研究者紹介システム

梶川 義幸
カジカワ ヨシユキ
都市安全研究センター
教授
地学関係
Last Updated :2022/06/13

研究者情報

所属

  • 【主配置】

    都市安全研究センター
  • 【配置】

    工学部 市民工学科

学位

  • 博士(理学), 名古屋大学

授業科目

研究活動

研究キーワード

  • アジアモンスーン
  • 気象学
  • 気候学
  • 西部太平洋
  • 季節内変動
  • 気候変動
  • 大気海洋相互作用
  • 豪雨
  • 対流活動
  • 気候システム
  • モンスーン

研究分野

  • 社会基盤(土木・建築・防災) / 防災工学
  • 人文・社会 / 地理学 / 気候学
  • 自然科学一般 / 大気水圏科学

委員歴

  • 2018年04月 - 現在, 日本学術会議 環境学委員会・地球惑星科学委員会合同 FE・WCRP 合同分科会 GEWEX小委員会, 幹事
  • 2016年05月 - 現在, 日本気象学会, 気象集誌編集委員
  • 2015年04月 - 2017年09月, 日本学術会議 環境学委員会・地球惑星科学委員会合同IGBP・WCRP・DIVERSITAS合同分科会 MAHASRI・GEWEX小委員会, 委員

論文

  • Nishizawa, Seiya, Adachi, Sachiho A., Kajikawa, Yoshiyuki, Yamaura, Tsuyoshi, Ando, Kazuto, Yoshida, Ryuji, Yashiro, Hisashi, Tomita, Hirofumi

    2018年, Progress in Earth and Planetary Science, 5, 1 - 13

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    研究論文(学術雑誌)

  • Tsuyoshi Yamaura, Yoshiyuki Kajikawa

    A decadal change in activity of the boreal summer intraseasonal oscillation (BSISO) was identified at a broad scale. The change was more prominent during August-October in the boreal summer. The BSISO activity during 1999-2008 (P2) was significantly greater than that during 1984-1998 (P1). Compared to P1, convection in the BSISO was enhanced and the phase speed of northward-propagating convection was reduced in P2. Under background conditions, warm sea surface temperature (SST) anomalies in P2 were apparent over the tropical Indian Ocean and the western tropical Pacific. The former supplied favorable conditions for the active convection of the BSISO, whereas the latter led to a strengthened Walker circulation through enhanced convection. This induced descending anomalies over the tropical Indian Ocean. Thermal convection tends to be suppressed by descending anomalies, whereas once an active BSISO signal enters the Indian Ocean, convection is enhanced through convective instability by positive SST anomalies. After P2, the BSISO activity was weakened during 2009-2014 (P3). Compared to P2, convective activity in the BSISO tended to be inactive over the southern tropical Indian Ocean in P3. The phase speed of the northward-propagating convection was accelerated. Under background conditions during P3, warmer SST anomalies over the maritime continent enhance convection, which strengthened the local Hadley circulation between the western tropical Pacific and the southern tropical Indian Ocean. Hence, the convection in the BSISO over the southern tropical Indian Ocean was suppressed. The decadal change in BSISO activity correlates with the variability in seasonal mean SST over the tropical Asian monsoon region, which suggests that it is possible to predict the decadal change.

    SPRINGER, 2017年05月, CLIMATE DYNAMICS, 48 (9-10), 3003 - 3014, 英語

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    研究論文(学術雑誌)

  • Masaki Satoh, Hirofumi Tomita, Hisashi Yashiro, Yoshiyuki Kajikawa, Yoshiaki Miyamoto, Tsuyoshi Yamaura, Tomoki Miyakawa, Masuo Nakano, Chihiro Kodama, Akira T. Noda, Tomoe Nasuno, Yohei Yamada, Yoshiki Fukutomi

    This article reviews the major outcomes of a 5-year (2011-2016) project using the K computer to perform global numerical atmospheric simulations based on the non-hydrostatic icosahedral atmospheric model (NICAM). The K computer was made available to the public in September 2012 and was used as a primary resource for Japan's Strategic Programs for Innovative Research (SPIRE), an initiative to investigate five strategic research areas; the NICAM project fell under the research area of climate and weather simulation sciences. Combining NICAM with high-performance computing has created new opportunities in three areas of research: (1) higher resolution global simulations that produce more realistic representations of convective systems, (2) multi-member ensemble simulations that are able to perform extended-range forecasts 10-30 days in advance, and (3) multi-decadal simulations for climatology and variability. Before the K computer era, NICAM was used to demonstrate realistic simulations of intra-seasonal oscillations including the Madden-Julian oscillation (MJO), merely as a case study approach. Thanks to the big leap in computational performance of the K computer, we could greatly increase the number of cases of MJO events for numerical simulations, in addition to integrating time and horizontal resolution. We conclude that the high-resolution global non-hydrostatic model, as used in this five-year project, improves the ability to forecast intra-seasonal oscillations and associated tropical cyclogenesis compared with that of the relatively coarser operational models currently in use. The impacts of the sub-kilometer resolution simulation and the multi-decadal simulations using NICAM are also reviewed

    SPRINGER, 2017年04月, PROGRESS IN EARTH AND PLANETARY SCIENCE, 4, 英語

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  • Ryuji Yoshida, Yoshiaki Miyamoto, Hirofumi Tomita, Yoshiyuki Kajikawa

    The environmental conditions for tropical cyclone genesis are examined by numerical experiment. We focus on the case of a non-developing disturbance showed features for tropical cyclone genesis in the Pacific Area Long-term Atmospheric observation for Understanding climate change in 2010 (PALAU2010) observation campaign over the western North Pacific. We clarify the importance of the presence of abundant moisture around the disturbance for continuous convection and demonstrate that the collocation of a mid-level vortex and a low-level vortex, i.e., the persistence of an upright structure of vortices, is important in tropical cyclone genesis. We conduct two numerical experiments using the Weather Research and Forecasting Model Advanced Research WRF model in double nested domains with a horizontal grid space of 27 km and 9 km for the outer domain and the inner domain, respectively. The first experiment is based on reanalysis data (a control experiment) and the second includes increased water vapor content over the northwestern dry area of the disturbance. In the control experiment, the disturbance did not develop into a tropical cyclone in spite of the existence of the mid-level and low-level vortices. In contrast, the sensitivity experiment shows that a tropical cyclone was formed from the disturbance with increased water vapor content. The presence of persistent upright vortices was supported by continuous convection until the genesis of the tropical cyclone.

    METEOROLOGICAL SOC JAPAN, 2017年, JOURNAL OF THE METEOROLOGICAL SOCIETY OF JAPAN, 95 (1), 35 - 47, 英語

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    研究論文(学術雑誌)

  • Sachiho A. Adachi, Seiya Nishizawa, Ryuji Yoshida, Tsuyoshi Yamaura, Kazuto Ando, Hisashi Yashiro, Yoshiyuki Kajikawa, Hirofumi Tomita

    Springer Nature, 2017年, Nature Communications, 8 (1), 2224

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    研究論文(学術雑誌)

  • Yoshiaki Miyamoto, Tsuyoshi Yamaura, Ryuji Yoshida, Hisashi Yashiro, Hirofumi Tomita, Yoshiyuki Kajikawa

    Deep moist convection in the atmosphere plays an important role in cloudy weather disturbances, such as hurricanes, and even in the global climate. The convection often causes disastrous heavy rainfall, and predicting such convection is therefore critical for both disaster prevention and climate projection. Although the key parameters for convection have been pointed out, understanding the preprocesses of convection is a challenging issue. Here we identified the precursors of convection by analyzing a global simulated data set with very high resolution in time and space. We found that the mass convergence near the Earth's surface changed significantly several minutes before the initiation of early convection (the formation of cumulus clouds), which occurred with the increase in the convective available potential energy (CAPE). Decomposition of the statistical data revealed that a higher-CAPE environment resulted in stronger convection than in the stronger-convergence case. Furthermore, for the stronger-convergence case, the precursor was detected earlier than the total average (10-15min before the initiation), whereas the amplitude of maximum velocity was not so strong as the higher-CAPE case. This suggests that the strength of convection is connected with CAPE, and the predictability is sensitive to the convergence.

    AMER GEOPHYSICAL UNION, 2016年10月, JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, 121 (20), 12080 - 12088, 英語

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    研究論文(学術雑誌)

  • Yoshiyuki Kajikawa, Yoshiaki Miyamoto, Ryuji Yoshida, Tsuyoshi Yamaura, Hisashi Yashiro, Hirofumi Tomita

    The success of sub-kilometer global atmospheric simulation opens the door for resolving deep convections, which are fundamental elements of cloudy disturbances that drive global circulation. A previous study found that the essential change in the simulated convection properties occurred at a grid spacing of about 2 km as a global mean. In grid-refinement experiments, we conducted further comprehensive analysis of the global-mean state and the characteristics of deep convection, to clarify the difference of the essential change by location and environment. We found that the essential change in convection properties was different in the location and environment for each cloudy disturbance. The convections over the tropics show larger resolution dependence than convections over mid-latitudes, whereas no significant difference was found in convections over land or ocean. Furthermore, convections over cloudy disturbances [(i.e., Madden-Julian oscillation (MJO), tropical cyclones (TCs)] show essential change of convection properties at about 1 km grid spacing, suggesting resolution dependence. As a result, convections not categorized as cloudy disturbances make a large contribution to the global-mean convection properties. This implies that convections in disturbances are largely affected organization processes and hence have more horizontal resolution dependence. In contrast, other categorized convections that are not involved in major cloudy disturbances show the essential change at about 2 km grid spacing. This affects the latitude difference of the resolution dependence of convection properties and hence the zonal-mean outgoing longwave radiation (OLR). Despite the diversity of convection properties, most convections are resolved at less than 1 km grid spacing. In the future, longer integration of global atmosphere, to 0.87 km grid spacing, will stimulate significant discussion about the interaction between the convections and cloudy disturbances.

    SPRINGER, 2016年06月, PROGRESS IN EARTH AND PLANETARY SCIENCE, 3, 英語

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    研究論文(学術雑誌)

  • Hisashi Yashiro, Yoshiyuki Kajikawa, Yoshiaki Miyamoto, Tsuyoshi Yamaura, Ryuji Yoshida, Hirofumi Tomita

    Resolution dependence was found in the simulated diurnal precipitation cycle over land in the tropics. We conducted a series of grid refinement experiments of the atmosphere from 14 km to 0.87 km using a global high-resolution model without any convection parameterizations. In the high-resolution experiment, the peak of the cycle was earlier and precipitation at the peak was higher. The characteristics of the simulated diurnal precipitation cycle changed at a grid spacing of around 2-3 km. The precipitation started to increase in the morning in the high-resolution experiments, suggesting that small-scale moist convection became active in the late morning. In the lower-resolution experiments, convection and precipitation began in the late afternoon. As well as the enhancement of moisture transport from the boundary layer to the middle troposphere, the rapid formation of rain can also be attributed to the difference in diurnal precipitation cycles between lower and higher resolution experiments.

    METEOROLOGICAL SOC JAPAN, 2016年, SOLA, 12, 272 - 276, 英語

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    研究論文(学術雑誌)

  • Bin Wang, Yoshiyuki Kajikawa

    AMER METEOROLOGICAL SOC, 2015年11月, JOURNAL OF CLIMATE, 28 (22), 9036 - 9039, 英語

    [査読有り]

  • Yousuke Sato, Seiya Nishizawa, Hisashi Yashiro, Yoshiaki Miyamoto, Yoshiyuki Kajikawa, Hirofumi Tomita

    Springer Science $\mathplus$ Business Media, 2015年08月, Prog. in Earth and Planet. Sci., 2 (1)

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    研究論文(学術雑誌)

  • Yoshiaki Miyamoto, Ryuji Yoshida, Tsuyoshi Yamaura, Hisashi Yashiro, Hirofumi Tomita, Yoshiyuki Kajikawa

    Deep moist convection is an element of cloud disturbances such as Madden-Julian oscillation (MJO), tropical cyclones (TCs), mid-latitudinal low depressions (MDL), and fronts (FRT). However, differences in convection characteristics in disturbances remain unclear. We first clarified the statistical features of the convection (structure, intensity, and environmental parameters) in various disturbances simulated by a global simulation with a sub-kilometre grid spacing. The convection in MJO (TC) was tall with a strong (weak) upward motion, and was driven by large convective available potential energy (strong low-level convergence). The convection in MDL and FRT was shorter and characterized by a strong vertical wind shear.

    WILEY-BLACKWELL, 2015年07月, ATMOSPHERIC SCIENCE LETTERS, 16 (3), 305 - 309, 英語

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    研究論文(学術雑誌)

  • Yoshiyuki Kajikawa, Tsuyoshi Yamaura, Hirofumi Tomita, Masaki Satoh

    The onset of the Indian summer monsoon (ISM) in 2012 was investigated using the nonhydrostatic icosahedral atmospheric model (NICAM), a global cloud-system resolving model. We focused on the effect of tropical disturbances on ISM onset and considered the potential extension of onset predictability. A series of NICAM experiments was performed under various initial conditions for the period 10 May to 10 June, 2012. NICAM showed promising performance by realistically simulating ISM onset based on the initial conditions two weeks before the onset. ISM onset in both observations and simulations was accompanied by northward-migrating tropical disturbances over the Bay of Bengal and the Arabian Sea. These disturbances were generated by the eastward propagating disturbance along the equatorial Indian Ocean. As indicated by a comparison of NICAM experimental results with those obtained by the Japan Meteorological Agency Operational Ensemble Prediction System, we suggest that the better reproducing the tropical disturbance enhances the potential to extend the predictability of the transition phase in the Asian summer monsoon.

    METEOROLOGICAL SOC JAPAN, 2015年, SOLA, 11, 80 - 84, 英語

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    研究論文(学術雑誌)

  • Yousuke Sato, Yoshiaki Miyamoto, Seiya Nishizawa, Hisashi Yashiro, Yoshiyuki Kajikawa, Ryuji Yoshida, Tsuyoshi Yamaura, Hirofumi Tomita

    Meteorological Society of Japan, 2015年, SOLA, 11 (0), 75 - 79

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    研究論文(学術雑誌)

  • Chihiro Kodama, Yohei Yamada, Akira T. Noda, Kazuyoshi Kikuchi, Yoshiyuki Kajikawa, Tomoe Nasuno, Tomohiko Tomita, Tsuyoshi Yamaura, Hiroshi G. Takahashi, Masayuki Hara, Yoshio Kawatani, Masaki Satoh, Masato Sugi

    A 20-year integration by the nonhydrostatic icosahedral atmospheric model (NICAM) with a 14 km mesh was conducted for the first time to obtain a climatological mean and diurnal to interannual variability of a simulated atmosphere. Clouds were explicitly calculated using a cloud microphysics scheme without cumulus convection scheme. The simulation was performed under the atmospheric model intercomparison project-type conditions, except that sea surface temperature was nudged toward observed historical values using the slab ocean model. The results are analyzed with a focus on tropical disturbances, including tropical cyclones (TCs) and the Madden-Julian oscillation (MJO).NICAM simulates many aspects of atmospheric climatological mean state and variability. The geographical distributions of precipitation, including interannual, seasonal, and diurnal variations, are well reproduced. Zonal mean basic states, clouds, and top-of-atmosphere radiation are qualitatively simulated, though some severe biases such as underestimated low clouds, shortwave reflection, warmer surface, and tropical upper troposphere exist.TCs and MJO are the main focus of the simulation. In the simulation, TCs are detected with the objective thresholds of maximum wind speed due to the realistic intensity of simulated TCs. The seasonal march of TC genesis in each ocean basin is well simulated. The statistical property of the MJO and tropical waves is well reproduced in the space-time power spectra, consistent with previous NICAM studies. This implies that the stratospheric variability is also reproduced, as partially revealed in this study. Asian monsoon analysis shows that climatological western North Pacific monsoon onset occurs near the observed onset, and that the Baiu front is reproduced to some extent. Some significant model biases still exist, which indicates a need for further model improvements. The results indicate that a high-resolution global nonhydrostatic model has the potential to reveal multiscale phenomena in the climate system.

    METEOROLOGICAL SOC JAPAN, 2015年, JOURNAL OF THE METEOROLOGICAL SOCIETY OF JAPAN, 93 (4), 393 - 424, 英語

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    研究論文(学術雑誌)

  • Kyung-Sook Yun, Ye-Won Seo, Kyung-Ja Ha, June-Yi Lee, Yoshiyuki Kajikawa

    Interdecadal changes in the Asian winter monsoon (AWM) variability are investigated using three surface air temperature datasets for the 55-year period of 1958-2012 from (1) the National Centers for Environmental Prediction-National Center for Atmospheric Research reanalysis 1 (NCEP), (2) combined datasets from the European Centre for Medium-range Weather Forecasts (ECMWF) 40-yr reanalysis and interim data (ERA), and (3) Japanese 55-year reanalysis (JRA). Particular attention has been paid to the first four empirical orthogonal function (EOF) modes of the AWM temperature variability that together account for 64% of the total variance and have been previously identified as predictable modes. The four modes are characterized as follows: the first mode by a southern warming over the Indo-western Pacific Ocean associated with a gradually increasing basin-wide warming trend; the second mode by northern warming with the interdecadal change after the late 1980s; the third and fourth modes by north-south triple pattern, which reveal a phase shift after the late 1970s. The three reanalyses agree well with each other when producing the first three modes, but show large discrepancy in capturing both spatial and temporal characteristics of the fourth mode. It is therefore considered that the first three leading modes are more reliable than the rest higher modes. Considerable interdecadal changes are found mainly in the first two modes. While the first mode shows gradually decreasing variance, the second mode exhibits larger interannual variance during the recent decade. In addition, after the late 1970s, the first mode has a weakening relationship with the El Nio-Southern Oscillation (ENSO) whereas the second mode has strengthening association with the Artic Oscillation (AO). This indicates an increasing role of AO but decreasing role of ENSO on the AWM variability. A better understanding of the interdecadal change in the dominant modes would contribute toward advancing in seasonal prediction and the predictability of the AWM variability.

    KOREAN METEOROLOGICAL SOC, 2014年08月, ASIA-PACIFIC JOURNAL OF ATMOSPHERIC SCIENCES, 50 (4), 531 - 540, 英語

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    研究論文(学術雑誌)

  • Ryuji Yoshida, Yoshiyuki Kajikawa, Hirohiko Ishikawa

    The impact of intraseasonal oscillation on tropical cyclone genesis (TCG) over the western North Pacific during boreal summer was examined in association with categorized synoptic-scale low-level flow patterns. Five synoptic-scale flow patterns were considered as synoptic-scale environment connecting the large-scale intraseasonal oscillation and meso-scale TCG: a shear line, a confluence region, an easterly wave, a monsoon gyre, and a pre-existing tropical cyclone. The phase and amplitude of the boreal summer intraseasonal oscillation (BSISO) were used. It is found that the phase 7 was favorable for TCG associated with the shear line, and the phases 7 and 8 were also favorable for TCG associated with the confluence region. During the favorable phases for each flow pattern associated with TCG, the BSISO affected the large-scale zonal wind distribution, and the large-scale zonal wind forms synoptic-scale flow patterns over the suitable environment for TCG. The link between the intraseasonal oscillation and synoptic-scale flow patterns is an important factor in TCG.

    METEOROLOGICAL SOC JAPAN, 2014年, SOLA, 10, 15 - 18, 英語

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    研究論文(学術雑誌)

  • Yoshiaki Miyamoto, Yoshiyuki Kajikawa, Ryuji Yoshida, Tsuyoshi Yamaura, Hisashi Yashiro, Hirofumi Tomita

    Deep moist atmospheric convection is a key element of the weather and climate system for transporting mass, momentum, and thermal energy. It has been challenging to simulate convection realistically in global atmospheric models because of the large gap in spatial scales between convection (10(0)km) and global motions (10(4)km). We conducted the first ever subkilometer global simulation and described the features of convection. Through a series of grid-refinement resolution testing, we found that an essential change for convection statistics occurred around 2 km grid spacing. The convection structure, number of convective cells, and distance to the nearest convective cell dramatically changed at this resolution. The convection core was resolved using multiple grids in simulations with grid spacings less than 2.0 km.

    AMER GEOPHYSICAL UNION, 2013年09月, GEOPHYSICAL RESEARCH LETTERS, 40 (18), 4922 - 4926, 英語

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    研究論文(学術雑誌)

  • Sun-Seon Lee, June-Yi Lee, Kyung-Ja Ha, Bin Wang, Akio Kitoh, Yoshiyuki Kajikawa, Manabu Abe

    This study reexamines how the Tibetan Plateau (TP) modulates the annual variation of atmospheric circulation and storm-track activity based on the Meteorological Research Institute's atmosphere-ocean coupled model experiments with a progressive TP uplift from 0% to 100% of the present height. Three major roles of the TP on atmospheric circulation and storm-track activity are identified. First, consistent with a previous finding, the TP tends to intensify the upper-level jet and enhance baroclinicity in the North Pacific Ocean but significantly weaken storm-track activity over the TP, East Asia, and the western North Pacific during the cold season. Second, the TP amplifies stationary waves that are closely linked to transient eddies. In particular, the TP enhances the Siberian high and the Aleutian low, which together contribute to the strengthening of the East Asian winter monsoon circulation and the weakening of storm-track activity. Third, the TP significantly modulates the subseasonal variability of the Pacific storm-track (PST) activity. In particular, the TP tends to suppress PST activity during midwinter despite the fact that it strengthens baroclinicity along the Pacific jet. The midwinter suppression of PST activity, which is well reproduced in a control run with a realistic TP, gradually disappears as the TP height decreases. Major factors for the midwinter suppression of the PST associated with the TP include the 1) destructive effect of an excessively strong jet leading to an inefficiency of barotropic energy conversion, 2) reduction of baroclinicity over the northern part of the TP, and 3) subseasonally varying SST change and resulting moist static energy.©2013 American Meteorological Society.

    2013年07月, Journal of Climate, 26 (14), 5270 - 5286, 英語

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    研究論文(学術雑誌)

  • Tsuyoshi Yamaura, Yoshiyuki Kajikawa, Hirofumi Tomita, Masaki Satoh

    The impact of a tropical cyclone on the northward migration of the Baiu frontal zone (BFZ) is investigated in the case of the tropical cyclone MAWAR (2012) using a global cloud-system resolving model, called NICAM. From 4 to 6 June in 2012, the BFZ rapidly shifts northward with MAWAR. A simulation with the initial data of 29 May reproduces the northward migration of the BFZ and the tropical cyclone. Strong southerlies on the eastern side of the tropical cyclone transport moist and high-temperature air into the BFZ. This horizontal advection affects the northward migration of the BFZ. In contrast, the BFZ stagnates to the south of Japan in another simulation with the initial data of 30 May because the tropical cyclone track is diverted eastward. Thus, realistic reproducibility of a tropical cyclone is needed for better simulations and prediction of the BFZ migration.

    METEOROLOGICAL SOC JPN, 2013年, SOLA, 9, 89 - 93, 英語

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    研究論文(学術雑誌)

  • Yoshiyuki Kajikawa, Bin Wang

    A significant advance in the onset dates of the South China Sea summer monsoon (SCSSM) is detected around 1993/94: the epochal mean onset date is 30 May for 1979-93 and 14 May for 1994-2008. The relatively late onset during the first epoch is primarily determined by the northward seasonal march of the intertropical convergence zone, whereas the advanced onset during the second epoch is affected by the enhanced activity of northwestward-moving tropical disturbances from the equatorial western Pacific. During 1994-2008, the intraseasonal variability (ISV) over the western Pacific was enhanced during the period from mid-April to mid-May; further, the number of tropical cyclones (TCs), which passed through the South China Sea (SCS) and Philippine Sea during the same period, is about doubled compared with those occurring during 1979-93. This enhanced ISV and TC activity over the SCS and Philippine Sea are attributed to a significant increase in SST over the equatorial western Pacific from the 1980s to 2000s. Therefore, the advanced SCSSM onset is rooted in the decadal change of the SST over the equatorial western Pacific.

    AMER METEOROLOGICAL SOC, 2012年05月, JOURNAL OF CLIMATE, 25 (9), 3207 - 3218, 英語

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    研究論文(学術雑誌)

  • Kazuyoshi Kikuchi, Bin Wang, Yoshiyuki Kajikawa

    The tropical intraseasonal oscillation (ISO) shows distinct variability centers and propagation patterns between boreal winter and summer. To accurately represent the state of the ISO at any particular time of a year, a bimodal ISO index was developed. It consists of Madden-Julian Oscillation (MJO) mode with predominant eastward propagation along the equator and Boreal Summer ISO (BSISO) mode with prominent northward propagation and large variability in off-equatorial monsoon trough regions. The spatial-temporal patterns of the MJO and BSISO modes are identified with the extended empirical orthogonal function analysis of 31 years (1979-2009) OLR data for the December-February and June-August period, respectively. The dominant mode of the ISO at any given time can be judged by the proportions of the OLR anomalies projected onto the two modes. The bimodal ISO index provides objective and quantitative measures on the annual and interannual variations of the predominant ISO modes. It is shown that from December to April the MJO mode dominates while from June to October the BSISO mode dominates. May and November are transitional months when the predominant mode changes from one to the other. It is also shown that the fractional variance reconstructed based on the bimodal index is significantly higher than the counterpart reconstructed based on the Wheeler and Hendon's index. The bimodal ISO index provides a reliable real time monitoring skill, too. The method and results provide critical information in assessing models' performance to reproduce the ISO and developing further research on predictability of the ISO and are also useful for a variety of scientific and practical purposes.

    SPRINGER, 2012年05月, CLIMATE DYNAMICS, 38 (9-10), 1989 - 2000, 英語

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    研究論文(学術雑誌)

  • Yoshiyuki Kajikawa, Tetsuzo Yasunari, Shuhei Yoshida, Hatsuki Fujinami

    In this paper, we first elucidate the significant seasonality in long-term trends in the Asian monsoon on a monthly mean basis. Advanced monsoon onsets over the Bay of Bengal and the western Pacific were evident in recent decades. Increasing rainfall in May along 10 degrees N reflected the advanced monsoon onset. Decreasing rainfall trends in June along 10 degrees N were also detected. Because the rainfall trends in July and August showed less significance, the monsoon transition phase should be discussed in the context of climate change rather than boreal summer mean field. The advanced monsoon onset and weakening of the monsoon during early summer are most likely to be attributed to the heat contrast between the Asian landmass and the tropical Indian Ocean. The heating trend over the Asian landmass primarily contributes to the heat contrast variability with the persistent SST increase in the Indian Ocean throughout the season. Citation: Kajikawa, Y., T. Yasunari, S. Yoshida, and H. Fujinami (2012), Advanced Asian summer monsoon onset in recent decades, Geophys. Res. Lett., 39, L03803, doi:10.1029/2011GL050540.

    AMER GEOPHYSICAL UNION, 2012年02月, GEOPHYSICAL RESEARCH LETTERS, 39, 英語

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    研究論文(学術雑誌)

  • Yoshiyuki Kajikawa, Bin Wang, Jing Yang

    A broad-scale Australian monsoon index (AUSMI) describing multi-time scale variations is defined by using 850 hPa zonal wind averaged over the area (5 degrees S-15 degrees S, 110 degrees E-130 degrees E). This circulation index reflects monsoonal rainfall variability over Northern Australia and maritime continent. The index can be used to depict the seasonal cycle (for instance the onset) and measure the intraseasonal, interannual, and interdecadal variations of the Australian monsoon. The interannual variation of the Australian monsoon onset determined by the AUSMI agrees well with that derived from the rainfall and winds at Darwin in the previous studies. We found a significant anti-correlation between the monsoon onset date and the seasonal (DJF) mean AUSMI anomalies; namely an early onset is accompanied by a strong Australian summer monsoon and vice versa. These interannual variations are also strongly associated with El Nino-Southern Oscillation (ENSO). In contrast, the retreat dates are not significantly different between the strong and weak Australian summer monsoon years. The AUSMI is useful in monitoring the weather and climate variations of the Australian monsoon and validating the performance of climate models. Copyright (C) 2009 Royal Meteorological Society

    JOHN WILEY & SONS LTD, 2010年06月, INTERNATIONAL JOURNAL OF CLIMATOLOGY, 30 (8), 1114 - 1120, 英語

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    研究論文(学術雑誌)

  • Ping Liu, Yoshiyuki Kajikawa, Bin Wang, Akio Kitoh, Tetsuzo Yasunari, Tim Li, H. Annamalai, Xiouhua Fu, Kazuyoshi Kikuchi, Ryo Mizuta, Kavirajan Rajendran, Duane E. Waliser, Daehyun Kim

    This study documents the detailed characteristics of the tropical intraseasonal variability (TISV) in the MRI-20km60L AGCM that uses a variant of the Arakawa-Schubert cumulus parameterization. Mean states, power spectra, propagation features, leading EOF modes, horizontal and vertical structures, and seasonality associated with the TISV are analyzed. Results show that the model reproduces the mean states in winds realistically and in convection comparable to that of the observations. However, the simulated TISV is less realistic. It shows low amplitudes in convection and low-level winds in the 30-60-day band. Filtered anomalies have standing structures. Power spectra and lag correlation of the signals do not propagate dominantly either in the eastward direction during boreal winter or in the northward direction during boreal summer. A combined EOF (CEOF) analysis shows that winds and convection have a loose coupling that cannot sustain the simulated TISV as realistically as that observed. In the composited mature phase of the simulated MJO, the low-level convergence does not lead convection clearly so that the moisture anomalies do not tilt westward in the vertical, indicating that the low-level convergence does not favor the eastward propagation. The less realistic TISV suggests that the representation of cumulus convection needs to be improved in this model.

    AMER METEOROLOGICAL SOC, 2009年04月, JOURNAL OF CLIMATE, 22 (8), 2006 - 2022, 英語

    [査読有り]

    研究論文(学術雑誌)

  • Yoshiyuki Kajikawa, Tetsuzo Yasunari, Bin Wang

    Evidence is presented to reveal a decadal change around mid-1990s in the behavior of intraseasonal variability (ISV) over the South China Sea (SCS). During 1979-1993, the ISV has a spectral peak around 64 days, which is longer than in the recent epoch of 1994-2007 (around 42 days). The ISV event in 1979-1993 involves a merging process of the northward and westward propagating convection anomalies over the western North Pacific. The ISV in 1994-2007 has no such a merging process but exhibits a tilted band structure extending from the northern Indian Ocean to the SCS, which is strongly connected to the equatorial eastward propagating Madden-Julian Oscillation. The merging process during 1979-1993 modified the ISV over the SCS, resulting in the prolonged period, enhanced convective activity and a weakened relationship with the eastward propagating MJO. The possible cause of this change is discussed. Citation: Kajikawa, Y., T. Yasunari, and B. Wang (2009), Decadal change in intraseasonal variability over the South China Sea, Geophys. Res. Lett., 36, L06810, doi: 10.1029/2009GL037174.

    AMER GEOPHYSICAL UNION, 2009年03月, GEOPHYSICAL RESEARCH LETTERS, 36, 英語

    [査読有り]

    研究論文(学術雑誌)

  • Koji Fujita, Lonnie G. Thompson, Yutaka Ageta, Tetsuzo Yasunari, Yoshiyuki Kajikawa, Akiko Sakai, Nozomu Takeuchi

    [ 1] Two net balance records of neighboring glaciers under different conditions are analyzed to extract temporal variations in glacier melting in the Himalayas. Significant melt was observed every year at one site ( wet site), whereas no melt occurred at the second site because of its high elevation ( dry site). Accumulation at the wet site of a glacier is estimated from the dry site neighboring another glacier through a measured precipitation record for a short time period. The difference between the estimated accumulation and the net balances at the wet site is obtained as the "melt index,'' which represents the glacier melting conditions. The melt index with an interannual timescale is significant as a climatic proxy at high elevation since no relationship between stable isotopes and temperature is established and few long-term temperature records are available at high elevations in the Himalayas. The melt index showed a decadal fluctuation with a major amplitude never reported in previous studies with respect to temperature and ice cores analyses in the Himalayas. Ice cores from a site where significant melt occurs every year have not been considered available in reconstructing past climates since climatic signals in ice were disturbed by meltwater infiltration. However, we suggest a new approach to glean temperature information by a combination of wet and dry cores, not obtainable from a good-quality ice core alone.

    AMER GEOPHYSICAL UNION, 2006年02月, JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, 111 (D13), 英語

    [査読有り]

    研究論文(学術雑誌)

  • Kajikawa Yoshiyuki, Tetsuzo Yasunari

    2005年, GEOPHYSICAL RESEARCH LETTERS, 32

    [査読有り]

  • The role of the local hadley circulation over the western Pacific on the zonally asymmetric anomalies over the Indian Ocean

    Y Kajikawa, T Yasunari, R Kawamura

    The onset processes of the zonally asymmetric anomalies of convection and sea surface temperature (SST) over the tropical Indian Ocean are investigated with considering seasonal evolution, and inter-annual variability, of the large-scale convection anomalies in the Asian summer monsoon, using outgoing longwave radiation (OLR), SST, and NCEP/NCAR reanalysis data. This asymmetric pattern of the convection anomalies is particularly dominated in boreal autumn. Some recent studies have noted that these anomalies, based on the atmosphere-ocean coupling phenomenon, can be developed and maintained by itself. The time evolution shows that the eastern part of the zonally asymmetric anomalies over the Indian Ocean lead the western part of those. In July, the negative SST anomalies and positive OLR anomalies first appeared off the Sumatra coast, and southeasterly wind anomaly accelerated the climatological southeasterly wind along the west coast of Sumatra. This southeasterly wind acceleration provide a SST cooling over the southeastern Indian Ocean, and play a role in triggering of the zonally asymmetric anomalies in the following autumn. It is suggested that this southeasterly wind acceleration over the southeastern Indian Ocean is closely linked to the meridionally asymmetric anomalies of convection, between the maritime continent and the South China Sea/Philippine Sea (SCS/PS). That is, the intensification of the local Hadley circulation over the western Pacific associated with the enhanced convection over the SCS/PS, and suppressed convection over the maritime continent, is found to be a clear precursory signal of the zonally asymmetric anomalies over the Indian Ocean. It has also been noted that the convection anomalies over the southern and northern parts of the meridionally asymmetric anomalies over the western Pacific are not always the opposite sign, and seem to have different inter-annual variability respectively. It is likely that the former might be strongly influenced by the ENSO, through the Walker circulation anomalies and the latter might be affected by the modulation of the intraseasonal variation of the Asian summer monsoon. The seasonality of the zonally asymmetric anomalies is also suggested from the occurrence of the intensification of the local Hadley circulation in boreal summer.

    METEOROLOGICAL SOC JPN, 2003年04月, JOURNAL OF THE METEOROLOGICAL SOCIETY OF JAPAN, 81 (2), 259 - 276, 英語

    [査読有り]

    研究論文(学術雑誌)

  • An inter-comparison between ECMWF and NCEP/NCAR reanalysis data concerning the Asian monsoon and ENSO systems

    Kawamura, R, Y. Kajikawa, T. Yasunari

    1999年, Report of the National Research Institute for Earth Science and Disaster Prevention, (59), 61 - 72, 日本語

    [査読有り]

    研究論文(大学,研究機関等紀要)

MISC

  • 第6回WMOモンスーン国際ワークショップ参加報告

    梶川義幸, 藤波初木, 神澤 望, 高谷祐平, 楠昌司, 米山邦夫, 鬼頭昭雄, 尾瀬智昭

    日本気象学会, 2018年, 天気, 65 (5), 321 - 329, 日本語

  • 第3回非静力学モデルに関する国際ワークショップ・第6回全球雲解像モデリングワークショップの開催報告

    富田浩文, 梶川義幸, 宮本佳明, 吉村裕正, 榎本剛, 北村祐二, 佐藤陽祐, 清木達也, 大塚成徳, 柳瀬亘

    2015年, 天気, 61, 57 - 62, 日本語

  • シリーズ「発想のたまご」: 美味しいプレゼン

    梶川 義幸

    2013年, 水文・水資源学会誌, 26 (3), 179

  • 第3回国際モンスーンワークショップ (IWM-III) 参加報告

    松本淳, 高橋洋, 篠田太郎, 梶川義幸, 井上知栄

    2005年, 天気, 52, 685 - 690, 日本語

  • 国際アジアモンスーンシンポジウム(IAMS)参加報告

    安成哲三, 梶川義幸, 阿部学, 吉兼隆生, 名倉元樹, 森修一, 斎藤和之, 徐健青, 高橋洋, 井上知栄, 福富慶樹, 横井覚

    2004年, 天気, 51, 525 - 532, 日本語

書籍等出版物

  • 異常気象と気候変動についてわかっていることいないこと (BERET SCIENCE)

    筆保弘徳, 川瀬宏明, 梶川義幸, 高谷康太郎, 堀正岳, 竹村俊彦, 竹下秀

    共著, ベレ出版, 2014年11月21日, ISBN: 4860644158

所属学協会

  • 日本地球惑星科学連合

  • アメリカ気象学会

  • アメリカ地球物理学連合

  • 日本気象学会

共同研究・競争的資金等の研究課題

  • 広域高解像度シミュレーションによるアジアモンスーン降水システムの解明

    梶川 義幸

    公益財団法人ひょうご科学技術協会, 学術研究助成, 2018年, 研究代表者

    競争的資金

  • 東アジアと西部太平洋の気候変動を繋ぐ東シナ海/南シナ海の役割

    梶川 義幸

    文部科学省, 科学研究費補助金(基盤研究(C)), 2015年 - 2018年, 研究代表者

    競争的資金

  • 全球非静力学大気モデルを用いたアジアモンスーンオンセットと熱帯擾乱の研究

    梶川 義幸

    理化学研究所, 平成 26年度奨励課題 (研究奨励ファンド), 2014年, 研究代表者

    競争的資金