論文 - 山田　広幸

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年10月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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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年12月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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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年10月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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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年06月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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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年04月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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The Double Warm-Core Structure of Typhoon Lan (2017) as Observed through the First Japanese Eyewall-Penetrating Aircraft Reconnaissance

YAMADA Hiroyuki, ITO Kosuke, TSUBOKI Kazuhisa, SHINODA Taro, OHIGASHI Tadayasu, YAMAGUCHI Munehiko, NAKAZAWA Tetsuo, NAGAHAMA Norio, SHIMIZU Kensaku

気象集誌. 第2輯 ( 公益社団法人 日本気象学会 )  99 ( 5 )   2021年 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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<p> Upper-tropospheric aircraft reconnaissance was carried out for Typhoon Lan (2017) using a civil jet with a newly developed dropsonde system. This was the first case of a Japanese research group observing the inner core of an intense typhoon using dropsondes. This paper describes the warm-core structure in the eye and the associated thermodynamic and kinematic features of the eyewall. During two days of reconnaissance, this typhoon preserved its peak intensity in an environment with a strengthening vertical shear. Dropsondes captured a double warm-core structure with a higher perturbation temperature in the middle and upper troposphere, which persisted between the two flight missions. The two warm cores show a difference in the equivalent potential temperature (<i>θ_e</i>) of more than 10 K, suggesting different air origins. Saturation point analysis suggest that air observed in the upper warm core was entrained from the eyewall. The eyewall updraft in the left-of-shear semicircle had a two-layer structure with a higher <i>θ_e</i> and lower absolute angular momentum on the inner side of the updraft core. Analyses of the saturation point and parcel method suggest that the warmer air with a <i>θ_e</i> exceeding 370 K on the inner side of the updrafts originated from the eye boundary layer and was eventually transported into the upper warm core. These results led us to hypothesize that the vertical transport of high-<i>θ_e</i> air from the eye boundary layer contributed to the continuous eye warming in the upper troposphere against the negative effect of a strengthening environmental wind shear on the storm intensity. This study demonstrates the significance of eyewall-penetrating upper-tropospheric reconnaissance for monitoring the warm-core structure in the present situation where accurate measurements of both humidity and temperature for calculating <i>θ_e</i> can only be made with dropsonde-type expendables.</p>

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Intensification and Maintenance of a Double Warm-core Structure in Typhoon Lan (2017) Simulated by a Cloud-resolving Model

Satoki Tsujino, Kazuhisa Tsuboki, Hiroyuki Yamada, Tadayasu Ohigashi, Kosuke Ito, Norio Nagahamato

Journal of the Atmospheric Sciences ( American Meteorological Society )    2020年11月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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<title>Abstract</title>Knowledge of the development and maintenance processes of double warm cores in tropical cyclones is important for full understanding of the dynamics of storm intensity changes. During its mature stage, Typhoon Lan (2017) had a clear double warm-core structure, which was observed by dropsondes. In this study, to investigate the intensification and maintenance of the double warm-core structure, a numerical simulation of the storm is performed with a cloud-resolving model and verified by dropsonde and satellite observations. A potential temperature budget and backward trajectories are diagnosed to examine intensification and maintenance processes in the simulated eye. The budget analysis indicates that, during the most rapidly intensifying stage, a double warm core is enhanced by axisymmetric subsidence warming in the eye. In the mature stage, upper-core warming is mostly canceled by ventilation due to vertical wind shear, but the lower core continues to warm by asymmetric advection, possibly associated with dynamical instability in the eyewall. The results raise a topic of interest: It is difficult to fully explain the axisymmetric subsidence warming process during the most rapidly intensifying stage by the dynamical response in an axisymmetric balanced vortex. The back-trajectory analysis indicates that the air mass associated with the subsidence is partly induced by inward acceleration in subgradient regions (unbalanced processes) in the eyewall.

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Characteristics of upper-tropospheric outflow-layer clouds of Typhoon Francisco (2013) observed by hydrometeor videosonde

T. Ohigashi, K. Tsuboki, Y. Suzuki, H. Yamada, K. Nakagawa

Atmospheric Research   235   2020年 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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Effect of air-sea environmental conditions and interfacial processes on extremely intense typhoon Haiyan (2013)

Wada, A., S. Kanada, and H. Yamada

Journal of Geophysical Research (Atmospheres) ( Journal of Geophysical Research: Atmospheres )  123 ( 18 ) 10,379 - 10,405   2018年09月

掲載種別: 研究論文（学術雑誌）

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Intensity and inner-core structure of Typhoon Haiyan (2013) near landfall: Doppler radar analysis

Shimada, U., H. Kubota, H. Yamada, E. O. Cayanan, and F. Hilario

Monthly Weather Review ( Monthly Weather Review )  146 ( 2 ) 183 - 597   2018年02月

掲載種別: 研究論文（学術雑誌）

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Analysis and Forecast Using Dropsonde Data from the Inner-Core Region of Tropical Cyclone Lan (2017) Obtained during the First Aircraft Missions of T-PARCII

Ito Kosuke, Yamada Hiroyuki, Yamaguchi Munehiko, Nakazawa Tetsuo, Nagahama Norio, Shimizu Kensaku, Ohigashi Tadayasu, Shinoda Taro, Tsuboki Kazuhisa

SOLA ( 公益社団法人 日本気象学会 )  14 ( 0 ) 105 - 110   2018年

掲載種別: 研究論文（学術雑誌）

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<p>The inner core of Tropical Cyclone Lan was observed on 21-22 October 2017 by GPS dropsondes during the first aircraft missions of the Tropical Cyclones-Pacific Asian Research Campaign for the Improvement of Intensity Estimations/Forecasts (T-PARCII). To evaluate the impact of dropsondes on forecast skill, 12 36-h forecasts were conducted using a Japan Meteorological Agency non-hydrostatic model (JMA-NHM) with a JMA-NHM-based mesoscale four-dimensional data assimilation (DA) system. Track forecast skill improved over all forecast times with the assimilation of the dropsonde data. The improvement rate was 8-16% for 27-36-h forecasts. Minimum sea level pressure (Pmin) forecasts were generally degenerated (improved) for relatively short-term (long-term) forecasts by adding the dropsonde data, and maximum wind speed (Vmax) forecasts were degenerated. Some of the changes in the track and Vmax forecasts were statistically significant at the 95% confidence level. It is notable that the dropsonde-derived estimate of Pmin was closer to the real-time analysis by the Regional Specialized Meteorological Center (RSMC) Tokyo than the RSMC Tokyo best track analysis. The degeneration in intensity forecast skill due to uncertainties in the best track data is discussed.</p>

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Assessment of western Indian Ocean SST bias of CMIP5 models

Ibnu Fathrio, Satoshi Iizuka, Atsuyoshi Manda, Yasu-Masa Kodama, Sachinobu Ishida, Qoosaku Moteki, Hiroyuki Yamada, Yoshihiro Tachibana

JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS ( AMER GEOPHYSICAL UNION )  122 ( 4 ) 3123 - 3140   2017年04月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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The western Indian Ocean sea surface temperature (SST) is among the key factors that affect precipitation over India and East Africa. This study examined the western Indian Ocean SST biases among the Coupled Model Intercomparison Project phase 5 (CMIP5) models. It was found that the multimodel ensemble-mean SST biases over the western equatorial Indian Ocean are warmer than the observations during the summer monsoon season. However, about half the models show positive SST biases, whereas negative ones in the other half. The models with warmer SST biases exhibit a pattern similar to the Indian Ocean Dipole, with stronger equatorial easterly wind biases during fall and a deeper thermocline in the western equatorial Indian Ocean. In the models with cooler SST biases, negative SST biases are observed over the entire tropical Indian Ocean throughout the year and the wind biases over the equatorial Indian Ocean are southeasterly during summer and fall. Heat budget analysis revealed the importance of ocean currents in forming the early summer development of SST biases over the western equatorial Indian Ocean. The formation of SST biases is related to surface current biases induced by the weaker biases of southwesterly monsoon winds and SST biases over the southwestern equatorial Indian Ocean, which are advected by the East African Coastal Currents. On the other hand, almost of all the CMIP5 models show prominent cold SST biases over the northern Arabian Sea during the premonsoon season. The SST biases are induced by excess surface cooling during the winter monsoon season.

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Doppler radar analysis of the rapid intensification of Typhoon Goni (2015) after eyewall replacement

Shimada, U., M. Sawada, and H. Yamada

Journal of Atmospheric Sciences ( Journal of the Atmospheric Sciences )  75 ( 1 ) 143 - 162   2017年

掲載種別: 研究論文（学術雑誌）

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Intra-seasonal variation of rainfall and climate characteristics in Kabul River Basin

Shokory, J. A. N, J. G. Tsutsumi, H. Yamada, B. Klove

Central Asian Journal of Water Research   3   24 - 40   2017年 [ 査読有り ]

掲載種別: 研究論文（その他学術会議資料等）

Role of the Vertical Structure of a Simulated Tropical Cyclone in Its Motion: A Case Study of Typhoon Fengshen (2008)

Yamada Hiroyuki, Nasuno Tomoe, Yanase Wataru, Satoh Masaki

SOLA ( 公益社団法人 日本気象学会 )  12 ( 0 ) 203 - 208   2016年

掲載種別: 研究論文（学術雑誌）

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<p>Typhoon Fengshen (2008) was marked by a persistent track toward the northwest, which was poorly predicted by an operational hydrostatic model, which indicated a significant northward bias. Using a global nonhydrostatic model with finer grid spacing, we have simulated a reliable track of this typhoon. The purpose of this study is to clarify the causes of the northward bias by comparing the output of the two models. This typhoon was marked by the asymmetry of rainfall concentrating in the downshear side. While both models could reproduce the asymmetric structure, a significant difference between them was found in the vertical structure. In the hydrostatic model, the vortex tilted to the downshear side with a displacement from lower to upper levels exceeding 100 km. This tilt was related to weak updrafts of, at most, 0.5 m s⁻¹. Diagnosis using vorticity budget demonstrated that the tilt of the vortex resulted from a lack of vertical coupling that was too weak to withstand differential advection between the lower and upper levels. These results suggest the importance of reproducing inner-core updrafts for better track prediction of a typhoon in an environment with strong vertical shear.</p>

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Global cloud-permitting simulations of Typhoon Fengshen (2008)

Nasuno, T., H. Yamada, M. Nakano, H. Kubota, M. Sawada and R. Yoshida

Geoscience Letters ( Geoscience Letters )  3 ( 1 )   2016年

掲載種別: 研究論文（学術雑誌）

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Evaluation of the accuracy and utility of tropical cyclone intensity estimation using single ground-based Doppler radar observations

Shimada, U., M. Sawada, and H. Yamada

Monthly Weather Review ( Monthly Weather Review )  144 ( 5 ) 1823 - 1840   2016年

掲載種別: 研究論文（学術雑誌）

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気象レーダーが捉えた2015年台風第15号および第21号の暴風

山田 広幸, 嶋田 宇大

暴風（かじふち）   44   2016年

掲載種別: 研究論文（大学，研究機関紀要）

熱帯域における台風の観測とシミュレーション : 雲と降水をどこまで再現できれば満足か? (2013年度春季大会シンポジウム「変化する地球環境と気象学の役割」の報告)

山田 広幸

天気 ( 日本気象学会 )  62 ( 4 ) 253 - 257   2015年04月

掲載種別: 研究論文（学術雑誌）

シンポジウム 第10回「メソスケール気象と熱帯低気圧に関する国際会議(ICMCS-X)」参加報告

加藤 輝之, 柳瀬 亘, 嶋田 宇大, 末木 健太, 本田 匠, 小司 禎教, 津口 裕茂, 山田 広幸, 横田 祥, 若月 泰孝, 南雲 信宏, 村田 文絵

天気 ( 日本気象学会 )  62 ( 1 ) 25 - 32   2015年01月

掲載種別: 研究論文（学術雑誌）