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Static-Stability Control of the Structure and Intensity of Mesoscale Precipitating Systems
No full text本研究は，メソ降水系に伴う降水の構造や強度に及ぼす環境の気温減率の影響について，理想化した条件設定による雲解像数値実験を多数実行することにより調べた。CAPEを一定に保ちつつ気温減率を変化させた感度実験により，対流不安定成層中の静的安定度に応じてメソ降水系の強度が決まることが分かった。CAPEは，環境の静的安定度が同じ条件の場合においてメソ降水系の強度を診断する際の良い指標となることが示された。梅雨期強雨の事例に対して数値シミュレーションを行い，いくつかの安定度指標について調べた結果，気温減率が良い環境指標のひとつになりうることが確認された。The present study investigates the effects of environmental temperature lapse rate on the precipitation structure and intensity in mesoscale convective systems by conducting systematically a large number of idealized convection-resolving simulations of the precipitating systems that develop under low-level shear conditions. Changing the temperature lapse rate with CAPE being unchanged, we showed that the environmental stability in a convectively unstable layer well delineates the intensity of the simulated precipitating systems. CAPE can only be a good measure for diagnosing the development and intensity of the convective systems so long as the environmental static stability is identical. Some static stability measures were examined for a real heavy rain case during the Baiu season.本研究は，メソ降水系に伴う降水の構造や強度に及ぼす環境の気温減率の影響について，理想化した条件設定による雲解像数値実験を多数実行することにより調べた。CAPEを一定に保ちつつ気温減率を変化させた感度実験により，対流不安定成層中の静的安定度に応じてメソ降水系の強度が決まることが分かった。CAPEは，環境の静的安定度が同じ条件の場合においてメソ降水系の強度を診断する際の良い指標となることが示された。梅雨期強雨の事例に対して数値シミュレーションを行い，いくつかの安定度指標について調べた結果，気温減率が良い環境指標のひとつになりうることが確認された。The present study investigates the effects of environmental temperature lapse rate on the precipitation structure and intensity in mesoscale convective systems by conducting systematically a large number of idealized convection-resolving simulations of the precipitating systems that develop under low-level shear conditions. Changing the temperature lapse rate with CAPE being unchanged, we showed that the environmental stability in a convectively unstable layer well delineates the intensity of the simulated precipitating systems. CAPE can only be a good measure for diagnosing the development and intensity of the convective systems so long as the environmental static stability is identical. Some static stability measures were examined for a real heavy rain case during the Baiu season
High-Resolution Meteorological Modeling of Local-Scale Wind Fields over Eastern Fukushima in March 2011
No full text2011年3月11日に発生した東日本大震災によって生じた原子力発電所施設からの放射性物質の拡散問題を考えるための基礎情報として，複雑地形における局所的な気流の時空間変動の特性を高分解能気象モデルによる数値シミュレーションによって解析した。水平格子幅400 mの高分解能計算によって，地形の微細構造に対応した風速変動の微細性や局所性が表現された。地形が風速変動に及ぼす影響は，地上近傍のみならず地上高200 mでの風速にまで認められた。地上近傍および大気境界層の中下層での風速変動を解析する上で，複雑地形を適切に表現できる高分解能計算は必要不可欠である。This study investigated the spatial and temporal changes of local-scale winds over the complex terrain of Fukushima Prefecture in March 2011 by conducting high-resolution numerical simulations with a regional meteorological model. The analyses were intended to gain insights into the airflows relevant to the dispersion of radioactive materials from the Fukushima Daiichi nuclear power plant that was damaged by the great Tohoku earthquake on 11 March 2011. Micro-scale characteristics and local peaks of surface winds due to the micro-scale structures of the terrain were clearly represented by the high-resolution simulations at the 400-m horizontal grid spacing. The effects of the terrain on the variability of winds were identified not only near the surface level but also at the levels of up to the 200-m height above the ground level. A high resolution that is adequate to represent complex terrain features is indispensable for analyzing the spatial and temporal variability of winds near the surface and in the lower part of the atmospheric boundary layer.2011年3月11日に発生した東日本大震災によって生じた原子力発電所施設からの放射性物質の拡散問題を考えるための基礎情報として，複雑地形における局所的な気流の時空間変動の特性を高分解能気象モデルによる数値シミュレーションによって解析した。水平格子幅400 mの高分解能計算によって，地形の微細構造に対応した風速変動の微細性や局所性が表現された。地形が風速変動に及ぼす影響は，地上近傍のみならず地上高200 mでの風速にまで認められた。地上近傍および大気境界層の中下層での風速変動を解析する上で，複雑地形を適切に表現できる高分解能計算は必要不可欠である。This study investigated the spatial and temporal changes of local-scale winds over the complex terrain of Fukushima Prefecture in March 2011 by conducting high-resolution numerical simulations with a regional meteorological model. The analyses were intended to gain insights into the airflows relevant to the dispersion of radioactive materials from the Fukushima Daiichi nuclear power plant that was damaged by the great Tohoku earthquake on 11 March 2011. Micro-scale characteristics and local peaks of surface winds due to the micro-scale structures of the terrain were clearly represented by the high-resolution simulations at the 400-m horizontal grid spacing. The effects of the terrain on the variability of winds were identified not only near the surface level but also at the levels of up to the 200-m height above the ground level. A high resolution that is adequate to represent complex terrain features is indispensable for analyzing the spatial and temporal variability of winds near the surface and in the lower part of the atmospheric boundary layer
Influences of Typhoon Tracks on the Severity of Rain and Wind Storms
Get PDFThe severity of meteorological disasters spawned by typhoons critically depends on not only the intensity but also the track of typhoons. A slight change of the track of typhoons would induce a large difference in the intensity and spatial distribution of heavy rainfall and high winds. The present study explores the influences of typhoon tracks on the representations of heavy rainfall and high winds in numerical simulations of typhoon-induced events with the use of a regional meteorological model. The analyses are focused on high-impact typhoons over the Kanto Plain. A nesting capability is used to resolve convective storms embedded in typhoons at the 1-km horizontal grid spacing. A large variability in the representations of heavy rainfall and high winds is demonstrated.The severity of meteorological disasters spawned by typhoons critically depends on not only the intensity but also the track of typhoons. A slight change of the track of typhoons would induce a large difference in the intensity and spatial distribution of heavy rainfall and high winds. The present study explores the influences of typhoon tracks on the representations of heavy rainfall and high winds in numerical simulations of typhoon-induced events with the use of a regional meteorological model. The analyses are focused on high-impact typhoons over the Kanto Plain. A nesting capability is used to resolve convective storms embedded in typhoons at the 1-km horizontal grid spacing. A large variability in the representations of heavy rainfall and high winds is demonstrated
High-Resolution Simulation of the 28 July 2008 Heavy Rain Events over the Kinki and Hokuriku Area
No full text局地豪雨の数値予報・解析のためには積乱雲スケールでの気象場の再現性とともに地形表現の精度も重要である。本研究では，2008年7月28日に近畿地方および北陸地方の各地で局所的な豪雨災害を発生させた降水システムおよび降雨特性について高分解能地形を用いた高解像度での領域気象シミュレーションにより再現し，その発生機構について調べる。7月27日21時を初期時刻とした計算により，豪雨をもたらした降水システムはモデルで再現された。28日午前中に播磨平野・大阪平野など沿岸平野部で強い不安定性がモデルで表現され，降水システムの急発達に繋がった。格子幅100 mの計算領域では，都賀川増水事故をもたらした豪雨に対応する降水システムがモデルで良く再現された。100 m格子計算において，モデル地形の表現精度が降水量の再現にインパクトをもたらす可能性があることが示された。This study investigates the development and evolution of locally induced heavy rainfall over the Kinki and Hokuriku areas on 28 July 2008 by conducting high-resolution numerical simulations with a numerical weather prediction model. By employing the nesting capability, the areas of interest are represented with 500-m and 100-m grid spacings. Initialized with the meteorological analysis data at 21 JST 27 July, the model well represents precipitating convective systems that produced local heavy rains in reality. Strong instability over the Harima and Osaka Plains is produced in the simulation, which leads to the generation of intense convective systems. In the 100-m grid domain, the precipitating convective system relevant to the Toga River flooding on 28 July is represented. The present case study indicates that the representation of the terrain has an impact on quantitative precipitation forecasts in a high-resolution simulation down to 100-m grid spacing.局地豪雨の数値予報・解析のためには積乱雲スケールでの気象場の再現性とともに地形表現の精度も重要である。本研究では，2008年7月28日に近畿地方および北陸地方の各地で局所的な豪雨災害を発生させた降水システムおよび降雨特性について高分解能地形を用いた高解像度での領域気象シミュレーションにより再現し，その発生機構について調べる。7月27日21時を初期時刻とした計算により，豪雨をもたらした降水システムはモデルで再現された。28日午前中に播磨平野・大阪平野など沿岸平野部で強い不安定性がモデルで表現され，降水システムの急発達に繋がった。格子幅100 mの計算領域では，都賀川増水事故をもたらした豪雨に対応する降水システムがモデルで良く再現された。100 m格子計算において，モデル地形の表現精度が降水量の再現にインパクトをもたらす可能性があることが示された。This study investigates the development and evolution of locally induced heavy rainfall over the Kinki and Hokuriku areas on 28 July 2008 by conducting high-resolution numerical simulations with a numerical weather prediction model. By employing the nesting capability, the areas of interest are represented with 500-m and 100-m grid spacings. Initialized with the meteorological analysis data at 21 JST 27 July, the model well represents precipitating convective systems that produced local heavy rains in reality. Strong instability over the Harima and Osaka Plains is produced in the simulation, which leads to the generation of intense convective systems. In the 100-m grid domain, the precipitating convective system relevant to the Toga River flooding on 28 July is represented. The present case study indicates that the representation of the terrain has an impact on quantitative precipitation forecasts in a high-resolution simulation down to 100-m grid spacing
Numerical Experiments on the Mechanism for Maintenance of a Squall Line
No full text1993年5月5日に中国乾燥地で発達した寿命の長いスコールラインの維持メカニズムを数値実験により調べた。実験に用いたモデルは非静水圧の局地予報モデル(ARPS)である。大気上層の風の鉛直シアー及び対流混合層の深さの変化によって、スコールラインの構造・進化がどのように応答するかに注目した。上層の鉛直シアーの有無の実験によって、上層の鉛直シアーはcold poolと相互作用しスコールラインの構造・発達過程を決定付けることが示された。対流混合層の深さに対する感度実験によって、乾燥地におけるスコールラインの維持には対流混合層が十分深いことが必要であることが示された。Numerical experiments are conducted to investigate the mechanism for maintenance of the long-lived squall line that occurred over the arid region of China on 5 May 1993 by using the Advanced Regional Prediction System. Two kinds of experiments are conducted focusing on the effect of upper-level vertical wind shear and the impact of the mixed-layer depth. The upper-level vertical wind shear interacting with a surface cold pool determines the structure and evolution of the simulated squall line. The mixed-layer depth controls the longevity and maintenace of the simulated squall line. It is shown that a deep mixed layer is necessary to the maintenace of a squall line over an arid region.1993年5月5日に中国乾燥地で発達した寿命の長いスコールラインの維持メカニズムを数値実験により調べた。実験に用いたモデルは非静水圧の局地予報モデル(ARPS)である。大気上層の風の鉛直シアー及び対流混合層の深さの変化によって、スコールラインの構造・進化がどのように応答するかに注目した。上層の鉛直シアーの有無の実験によって、上層の鉛直シアーはcold poolと相互作用しスコールラインの構造・発達過程を決定付けることが示された。対流混合層の深さに対する感度実験によって、乾燥地におけるスコールラインの維持には対流混合層が十分深いことが必要であることが示された。Numerical experiments are conducted to investigate the mechanism for maintenance of the long-lived squall line that occurred over the arid region of China on 5 May 1993 by using the Advanced Regional Prediction System. Two kinds of experiments are conducted focusing on the effect of upper-level vertical wind shear and the impact of the mixed-layer depth. The upper-level vertical wind shear interacting with a surface cold pool determines the structure and evolution of the simulated squall line. The mixed-layer depth controls the longevity and maintenace of the simulated squall line. It is shown that a deep mixed layer is necessary to the maintenace of a squall line over an arid region
Sensitivity Experiments of Severe Local Rainstorms to Parameterizations of Boundary-Layer and Cloud Processes
No full text領域気象モデルWRFを用いて水平解像度500mで局地豪雨の再現実験を行った。特に, 局地豪雨の再現に重要な物理過程である境界層乱流および雲微物理過程のモデル化(パラメタリゼーション)に対する感度に注目して再現性を検討した。対象とした事例は, 2009年8月に佐用町で生じた局地豪雨である。本事例は, 台風9号に発達した熱帯低気圧の接近に伴って発生したものである。ある特定の組み合わせのパラメタリゼーションを選択することで, 佐用町付近に降水が集中化する様子を気象モデルで再現することに成功した。ただし, パラメタリゼーションの選択によって降水の局地性の表現は大きく異なり, 局地豪雨の再現においてはパラメタリゼーション依存性が極めて大きいことを示している。このことは, 決定論的な降水予測の困難さを示唆するものである。また, 気象モデル計算の初期値・境界値に用いたメソスケールの客観解析値の妥当性についても検討した。Representations of severe local rainfall in regional meteorological simulations at the 500-m horizontal grid resolutions are investigated. The simulations are intended to examine the sensitivity of the model simulations to parameterizations for boundary-layer and cloud-microphysics processes by the use of the Weather Research and Forecasting (WRF) model. The heavy rain case that occurred in Sayo Town, Hyogo Prefecture in August 2009, which was spawned by an approaching tropical cyclone that became Typhoon Etau (2009), is chosen for the present study. A combination of choices in the physics parameterizations well captures locally concentrated characteristics of the severe rainfall. The results indicate that there are significant sensitivities of the rainfall representations to the physics parameterizations. The utility of the ingested meteorological analysis data, i.e., Mesoscale-Model analyses by Japan Meteorological Agency, is also examined.領域気象モデルWRFを用いて水平解像度500mで局地豪雨の再現実験を行った。特に, 局地豪雨の再現に重要な物理過程である境界層乱流および雲微物理過程のモデル化(パラメタリゼーション)に対する感度に注目して再現性を検討した。対象とした事例は, 2009年8月に佐用町で生じた局地豪雨である。本事例は, 台風9号に発達した熱帯低気圧の接近に伴って発生したものである。ある特定の組み合わせのパラメタリゼーションを選択することで, 佐用町付近に降水が集中化する様子を気象モデルで再現することに成功した。ただし, パラメタリゼーションの選択によって降水の局地性の表現は大きく異なり, 局地豪雨の再現においてはパラメタリゼーション依存性が極めて大きいことを示している。このことは, 決定論的な降水予測の困難さを示唆するものである。また, 気象モデル計算の初期値・境界値に用いたメソスケールの客観解析値の妥当性についても検討した。Representations of severe local rainfall in regional meteorological simulations at the 500-m horizontal grid resolutions are investigated. The simulations are intended to examine the sensitivity of the model simulations to parameterizations for boundary-layer and cloud-microphysics processes by the use of the Weather Research and Forecasting (WRF) model. The heavy rain case that occurred in Sayo Town, Hyogo Prefecture in August 2009, which was spawned by an approaching tropical cyclone that became Typhoon Etau (2009), is chosen for the present study. A combination of choices in the physics parameterizations well captures locally concentrated characteristics of the severe rainfall. The results indicate that there are significant sensitivities of the rainfall representations to the physics parameterizations. The utility of the ingested meteorological analysis data, i.e., Mesoscale-Model analyses by Japan Meteorological Agency, is also examined
Features of rainfall during landslide disasters caused by torrential rains and typhoons in the area surrounding the Seto Inland Sea
Get PDFThis study analyzes landslide disasters in the Seto Inland Sea area since 2006. When a landslide occurs, mountainous areas are directly affected by the landslide, while urban areas are indirectly affected by the blockage of traffic from rural areas. Therefore, in this study, rainfall data and landslide case study data from prefectural governments were used to analyze the type of rainfall at the time of a landslide disaster, using the soil rainfall index and accumulated precipitation. The results show that the characteristics of rainfall in a landslide disaster vary greatly depending on the region and meteorological factors
Characteristics of stationary precipitating systems and environmental conditions for the occurrence of recent heavy rainfall events in Japan
No full text2022年度春季大会シンポジウム「線状降水帯に関する研究の最前線と今後の展望～メカニズム解明，観測，予測の現状と将来～」の報
Characteristics and Environmental Conditions for the development of Quasi-Stationary Mesoscale Convective Systems during Warm Season in Japan
Get PDFThis study investigates the characteristics of the development of quasi-stationary mesoscale convective systems (QSMCSs) over the Japanese islands during warm season. For this purpose, we use the operational radar data of Japan Meteorological Agency (JMA) from May to October during 2005 and 2012. In addition, the upper-air sounding data ob- tained at the Japanese sites are used to examine the environmental conditions before the development of QSMCSs. In order to determine the QSMCSs from radar data, we use Algorithm for the Identification and Tracking Convective Cells (AITCC). It is found that we can classify the QSMCSs into three regions based on the frequency of the development of QSMCSs and the amount of precipitation. The common features of the environmental conditions for the development of QSMCSs throughout the warm season are characterized as having higher precipitable water (PW) and larger low-level wind speed differences com- pared to the environments for no-rain cases. It is suggested that the development of the QSMCSs is controlled by PW and the vertical distribution of moisture.This study investigates the characteristics of the development of quasi-stationary mesoscale convective systems (QSMCSs) over the Japanese islands during warm season. For this purpose, we use the operational radar data of Japan Meteorological Agency (JMA) from May to October during 2005 and 2012. In addition, the upper-air sounding data ob- tained at the Japanese sites are used to examine the environmental conditions before the development of QSMCSs. In order to determine the QSMCSs from radar data, we use Algorithm for the Identification and Tracking Convective Cells (AITCC). It is found that we can classify the QSMCSs into three regions based on the frequency of the development of QSMCSs and the amount of precipitation. The common features of the environmental conditions for the development of QSMCSs throughout the warm season are characterized as having higher precipitable water (PW) and larger low-level wind speed differences com- pared to the environments for no-rain cases. It is suggested that the development of the QSMCSs is controlled by PW and the vertical distribution of moisture
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