According to the analysis of the turbulent intensity level around the high-speed train, the maximum turbulent intensity ranges from 0.2 to 0.5 which belongs to high turbulent flow. The flow field distribution law was ...According to the analysis of the turbulent intensity level around the high-speed train, the maximum turbulent intensity ranges from 0.2 to 0.5 which belongs to high turbulent flow. The flow field distribution law was studied and eight types of flow regions were proposed. They are high pressure with air stagnant region, pressure decreasing with air accelerating region, low pressure with high air flow velocity region I, turbulent region, steady flow region, low pressure with high air flow velocity region II,pressure increasing with air decelerating region and wake region. The analysis of the vortex structure around the train shows that the vortex is mainly induced by structures with complex mutation and large curvature change. The head and rear of train, the underbody structure, the carriage connection section and the wake region are the main vortex generating sources while the train body with even cross-section has rare vortexes. The wake structure development law studied lays foundation for the train drag reduction.展开更多
Since the South China Sea (SCS) summer monsoon (SCSSM) is pronouncedly featured by abruptly intensified southwesterly and obviously increased precipitation over the SCS,the lower-tropospheric winds and/or convection i...Since the South China Sea (SCS) summer monsoon (SCSSM) is pronouncedly featured by abruptly intensified southwesterly and obviously increased precipitation over the SCS,the lower-tropospheric winds and/or convection intensities are widely used to determine the SCSSM onset.The methods can be used successfully in most of the years but not in 2006.Due to the intrusion of Typhoon Chanchu(0601)that year,the usual method of determining SCSSM onset date by utilizing the SCS regional indices is less capable of pinpointing the real onset date.In order to solve the problem,larger-scale situations have to be taken into account.Zonal and meridional circulations would be better to determine the break-out date of SCSSM in 2006.The result indicates that its onset date is May 16.Moreover,similar onset dates for other years can be obtained using various methods,implying that large-scale zonal and meridional circulations can be used as an alternative method for determining the SCSSM onset date.展开更多
Under global warming, storm events tend to intensify, particularly in monsoon-affected regions. As an important agricultural area in China, the purple soil region in the Sichuan Basin, where it has a prevailing monsoo...Under global warming, storm events tend to intensify, particularly in monsoon-affected regions. As an important agricultural area in China, the purple soil region in the Sichuan Basin, where it has a prevailing monsoon climate, is threatened by serious soil erosion. Tillage operations alter runoff and soil erosion processes on croplands by changing the physical properties of the soil surface. To clarify the relationship between tillage and soil erosion in the purple soil region, three different tillage practices in this region were investigated at the plot scale over 4 years： bare land with minimum tillage （BL）, conventional tillage （CT） and seasonal no-tillage ridges （SNTR） which was initially designed to prevent soil erosion by contoured ridges and no-tillage techniques. The results showed that although there were no significant differences in the surface runoff and soil erosion among the three oractices, BL caused relatively high surface runoff and soil erosion, followed by CT and SNTR. Classification and comparison of the rainfall events based on cluster analysis （CA） verified that the surface runoff was not significantly different between most intensive event and long intensive events but was significantly different between most intensive and short and medium-duration events. Only the rainfall events with the highest rainfall intensity could trigger serious soil erosion, up to 1000 kg ha^-1 in the region. Further detailed investigations on the effects of tillage operations on the soil erosion in a subtropical region with a monsoon climate are needed to provide a basis for modeling catchments and designing better management practices.展开更多
The different spatial distributions of aerosol-induced direct radiative forcing and climatic effects in a weak （2003） and a strong （2006） East Asian summer monsoon （EASM） circulation were simulated using a high-...The different spatial distributions of aerosol-induced direct radiative forcing and climatic effects in a weak （2003） and a strong （2006） East Asian summer monsoon （EASM） circulation were simulated using a high-resolution regional climate model （RegCM3）.Results showed that the atmospheric circulations of summer monsoon have direct relations with transport of aerosols and their climatic effects.Both the top-of-the-atmosphere （TOA） and the surface-negative radiative forcing of aerosols were stronger in weak EASM circulations.The main difference in aerosol-induced negative forcing in two summers varied between 2 and 14 W m-2 from the Sichuan Basin to North China,where a maximum in aerosol-induced negative forcing was also noticed in the EASM-dominated areas.The spatial difference in the simulated aerosol optical depth （AOD） in two summers generally showed the similar pictures.Surface cooling effects induced by aerosols were spatially more uniform in weak EASM circulations and cooler by about 1-4.5℃.A preliminary analysis here indicated that a weaker low-level wind speed not conducive to the transport and diffusion of aerosols could make more contributions to the differences in the two circulations.展开更多
基金Project(U1134203)supported by the National Natural Science Foundation of China
文摘According to the analysis of the turbulent intensity level around the high-speed train, the maximum turbulent intensity ranges from 0.2 to 0.5 which belongs to high turbulent flow. The flow field distribution law was studied and eight types of flow regions were proposed. They are high pressure with air stagnant region, pressure decreasing with air accelerating region, low pressure with high air flow velocity region I, turbulent region, steady flow region, low pressure with high air flow velocity region II,pressure increasing with air decelerating region and wake region. The analysis of the vortex structure around the train shows that the vortex is mainly induced by structures with complex mutation and large curvature change. The head and rear of train, the underbody structure, the carriage connection section and the wake region are the main vortex generating sources while the train body with even cross-section has rare vortexes. The wake structure development law studied lays foundation for the train drag reduction.
基金Major State Basic Research Development Program of China(973 Program)(2010CB950304)
文摘Since the South China Sea (SCS) summer monsoon (SCSSM) is pronouncedly featured by abruptly intensified southwesterly and obviously increased precipitation over the SCS,the lower-tropospheric winds and/or convection intensities are widely used to determine the SCSSM onset.The methods can be used successfully in most of the years but not in 2006.Due to the intrusion of Typhoon Chanchu(0601)that year,the usual method of determining SCSSM onset date by utilizing the SCS regional indices is less capable of pinpointing the real onset date.In order to solve the problem,larger-scale situations have to be taken into account.Zonal and meridional circulations would be better to determine the break-out date of SCSSM in 2006.The result indicates that its onset date is May 16.Moreover,similar onset dates for other years can be obtained using various methods,implying that large-scale zonal and meridional circulations can be used as an alternative method for determining the SCSSM onset date.
基金support of this study was provided by the National Natural Science Foundation of China (Grant No. 41371241 and 41101202)the Western Development Plan of Chinese Academy of Sciences (Grant No. KZCX2XB3-09)the National Basic Research Program of the Ministry of Science and Technology of China (Grant No. 2012CB417101)
文摘Under global warming, storm events tend to intensify, particularly in monsoon-affected regions. As an important agricultural area in China, the purple soil region in the Sichuan Basin, where it has a prevailing monsoon climate, is threatened by serious soil erosion. Tillage operations alter runoff and soil erosion processes on croplands by changing the physical properties of the soil surface. To clarify the relationship between tillage and soil erosion in the purple soil region, three different tillage practices in this region were investigated at the plot scale over 4 years： bare land with minimum tillage （BL）, conventional tillage （CT） and seasonal no-tillage ridges （SNTR） which was initially designed to prevent soil erosion by contoured ridges and no-tillage techniques. The results showed that although there were no significant differences in the surface runoff and soil erosion among the three oractices, BL caused relatively high surface runoff and soil erosion, followed by CT and SNTR. Classification and comparison of the rainfall events based on cluster analysis （CA） verified that the surface runoff was not significantly different between most intensive event and long intensive events but was significantly different between most intensive and short and medium-duration events. Only the rainfall events with the highest rainfall intensity could trigger serious soil erosion, up to 1000 kg ha^-1 in the region. Further detailed investigations on the effects of tillage operations on the soil erosion in a subtropical region with a monsoon climate are needed to provide a basis for modeling catchments and designing better management practices.
基金supported by the National Basic Research Program of China (2009CB421407)the Special Public Welfare Research Fund for Meteorological Profession of China Meteorological Administration (GYHY201006022)
文摘The different spatial distributions of aerosol-induced direct radiative forcing and climatic effects in a weak （2003） and a strong （2006） East Asian summer monsoon （EASM） circulation were simulated using a high-resolution regional climate model （RegCM3）.Results showed that the atmospheric circulations of summer monsoon have direct relations with transport of aerosols and their climatic effects.Both the top-of-the-atmosphere （TOA） and the surface-negative radiative forcing of aerosols were stronger in weak EASM circulations.The main difference in aerosol-induced negative forcing in two summers varied between 2 and 14 W m-2 from the Sichuan Basin to North China,where a maximum in aerosol-induced negative forcing was also noticed in the EASM-dominated areas.The spatial difference in the simulated aerosol optical depth （AOD） in two summers generally showed the similar pictures.Surface cooling effects induced by aerosols were spatially more uniform in weak EASM circulations and cooler by about 1-4.5℃.A preliminary analysis here indicated that a weaker low-level wind speed not conducive to the transport and diffusion of aerosols could make more contributions to the differences in the two circulations.
