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• Observation and numerical simulation of the dynamical processes leading tropical cyclogenesis

Published Papers 【 display / non-display 】

Published Papers 【 display / non-display 】

• Stationary and Transient Asymmetric Features in Tropical Cyclone Eye with Wavenumber-one Instability: Case Study for Typhoon Haishen (2020) with Atmospheric Motion Vectors from 30-second Imaging

  Takeshi Horinouchi, Satoki Tsujino, Masahiro Hayashi, Udai Shimada, Wataru Yanase, Akiyoshi Wada, Hiroyuki Yamada

  Monthly Weather Review ( American Meteorological Society )  151 ( 1 ) 253 - 273   2022.10 [ Peer Review Accepted ]

  Type of publication: Research paper (scientific journal)

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  Abstract Dynamics of low-level flows in the eye of Typhoon Haishen (2020) in its late phase of intensification are investigated with a special rapid-scan observation of the Himawari-8 geosynchronous satellite conducted every 30 seconds. This is accomplished by deriving storm-relative atmospheric motion vectors at an unprecedentedly high spatiotemporal resolution by tracking clouds across five consecutive visible-light reflectivity. The overall low-level circulation center was situated several kilometers away from the storm center defined in terms of the inner edge of the lower part of eyewall clouds. The shift direction is rearward the storm translation, consistently with a numerical study of tropical cyclone (TC) boundary layer. Over the analysis period of 10 hours, azimuthal-mean tangential wind around this center was increased at each radius within the eye, and the rotational angular velocity was nearly homogenized. The instantaneous low-level circulation center is found to orbit around the overall circulation center at distances around 5 km. Its orbital angular speed was close to the maximum angular speed of azimuthal-mean tangential winds. This rotating transient disturbance is found to transport angular momentum inward, which explains the tangential wind increase and the angular velocity homogenization in the eye. These features are consistent with an algebraically growing wavenumber-1 barotropic instability, whose impact on TC structures has not been explored. This instability enhances wavenuber-1 asymmetry in ring shaped vorticity, which can be induced by various processes such as translation, environmental shear, and exponential barotropic instability. Therefore, it may appear broadly in TCs to affect wind distribution in their eyes.

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• Deep Eye Clouds Observed in Tropical Cyclone Trami (2018) during T-PARCII Dropsonde Observations

  伊藤 耕介, 山田 広幸, 坪木 和久

  Journal of the Atmospheric Sciences ( American Meteorological Society )  79 ( 3 ) 683 - 703   2021.12 [ Peer Review Accepted ]

  Type of publication: Research paper (scientific journal)

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  <jats:title>Abstract</jats:title> <jats:p>The sporadic formation of short-lived convective clouds in the eye of Tropical Cyclone (TC) Trami (2018) is investigated using dropsonde data and simulation results from a coupled atmosphere–ocean model. According to the satellite data, top height of the convective clouds exceeds 9 km above mean sea level, considerably taller than that of typical hub clouds (2–3 km). These clouds are located 10–30 km away from the TC center. Hence, these convective clouds are called deep eye clouds (DECs) in this study. The dropsonde data reveal increase in relative humidity in the eye region during the formation of DECs. Short-lived convective clouds are simulated up to the middle troposphere in the eye region in the coupled model.</jats:p> <jats:p>Investigation of thermodynamic conditions shows a weakened low-level warm core and associated favorable conditions for convection in the eye region during the formation of DECs. DECs are formed after the weakening and outward displacement of convective heating within the eyewall. To elucidate the influence of the changes in convective heating within the eyewall on the formation of DECs, we calculate secondary circulation and associated adiabatic warming induced by convective heating within the eyewall using the Sawyer–Eliassen equation. In the eye region, weakenings of subsidence and associated vertical potential temperature advection are observed as DECs are formed. This suggests that the weakening and outward displacement of convective heating within the eyewall create favorable conditions for the sporadic formation of DECs.</jats:p>

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• Mammatus‐Like Echo Structures Along the Base of Upper‐Tropospheric Outflow‐Layer Clouds of Typhoons Observed by Cloud Radar

  Tadayasu Ohigashi, Kazuhisa Tsuboki, Taro Shinoda, Haruya Minda, Moeto Kyushima, Hiroyuki Yamada, Hironori Iwai

  Geophysical Research Letters ( American Geophysical Union (AGU) )  48 ( 19 )   2021.10 [ Peer Review Accepted ]

  Type of publication: Research paper (scientific journal)

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• Domain knowledge integration into deep learning for typhoon intensity classification

  Maiki Higa, Shinya Tanahara, Yoshitaka Adachi, Natsumi Ishiki, Shin Nakama, Hiroyuki Yamada, Kosuke Ito, Asanobu Kitamoto, Ryota Miyata

  Scientific Reports ( Springer Science and Business Media LLC )  11 ( 1 )   2021.06 [ Peer Review Accepted ]

  Type of publication: Research paper (scientific journal)

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  <title>Abstract</title>In this report, we propose a deep learning technique for high-accuracy estimation of the intensity class of a typhoon from a single satellite image, by incorporating meteorological domain knowledge. By using the Visual Geometric Group’s model, VGG-16, with images preprocessed with fisheye distortion, which enhances a typhoon’s eye, eyewall, and cloud distribution, we achieved much higher classification accuracy than that of a previous study, even with sequential-split validation. Through comparison of t-distributed stochastic neighbor embedding (t-SNE) plots for the feature maps of VGG with the original satellite images, we also verified that the fisheye preprocessing facilitated cluster formation, suggesting that our model could successfully extract image features related to the typhoon intensity class. Moreover, gradient-weighted class activation mapping (Grad-CAM) was applied to highlight the eye and the cloud distributions surrounding the eye, which are important regions for intensity classification; the results suggest that our model qualitatively gained a viewpoint similar to that of domain experts. A series of analyses revealed that the data-driven approach using only deep learning has limitations, and the integration of domain knowledge could bring new breakthroughs.

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• Inner‐Core Wind Field in a Concentric Eyewall Replacement of Typhoon Trami (2018): A Quantitative Analysis Based on the Himawari‐8 Satellite

  S. Tsujino, T. Horinouchi, T. Tsukada, H.‐C. Kuo, H. Yamada, K. Tsuboki

  Journal of Geophysical Research: Atmospheres ( American Geophysical Union (AGU) )  126 ( 7 )   2021.04 [ Peer Review Accepted ]

  Type of publication: Research paper (scientific journal)

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Books 【 display / non-display 】

Books 【 display / non-display 】

• Nature in the Ryukyu Archipelago: Coral Reefs, Biodiversity, and Natural Environment

  YAMADA Hiroyuki ( Part: Single Author ,  Weather and clouds in the Ryukyu Archipelago )

  2015.03

Other Papers 【 display / non-display 】

Other Papers 【 display / non-display 】

• Observation of Strong Wind Fields during Passage of Cold Front by Doppler Lidar

  MARUYAMA Takashi, TAKEMI Tetsuya, YAMADA Hiroyuki, YAMAGUCHI Kosei

  Disaster Prevention Research Institute Annuals. B   64 ( B ) 131 - 136   2021.12

   

  CiNii Research

• Observation of Strong Wind under Front passage using Doppler Lidar

  Maruyama Takashi, TAKEMI Tetsuya, YAMADA Hiroyuki, YAMAGUCHI Kosei

  Summaries to Technical Papers of Annual Meeting, Japan Association for Wind Engineering ( Japan Association for Wind Engineering )  2021 ( 0 ) 91   2021

   

  DOI CiNii Research

• Report on the 17th Workshop on Non-hydrostatic numerical modeling

  山田 広幸, 伊藤 耕介, 金田 幸恵, 林 修吾, 西澤 誠也, 宮川 知己, 前島 康光, 川畑 拓矢, 加藤 亮平, 野田 暁, 岩崎 俊樹

  天気 ( 日本気象学会 )  63 ( 5 ) 435 - 440   2016.05

   

  J-GLOBAL

Grant-in-Aid for Scientific Research 【 display / non-display 】

Grant-in-Aid for Scientific Research 【 display / non-display 】

• Grant-in-Aid for Scientific Research(S)

  Project Year: 2021.07  -  2026.03 

  Direct: 145,500,000 (YEN)  Overheads: 189,150,000 (YEN)  Total: 43,650,000 (YEN)

• Grant-in-Aid for Scientific Research(S)

  Project Year: 2021.07  -  2026.03 

  Direct: 145,500,000 (YEN)  Overheads: 189,150,000 (YEN)  Total: 43,650,000 (YEN)

• Grant-in-Aid for Scientific Research(C)

  Project Year: 2019.04  -  2022.03 

  Direct: 3,300,000 (YEN)  Overheads: 4,290,000 (YEN)  Total: 990,000 (YEN)

• Grant-in-Aid for Scientific Research(C)

  Project Year: 2019.04  -  2022.03 

  Direct: 3,300,000 (YEN)  Overheads: 4,290,000 (YEN)  Total: 990,000 (YEN)

• Grant-in-Aid for Scientific Research(C)

  Project Year: 2019.04  -  2022.03 

  Direct: 3,300,000 (YEN)  Overheads: 4,290,000 (YEN)  Total: 990,000 (YEN)

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