とりわけ、黒潮と黒潮続流域を除く中緯度帯で大きくなっていた。また、R-MGDの解析時間の72時間前までに得られた現場観測を追加の最適内挿法で同化することにより、バイアスは軽減されることが分かった。これは、この過程により短周期の変動が復元されたためである。台風予報への影響評価および最適内挿法の独立な観測に対する検証も実施した。

著者

Asami Komatsu Kouichi Nishimura

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.18, pp.71-75, 2022 (Released:2022-04-22)

参考文献数

20

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We introduce a new procedure to evaluate the snowdrift distribution over complex topography and improve the accuracy of snow avalanche warning systems. We select the Niseko region, Japan, as the target area, and first obtain the wind distribution map at a 50-m grid spacing for 16 wind directions. We then employ these maps to calculate the amount of snow erosion and deposition. We present a case study to demonstrate that the model output agrees fairly well with measurements of local wind speed and observed snowdrift distribution. While improvements can be made to improve the accuracy of the model results, including more comprehensive calculation procedures and quantitative comparisons of snowdrift formation and evolution, it appears that the presented snowdrift analysis is an effective tool that can be incorporated into a snow avalanche warning system that employs a simple snow-cover model.

著者

Kazuo Saito Takumi Matsunobu Tsutao Oizumi

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.18, pp.81-87, 2022 (Released:2022-04-25)

参考文献数

26

被引用文献数

3

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As a complement work to the authors' previous studies, we examined the pre-typhoon rainfalls (PRE) ahead of typhoon T0918 (Melor) in October 2009. The influence of moistening in the upper atmosphere induced by the northward ageostrophic winds on PRE precipitation was examined by a sensitivity experiment using a cloud resolving model with a horizontal resolution of 2 km. The cloud resolving simulation showed a large impact of the water vapor in the upper atmosphere on the precipitation over western Japan. In the sensitivity experiment where the moisture in the middle and upper layers was reduced over the area off the south coast of western Japan, the water vapor reduction area was advected northward, and the snow in the middle and upper layers and the cloud ice in the upper layer decreased, reducing the rain below the melting level. The intrusion of drying air into the upper atmosphere reduced the thickness of the moist absolutely unstable layer (MAUL), and the maximum intensity of convective updrafts decreased by about 10% in the test experiment. In this case, the increase of rain in PRE was primarily caused by the deep northward water vapor transport which yielded a large amount of condensation in the middle and upper layers, and change of moist instability in the upper atmosphere subsidiarily enhanced the convective updrafts.

著者

Koichi Watanabe Hirohito Satoh Teruya Maki

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2022-017, (Released:2022-04-12)

被引用文献数

1

---

The number concentrations of microbial (counted as viable) particles and size-separated particles were measured continuously in Imizu City, Toyama, in the coastal region of the Sea of Japan, in 2015 using a commercial real time viable particle counter. From February to June, large increases in the number concentrations of coarse particles with rapid increases of viable particles were observed during Asian dust events. In mid-July, a phenomenon was observed in which the number concentrations of viable particles decreased, although coarse particles significantly increased. From the results of the backward trajectory analysis, the phenomenon was considered to be due to the transport of volcanic ash from Nishinoshima. The monthly average number concentrations of the viable particles were highest in September, whereas the average concentrations of coarse particles were at a maximum in April.

著者

Kazuo Saito Takumi Matsunobu Tsutao Oizumi

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2022-014, (Released:2022-04-06)

被引用文献数

3

---

As a complement work to the authors' previous studies, we examined the pre-typhoon rainfalls (PRE) ahead of typhoon T0918 (Melor) in October 2009. The influence of moistening in the upper atmosphere induced by the northward ageostrophic winds on PRE precipitation was examined by a sensitivity experiment using a cloud resolving model with a horizontal resolution of 2 km. The cloud resolving simulation showed a large impact of the water vapor in the upper atmosphere on the precipitation over western Japan. In the sensitivity experiment where the moisture in the middle and upper layers was reduced over the area off the south coast of western Japan, the water vapor reduction area was advected northward, and the snow in the middle and upper layers and the cloud ice in the upper layer decreased, reducing the rain below the melting level. The intrusion of drying air into the upper atmosphere reduced the thickness of the moist absolutely unstable layer (MAUL), and the maximum intensity of convective updrafts decreased by about 10% in the test experiment. In this case, the increase of rain in PRE was primarily caused by the deep northward water vapor transport which yielded a large amount of condensation in the middle and upper layers, and change of moist instability in the upper atmosphere subsidiarily enhanced the convective updrafts.

著者

Haruka Sasaki Tatsuo Motoi

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.18, pp.65-70, 2022 (Released:2022-04-08)

参考文献数

31

被引用文献数

3

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Previous studies suggested that increases in ocean heat content result in strengthening of tropical cyclone (TC) and causing the associated disasters. In the western North Pacific (WNP), acceleration of increasing rates of tropical cyclone heat potential (TCHP: ocean heat content above 26°C from the surface) in the TC rapidly intensifying (RI: a 24-h intensity change of ≥ 30 kt) zone may have contributed to increases in TC intensity. However, there is no research on the relation of the acceleration of increasing rates to the variations in TCHP in a climatological view, differently from the relation to decadal variations such as Pacific Decadal Oscillation (PDO). This study focused on the relation of the variations in TCHP anomalies (TCHPA) to RITCs over the past six decades. Although the annual mean TCHPA in the global ocean was not accelerated, the TCHPA accelerated recently in the late 1990s over the RI zone particularly in fall (October-December) in the WNP. The acceleration of the increase in TCHPA was possibly explained by the intensification of trade wind-driven ocean general circulation and the combination of the linear trend of TCHPA with PDO phase change.

著者

Tomoe Nasuno Masuo Nakano Hiroyuki Murakami Kazuyoshi Kikuchi Yohei Yamada

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2022-015, (Released:2022-04-01)

被引用文献数

3

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In this study, we explored the impacts of midlatitude western North Pacific (WNP) sea surface temperature (SST) on tropical cyclone (TC) activity at intraseasonal to seasonal time scales during the 2018 boreal summer. During this period, a positive SST anomaly occurred in the midlatitude WNP and subtropical central Pacific; TC activity was abnormally high under the influence of the strong Asian summer monsoon. We performed sensitivity experiments using a global cloud system-resolving model for global SST (control, CTL) and SST that were regionally restored according to midlatitude WNP climatology (MWNPCLM). TC track density in the eastern WNP was higher in CTL than in MWNPCLM, in association with large-scale atmospheric responses; enhanced monsoon westerlies in the subtropical WNP, moist rising (dry subsiding) tendencies, and reduced vertical wind shear in the eastern (western) WNP. Enhanced TC activity in the eastern WNP was more distinct for intense TCs and during the active phase of intraseasonal oscillation (ISO). These results suggest that the impacts of midlatitude SST anomalies can reach lower latitudes to affect TC activity via large-scale atmospheric responses and ISO, which are usually overwhelmed by the impacts of SST anomalies in the tropics and subtropics.

著者

Chih-Chien Chang Shu-Chih Yang Stephen G. Penny

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.18, pp.33-40, 2022 (Released:2022-03-18)

参考文献数

32

被引用文献数

2

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A regional hybrid gain data assimilation (HGDA) system is newly developed using Weather Research and Forecasting model (WRF). The WRF-HGDA augments an ensemble-based Kalman filter (WRF-LETKF) with information from the variational analysis system (WRF-3DVAR) by combining their gain matrices. The performance of WRF-HGDA is evaluated by assimilating the GNSS radio occultation (RO) observations from the FORMOSAT-3/COSMIC (FS3/C) and the FORMOSAT-7/COSMIC2 (FS7/C2) under an Observing System Simulation Experiment (OSSE) framework. The results demonstrate that the variational correction improves the WRF-LETKF, with the equal-weighted WRF-HGDA outperforming its component DA systems in the moisture and wind fields when only conventional observations are assimilated. Assimilating additional RO data from FS7/C2 further improves the WRF-LETKF and WRF-HGDA systems. Although the variational correction for the mid-level temperature causes degradation in the WRF-HGDA analysis, this can be alleviated by adjusting the combination weight to include more flow-dependent information in WRF-HGDA at these levels. Further tuning of the static background error covariance used in WRF-3DVAR also brings some improvement in the WRF-HGDA wind analysis. Our results imply that a well-tuned variational system is critical for the accuracy of the regional HGDA analysis.

著者

Ju-Young Shin Kyu Rang Kim Yong Hee Lee

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.18, pp.41-46, 2022 (Released:2022-03-18)

参考文献数

28

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Determining the thresholds for risk assessment is critical for the successful implementation of thermal health warning systems. A risk assessment methodology with multiple thresholds must be developed to provide detailed warning information to the public and decision makers. This study developed a new methodology to identify multiple thresholds for different risk levels for heat or cold wave events by considering simultaneously impact on public health. A new objective function was designed to optimize segmented Poisson regression, which relates public health to temperature indicators. Thresholds were identified based on the values of the objective functions for all threshold candidates. A case study in identifying thresholds for cold and heat wave events in Seoul, South Korea, from 2014 to 2018, was conducted to evaluate the appropriateness of the proposed methodology. Daily minimum or maximum air temperature, mortality, and morbidity data were used for threshold identification and evaluation. The proposed methodology can successfully identify multiple thresholds to simultaneously represent different risk levels. These thresholds show comparable performance to those using the relative frequency approach.