青藏高原横切变线(简称切变线)是引发青藏高原夏季暴雨的主要天气系统之一。本文基于欧洲中期天气预报中心(European Centre for Medium-Range Weather Forecasts,简称ECMWF)提供的ERA-5再分析资料,选取14个生成于6~8月、生命史为38小...青藏高原横切变线(简称切变线)是引发青藏高原夏季暴雨的主要天气系统之一。本文基于欧洲中期天气预报中心(European Centre for Medium-Range Weather Forecasts,简称ECMWF)提供的ERA-5再分析资料,选取14个生成于6~8月、生命史为38小时且引发高原暴雨的切变线个例进行合成分析,探究动力和热力作用对夏季切变线生成和强度演变的影响。结果表明:(1)500 hPa切变线生成于伊朗高压和西太平洋副热带高压两高之间的鞍形场中,处于580 dagpm闭合低值中心和272 K高温中心内,比湿大值区的北侧;200 hPa南亚高压北部边缘、西风急流入口区南侧。(2)切变线强度表现出明显的日变化特征,在当地时间(LT=UTC+6h)23时最强,13时最弱。(3)涡度收支诊断表明,青藏高原上空高低层散度变化对切变线强度变化具有指示意义,500 hPa涡度最大值(最小值)出现时间滞后于辐合作用最大值(最小值)3小时。(4)切变线演变过程中,切变线发展时位涡随之增大。位涡收支诊断表明,青藏高原上空的水汽和非绝热加热对切变线的生成和发展演变起到重要作用。当边界层感热加热增强时,低层辐合增强,上升运动增强,在充足的水汽配合下,凝结潜热释放使非绝热加热中心抬高至大气中层,从而有利于切变线生成及发展。展开更多
该文利用自动站观测资料、探空资料及NCEP再分析资料,对2015年6月的4次MCC造成的贵州大暴雨过程进行分析。受厄尔尼诺事件影响,2015年6月中上旬,长江中下游地区和贵州降水量较常年都明显偏多。6月中上旬长江横切变长期维持,位于湖南境...该文利用自动站观测资料、探空资料及NCEP再分析资料,对2015年6月的4次MCC造成的贵州大暴雨过程进行分析。受厄尔尼诺事件影响,2015年6月中上旬,长江中下游地区和贵州降水量较常年都明显偏多。6月中上旬长江横切变长期维持,位于湖南境内的长江横切变西段降雨云系带动了黔东南对流云系的发展,与来自贵州西部的对流云系共同发展为MCC,造成了＂6.8＂,＂6.18＂,＂6.21＂3次大暴雨过程,这3次降雨过程落区的主关键区与传统的贵州MCC降雨过程也发生了明显改变,降雨落区的主关键区变为黔南、黔东南,安顺、黔西南为次关键区。而＂6.7＂暴雨过程则是受毕节赫章的单核对流云团影响造成的,降雨落区的主关键区与传统的MCC个例比较一致。4次MCC暴雨过程都是在暴雨发生当日的下午在毕节赫章有对流云系发展加强最后演变为MCC云系,后3次MCC还受长江横切变西段的降雨云系影响。前3次暴雨过程600～400 h Pa附近都有一＂漏斗＂状高湿位涡伸展区,表明对流层高层为稳定区,并带动冷空气向下入侵。前3次暴雨过程中,在贵州西部地区对流层低层都有负值中心与对流层高层正的大值区相对,使得低层的不稳定能量得到释放,加速了对流不稳定的发展。这种MPV1＂正负值区垂直迭加＂的配置促使了暴雨的发生发展。展开更多
Shear-wave velocity is a key parameter for calibrating monitoring time-lapse 4D seismic data during CO2-EOR （Enhanced Oil Recovery） and CO2 sequestration. However, actual S-wave velocity data are lacking, especially...Shear-wave velocity is a key parameter for calibrating monitoring time-lapse 4D seismic data during CO2-EOR （Enhanced Oil Recovery） and CO2 sequestration. However, actual S-wave velocity data are lacking, especially in 4D data for CO2 sequestration because wells are closed after the CO2 injection and seismic monitoring is continued but no well log data are acquired. When CO2 is injected into a reservoir, the pressure and saturation of the reservoirs change as well as the elastic parameters of the reservoir rocks. We propose a method to predict the S-wave velocity in reservoirs at different pressures and porosities based on the Hertz-Mindlin and Gassmann equations. Because the coordination number is unknown in the Hertz Mindlin equation, we propose a new method to predict it. Thus, we use data at different CO2 injection stages in the Gao89 well block, Shengli Oilfield. First, the sand and mud beds are separated based on the structural characteristics of the thin sand beds and then the S-wave velocity as a function of reservoir pressure and porosity is calculated. Finally, synthetic seismic seismograms are generated based on the predicted P- and S-wave velocities at different stages of CO2 injection.展开更多
Almost all works in the field of boundary layer flow under the breaking wave consider the flow similar as the flow in an oscillating pressure tube. Although the two flows are similar, there are many differences. The r...Almost all works in the field of boundary layer flow under the breaking wave consider the flow similar as the flow in an oscillating pressure tube. Although the two flows are similar, there are many differences. The results achieved in such manner are therefore also only similar to the results that can be achieved during measurements in the surf zone. Present article deals with boundary layer measurements on an inclined bottom under breaking waves. The measurements over the whole wave cycle were carried out, and the shear velocity under the breaking wave was calculated based on the measurements. It was found that there is a considerable space and time variation of the term in the surf zone. The turbulence generated during the wave breaking changes the shape of the shear velocity profile in comparison to the profile measured before breaking. As the values of shear velocity are directly correlated with the description of the whole velocity field in the wave, it can be assumed that the enhanced description of the shear velocity results in better understanding of the whole velocity field under breaking waves. Therefore, the article brings a new insight into the field and aims to make a discussion about the need to rethink the way of describing the boundary layer flow in the surf zone.展开更多
In this paper,an approach of square coordinate transformation is proposed to approximate the spectral abscissa for continuous-time switched linear systems.By applying elementary transformations iteratively,a series of...In this paper,an approach of square coordinate transformation is proposed to approximate the spectral abscissa for continuous-time switched linear systems.By applying elementary transformations iteratively,a series of minimums of least μ1 matrix set measures are obtained,which are utilized to approximate the spectral abscissa of the switched system.The approach is developed into tractable numerical algorithms that provide upper bound estimates of the spectral abscissa.Numerical simulations show the effectiveness of the proposed method.展开更多
文摘该文利用自动站观测资料、探空资料及NCEP再分析资料,对2015年6月的4次MCC造成的贵州大暴雨过程进行分析。受厄尔尼诺事件影响,2015年6月中上旬,长江中下游地区和贵州降水量较常年都明显偏多。6月中上旬长江横切变长期维持,位于湖南境内的长江横切变西段降雨云系带动了黔东南对流云系的发展,与来自贵州西部的对流云系共同发展为MCC,造成了＂6.8＂,＂6.18＂,＂6.21＂3次大暴雨过程,这3次降雨过程落区的主关键区与传统的贵州MCC降雨过程也发生了明显改变,降雨落区的主关键区变为黔南、黔东南,安顺、黔西南为次关键区。而＂6.7＂暴雨过程则是受毕节赫章的单核对流云团影响造成的,降雨落区的主关键区与传统的MCC个例比较一致。4次MCC暴雨过程都是在暴雨发生当日的下午在毕节赫章有对流云系发展加强最后演变为MCC云系,后3次MCC还受长江横切变西段的降雨云系影响。前3次暴雨过程600～400 h Pa附近都有一＂漏斗＂状高湿位涡伸展区,表明对流层高层为稳定区,并带动冷空气向下入侵。前3次暴雨过程中,在贵州西部地区对流层低层都有负值中心与对流层高层正的大值区相对,使得低层的不稳定能量得到释放,加速了对流不稳定的发展。这种MPV1＂正负值区垂直迭加＂的配置促使了暴雨的发生发展。
基金supported by the National High Techology Research and Development Program(No.2012AA050103)
文摘Shear-wave velocity is a key parameter for calibrating monitoring time-lapse 4D seismic data during CO2-EOR （Enhanced Oil Recovery） and CO2 sequestration. However, actual S-wave velocity data are lacking, especially in 4D data for CO2 sequestration because wells are closed after the CO2 injection and seismic monitoring is continued but no well log data are acquired. When CO2 is injected into a reservoir, the pressure and saturation of the reservoirs change as well as the elastic parameters of the reservoir rocks. We propose a method to predict the S-wave velocity in reservoirs at different pressures and porosities based on the Hertz-Mindlin and Gassmann equations. Because the coordination number is unknown in the Hertz Mindlin equation, we propose a new method to predict it. Thus, we use data at different CO2 injection stages in the Gao89 well block, Shengli Oilfield. First, the sand and mud beds are separated based on the structural characteristics of the thin sand beds and then the S-wave velocity as a function of reservoir pressure and porosity is calculated. Finally, synthetic seismic seismograms are generated based on the predicted P- and S-wave velocities at different stages of CO2 injection.
文摘Almost all works in the field of boundary layer flow under the breaking wave consider the flow similar as the flow in an oscillating pressure tube. Although the two flows are similar, there are many differences. The results achieved in such manner are therefore also only similar to the results that can be achieved during measurements in the surf zone. Present article deals with boundary layer measurements on an inclined bottom under breaking waves. The measurements over the whole wave cycle were carried out, and the shear velocity under the breaking wave was calculated based on the measurements. It was found that there is a considerable space and time variation of the term in the surf zone. The turbulence generated during the wave breaking changes the shape of the shear velocity profile in comparison to the profile measured before breaking. As the values of shear velocity are directly correlated with the description of the whole velocity field in the wave, it can be assumed that the enhanced description of the shear velocity results in better understanding of the whole velocity field under breaking waves. Therefore, the article brings a new insight into the field and aims to make a discussion about the need to rethink the way of describing the boundary layer flow in the surf zone.
基金supported by the National Key Basic Research Program(973 Plan)under Grant No.2014CB845302the National Natural Science Foundation of China under Grant No.61273121
文摘In this paper,an approach of square coordinate transformation is proposed to approximate the spectral abscissa for continuous-time switched linear systems.By applying elementary transformations iteratively,a series of minimums of least μ1 matrix set measures are obtained,which are utilized to approximate the spectral abscissa of the switched system.The approach is developed into tractable numerical algorithms that provide upper bound estimates of the spectral abscissa.Numerical simulations show the effectiveness of the proposed method.
