ワカヅキ　ヤスタカ
若月　泰孝准教授
Yasutaka Wakazuki

■研究者基本情報

組織

  • 理学部 理学科 地球環境科学コース
  • 理工学研究科（博士前期課程） 理学専攻
  • 理工学研究科（博士後期課程） 複雑系システム科学専攻
  • 基礎自然科学野 地球環境科学領域

研究分野

  • 社会基盤（土木・建築・防災）, 防災工学
  • 自然科学一般, 大気水圏科学

研究キーワード

  • 降水
  • 気象・気候

学位

  • 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）

■研究活動情報

論文

  • 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, 2024年09月, ［査読有り］
  • 気候変動による計画規模降雨のピーク流量増加と降雨波形変化の関係－茨城県内主要河川を対象として－
    阿部 紫織; 若月 泰孝; 渡部 哲史; 中村 要介, 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．, 公益社団法人 土木学会
    河川技術論文集, 2024年04月, ［査読有り］
  • 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年, ［査読有り］
  • 気候変動下のSSP・RCP別将来像に基づく市街地の夏季温度分布の日変化解析－実測結果との比較を踏まえた解析モデルを用いて－
    山崎 潤也; 若月 泰孝; 飯塚 悟; 吉田 崇紘; 似内 遼一; 真鍋 陸太郎; 村山 顕人, 気候変動に伴う気温上昇の影響は我が国でも顕在化しており、特に都市部における屋外環境の高温化が顕著である。本論文は都心市街地を対象とし、SSP・RCP別将来像における夏季温度分布の日変化をCFDにより解析した内容を報告する。その際、将来の市街地形態はエキスパートジャッジメントに基づいて決定し、気象条件は全球気候モデルより構築された将来の気候データを参照して決定した。本論文の既往研究からの発展性は以下にある。 1. 解析結果と実測結果の比較を踏まえた解析モデルを用意した。 2. 各解析を非定常で実施し、夏季日中の10時から18時の経時変化を把握した。 3. SSP1-1.9、SSP2-4.5、SSP5-8.5の3つの将来シナリオを用意した。 解析の結果、SSP1-1.9は気温上昇が小さい点、SSP5-8.5は建築物の高層化により日陰面積が拡大する点で他のシナリオよりも暑熱リスクが小さくなることが示唆された。これより、まちづくり分野における気候変動適応の推進に向けて新たな知見が創出されたものと結論づける。, 公益社団法人 日本都市計画学会
    都市計画論文集, 2023年10月25日, ［査読有り］
  • 気候変動下の都心市街地におけるSSP・RCP 別将来像を対象とした温熱環境シミュレーション- 名古屋市中区錦二丁目地区に着目して -
    山崎潤也; 増渕正博; 若月泰孝; 飯塚悟; 吉田崇紘; 似内遼一; 真鍋陸太郎; 村山顕人, 昨今の地区スケールのまちづくりにおいては、将来的な気候変動の影響を考慮した中長期的な計画を持つことが求められる。本論文は都心市街地の対象地区におけるSSP・RCPに基づく将来の市街地形態と気象条件を予測し、それらの3Dモデルを対象とした温熱環境シミュレーションを実施した。ケーススタディ対象地として愛知県名古屋市中区錦二丁目地区を選定し、2021年、2030年、2050年、2090年の夏季日中の屋外空間を対象とした複数のシナリオ下における温熱環境をCFD解析により再現した。対象地のSSP別の市街地形態については同地区のまちづくりに関わる専門家を中心としたエキスパートジャッジメントによって将来変容を予測し、RCP別の気象条件については全球気候モデル（GCM）の将来気候データを参照して導出した。SSP1-2.6（持続可能シナリオ）と比較してSSP5-8.5（化石燃料依存シナリオ）では21世紀末に高層建築物が乱立する将来像を想定した結果、気温上昇と建築側面からの日射反射等が相まって市街地の温熱環境が悪化する状態が解析により確認された。, 公益社団法人 日本都市計画学会
    都市計画論文, 2022年10月25日, ［査読有り］
  • 令和元年東日本台風による河川氾濫の地球温暖化による変化応答予測
    若月泰孝; 小林香澄; 阿部紫織; 今田由紀子, 地球温暖化に伴い，豪雨災害リスクの増大が懸念される．令和元年東日本台風では，東日本各地で河川氾濫が発生した．本研究では，高解像度大気モデル実験によって令和元年東日本台風の降水を再現し，良好な再現性を確認した．疑似温暖化法を用いて地球温暖化した将来（1.1℃と3.4℃の気温上昇），同規模同経路で台風が襲来した場合の降水量の変化を調べ，水蒸気の増加効果とほぼ同程度の降水量増加が見積もられた．次に，茨城県内で発生した河川氾濫をRRIモデルで再現し，その気候変化応答も調査した．その結果，ピーク流量増加，ピーク水位の上昇，最大浸水深の上昇と浸水域の拡大が予測された．特に，1.1℃と3.4℃気温上昇する場合で，水害への影響の大きな違いが見られた．, 公益社団法人 土木学会
    土木学会論文集B1(水工学), 2022年09月, ［査読有り］
  • 地理的条件を考慮した災害からの事前避難促進要因の分析―2019年台風第19号水害における茨城県水戸市を事例として―
    田中耕市; 若月泰孝; 木村理穂; 伊藤哲司; 大塚理加; 臼田裕一郎, 本稿では，2019年台風第19号による大規模な浸水被害を事例として，地理的条件が住民の事前避難に寄与した要因を明らかにした．茨城県水戸市の那珂川右岸を事例対象地域として，アンケート調査によって，住民の当時の避難行動等に関する情報を得た．はじめに，以前から検証されてきた住民の基本属性等，情報取得，避難躊躇，事前対策の4側面の計43項目について，事前避難の有無に与える影響を明らかにした．次に，個々の住宅を単位として，地理的条件を定量化した変数を加えて分析を行った．その結果，自宅立地点の標高が低いほど，また，標高20 m地点までの道路距離が長いほど，住民は事前避難により積極的であることが明らかになった．事前避難をより促進させるためには，浸水の危険性がある範囲内で標高が相対的に高い場所の居住者，台地等の高所に比較的近い場所の居住者に，重点的に働きかけることが肝要である．, 公益社団法人 日本地理学会
    E-journal GEO, 2021年09月, ［査読有り］
  • 補正スキームと組み合わせた選択型降水補外アンサンブル予測
    若月泰孝; 五十嵐大地; 吉田翔; 高田望, 気象庁高解像度降水ナウキャストは，最先端の現業の短時間降水予測である．しかし，予測誤差の変化に追従して対応する修正や予測の不確実性の考慮が十分でない．そこで本研究では，補外予測をベースとした直近の過去の複数の予測結果を分析し，「経験上最も確からしい予測」を選択する方法を検討した．さらに，過去の予測の不確かさの情報をもとに，予測を補正するスキームも導入した．本研究では，非常に簡便な予測手法をとっているが，気象庁高解像度降水ナウキャストと同等程度の予測精度を示した．線状降水帯事例に対しては60分後予測の期間積算雨量の最大値の形状をより的確に表現し，降水の変化が激しい事例に対して降水の発生に対する高い応答性を示した．, 公益社団法人 土木学会
    土木学会論文集B1(水工学), 2018年11月, ［査読有り］
  • Xバンドマルチパラメータレーダを用いた雨滴粒径分布と降水量の推定
    若月泰孝; 因幡直希; 山口弘誠; 中北英一, Xバンドマルチパラメータレーダから雨滴粒径分布(DSD)と降雨量を精度よく推定するために，山口他が提案した方法(山口法)を元に，より高度化したアルゴリズムを開発した．山口法では，レーダ反射因子(Zh)と伝搬位相差変化率(KDP)からDSDパラメータを推定するが，降雨減衰が強い場合にZhが過小評価される．本研究では，KDPと反射因子差(ZDP)からDSDパラメータを推定するアルゴリズムを導入した．擬似観測実験の結果，強い降雨減衰下では，新手法の方がDSDパラメータや降雨量を山口法よりも精度よく推定した．これは，ZDPと比べてZhが強い降雨減衰の影響を大きく受けることによる．Xバンドマルチパラメータレーダと雨滴粒径分布計の観測データに適用した検証でも，より高精度での推定が確認された．, 公益社団法人 土木学会
    土木学会論文集B1(水工学), 2018年11月, ［査読有り］
  • RRIモデルを用いた鬼怒川・小貝川における水位・流量・浸水区域の気候変化影響評価
    阿部紫織; 若月泰孝; 中村要介; 佐山 敬洋, 地球温暖化の進行による河川災害リスクを評価するため，領域気候モデルによる2km解像度の数値シミュレーションの降雨データをRRIモデルに与え，流出・氾濫シミュレーションを行った．鬼怒川・小貝川流域を対象として水位・流量・浸水区域を評価した．その結果，特に低い基準水位の超過頻度が顕著に増加することがわかったが，高い基準水位の超過頻度の変化は不明瞭であった．また，豊平低渇流量は増加傾向にあるものの，渇水流量の変化は不明瞭であった．さらに，浸水区域が顕著に拡大する頻度が増加する傾向にあり，地域への氾濫リスクの増大が示唆された．しかしながら，本研究における31年間の実験のみでは不確実性が大きいため，今後，さらにケースを増やして検討する必要がある．, 公益社団法人 土木学会
    土木学会論文集B1(水工学), 2018年11月, ［査読有り］
  • 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 SA
    Frontiers in Earth Science, 2018年04月19日, ［査読有り］
  • 平成27年9月関東・東北豪雨における鬼怒川上流ダムによる洪水調節効果の分析
    近者敦彦; 中村要介; 阿部紫織; 佐山敬洋; 若月泰孝
    土木学会論文集B1(水工学), 2018年03月, ［査読有り］
  • 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 Science and Business Media LLC
    International Journal of Biometeorology, 2017年06月, ［査読有り］
  • 高解像RCM実験情報を活用した統計的ダウンスケーリングの試み
    若月 泰孝, 気候変化の不確実性をカバーするために必要な複数の超高解像気候情報を創出するために，統計的ダウンスケーリング法が開発された．その方法では，膨大な計算資源を使う1回の超高解像領域気候実験を実施し，その情報を統計モデル作成に利用する．そのモデルでは，空間内挿(SI)とバイアス補正(BC)が実施される．統計量に対する補正（差や比）が，一般化線形モデルなどを用いてモデル化された．このSI-BCモデルは，関東・中部山岳域を対象とした中解像度の領域気候実験に適用された．, 水文・水資源学会
    水文・水資源学会研究発表会要旨集, 2017年
  • RRIモデルを適用した鬼怒川・小貝川における水位・流量・浸水域の気候変化影響評価
    阿部 紫織; 中村 要介; 若月 泰孝; 佐山 敬洋, 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．, 水文・水資源学会
    水文・水資源学会研究発表会要旨集, 2017年
  • 長野県における年降雪量・年最深積雪・冬季降水量の経年変化
    栗林 正俊; 大和 広明; 浜田 崇; 富樫 均; 若月 泰孝, 公益社団法人 日本雪氷学会／日本雪工学会
    雪氷研究大会講演要旨集, 2017年
  • 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
    土木学会論文集B1（水工学）, 2016年, ［査読有り］
  • 気候差分ダウンスケーリング法による関東・中部山岳域の確率論的気候変化予測
    若月泰孝; 原政之; 藤田実季子; 馬燮銚; 井上忠雄; 木村富士男; 小池俊雄, Japan Society of Civil Engineers
    土木学会論文集 B1(水工学), 2016年, ［査読有り］
  • 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, 2015年12月, ［査読有り］
  • 放射性plume軌跡のためのシミュレータ開発
    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., 日本コンピュータ化学会
    Journal of Computer Chemistry, Japan, 2015年09月, ［査読有り］
  • 上流下層加湿による積雲対流の予測実験
    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., 公益社団法人 土木学会
    土木学会論文集 B1(水工学), 2015年03月, ［査読有り］
  • 理想化された梅雨前線様環境下でのメソαスケールの降水システムの数値実験
    WAKAZUKI Yasutaka; WATANABE Tomoya, 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 (Web), 2015年, ［査読有り］
  • 中部日本の山岳地帯での消雪日への気候変動の影響
    WAKAZUKI Yasutaka; WAKAZUKI Yasutaka; HARA Masayuki; FUJITA Mikiko; SUZUKI Chieko; MA Xieyao; KIMURA Fujio, 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 (Web), 2015年, ［査読有り］
  • 2011年3月15~16日の福島県中通り地方の 空間線量率シミュレーション
    若月泰孝; 青山智夫; 滝川雅之, 福島第1原発の事故に伴う放射性物質の拡散沈着量を推定するために，トレーサ濃度の質量沈着方程式を検討した．この沈着方程式は，大気中における放射性物質の拡散沈着シミュレーションによる大気中の濃度と降水量から，地上の空中線量率を求めるための式である．トレーサ中の放射性核種からのガンマ線束が評価され，空間線量率を理論的に計算することができる．空間線量率の観測値を用いて，方程式中の4つのパラメータを最適化した．この方程式は，大気の拡散沈着シミュレーション結果の経験的補正式として機能するだけでなく，物理的な沈着過程の理解にも結び付く．本経験式をパラメータ最適化地点以外の任意の地点(R114，R399，福島県の磐越高速道路沿いの32地点)の2011年3月15日∼16日の空間線量率の計算に適用した．これらは文部科学省，KEK，福島県によって測定されたものである．計算値の71％は誤差比率3.1以下であって，誤差は非最適の場合より有意に小さくなった．, 日本コンピュータ化学会
    Journal of Computer Chemistry, Japan, 2014年12月, ［査読有り］
  • 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, 2013年05月
  • 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年, ［査読有り］
  • 初冬早朝における緑地内外の気温分布調査―代々木公園・明治神宮の事例―
    岡田牧; 若月泰孝; 犬飼俊; 廣田陸; 日下博幸
    Journal of Heat Island Institute International, 2013年, ［査読有り］
  • 異なる陸面モデルを用いた高解像度シミュレーションによる日本中部域の積雪水当量推定値の比較
    KURIBAYASHI Masatoshi; NOH Nam Jin; SAITOH Taku M.; TAMAGAWA Ichiro; WAKAZUKI Yasutaka; MURAOKA Hiroyuki, 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 (Web), 2013年, ［査読有り］
  • ジョンソンのSB分布関数に基づく修正相対湿度
    WAKAZUKI Yasutaka; WAKAZUKI Yasutaka, 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
    SOLA (Web), 2013年, ［査読有り］
  • 日本の無雪季における時間及び日降水量に対する新分布関数
    WAKAZUKI Yasutaka, 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, 2011年02月, ［査読有り］
  • 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, 2010年03月, ［査読有り］
  • 領域スケールの強雨頻度の気候変化推定に関する研究
    若月 泰孝; 原 政之; 木村 富士男, 本研究は、領域スケールの強雨頻度の気候変化を精度よく推定するための手法開発に関係した研究について紹介するものである。統計的手法によって降水頻度を推定する方法と領域モデルによる予測のための境界値作成手法に関する2つの内容について、その途中経過を紹介する。いずれも、気候変化予測の不確実性を評価するのに必要なマルチＧＣＭからのダウンスケーリングを行うに際し、現実的な手法を念頭に開発している。前者では、開発している短時間雨量の確率分布関数の母数をＧＣＭの予測値を説明変数とする重回帰分析で推定する方法である。時間雨量の年最大値の気候変化の推定や、それをもとに作成した将来気候での降水量の時系列などを紹介する。後者はＲＣＭ用に複数のモデルの情報を組み込んだ境界値を作成する手法についてで、擬似温暖化実験手法とよばれる。この中で変動成分の気候変化を扱うための手法開発について簡略的に紹介する。, 水文・水資源学会
    水文・水資源学会研究発表会要旨集, 2010年
  • 気候変動が首都圏の都市気候に及ぼす影響－冬季を対象として－
    原政之; 日下博幸; 木村富士男; 若月泰孝, 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
    ながれ, 2010年, ［査読有り］
  • AGCMとの比較における高分解能非静力学RCMを使った梅雨季の豪雨の気候学的再現可能性評価と将来の気候予測
    WAKAZUKI Yasutaka; NAKAMURA Masaomi; KANADA Sachie; MUROI Chiashi, 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, 2008年12月, ［査読有り］
  • 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, 2008年02月, ［査読有り］
  • GCMのダウンスケーリングによる降水極値の領域気候変化予測の取り組み
    若月 泰孝; 中村 誠臣, 極端降水の気候変化予測に関する研究を紹介する。本研究では、はじめに非静力学モデルを用いた力学的ダウンスケーリングによる将来気候予測実験を紹介する。高解像度の非静力モデル実験は、GCMが苦手とする短時間降水の極値近傍の強雨も、気候学的によく再現していた。RR2002プロジェクトで気象研究所などが行った梅雨期の将来像予測では、九州を中心とする降水量や極値の増大を予測し、温暖化による非断熱加熱効果の増強と関連付けられた。次に、統計的ダウンスケーリングのための降水強度補正に関する研究を紹介する。低分解能GCMの情報から極値近傍の分位値を推定するために、指数分布のばらつきを考慮した新しい分布関数を導入し、その中の３つの定数をGCMの熱力学量から統計的に推定することで、極値近傍の分位値を推定できると考えた。適応性に関しては検討中だが、可能な限りの検討結果を紹介する。, 水文・水資源学会
    水文・水資源学会研究発表会要旨集, 2008年
  • 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年, ［査読有り］
  • 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, 2007年11月, ［査読有り］
  • 雲分解非静力学四次元変分法同化系による練馬豪雨の同化と予報実験
    KAWABATA Takuya; SEKO Hiromu; SAITO Kazuo; KURODA Tohru; KURODA Tohru; TAMIYA Kyuichiro; TSUYUKI Tadashi; HONDA Yuki; WAKAZUKI Yasutaka; WAKAZUKI Yasutaka, 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., 公益社団法人 日本気象学会
    Journal of the Meteorological Society of Japan, 2007年06月, ［査読有り］
  • 梅雨前線の雲クラスタ内で発達する多重規模降水系の周期的展開
    WAKAZUKI Yasutaka; WAKAZUKI Yasutaka; TSUBOKI Kazuhisa; TAKEDA Takao, 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, 2006年06月, ［査読有り］
  • 超高分解能全球及び雲分解領域気候モデルによってシミュレートした未来気候における梅雨前線活動の変動
    YASUNAGA Kazuaki; YASUNAGA Kazuaki; MUROI Chiashi; KATO Teruyuki; YOSHIZAKI Masanori; KURIHARA Kazuo; KUSUNOKI Shoji; WAKAZUKI Yasutaka; HASHIMOTO Akihiro; KANADA Sachie; OOUCHI Kazuyoshi; YOSHIMURA Hiromasa; MIZUTA Ryo; NODA Akira, 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, 2006年02月, ［査読有り］
  • Performance of Long-Term Integrations of the Japan Meteorological Agency Nonhydrostatic Model Using the Spectral Boundary Coupling Method
    Kazuaki Yasunaga; Hidetaka Sasaki; Yasutaka Wakazuki; Teruyuki Kato; Chiashi Muroi; Akihiro Hashimoto; Sachie Kanada; Kazuo Kurihara; Masanori Yoshizaki; Yasuo Sato, Abstract
    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., American Meteorological Society
    Weather and Forecasting, 2005年12月, ［査読有り］
  • 地球温暖化による西日本の梅雨前線帯に現れる擾乱特性の変動
    WAKAZUKI Yasutaka; YOSHIZAKI Masanori; YASUNAGA Kazuaki; MUROI Chiashi; KANADA Sachie; HASHIMOTO Akihiro; KATO Teruyuki; KURIHARA Kazuo; NODA Akira, 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 (Web), 2005年, ［査読有り］
  • 非静力学領域モデルでシミュレートした地球温暖化気候における梅雨末期のメソ規模対流系の構造
    KANADA Sachie; MUROI Chiashi; WAKAZUKI Yasutaka; YASUNAGA Kazuaki; HASHIMOTO Akihiro; KATO Teruyuki; KURIHARA Kazuo; YOSHIZAKI Masanori; NODA Akira, 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 (Web), 2005年, ［査読有り］
  • 非静力学領域気候モデルでシミュレートした梅雨季の降水体の平均鉛直分布の特徴
    HASHIMOTO Akihiro; MURAKAMI Masataka; MUROI Chiashi; YOSHIZAKI Masanori; WAKAZUKI Yasutaka; KANADA Sachie; YASUNAGA Kazuaki; KATO Teruyuki; KURIHARA Kazuo; NODA Akira, 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 (Web), 2005年, ［査読有り］
  • 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年, ［査読有り］

MISC

書籍等出版物

  • 環境研究総合推進費戦略的研究課題 S-18 報告書 日本の気候変動影響と適応策－レジリエントで持続可能な社会に向けて－　　　　　　　　　　　　　　　
    三村信男; ほか, 分担執筆
    環境研究総合推進費 S-18 プロジェクトチーム, 2025年03月
  • 令和6年度茨城県気候変動適応業務委託報告書　　　　　　　　　　　　　　　
    横木裕宗; 田村誠; 小寺昭彦; 若月泰孝; ほか, 分担執筆
    茨城県地域気候変動適応センター, 2025年03月
  • Climate Change Scenarios for Impacts and Adaptation Research　　　　　　　　　　　　　　　
    Wakazuki Y.; Shiogama H.; Ishizaki N.; Hayashi M., 共著
    Springer Nature, 2025年03月
    9789819624362

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