Yasutaka WakazukiAssociate Professor

■Researcher basic information

Organization

  • College of Science Department of Sciences Earth Sciences
  • Graduate School of Science and Engineering（Master's Program） Major in Science
  • Graduate School of Science and Engineerin（Doctoral Program） Major in Complex Systems Science
  • Faculty of Basic Natural Science Domain of Earth Sciences

Research Areas

  • Social infrastructure (civil Engineering, architecture, disaster prevention), Disaster prevention engineering
  • Natural sciences, Atmospheric and hydrospheric science

Research Keyword

  • Precipitation
  • Meteorology and Climatology

Degree

  • 2006年07月　博士（理学）（名古屋大学）
  • 1998年03月　修士（理学）（名古屋大学）

■Research activity information

Paper

  • Microclimate Simulation for Future Urban District under SSP/RCP: Reflecting changes in building stocks and temperature rises
    Junya Yamasaki; Yasutaka Wakazuki; Satoru Iizuka; Takahiro Yoshida; Ryoichi Nitanai; Rikutaro Manabe; Akito Murayama, Elsevier BV
    Urban Climate, Sep. 2024, [Reviewed]
  • RELATIONSHIP BETWEEN INCREASED PEAK DISCHARGE AND RAINFALL PATTERN CHANGES IN PROJECT SCALE RAINFALL EVENTS DUE TO CLIMATE CHANGE：A STUDY OF MAJOR RIVERS IN IBARAKI PREFECTURE
    ABE Shiori; WAKAZUKI Yasutaka; WATANABE Satoshi; NAKAMURA Yosuke, 令和元年に公表された「気候変動を踏まえた治水計画のあり方提言」の中で将来気候下での降雨変化倍率が示され，これを現行の計画対象降雨量に乗ずることで気候変動の影響を見積もることが基本とされている．しかし，実績降雨波形を引き伸ばす方法が将来気候下での河川流量を評価するために十分であるかは不明である．そこで，本研究では，将来気候下における降雨パターンの変化と河川ピーク流量変化の関係を明らかにするため，茨城県主要河川流域を対象に，d4PDFの降水量から整備計画規模相当降雨を抽出して流出計算を実施した．各河川の治水基準点上流における計画降雨継続時間の年最大降雨イベントをバイアス補正済み降水量から抽出し，100年確率降雨量を推定した．抽出した計画規模相当の降雨イベントを用いてRRIモデルによる流出計算を実施し，治水基準地点における河川流量を評価した．その結果から，将来気候下においてはピーク雨量や強雨の継続時間だけでなく，降雨波形の特徴が変化することが明らかになり，これを治水計画の立案において考慮する重要性が示唆された．, Japan Society of Civil Engineers
    Advances in River Engineering, Apr. 2024, [Reviewed]
  • Scenario Dependence of Future Precipitation Changes across Japan in CMIP6
    Michiya Hayashi; Hideo Shiogama; Noriko N. Ishizaki; Yasutaka Wakazuki, A bias-corrected downscaled 1-km mesh future climate dataset across Japan called NIES2020, based on five global climate models (GCMs) selected from the Coupled Model Intercomparison Project Phase 6 (CMIP6), has been used for regional impact assessments and adaptation studies under various emission scenarios. However, it is not yet revealed what determines the scenario dependence of the Japanese precipitation changes unscaled with global mean temperature changes. Here, we disentangled the inter-scenario differences in precipitation changes averaged across Japan. In the CMIP6 GCMs, the ensemble mean precipitation increases more in the mid-21st century under low-emission scenarios than higher-emission scenarios, consistent with NIES2020. In the low-emission scenarios, rapid reductions of anthropogenic aerosol emissions from East Asia enhance the surface downward shortwave radiation around Japan, promoting evaporation and precipitation. Such high precipitation sensitivity per degree of global warming is confirmed regardless of the season. In contrast, the precipitation increase is most suppressed under a high-emission scenario with weak air pollutant mitigation. Therefore, future precipitation changes across Japan are more constrained by aerosol emission changes than global warming levels, especially in the mid-21st century. This suggests climate response to air pollutant mitigations needs to be considered for implementing impact assessments and adaptation strategies in Japan., Meteorological Society of Japan
    SOLA, 2024, [Reviewed]
  • Diurnal Change of Summer Temperature Distribution in Urban Area Based on SSP/RCP Images under Climate Change
    Junya Yamasaki; Yasutaka Wakazuki; Satoru Iizuka; Takahiro Yoshida; Ryoichi Nitanai; Rikutaro Manabe; Akito Murayama, The impact of temperature rise due to climate change is becoming evident in Japan, and outdoor heat risks are increasing especially in urban areas. This study simulated diurnal changes of summer temperature distribution for SSP/RCP future images in the 2090s where climate change will have progressed, focusing on the urban center neighborhood in Nagoya City. The novelty of this study is three-fold: Using a CFD model based on comparison with actual measurement results in 2021; Visualizing thermal changes during daytime in summer based on transient analysis; Preparing three future scenarios of SSP1-1.9, SSP2-4.5, and SSP5-8.5. One of the findings was that SSP5-8.5 may bring a positive outcome for thermal environment as increasing building height generates expanding shaded area., The City Planning Institute of Japan
    Journal of the City Planning Institute of Japan, 25 Oct. 2023, [Reviewed]
  • Thermal Environment Simulation for Future Images Based on SSP/RCP in Urban Center Neighborhood under Climate Change
    Junya Yamasaki; Masahiro Masubuchi; Yasutaka Wakazuki; Satoru Iizuka; Takahiro Yoshida; Ryoichi Nitanai; Rikutaro Manabe; Akito Murayama, In community planning at neighborhood scale, a long-term vision with consideration of future climate change impact becomes increasingly important. This study demonstrated the projections of future build environment image and weather conditions based on SSP/RCP in an urban center neighborhood in Nagoya City and conducted thermal environment simulation of those 3D models. The result of the simulation of SSP5-8.5 (Fossil-fueled development scenario), which we assumed it for its future image that more high-rise buildings will be constructed by the end of the 21st century, confirmed that the neighborhood thermally deteriorated at noon in summer due to both the temperature rise and the reflections of sunlight from the building sides., The City Planning Institute of Japan
    Journal of the City Planning Institute of Japan, 25 Oct. 2022, [Reviewed]
  • CLIMATE CHANGE RESPONSE PROJECTIONS DUE TO GLOBAL WARMING TO RIVER FLOODS CAUSED BY TYPHOON HAGIBIS
    Yasutaka WAKAZUKI; Kasumi KOBAYASHI; Shiori ABE; Yukiko IMADA, Typhoon Hagibis in 2019 induced river floods in various parts of eastern Japan. The precipitation of Typhoon Hagibis was reproduced by a high-resolution atmospheric model experiment, and the model showed high reproducibility. Atmospheric model experiments with the pseudo-warming method, in which the environmental air temperature increases are assumed to be 1.1 and 3.4 degrees, were applied to estimate precipitation, where the future typhoons show almost the same intensities and tracks. The increases in rainfall, which was mostly comparable to the effect of increasing water vapor, were estimated in the future typhoon experiment. Next, the river inundation in Ibaraki Prefecture was reproduced with an RRI model experiment, and its climate change responses were also investigated. It was projected that the peak discharge would increase, the peak water level would rise, the maximum inundation depth would rise, and the inundation area would expand. In particular, there was a significant difference in the impact of flood influences between the cases where the environmental air temperatures increased by 1.1 and 3.4 degrees., Japan Society of Civil Engineers
    Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering), Sep. 2022, [Reviewed]
  • Analysis of Factors of Facilitating Early Evacuation from Disaster Sites Based on Geographical Conditions: A Case Study of a Flood by Typhoon Hagibis in Mito, Ibaraki Prefecture in 2019
    TANAKA Koichi; WAKAZUKI Yasutaka; KIMURA Riho; ITO Tetsuji; OHTSUKA Rika; USUDA Yuichiro, The purpose of this study was to clarify factors related to early evacuation in the case of widespread flooding caused by typhoon Hagibis in 2019. A questionnaire survey was conducted to determine the evacuation behavior of residents on the right bank of the Nakagawa River in the city of Mito, Ibaraki Prefecture. First, we analyzed the relationship between early evacuation and 43 variables obtained from four aspects of basic characteristics of residents, information acquisition, hesitation to evacuate, and advance countermeasures. Next, quantitative variables related to the geographic conditions of each resident’s house were added to the analysis. As a result, factors facilitating evacuation were the elevation of residences and a 20-m distance by road to an elevated site. In other words, residents who lived near or relatively close to slightly elevated areas within predicted flood zones tended to delay evacuation. Therefore, it is important to urge residents in such areas to evacuate early., The Association of Japanese Geographers
    E-journal GEO, Sep. 2021, [Reviewed]
  • Selective Precipitation Extrapolation Ensemble Prediction Combined with Correction Schemes
    Wakazuki, Y; D. Igarashi; S. Yoshida; N. Takada, High-resolution Precipitation Nowcasts (HN) provided by JMA (Japan Meteorological Agency) is a state-of-the-art operational short-term precipitation prediction. However, schemes covering uncertainties of prediction are not sufficiently considered in the single prediction. Also, modifications of predictions corresponding to the temporal change in prediction error are not sufficiently considered in the system. Thus, it is necessary to introduce ensemble prediction schemes. In addition, correcting schemes based on the systematic error of the prediction result are also expected. In this study, a precipitation prediction system is installed that the most accurate prediction is selected by the evaluation using scores of previously predicted precipitation among multiple predictions basing on precipitation motion extrapolation with various schemes. We also introduced a scheme to correct predictions based on information of errors in past predictions. The system showed the comparable scores to HN. For the line-shaped rain-band cases, the shapes and amounts of the maximum accumulated precipitation were more accurately predicted in the proposed system for the forecast time of 60 minutes. It showed high responsiveness to the occurrence of rainfall for cases with severe changes in precipitation. Further development of this system is expected in the future., Japan Society of Civil Engineers
    Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering), Nov. 2018, [Reviewed]
  • Estimation of Raindrop Size Distribution And Precipitation Using X-Band Multi-Parameter Radar Information
    Wakazuki, Y; N. Inaba; K. Yamaguchi; E. Nakakita, To accurately estimate raindrop size distribution (DSD) and rain rate from multi-parameter radar, in this study, an advanced estimation algorithm was proposed basing on a conventional method proposed by Yamaguchi (2012) (Yamaguchi method). Yamaguchi method retrieves DSD parameters from radar reflectivity (Zh) and specific differential phase shift (KDP). However, Zh is often underestimated due to rain attenuation, in the case that rain attenuation is strongly occurring. In this study, a new advanced method to retrieve accurate DSD information has been developed to solve the rain attenuation problem. DSD retrieved from KDP and difference reflectivity (ZDP) theoretically showed higher accuracy than that from KDP and Zh in large attenuation cases under pseudo observation experiments. This fact was also evaluated by observation data using an operational X-band multi-parameter radar and a raindrop disdrometer. These results are induced by the fact that Zh is largely affected by intense rainfall attenuation compared with ZDP. Therefore, it is concluded that the proposed new method is possible to retrieve DSD with higher accuracy than Yamaguchi method because rain attenuation is greatly affect retrieval accuracy of DSD., Japan Society of Civil Engineers
    Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering), Nov. 2018, [Reviewed]
  • Evaluation of Climate Change Impacts on Water Level, Discharge, And Inundation in Kinu And Kokai River Basins Using RRI Model
    Abe, S; Y. Wakazuki; Y. Nakamura; K. Sayama, In order to evaluate risks of river disasters due to global warming, rainfall data of super-high resolution numerical simulation estimated by a regional climate model were given to the Rainfall-Runoff-Inundation (RRI) model simulations in Kinu and Kokai river basins. We evaluated the impact of climate change on the risks of river floods with the three viewpoints of water level, discharge, and inundation area. As a result, the excess frequency for the lower-risk water level significantly increased, whereas the increase for the higher-risk water level was unclear. Water discharge amount mostly increased, whereas drought-flow amount did not significantly change. Furthermore, the frequency with which innundation areas expand remarkably increased, suggesting an increased risk of floods. However, the 31-year-experiments in this study involve large uncertainties with the narrow target areas such as the Kinu and Kokai River basins. It is necessary to further increase the number of cases in the future., Japan Society of Civil Engineers
    Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering), Nov. 2018, [Reviewed]
  • Physical responses of convective heavy rainfall to future warming condition: Case study of the hiroshima event
    Kenshi Hibino; Izuru Takayabu; Yasutaka Wakazuki; Tomomichi Ogata, An extreme precipitation event happened at Hiroshima in 2014. Over 200 mm of total rainfall was observed on the night of August 19th, which caused floods and many landslides. The rainfall event was estimated to be a rare event happening once in approximately 30 years. The physical response of this event to the change of the future atmospheric condition, which includes a temperature increase on average and convective stability change, is investigated in the present study using a 27-member ensemble experiment and pseudo global warming downscaling method. The experiment is integrated using the Japan Meteorological Research Institute non-hydrostatic regional climate model. A very high-resolution horizontal grid, 500 m, is used to reproduce dense cumulonimbus cloud formation causing heavy rainfall in the model. The future climate condition determined by a higher greenhouse gas concentration is prescribed to the model, in which the surface air temperature globally averaged is 4 K warmer than that in the preindustrial era. The total amounts of precipitation around the Hiroshima area in the future experiments are closer to or slightly lower than in the current experiments in spite of the increase in water vapor due to the atmospheric warming. The effect of the water vapor increase on extreme precipitation is found to be canceled out by the suppression of convection due to the thermal stability enhancement. The fact that future extreme precipitation like the Hiroshima event is not intensified is in contrast to the well-known result that extreme rainfall tends to be intensified in the future. The results in the present study imply that the response of extreme precipitation to global warming differs for each rainfall phenomenon., Frontiers Media S.A.
    Frontiers in Earth Science, 19 Apr. 2018, [Reviewed]
  • Analysis of The Flood Control Effect by Dams of Kinugawa River in 2015.09 Kanto-Tohoku Heavy Rainfall
    Konja, A; Y. Nakamura; S. Abe; K. Sayama
    Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering), Mar. 2018, [Reviewed]
  • Current and future carbon budget at Takayama site, Japan, evaluated by a regional climate model and a process-based terrestrial ecosystem model
    Masatoshi Kuribayashi; Nam-Jin Noh; Taku M. Saitoh; Akihiko Ito; Yasutaka Wakazuki; Hiroyuki Muraoka, Accurate projection of carbon budget in forest ecosystems under future climate and atmospheric carbon dioxide (CO2) concentration is important to evaluate the function of terrestrial ecosystems, which serve as a major sink of atmospheric CO2. In this study, we examined the effects of spatial resolution of meteorological data on the accuracies of ecosystem model simulation for canopy phenology and carbon budget such as gross primary production (GPP), ecosystem respiration (ER), and net ecosystem production (NEP) of a deciduous forest in Japan. Then, we simulated the future (around 2085) changes in canopy phenology and carbon budget of the forest by incorporating high-resolution meteorological data downscaled by a regional climate model. The ecosystem model overestimated GPP and ER when we inputted low-resolution data, which have warming biases over mountainous landscape. But, it reproduced canopy phenology and carbon budget well, when we inputted high-resolution data. Under the future climate, earlier leaf expansion and delayed leaf fall by about 10 days compared with the present state was simulated, and also, GPP, ER and NEP were estimated to increase by 25.2%, 23.7% and 35.4%, respectively. Sensitivity analysis showed that the increase of NEP in June and October would be mainly caused by rising temperature, whereas that in July and August would be largely attributable to CO2 fertilization. This study suggests that the downscaling of future climate data enable us to project more reliable carbon budget of forest ecosystem in mountainous landscape than the low-resolution simulation due to the better predictions of leaf expansion and shedding., SPRINGER
    INTERNATIONAL JOURNAL OF BIOMETEOROLOGY, Jun. 2017, [Reviewed]
  • Statistical downscaling of climate change projection using information of a super-high resolution RCM result
    Wakazuki Yasutaka, A statistical downscaling model was developed to create multiple super-high resolution climate change projections which are required to cover uncertainties of climate change projections. A result of super-high resolution regional climate model simulation, which use a huge computational cost, was used to create the statistical model. A horizontal interpolation model and bias correction were applied in the model. Differences or ratios for the corrections of statistical values were modeled by generalized linear models. The downscaling calculations were applied for middle resolution climate change projections with a target region including the Kanto District and the Japanese Alps., THE JAPAN SOCIETY OF HYDROLOGY AND WATER RESOURCES
    Proceeding of Annual Conference, 2017
  • Evaluation of climate change impact for water level, discharge, and inundation by RRI model at Kinu river and Kokai river
    Abe Shiori; Nakamura Yosuke; Wakazuki Yasutaka; Sayama Takahiro, 気候変動に関する政府間パネル(IPCC)において，IPCC第5次評価報告書が公表されており，人為的な気候変動の理論はもはや疑う余地がない．この気候変動が河川の流況や人間活動に及ぼす影響については，全球レベルでの研究は多数報告されているが，流域スケールでの影響評価事例はまだ十分ではない．一方，気候変動との因果関係は定かではないが，全国各地で浸水被害が発生しており，2015(平成27)年9月関東・東北豪雨による鬼怒川の堤防決壊や2016(平成28)年8月末の小本川の外水氾濫は記憶に新しい．現在気候下での外水氾濫のリスクを評価するだけでなく，将来気候下での浸水被害を定量的に評価することは，気候変動への適応策としても水防災意識社会の再構築の観点からも重要である．本研究では，利根川水系鬼怒川・小貝川を対象とし，気候変動が河川の流況やその氾濫原に及ぼす影響を定量的に評価することを目的とした．
    本研究では，CMIP-3，SRES-A1Bシナリオに基づいた21世紀末の気候場について，領域気象モデル(WRF)で予測を行った結果を用い，将来の気候場の予測を領域気候モデル実験で推定した．同様のモデルを用いて現在気候の再現計算を行い，現在気候と将来気候の比較を行った．気候変動を評価する水文モデルにはRRIモデルを用いた．シミュレーション期間は2007年～2009年の3年間とし，それぞれ2ヶ月のスピンナップ期間を除いた前年の11月1日～当該年の10月31日とした．
    河川への気候変動の影響を評価するため，①基準水位の超過頻度，②豊平低渇流量，③氾濫による浸水域について集計を行った結果，以下の推察が得られた．
    氾濫危険水位の超過が最大で2倍増加し，浸水リスクが増加傾向にあると予測された．また，平水～渇水流量は減少傾向にあり，渇水リスクが増加傾向にあることが示唆された．浸水リスク増加に伴い浸水域が10～40%程度増加し，地域の水害リスクが高まることが確認された．
    なお，気候変化影響評価には3年間の集計では不十分であり，今後30年分の計算結果を適用する予定である．また，本気候実験の降水量は過大であり，バイアス補正についても別途検討している．, THE JAPAN SOCIETY OF HYDROLOGY AND WATER RESOURCES
    Proceeding of Annual Conference, 2017
  • Interannual Variations of Annual Snowfall, Annual Maximum Snow Depth, and Winter Precipitation in Nagano Prefecture
    Kuribayashi Masatoshi; Yamato Hiroaki; Hamada Takashi; Togashi Hitoshi; Wakazuki Yasutaka, The Japanese Society of Snow and Ice / Japan Society for Snow Engineering
    Summaries of JSSI and JSSE Joint Conference on Snow and Ice Research, 2017
  • Assessment of Hydrologic Response to Future Climate Change in The Tone River Basin of Japan
    Shrestha M; T. Koike; P. A. Jaranilla-Sanchez; L. Wang; Y. Wakazuki
    Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering), 2016, [Reviewed]
  • PROBABILISTIC CLIMATE CHANGE PROJECTION IN KANTO AND JAPAN ALPS REGIONS USING INCREMENTAL DYNAMICAL DOWNSCALING
    Yasutaka WAKAZUKI; Masayuki HARA; Mikiko FUJITA; Xieyao MA; Tadao INOUE; Fujio KIMURA; Toshio KOIKE, Japan Society of Civil Engineers
    Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering), 2016, [Reviewed]
  • Incremental dynamical downscaling for probabilistic analysis based on multiple GCM projections
    Y. Wakazuki; R. Rasmussen, A dynamical downscaling method for probabilistic regional-scale climate change projections was developed to cover the inherent uncertainty associated with multiple general circulation model (GCM) climate simulations. The climatological increments estimated by GCM results were statistically analyzed using the singular vector decomposition. Both positive and negative perturbations from the ensemble mean with the magnitudes of their standard deviations were extracted and added to the ensemble mean of the climatological increments. The analyzed multiple modal increments were utilized to create multiple modal lateral boundary conditions for the future climate regional climate model (RCM) simulations by adding them to reanalysis data. The incremental handling of GCM simulations realized approximated probabilistic climate change projections with the smaller number of RCM simulations. For the probabilistic analysis, three values of a climatological variable simulated by RCMs for a mode were analyzed under an assumption of linear response to the multiple modal perturbations., AMER GEOPHYSICAL UNION
    GEOPHYSICAL RESEARCH LETTERS, Dec. 2015, [Reviewed]
  • Development of Trajectory Simulator for Radioactive Plumes
    青山智夫; 若月泰孝, Under nuclear power plant accident, by the ventilation of containment vessel, suspended particulate matter (SPM) is emitted; it attracts radioactive compounds, and the plume diffuses in air. It soaks into the human body. We are required to run away from the invisible plumes. The routes do not exist at any time. We recognize status soon, and should select priority persons to escape from there. We code a real-time plume tracer, which reads 4D-winds of Meso Scale Model (MSM), calculates time-development of plumes. The precision for reach time of plumes is 3–5 min, inner 8 km points from emission., Society of Computer Chemistry, Japan
    Journal of Computer Chemistry, Japan, Sep. 2015, [Reviewed]
  • Numerical Prediction Experiment Of Cumulus Convection By Upstream Lower-Level Humidification
    若月泰孝, A short-term precipitation prediction (nowcast) method was developed by using upstream low-level humidification (ULH) in a cloud-resolving atmospheric model simulation. The ULH plays a role in the approximated adjoint calculation for time integration of four-dimensional variational data assimilation. This method was applied to a heavy rainfall event observed in the Kanto Plain on September 2, 2013. The heavy rainfall caused by a few cumulonimbus clouds was predicted by the ULH well before 30 minutes. The upstream advection period of 20 minutes was appropriate for more accurate prediction. The predicted cumulonimbus cloud included a large vertical vorticity that seems to have been associated with the observed tornado., Japan Society of Civil Engineers
    土木学会論文集 B1(水工学), Mar. 2015, [Reviewed]
  • Numerical Experiments of Meso-alpha-Scale Precipitation Systems under Baiu-Front-Like Idealized Environments
    Yasutaka Wakazuki; Tomoya Watanabe, To investigate the variability of the structure and evolution of meso-alpha-scale precipitation systems generated in the Baiu frontal zone, numerical experiments using a cloud-resolving non-hydrostatic model were performed with idealized Baiu-front-like environments. The environment was constructed based on hydrostatic and geostrophic balances, and temperature and relative humidity were designed by using Gaussian functions to realize the frontal structure and moist conveyor belt in the lower atmosphere. In order to generate meso-alpha-scale precipitation systems, temperature perturbation associated with a shallow depression was introduced. Long-lived band-shaped meso-alpha-scale precipitation systems with the internal multiscale structures as are often observed in the Baiu frontal zone were simulated under the given simplified environments. The variability of features of the meso-alpha-scale precipitation systems with respect to relative humidity in the middle troposphere in the Baiu frontal zone was examined as an example. The moister environment produced the more rainfall. Additionally, rainfall was intensified under a specific humidity condition., METEOROLOGICAL SOC JAPAN
    SOLA, 2015, [Reviewed]
  • Effect of climate change on the snow disappearance date in mountainous areas of central Japan
    Yasutaka Wakazuki; Masayuki Hara; Mikiko Fujita; Chieko Suzuki; Xieyao Ma; Fujio Kimura, We investigated climate change in the annual snow cover period in mountainous areas of central Japan by downscaling simulations of four climate change projections based on a Coupled Model Intercomparison Project phase 3 (CMIP3) Special Report on Emission Scenarios (SRES) A1B emission scenario using a regional climate model. Our numerical simulation reproduced well the observed snow depths and areas of snow cover. The projected snow disappearance date in all areas occurred earlier in the future climate due to global warming and were substantially earlier in areas of both light and heavy snowpacks in the present climate. The time shift was smaller at areas where the present-day maximum snow depth is around 100 cm and the snow disappearance date is in mid-April. These projected changes in the duration of snow cover were associated with decreasing snowfall and accelerated snowmelt due to increasing surface air temperatures. The effect was interpreted using an idealized model of temporal variation in surface air temperature. Earlier snowmelt causes local enhancement of surface air temperature increases that will have considerable impact on mountain ecosystems., JSHWR, JAGH, JAHS, JSPH
    HYDROLOGICAL RESEARCH LETTERS, 2015, [Reviewed]
  • Simulation of Ambient Dose Rate in Nakadori District of Fukushima Prefecture on March 15 and 16, 2011
    Wakazuki, Y; T. Aoyama; M. Takigawa, We discuss mass deposition equations of radionuclides diffused by the Fukushima Daiichi nuclear disaster. The empirical equations of physical dry and moist depositions are constructed by using numerical atmospheric model simulation results including diffused radioactive substances and precipitation. The gamma-ray fluxes from radionuclides in the tracer are evaluated and the ambient dose rate is calculated. The rates are fitted to observations, and four parameters of the deposition equations are optimized. The equation is not only for empirical and statistical correction of numerical atmospheric model simulation results but also for understanding physical deposition processes.Using the optimized equation, we calculate ambient dose rates from March 15 to 16 in 2011, as for 32 points along R114, R399, and Ban-Etsu highway in Fukushima prefecture. They are measured by teams of MEXT, KEK, and Fukushima prefecture. 71% of the calculation errors are under the ratio 3.1. The error level is remarkably smaller than that of no-optimization., Society of Computer Chemistry, Japan
    Journal of Computer Chemistry, Japan, Dec. 2014, [Reviewed]
  • Depositions of radioactive dust in the atmosphere　　　　　　　　　　　　　　　
    T.,Aoyama; Y.,Wakazuki; R.,Ohmura; Y.,Onda, 日本地球惑星科学連合
    日本地球惑星科学連合2013年大会予稿集, May 2013
  • Simulating river discharge in a snowy region of Japan using output from a regional climate model
    X. Ma; H. Kawase; S. Adachi; M. Fujita; H. G. Takahashi; M. Hara; N. Ishizaki; T. Yoshikane; H. Hatsushika; Y. Wakazuki; F. Kimura, Snowfall amounts have fallen sharply along the eastern coast of the Sea of Japan since the mid-1980s. Toyama Prefecture, located approximately in the center of the Japan Sea region, includes high mountains of the northern Japanese Alps on three of its sides. The scarcity of meteorological observation points in mountainous areas limits the accuracy of hydrological analysis. With the development of computing technology, a dynamical downscaling method is widely applied into hydrological analysis. In this study, we numerically modeled river discharge using runoff data derived by a regional climate model (4.5-km spatial resolution) as input data to river networks (30-arcseconds resolution) for the Toyama Prefecture. The five main rivers in Toyama (the Oyabe, Sho, Jinzu, Joganji, and Kurobe rivers) were selected in this study. The river basins range in area from 368 to 2720 km2. A numerical experiment using climate comparable to that at present was conducted for the 1980s and 1990s. The results showed that seasonal river discharge could be represented and that discharge was generally overestimated compared with measurements, except for Oyabe River discharge, which was always underestimated. The average correlation coefficient for 10-year average monthly mean discharge was 0.8, with correlation coefficients ranging from 0.56 to 0.88 for all five rivers, whereas the Nash-Sutcliffe efficiency coefficient indicated that the simulation accuracy was insufficient. From the water budget analysis, it was possible to speculate that the lack of accuracy of river discharge may be caused by insufficient accuracy of precipitation simulation. © 2013 Author(s).
    Advances in Geosciences, 2013, [Reviewed]
  • An Investigation of air temperature distribution in-and outside of a wooded area in early winter morning-A case study for the Yoyogi-park and the Meiji-shrine-
    岡田牧; 若月泰孝; 犬飼俊; 廣田陸; 日下博幸
    Journal of Heat Island Institute International, 2013, [Reviewed]
  • Comparison of Snow Water Equivalent Estimated in Central Japan by High-Resolution Simulations Using Different Land-Surface Models
    Masatoshi Kuribayashi; Nam Jin Noh; Taku M. Saitoh; Ichiro Tamagawa; Yasutaka Wakazuki; Hiroyuki Muraoka, We estimated the snow water equivalent (SWE) of snowpack in central Japan from September 2006 to August 2008 by using a 3.3 km-mesh regional climate model with two land-surface models: Noah land-surface model (Noah LSM), and Noah land-surface model with multiparameterization options (Noah MP). The model validation for temporal variations of SWE at the Tohkamachi station and the comparison of modeled maximum SWE with estimated that from observed maximum snow depth at ten sites showed that Noah MP could simulate spatiotemporal variations of SWE better than Noah LSM which underestimated SWE. Simulated SWE in central Japan peaked in March, but the difference of SWE between the two land-surface models was greatest in April. SWE determined using Noah LSM (Noah MP) in analysis domain reached 18.1% (28.5%) of the total storage capacity of high dams in Japan in March 2007, whereas it reached 32.4% (44.1%) in March 2008. The difference of SWE between the two land-surface models was particularly high under warm conditions, that is, during the snowmelt season, and during a warmer than normal winter. Our results indicate that the choice of land-surface model for estimates of SWE is important under warm climatic conditions., METEOROLOGICAL SOC JPN
    SOLA, 2013, [Reviewed]
  • Modified relative humidity based on the Johnson's SB distribution function
    Yasutaka Wakazuki, A new atmospheric humidity variable called the modified relative humidity (MRH) is proposed based on properties of the Johnson's SB distribution function. The frequency distribution of MRH can be roughly approximated by the normal distribution, while other variables such as relative humidity and the water vapor mixing ratio cannot. This characteristic suggests that MRH is convenient for statistical variable controls such as data assimilation and climatological grid data controls. Super-saturation and negative water vapor states induced by positive and negative humidity increments are avoided by using MRH. Three types of MRH, Types-I, -II, and -III, were examined. Type-III, with three fixed parameters, was the best function for approximating to the normal distribution. However, Types-I and -II, each with two fixed parameters, were beneficial for stable statistical humidity variable estimations., Meteorological Society of Japan
    Scientific Online Letters on the Atmosphere, 2013, [Reviewed]
  • New Distribution Functions for Hourly and Daily Precipitation Intensities during the Snowless Season in Japan
    Yasutaka Wakazuki, In this study, various probability distribution functions for the entire intensity range of short-term precipitation, such as the hourly and daily precipitation intensities during the snowless season in Japan, were examined. The traditional distribution functions, i.e., the exponential, Weibull, Gamma, generalized Gamma, log-normal, and Johnson's S-B distributions, were insufficient to express the precipitation intensities within the rainy periods.
    Three types of distribution functions were newly proposed in association with the extension of the Weibull distribution. The new distributions were constructed to vary asymptotically from the exponential distribution on the weak intensity side to the Weibull distribution on the strong intensity side. The number of parameters of the distribution functions was four except for the parameter of the rainy period ratio. One or two parameters were fixed as unity parameters in all observation points in the parameter estimation in order to overcome a multi-solution problem caused by the strong non-linearity of the distribution functions. The unity parameters were determined to be the values at which the all-points average of mean square errors for logarithms of exceedance probabilities had the minimum value. Other parameters were estimated by the maximum likelihood estimation method. The new distribution functions were more suitable to express the short-term precipitation, including both weak and strong intensities, than the traditional distribution functions were. For the hourly precipitation, the boundary intensity between the exponential and Weibull distribution properties was considered to be associated with that between the main domination ranges of stratiform and convective precipitations. A two-parameter (except for the rainy period and the unity parameters) function with Type-I and three-parameter functions with Type-I and -III were proposed as the best functions for hourly precipitation intensities. A two-parameter function with Type-III was also proposed for daily precipitation., METEOROLOGICAL SOC JAPAN
    JOURNAL OF THE METEOROLOGICAL SOCIETY OF JAPAN, Feb. 2011, [Reviewed]
  • Hydrological response to future climate change in the Agano River basin, Japan
    Ma, X; T. Yoshikane; M. Hara; Y. Wakazuki; H. G. Takahashi; F. Kimura, To evaluate the impact of climate change on snowfall in Japan, a hydrological simulation was made in the Agano River basin by using a regional climate model's output. A hindcast experiment was carried out for the two decades from 1980 to 1999. The average correlation coefficient of 0.79 for the monthly mean discharge in the winter season showed that the interannual variation of the river discharge could be reproduced and that the method can be used for climate change study. The future hydrological response to global warming in the 2070s was investigated using a pseudo-global-warming method. In comparison to data from the 1990s, the monthly mean discharge for the 2070s was projected to increase by approximately 43% in January and 55% in February, but to decrease by approximately 38% in April and 32% in May. The flood peak in the hydrograph was moved forward by approximately one month, changing from April in the 1990s to March in the 2070s. Furthermore, the projection for the 10-year average snowfall amount was projected to be approximately 49.5% lower in the 2070s than in the 1990s.
    , THE JAPAN SOCIETY OF HYDROLOGY AND WATER RESOURCES
    Hydrological Research Letters, Mar. 2010, [Reviewed]
  • Study on estimation of regional-scale climate change in intense precipitation
    Wakazuki Yasutaka; Hara Masayuki; Kimura Fujio, We introduce studies on estimation methods of regional-scale climate changes in intense precipitation frequencies. Two themes are included. One of them is the development of a statistical estimation method of the intense precipitation frequency. Another is the formation method of lateral boundary data for regional climate model experiments. These estimation methods are developed to practically estimate regional climate changes associated with multi-GCM downscaling which are needed to cover uncertainties of the estimations. The former method uses probability distribution function developed by Wakazuki (2009). The parameters of the function are empirically estimated by a statistical relationship. The later are the introductions of pseudo-global-warming method and its further developments., THE JAPAN SOCIETY OF HYDROLOGY AND WATER RESOURCES
    Proceeding of Annual Conference, 2010
  • Effect of global climate change on urban heat island intensity of Tokyo metropolitan area : winter season case
    Hara, M; H. Kusaka; F. Kimura; Y. Wakazuki, 過去100年間における全球平均の地上気温上昇は0.66℃である一方,東京の地上気温上昇は約3℃である.この違いの原因は,この間に顕著になった都市ヒートアイランドによる影響が大きい.都市ヒートアイランドによる地上気温の上昇は,冬季に最大となる.本研究では,都市キャノピーモデルを含む高解像度領域気候モデルWRFを用いて過去気候の再現実験を実施し,さらに擬似温暖化手法を用いて,SRES A2における2070年代を想定した将来気候実験を行った.これらから全球規模の気候変動が冬の東京都市圏における都市ヒートアイランド強度(Urban Heat Island Intensity;UHII)に与える影響を評価した.その結果,気候変動によって,夜間のUHIIは約20%以上強まることが示唆された.During the recent 100 years, mean surface air temperature (SAT) increased about 3℃ in Tokyo, while the world mean SAT increased only 0.66℃. The major reason of the difference of the warming is the effect of urban heat island (UHI), whose intensity also increased during the period and often largest during winter. This study investigates the change in UHI intensity (UHII) of Tokyo metropolitan area by the effects of global climate change. Present climate simulation is conducted using a high-resolution numerical climate model (WRF) including an urban canopy sub-model. Future climate run is also conducted using Pseudo-Global-Warming method assuming the boundary conditions in 2070s estimated by a GCM under the SRES A2 scenario. The simulation results indicated that UHII would be enhanced more than 20% during night, due to the global climate change. SAT in the urban area is more slowly increase during daytime due to the larger heat capacity than the rural area. Heat release from the buildings in urban area is larger than that in rural area at night, when the dispersion of the released heat tends to be restricted in the lower atmosphere because of weak turbulence. These processes are sensitive on cloud fraction and the atmospheric stability in the lower atmosphere., 日本流体力学会
    Journal of Japan Society of Fluid Mechanics, 2010, [Reviewed]
  • Climatological Reproducibility Evaluation and Future Climate Projection of Extreme Precipitation Events in the Baiu Season Using a High-Resolution Non-Hydrostatic RCM in Comparison with an AGCM
    Yasutaka Wakazuki; Masaomi Nakamura; Sachie Kanada; Chiashi Muroi, This paper studies an evaluation of climatological reproducibility and one of future climate projections of extreme precipitation in the Baiu season (from mid-May to July) around Japan using data of numerical experiments. The models are a non-hydrostatic cloud-system-resolving atmospheric model with a horizontal grid size of 5 km (5km-NHM) utilized as a regional climate model (RCM), and an atmospheric general circulation model (AGCM) with a horizontal resolution of about 20 kin (20km-AGCM) which provided the boundary condition of 5km-NHM. Ten-year runs were performed by the time-slice method. The mean precipitation amount of the three heaviest precipitation events that ranked in order of precipitation amount in every year (P-Top3) at each grid point was used as an index to examine quantitatively extreme precipitation within a specific term with various precipitation accumulation periods (APs).
    The 5km-NHM experiment reproduced P-Top3 much better than that of 20km-AGCM, especially for shorter APs. In the projection of P-Top3 in the future climate with 5km-NHM, ratio in two climate states of P-Top3 for longer APs and that of precipitation amount show the roughly same pattern. The increase areas of those were localized around Kyushu, Japan. In particular, the P-Top3 for longer APs was projected to increase 30-70% in the mountainous areas along the Pacific coast of western Japan. This increase was due to a cyclonic circulation of an incremental low-pressure generated on the western side of Kyushu. On the other hand, large increases of P-Top3 for shorter APs spread widely with a scattered pattern to the area where precipitation decreases. Ibis characteristic was associated with the intensification of precipitation due to global warming., METEOROLOGICAL SOC JAPAN
    JOURNAL OF THE METEOROLOGICAL SOCIETY OF JAPAN, Dec. 2008, [Reviewed]
  • Effects of global warming on heavy rainfall during the Baiu season projected by a cloud-system-resolving model
    Nakamura, M; S. Kanada; Y. Wakazuki; C. Muroi; A. Hashimoto; T. Kato; A. Noda; M. Yoshizaki; K. Yasunaga, Under the Kyosei-4 Project, unprecedented high resolution global and regional climate models were developed on the Earth Simulator to investigate the effect of global warming on tropical cyclones, baiu frontal rainfall systems, and heavy rainfall events that could not be resolved using conventional climate models.For the regional climate model, a nonhydrostatic model (NHM) with a horizontal resolution of 5 km was developed to be used in the simulation of heavy rainfall during the baiu season in Japan. Simulations in June and July were executed for 10 years in present and future global warming climates. It was found that, due to global warming, mean rainfall is projected to increase except in eastern and northern Japan, the frequency of heavy rainfall events would increase and its increment rate become higher for heavier rainfall, and return values for extreme rainfall would grow.Experiments using an NHM with a horizontal resolution of 1 km were conducted to study the effects of resolution. Compared to 5 km resolution, it expresses the organization of rainfall systems causing heavy rainfall and the appearance-frequency distribution of rainfall for variable intensities more realistically., Fuji Technology Press Ltd.
    Journal of Disaster Research, Feb. 2008, [Reviewed]
  • Study on regional climate change projection of extreme precipitation with downscaling experiments of GCMs
    Wakazuki Yasutaka; Nakamura Masaomi, We introduce climate change projections of extreme precipitation. First, numerical experiments of climate changes in the Baiu frontal precipitation using a non-hydrostatic regional climate model were performed. The model well reproduced intense precipitation with shorter accumulation periods while GCMs could not. The characteristic feature of future climate shows that the enhancements of precipitation and extreme values around the Kyushu District in association with the enhancement of diabatic heating effect. Second, reproducing of more extreme precipitation from GCMs is considered using statistical approach. PDF of precipitation intensity with variation of atmospheric condition is newly introduced. Three parameters of the PDF are statistically estimated by the results of GCM., THE JAPAN SOCIETY OF HYDROLOGY AND WATER RESOURCES
    Proceeding of Annual Conference, 2008
  • Simulations of forecast and climate modes using non-hydrostatic regional models
    Masanori Yoshizaki; Chiashi Muroi; Hisaki Eito; Sachie Kanada; Yasutaka Wakazuki; Akihiro Hashimoto, Two applications with a cloud-resolving model are shown utilizing the Earth Simulator. The first application is a case in the winter cold-air outbreak situation observed over the Sea of Japan as a forecast mode. Detailed structures of the convergence zone (JPCZ) and formation of mechanism of transverse convective clouds (T-modes) are discussed. A wide domain in the horizontal (2000 x 2000) was used with a horizontal resolution of I km, and could reproduce detailed structures of the JPCZ as well as the cloud streets in the right positions. It is also found that the cloud streets of T-modes are parallel to the vertical wind shears and, thus, similar to the ordinary formation mechanism as longitudinal convective ones. The second application is changes in the Baiu frontal activity in the future warming climate from the present one as a climate mode. At the future warming climate, the Baiu front is more active over southern Japan, and the precipitation amounts increase there. On the other hand, the frequency of occurrence of heavy rainfall greater than 30 mm h(-1) increases over the Japan Islands., SPRINGER
    HIGH RESOLUTION NUMERICAL MODELLING OF THE ATMOSPHERE AND OCEAN, 2008, [Reviewed]
  • Regional Climate Projection Experiments on the Baiu Frontal Activity around the Japan Islands Using a Non-Hydrostatic Cloud-System-Resolving Model
    Wakazuki, Y; S. Kanada; C. Muroi; A. Hashimoto; T. Kato; M. Nakamura; A. Noda; M. Yoshizaki; K. Yasunaga
    Journal of the Earth. Simulator, Nov. 2007, [Reviewed]
  • An assimilation and forecasting experiment of the Nerima heavy rainfall with a cloud-resolving nonhydrostatic 4-dimensional variational data assimilation system
    Takuya Kawabata; Hiromu Seko; Kazuo Saito; Tohru Kuroda; Kyuichiro Tamiya; Tadashi Tsuyuki; Yuki Honda; Yasutaka Wakazuki, The Meteorological Research Institute of the Japan Meteorological Agency has developed a cloud-resolving nonhydrostatic 4-dimensional variational assimilation system (NHM-4DVAR), based on the Japan Meteorological Agency Nonhydrostatic Model (JMA-NHM), in order to investigate the mechanism of heavy rainfall events induced by mesoscale convective systems (MCSs). A horizontal resolution of the NHM-4DVAR is set to 2 km to resolve MCSs, and the length of the assimilation window is 1-hour. The control variables of the NHM-4DVAR are horizontal wind, vertical wind, nonhydrostatic pressure, potential temperature, surface pressure and pseudo relative humidity. Perturbations to the dynamical processes, and the advection of water vapor are considered, but these to the other physical processes are not taken into account. The NHM-4DVAR is applied to the heavy rainfall event observed at Nerima, central part of Tokyo metropolitan area, on 21 July 1999. Doppler radar's radial wind data, Global Positioning System's precipitable water vapor data, and surface temperature and wind data are assimilated as high temporal and spatial resolution data. The Nerima heavy rainfall is well reproduced in the assimilation and subsequent forecast, with respect to time sequence of 10-minute rainfall amount. The formation mechanism of the Nerima heavy rainfall is clarified from this study. A surface convergence line of horizontal winds was made of a southerly sea breeze and north-easterly winds over the Kanto plain around Nerima. Since the rise of temperature over the northern part of the Kanto plain was suppressed, due to a shield of clouds against sunshine, the difference of temperature between the convergence line and its northern side became large. Consequently, the wind convergence was enhanced around Nerima. An air with high equivalent potential temperature was lifted over this enhanced convergence line to generate cumulonimbi that caused the Nerima heavy rainfall. © 2007, Meteorological Society of Japan., Meteorological Society of Japan
    Journal of the Meteorological Society of Japan, Jun. 2007, [Reviewed]
  • Periodic evolution of multiscale precipitation systems developed within a Baiu frontal cloud cluster
    Yasutaka Wakazuki; Kazuhisa Tsuboki; Takao Takeda, A meso-α-scale cloud cluster (CC) was observed in the Baiu frontal zone, located southwest of Kyushu, Japan, on July 7, 1996. It was characterized by a lifespan of approximately 20 hours, stationary motion, and heavy precipitation of over 200 mm in a period of 12 hours. This paper contains a report of the characteristic features of internal multiscale precipitation systems observed within the CC, and their periodic evolutions as newly found facts. The CC consisted of a convective rainfall region, characterized by a meso-βL-scale (100-200 km) lineshaped convective system (convective line, MβLCL), and a weak stratiform rainfall region on the lee side of the MβLCL. The MβLCL consisted of several band-shaped meso-βS-scale (20-100 km) convective systems (MβSCSs), and each MβSCS consisted of meso-γ-scale cumulonimbus clouds. The environmental atmosphere was characterized by a warm and moist inflow in the shallow layer (below 500 m in height) associated with a cyclonic circulation of slow moving and shallow depression. Additionally, the CC was located within a large temperature gradient zone in the lower atmosphere (below 4000 m in height) along the Baiu front. These were favorable environments for the generation and maintenance of the MβLCL. The MβLCLs were periodically generated with an interval of 5-6 hours in almost the same region, and they showed a common evolution of structure and processes. The behavior of cold pools formed by the MβLCLs on the northern side of the MβLCL played a key role in the periodic evolution. The developed cold pool intensified the MβCSs in the MβLCL and modified one of the MβsCSs into an arc-shaped MβsCS, that had similar characteristics to those of squall lines. Simultaneously, the arc-shaped MβsCS became the sole MβsCS that constituted MβLCL. Finally, the MβLCL decayed with the expansion of the cold pool. Another MβLCL was generated when the favorable environment was restored after the cold pool dissipated, and the evolution process of the MβLCL was repeated. © 2006, Meteorological Society of Japan., Meteorological Society of Japan
    Journal of the Meteorological Society of Japan, Jun. 2006, [Reviewed]
  • Changes in the Baiu frontal activity in the future climate simulated by super-high-resolution global and cloud-resolving regional climate models
    Kazuaki Yasunaga; Masanori Yoshizaki; Yasutaka Wakazuki; Chiashi Muroi; Kazuo Kurihara; Akihiro Hashimoto; Sachie Kanada; Teruyuki Kato; Shoji Kusunoki; Kazuyoshi Oouchi; Hiromasa Yoshimura; Ryo Mizuta; Akira Noda, Changes in the Baiu frontal activity in the future climate are examined, making use of super-high-resolution global and cloud-resolving regional climate models (20-km-mesh AGCM and 5-km-mesh NHM). In the present study, the focus is on the lengthened duration of the Baiu, and the characteristics of the precipitation during the Baiu season in the future climate. First, 10-year global-scale simulations of the present, and future climates are conducted by the 20-km-mesh AGCM. The present climate simulation accurately reproduces the northward shift of the Baiu front with time, and the end of the Baiu season around Japan. In the future climate, the Pacific anticyclone remains at the south of the Japan islands even late in July, resulting in the obscure migration of the Baiu front to the north and the lengthened Baiu season. Second, regional climate simulations are conducted by the 5-km-mesh NHM covering East Asia, in order to investigate the small-scale response to large-scale conditions, simulated by the 20-km-mesh AGCM. While the rainfall does not vary in June between the present and future climates, there is more rainfall in July in the future climate. Moreover, the frequency of the precipitation greatly increases with the intensity of the precipitation in July in the future climate simulation. In order to investigate the typical size of the precipitation systems that bring rainfall during the Baiu season, precipitation systems are classified according to the area coverage of the systems. Precipitation systems with an area larger than 90,000 km2 are more frequently seen in July in the future climate, than in the present climate, which corresponds to more rainfall. The increase of the large system in July is most remarkable in the vicinity of Kyushu Island, and the baroclinicity in that area is stronger in the future climate. © 2006, Meteorological Society of Japan., Meteorological Society of Japan
    Journal of the Meteorological Society of Japan, Feb. 2006, [Reviewed]
  • Performance of long-term integrations of the Japan Meteorological Agency nonhydrostatic model using the spectral boundary coupling method
    K Yasunaga; H Sasaki; Y Wakazuki; T Kato; C Muroi; A Hashimoto; S Kanada; K Kurihara; M Yoshizaki; Y Sato, The spectral boundary coupling ( SBC) method, which is an approach used to couple a limited-area model with a large-scale model, was introduced into a nonhydrostatic model. To investigate whether the SBC method works well in a long-term integration of a high-resolution nonhydrostatic model, two numerical experiments were conducted with a model having a horizontal grid interval of 5 km. In one experiment, the SBC method was employed, while it was not in the other experiment. The time integration in both experiments was over a 40-day period. The nonhydrostatic model was nested into objectively analyzed fields, instead of the forecasts from an extended-area model.
    Predicted patterns of sea level pressure and precipitation were compared with objective analyses, and data provided by the Global Precipitation Climatology Project ( GPCP), respectively. The predicted rainfall amounts and surface temperature over the Japanese islands were statistically evaluated, making use of the analyzed rainfall and surface data observed by the Japan Meteorological Agency ( JMA). All results examined in the present study exhibited better performances with use of the SBC method than those without the SBC method. It was found that the SBC method was highly useful in long-term simulations by a high-resolution nonhydrostatic model., AMER METEOROLOGICAL SOC
    WEATHER AND FORECASTING, Dec. 2005, [Reviewed]
  • Changes in the Characteristic Features of Disturbances Appearing in the Baiu Frontal Zone over Western Japan Due to Global Warming
    Yasutaka Wakazuki; Masanori Yoshizaki; Kazuaki Yasunaga; Chiashi Muroi; Sachie Kanada; Akihiro Hashimoto; Teruyuki Kato; Kazuo Kurihara; Akira Noda, Numerical experiments are performed using a non-hydrostatic regional climate model with a horizontal resolution of 5 km to study changes in the characteristic features of disturbances appearing over the Baiu frontal zones due to global warming. In this study, disturbances are defined as those with precipitation greater than 20 mm/6 hr within a radius of 100 km. An increase in the number of disturbances is found in the Baiu frontal zone over western Japan in the warming climate. The increase is caused by the lengthening of the Baiu duration. In addition, the disturbances are likely to be much more detected by the intensification of precipitation. Among such disturbances, those with intense precipitation and eastward-tilting vertical structures in high-pass-filtered fields are more frequently seen in the warming climate. They are considered to be meso-alpha-scale baroclinic instability modified by diabatic heating due to large precipitation. Our results suggest that the changes in the numbers of disturbances are induced by an increase in the supply of water vapor to the Baiu frontal zone and convectively unstable stratifications in the lower atmosphere., METEOROLOGICAL SOC JPN
    SOLA, 2005, [Reviewed]
  • Structure of Mesoscale Convective Systems during the Late Baiu Season in the Global Warming Climate Simulated by a Non-Hydrostatic Regional Model
    Sachie Kanada; Chiashi Muroi; Yasutaka Wakazuki; Kazuaki Yasunaga; Akihiro Hashimoto; Teruyuki Kato; Kazuo Kurihara; Masanori Yoshizaki; Akira Noda, Mesoscale convective systems (MCSs) that bring rainfall in the vicinity of Kyushu Island, Japan during the late Baiu season in the present and global warming climates are examined by a non-hydrostatic regional climate model (NHM) with the horizontal grid of 5 km.
    In the global warming climate, two types of MCSs appear in the vicinity of Kyushu Island. One travels from the Chinese Continent and the other from the southern part of the East China Sea to Kyushu Island. These two MCSs often merge over the sea southwest of Kyushu Island, and they rapidly develop to bring heavy precipitation to the vicinity of Kyushu Island. Among the latter, MCSs with low cloud-tops below 4 km MSL (Mean Sea Level) are found.
    In the comparison with the present climate, the averaged cloud and rain water mixing ratios in the vicinity of Kyushu Island become much larger, and the peak altitude of the mixing ratios are about 0.5-1.0 km higher in the global warming climate. The cloud water mixing ratio between 2-4 km MSL increases in the global warming climate, corresponding to MCSs with low cloud-tops.
    These results suggest one of the processes to produce heavy rainfall in the vicinity of Kyushu Island in July in the global warming climate., METEOROLOGICAL SOC JPN
    SOLA, 2005, [Reviewed]
  • Characteristics of the Averaged Vertical Profiles of Hydrometeors in the Baiu Season Simulated with a Non-hydrostatic Regional Climate Model
    Akihiro Hashimoto; Masataka Murakami; Chiashi Muroi; Masanori Yoshizaki; Yasutaka Wakazuki; Sachie Kanada; Kazuaki Yasunaga; Teruyuki Kato; Kazuo Kurihara; Akira Noda, The Baiu (Mei-yu) front over East Asia in the global warming climate as well as that in the present climate is simulated using a non-hydrostatic regional climate model (NHM) with a horizontal resolution of 5 km, which explicitly calculates the microphysical processes without a cumulus parameterization. The simulation results of the present and global warming climates were compared to clarify the change in the characteristics of the distributions of cloud and precipitation particles. The vertical profile of the mixing ratio of each hydrometeor category slightly shifts about 1 km higher in the global warming climate. The mixing ratios are generally larger in the global warming climate by a factor of about 1.3 at the middle of the Baiu frontal zone. No significant difference is found in the mass ratios of solid precipitating water to total water and non-precipitating water to total water between the climates. This is a reflection of that the shape of each hydrometeor profile is similar between the climates. The approximate formulas of the mass ratios among water substances were obtained., METEOROLOGICAL SOC JPN
    SOLA, 2005, [Reviewed]
  • Changes of Baiu (Mei-yu) Frontal Activity in the Global Warming Climate Simulated by a Non-hydrostatic Regional Model
    Masanori Yoshizaki; C. Muroi; S. Kanada; Y. Wakazuki; K. Yasunaga; A. Hashimoto; T. Kato; K. Kurihara; A. Noda; S. Kusunoki, The Baiu (Mei-yu) front over East Asia in the global warming climate as well as that in the present one, is studied using outputs of a non-hydrostatic regional model with a horizontal grid size of 5 km (NHM). The NHM was run in June and July for ten years, applying a spectral boundary coupling method to reduce the horizontal phase differences of large-scale disturbances using the outputs of a global climate model with a grid size of 20 km. In the global warming climate, the Baiu front is likely to stay over the southern Japan Islands around the latitudes of 30 N-32 N and will not move northward. Therefore, the activity of the Baiu front maintains longer than that in the present climate, and the precipitation increases. On the other hand, the precipitation decreases over the northern Japan Islands and the northern Korean Peninsula. Years with no end of the Baiu season are often seen, and the frequency of occurrence of heavy rainfall greater than 30 mm h(-1) increases over the Japan Islands., METEOROLOGICAL SOC JPN
    SOLA, 2005, [Reviewed]

MISC

Research Themes