A mei-yu front process in the lower reaches of the Yangtze River on 23 June 1999 was simulated by using the fifth-generation Pennsylvania State University-NCAR （PSU/NCAR） Mesoscale Model （MM5） with FDDA （Four Dim...A mei-yu front process in the lower reaches of the Yangtze River on 23 June 1999 was simulated by using the fifth-generation Pennsylvania State University-NCAR （PSU/NCAR） Mesoscale Model （MM5） with FDDA （Four Dimension Data Assimilation）. The analysis shows that seven weak small mesoscale vortexes of tens of kilometers, correspondent to surface low trough or mesoscale centers, in the planetary boundary layer （PBL） in the mei-yu front were heavily responsible for the heavy rainfall. Sometimes, several weak small-scale vortexes in the PBL could form a vortex group, some of which would weaken locally, and some would develop to be a meso-α-scale low vortex through combination. The initial dynamical triggering mechanism was related to two strong currents： one was the northeast flow in the PBL at the rear of the mei-yu front, the vortexes occurred exactly at the side of the northeast flow; and the other was the strong southwest low-level jet （LLJ） in front of the Mei-yu front, which moved to the upper of the vortexes. Consequently, there were notable horizontal and vertical wind shears to form positive vorticity in the center of the southwest LLJ. The development of mesoscale convergence in the PBL and divergence above, as well as the vertical positive vorticity column, were related to the small wind column above the nose-shaped velocity contours of the northeast flow embedding southwestward in the PBL, which intensified the horizontal wind shear and the positive vorticity column above the vortexes, baroclinicity and instability.展开更多
With the Weather Research and Forecasting model(WRFV3.2.1), the application of spectrum nudging techniques in numerical simulation of the genesis and development of typhoon Longwang(2005) is evaluated in this work via...With the Weather Research and Forecasting model(WRFV3.2.1), the application of spectrum nudging techniques in numerical simulation of the genesis and development of typhoon Longwang(2005) is evaluated in this work via four numerical experiments with different nudging techniques. It is found that, due to the ability to capture the large-scale fields and to keep the meso-to small-scale features derived from the model dynamics, the experiment with spectrum nudging technique can simulate the formation, intensification and motion of Longwang properly. The improvement on the numerical simulation of Longwang induced by the spectrum nudging depends on the nudging coefficients.A weak spectrum nudging does not make significant improvement on the simulation of Longwang. Although the experiment with four-dimensional data assimilation, i.e., FDDA, also derives the genesis and movement of Longwang appropriately, it fails to simulate the intensifying process of Longwang properly. The reason is that, as the large-scale features derived from the model are nudged to the observational data, the meso- to small-processes produced by the model dynamics important to the intensification of typhoon are nearly smoothed by FDDA.展开更多
为了客观评价Wind Energy Resource Assessment System/CMA(简称WERAS/CMA)系统(CTL方案)和将其中的客观分析法改成四维同化系统(简称FDDA方案)对既受狭管效应影响、又受湖陆风影响的阿拉山口和达坂城-小草湖风区起伏下垫面中的风能资...为了客观评价Wind Energy Resource Assessment System/CMA(简称WERAS/CMA)系统(CTL方案)和将其中的客观分析法改成四维同化系统(简称FDDA方案)对既受狭管效应影响、又受湖陆风影响的阿拉山口和达坂城-小草湖风区起伏下垫面中的风能资源数值模拟的优劣,根据2009年7、10月和2010年1、4月12UTC的NCEP再分析资料以及同期CMACAST下发的WMO各种常规观测资料开展了风场预报效果对比实验。结果表明:(1)对复杂区域而言,两种方案比过去单纯只用中尺度模式进行风场模拟的平均相对误差至少减小10%;(2)总体而言,两种方案对70m高度处的风速模拟误差要大于30、50、100m处的误差,在受多种环流尺度影响区域,模式在刻画平均风速/风向频率廓线方面的缺陷均极其相似;(3)在70m高度上,两种方案5m·s-1以内的风速平均相对误差可达60%~130%,>5m·s-1的误差可控制在15%以内;对受湖陆风影响区域的模拟误差明显偏大,误差大小与湖陆风效应的季节变化有关;(4)两种方案均能抓住70m左右高度上不同等级风速段的气候背景,对达坂城风区5~15m·s-1风速段的Ts预报评分可达0.6~0.7,对阿拉山口和小草湖风区≤5m·s-1风速段的Ts预报评分分别可达0.6~0.7和0.9左右。然而,对达坂城风区≤5m·s-1风速段的Ts预报评分仅0.3~0.4;(5)两种方案对所有风区需采取停机保护措施的、15m·s-1以上强风预报的Ts评分仅在0.4~0.6;(6)同一测风塔不同高度上,FDDA方案对风的预报效果不一定总优于CTL方案,但在70m高度上,FDDA总体略优于CTL;即使同一风区,各个测风塔之间两种方案的预报效果也是因局地多尺度环流影响的不同或因预报的高度不同或预报季节的不同而异,这种预报误差差异的机理还有待探究。展开更多
基金supported by the National Natural Science Foundation of China under Grant No.40505011.
文摘A mei-yu front process in the lower reaches of the Yangtze River on 23 June 1999 was simulated by using the fifth-generation Pennsylvania State University-NCAR （PSU/NCAR） Mesoscale Model （MM5） with FDDA （Four Dimension Data Assimilation）. The analysis shows that seven weak small mesoscale vortexes of tens of kilometers, correspondent to surface low trough or mesoscale centers, in the planetary boundary layer （PBL） in the mei-yu front were heavily responsible for the heavy rainfall. Sometimes, several weak small-scale vortexes in the PBL could form a vortex group, some of which would weaken locally, and some would develop to be a meso-α-scale low vortex through combination. The initial dynamical triggering mechanism was related to two strong currents： one was the northeast flow in the PBL at the rear of the mei-yu front, the vortexes occurred exactly at the side of the northeast flow; and the other was the strong southwest low-level jet （LLJ） in front of the Mei-yu front, which moved to the upper of the vortexes. Consequently, there were notable horizontal and vertical wind shears to form positive vorticity in the center of the southwest LLJ. The development of mesoscale convergence in the PBL and divergence above, as well as the vertical positive vorticity column, were related to the small wind column above the nose-shaped velocity contours of the northeast flow embedding southwestward in the PBL, which intensified the horizontal wind shear and the positive vorticity column above the vortexes, baroclinicity and instability.
基金Nature Science Foundation of China(41475046,41130964)State Key Program of China(2012CB417201)
文摘With the Weather Research and Forecasting model(WRFV3.2.1), the application of spectrum nudging techniques in numerical simulation of the genesis and development of typhoon Longwang(2005) is evaluated in this work via four numerical experiments with different nudging techniques. It is found that, due to the ability to capture the large-scale fields and to keep the meso-to small-scale features derived from the model dynamics, the experiment with spectrum nudging technique can simulate the formation, intensification and motion of Longwang properly. The improvement on the numerical simulation of Longwang induced by the spectrum nudging depends on the nudging coefficients.A weak spectrum nudging does not make significant improvement on the simulation of Longwang. Although the experiment with four-dimensional data assimilation, i.e., FDDA, also derives the genesis and movement of Longwang appropriately, it fails to simulate the intensifying process of Longwang properly. The reason is that, as the large-scale features derived from the model are nudged to the observational data, the meso- to small-processes produced by the model dynamics important to the intensification of typhoon are nearly smoothed by FDDA.
文摘为了客观评价Wind Energy Resource Assessment System/CMA(简称WERAS/CMA)系统(CTL方案)和将其中的客观分析法改成四维同化系统(简称FDDA方案)对既受狭管效应影响、又受湖陆风影响的阿拉山口和达坂城-小草湖风区起伏下垫面中的风能资源数值模拟的优劣,根据2009年7、10月和2010年1、4月12UTC的NCEP再分析资料以及同期CMACAST下发的WMO各种常规观测资料开展了风场预报效果对比实验。结果表明:(1)对复杂区域而言,两种方案比过去单纯只用中尺度模式进行风场模拟的平均相对误差至少减小10%;(2)总体而言,两种方案对70m高度处的风速模拟误差要大于30、50、100m处的误差,在受多种环流尺度影响区域,模式在刻画平均风速/风向频率廓线方面的缺陷均极其相似;(3)在70m高度上,两种方案5m·s-1以内的风速平均相对误差可达60%~130%,>5m·s-1的误差可控制在15%以内;对受湖陆风影响区域的模拟误差明显偏大,误差大小与湖陆风效应的季节变化有关;(4)两种方案均能抓住70m左右高度上不同等级风速段的气候背景,对达坂城风区5~15m·s-1风速段的Ts预报评分可达0.6~0.7,对阿拉山口和小草湖风区≤5m·s-1风速段的Ts预报评分分别可达0.6~0.7和0.9左右。然而,对达坂城风区≤5m·s-1风速段的Ts预报评分仅0.3~0.4;(5)两种方案对所有风区需采取停机保护措施的、15m·s-1以上强风预报的Ts评分仅在0.4~0.6;(6)同一测风塔不同高度上,FDDA方案对风的预报效果不一定总优于CTL方案,但在70m高度上,FDDA总体略优于CTL;即使同一风区,各个测风塔之间两种方案的预报效果也是因局地多尺度环流影响的不同或因预报的高度不同或预报季节的不同而异,这种预报误差差异的机理还有待探究。
