发展高分辨区域中尺度天气预报模式是改进暴雨落区预报的一个重要途径。区域中尺度模式空间分辨率达到100 m,对当前计算资源提出了严峻挑战。一种可行的解决方案是发展滤除声波的模式替代全弹性模式。滤除声波的模式可以使用较大的时间...发展高分辨区域中尺度天气预报模式是改进暴雨落区预报的一个重要途径。区域中尺度模式空间分辨率达到100 m,对当前计算资源提出了严峻挑战。一种可行的解决方案是发展滤除声波的模式替代全弹性模式。滤除声波的模式可以使用较大的时间步长积分,能显著提高积分效率。作者在2018年利用一种声波滤除理论——假不可压理论,初步在地形追随质量坐标系(η坐标系)下建立了假不可压模式。数值试验表明模式的结果是合理可信的,然而关键问题是没有滤除声波。本文改进了假不可压模式,建立新的假不可压模式干动力框架。新动力框架控制方程的关键改进是使用椭圆方程求解扰动气压,理论上保证了声波的滤除。新动力框架的时间积分方案更简洁,不使用时步分裂算法。对比改进的假不可压模式和WRF(Weather Research and Forecasting)模式的干热泡对流数值试验结果,发现假不可压模式获得了与WRF模式相似的动力场和热力场分布,且模拟的气压扰动时间序列平滑,说明声波已被滤除,相比2018版本的假不可压模式,这是较大的改进。展开更多
To study the amplitude and the frequency of the aerodynamic force on stator blades, micro-sensors are embedded on the surface of stator blades of a low-speed single-stage axial compressor rig. The unsteady pressure di...To study the amplitude and the frequency of the aerodynamic force on stator blades, micro-sensors are embedded on the surface of stator blades of a low-speed single-stage axial compressor rig. The unsteady pressure distribution on stator blades is measured under the conditions of different axial spacing between the rotor and the stator, different rotating speeds and an extensive range of the mass flow. Amplitudes and frequencies of aerodynamic forces are analyzed by the Fourier transform. Experimental results show that under the effect of the rotor wake, the dominant frequencies of pressure fluctuations on stator blades are the rotor blade passing frequency （BPF） and its harmonics. The higher harmonics of the rotor BPF in the fore part of the suction side are more prominent than that in the other parts of the stator blade. Otherwise, fluctuations of the pressure and the aerodynamic force on stator blades vary with the mass flow, the rotating speed and the axial spacing between the rotor and the stator.展开更多
Heavy precipitation events occur often over the western Sichuan Basin in summer, near the transition zone between the Sichuan Basin and the steep terrain of the Tibetan Plateau. One such event -- a heavy precipitation...Heavy precipitation events occur often over the western Sichuan Basin in summer, near the transition zone between the Sichuan Basin and the steep terrain of the Tibetan Plateau. One such event -- a heavy precipitation process that occurred on 18-20 August 2010, with clear nocturnal peaks -- is chosen as a case to tentatively explore how the convection associated with convectivescale precipitation is initiated and propagated. By utilizing the vertical momentum equation from the viewpoint of separating perturbation pressure into dynamic and thermal parts, it is demonstrated that the vertical momentum is induced by the imbalance of several forces, including the dynamic/buoyant part of the perturbation pressure gradient force and the buoyancy force, with the latter dominating during the nocturnal-peak period. Although a negative value of the dynamic perturbation pressure gradient force partly offsets the positive buoyant forcing inside the strong updraft, the pattern of vertical motion tendency is largely attributable to its buoyancy because of its larger magnitude. Relative to the buoyancy component, the dynamic part of the vertical perturbation pressure gradient is also examined, revealing a smaller order of magnitude. Thus, it is the thermal effect that should be responsible for the initiation and propagation of convection. As for the convective-scale precipitation, it always presents a trailing morphology relative to the strong leading-side updraft. Furthermore, overlapping strong signals of vertical motion and its tendency point towards strong precipitation in the future.展开更多
Tropical disturbances over the South China Sea (SCS) during the period of 1997-2006 are analyzed using the Tropical Storm and Hurricane WX products. A total of 158 tropical disturbances were formed over the SCS from 1...Tropical disturbances over the South China Sea (SCS) during the period of 1997-2006 are analyzed using the Tropical Storm and Hurricane WX products. A total of 158 tropical disturbances were formed over the SCS from 1997 to 2006, with 54 de-veloping tropical disturbances which developed into tropical depressions and 104 non-developing tropical disturbances which never developed into tropical depressions. The development rate of tropical disturbances into tropical depressions was 34.18% in these ten years. During the period of this study, total annual numbers of tropical disturbances and developing tropical disturbances over the SCS had significant decreasing trends; however, the development rate of tropical disturbances had an insignificant increasing trend.展开更多
文摘发展高分辨区域中尺度天气预报模式是改进暴雨落区预报的一个重要途径。区域中尺度模式空间分辨率达到100 m,对当前计算资源提出了严峻挑战。一种可行的解决方案是发展滤除声波的模式替代全弹性模式。滤除声波的模式可以使用较大的时间步长积分,能显著提高积分效率。作者在2018年利用一种声波滤除理论——假不可压理论,初步在地形追随质量坐标系(η坐标系)下建立了假不可压模式。数值试验表明模式的结果是合理可信的,然而关键问题是没有滤除声波。本文改进了假不可压模式,建立新的假不可压模式干动力框架。新动力框架控制方程的关键改进是使用椭圆方程求解扰动气压,理论上保证了声波的滤除。新动力框架的时间积分方案更简洁,不使用时步分裂算法。对比改进的假不可压模式和WRF(Weather Research and Forecasting)模式的干热泡对流数值试验结果,发现假不可压模式获得了与WRF模式相似的动力场和热力场分布,且模拟的气压扰动时间序列平滑,说明声波已被滤除,相比2018版本的假不可压模式,这是较大的改进。
文摘To study the amplitude and the frequency of the aerodynamic force on stator blades, micro-sensors are embedded on the surface of stator blades of a low-speed single-stage axial compressor rig. The unsteady pressure distribution on stator blades is measured under the conditions of different axial spacing between the rotor and the stator, different rotating speeds and an extensive range of the mass flow. Amplitudes and frequencies of aerodynamic forces are analyzed by the Fourier transform. Experimental results show that under the effect of the rotor wake, the dominant frequencies of pressure fluctuations on stator blades are the rotor blade passing frequency （BPF） and its harmonics. The higher harmonics of the rotor BPF in the fore part of the suction side are more prominent than that in the other parts of the stator blade. Otherwise, fluctuations of the pressure and the aerodynamic force on stator blades vary with the mass flow, the rotating speed and the axial spacing between the rotor and the stator.
基金supported by the National Department Public Benefit Research Foundation[grant number GYHY201406003]the Open Research Fund Program of the Plateau Atmosphere and Environment Key Laboratory of Sichuan Province[grant number PAEKL-2015-K3]+2 种基金the National Natural Science Foundation of China[grant numbers 413750544157506441375052]
文摘Heavy precipitation events occur often over the western Sichuan Basin in summer, near the transition zone between the Sichuan Basin and the steep terrain of the Tibetan Plateau. One such event -- a heavy precipitation process that occurred on 18-20 August 2010, with clear nocturnal peaks -- is chosen as a case to tentatively explore how the convection associated with convectivescale precipitation is initiated and propagated. By utilizing the vertical momentum equation from the viewpoint of separating perturbation pressure into dynamic and thermal parts, it is demonstrated that the vertical momentum is induced by the imbalance of several forces, including the dynamic/buoyant part of the perturbation pressure gradient force and the buoyancy force, with the latter dominating during the nocturnal-peak period. Although a negative value of the dynamic perturbation pressure gradient force partly offsets the positive buoyant forcing inside the strong updraft, the pattern of vertical motion tendency is largely attributable to its buoyancy because of its larger magnitude. Relative to the buoyancy component, the dynamic part of the vertical perturbation pressure gradient is also examined, revealing a smaller order of magnitude. Thus, it is the thermal effect that should be responsible for the initiation and propagation of convection. As for the convective-scale precipitation, it always presents a trailing morphology relative to the strong leading-side updraft. Furthermore, overlapping strong signals of vertical motion and its tendency point towards strong precipitation in the future.
基金supported by Chinese Academy of Sciences(Grant KZCX2-YW-214)NSFC Grants 40875020 and 41075054+2 种基金the Fundamental Research Funds for the Central Universities(Nos.11lgpy13 and 11lgjc10)sponsored by the tropical marine meteorology fund from the Institute of Tropical and Marine Meteorology,CMA,SOED1108Scientific Research Foundation for the Young Teachers Program of Sun Yat-sen University(No. 38000-3181402)
文摘Tropical disturbances over the South China Sea (SCS) during the period of 1997-2006 are analyzed using the Tropical Storm and Hurricane WX products. A total of 158 tropical disturbances were formed over the SCS from 1997 to 2006, with 54 de-veloping tropical disturbances which developed into tropical depressions and 104 non-developing tropical disturbances which never developed into tropical depressions. The development rate of tropical disturbances into tropical depressions was 34.18% in these ten years. During the period of this study, total annual numbers of tropical disturbances and developing tropical disturbances over the SCS had significant decreasing trends; however, the development rate of tropical disturbances had an insignificant increasing trend.
