云滴谱宽度对模式中云的光学厚度的参数化、气溶胶间接效应的评估以及降水形成过程的研究至关重要。本文利用美国POST(Physics of Stratocumulus Top)项目2008年7月19日的飞机观测资料,分析了微物理量和云滴谱的垂直分布及微物理过程。...云滴谱宽度对模式中云的光学厚度的参数化、气溶胶间接效应的评估以及降水形成过程的研究至关重要。本文利用美国POST(Physics of Stratocumulus Top)项目2008年7月19日的飞机观测资料,分析了微物理量和云滴谱的垂直分布及微物理过程。结果表明,该云系云滴谱宽度在云底附近较大,这是由低层核化过程导致的;中层凝结增长过程使得云滴谱宽度随高度增加逐渐减小;云顶附近夹卷混合过程导致云滴谱宽度增大。绝热云中垂直速度的增大会促进云凝结核的活化使云滴数浓度增大,促进凝结增长使云滴尺度增大、云滴谱宽度减小,云滴谱宽度与云滴数浓度、云滴尺度呈现负相关关系;云洞中受夹卷混合过程影响,垂直速度减小,云滴蒸发,云滴数浓度和云滴尺度减小、云滴谱宽度增大,且该效应随绝热程度减小而增强。建议云滴谱宽度的参数化将垂直速度、云滴数浓度、云滴尺度和绝热程度等考虑在内。展开更多
Although there are numerous optical spectroscopy techniques and methods that have been used to extract the fundamental bandgap of a semiconductor,most of them belong to one of these three approaches:(1)the excitonic a...Although there are numerous optical spectroscopy techniques and methods that have been used to extract the fundamental bandgap of a semiconductor,most of them belong to one of these three approaches:(1)the excitonic absorption,(2)modulation spectroscopy,and(3)the most widely used Tauc-plot.The excitonic absorption is based on a many-particle theory,which is physically the most correct approach,but requires more stringent crystalline quality and appropriate sample preparation and experimental implementation.The Tauc-plot is based on a single-particle theo⁃ry that neglects the many-electron effects.Modulation spectroscopy analyzes the spectroscopy features in the derivative spectrum,typically,of the reflectance and transmission under an external perturbation.Empirically,the bandgap ener⁃gy derived from the three approaches follow the order of E_(ex)>E_(MS)>E_(TP),where three transition energies are from exci⁃tonic absorption,modulation spectroscopy,and Tauc-plot,respectively.In principle,defining E_(g) as the single-elec⁃tron bandgap,we expect E_(g)>E_(ex),thus,E_(g)>E_(TP).In the literature,E_(TP) is often interpreted as E_(g),which is conceptual⁃ly problematic.However,in many cases,because the excitonic peaks are not readily identifiable,the inconsistency be⁃tween E_(g) and E_(TP) becomes invisible.In this brief review,real world examples are used(1)to illustrate how excitonic absorption features depend sensitively on the sample and measurement conditions;(2)to demonstrate the differences between E_(ex),E_(MS),and E_(TP) when they can be extracted simultaneously for one sample;and(3)to show how the popular⁃ly adopted Tauc-plot could lead to misleading results.Finally,it is pointed out that if the excitonic absorption is not ob⁃servable,the modulation spectroscopy can often yield a more useful and reasonable bandgap than Tauc-plot.展开更多
文摘云滴谱宽度对模式中云的光学厚度的参数化、气溶胶间接效应的评估以及降水形成过程的研究至关重要。本文利用美国POST(Physics of Stratocumulus Top)项目2008年7月19日的飞机观测资料,分析了微物理量和云滴谱的垂直分布及微物理过程。结果表明,该云系云滴谱宽度在云底附近较大,这是由低层核化过程导致的;中层凝结增长过程使得云滴谱宽度随高度增加逐渐减小;云顶附近夹卷混合过程导致云滴谱宽度增大。绝热云中垂直速度的增大会促进云凝结核的活化使云滴数浓度增大,促进凝结增长使云滴尺度增大、云滴谱宽度减小,云滴谱宽度与云滴数浓度、云滴尺度呈现负相关关系;云洞中受夹卷混合过程影响,垂直速度减小,云滴蒸发,云滴数浓度和云滴尺度减小、云滴谱宽度增大,且该效应随绝热程度减小而增强。建议云滴谱宽度的参数化将垂直速度、云滴数浓度、云滴尺度和绝热程度等考虑在内。
基金Supported by Bissell Distinguished Professor Endowment Fund at UNC-Charlotte。
文摘Although there are numerous optical spectroscopy techniques and methods that have been used to extract the fundamental bandgap of a semiconductor,most of them belong to one of these three approaches:(1)the excitonic absorption,(2)modulation spectroscopy,and(3)the most widely used Tauc-plot.The excitonic absorption is based on a many-particle theory,which is physically the most correct approach,but requires more stringent crystalline quality and appropriate sample preparation and experimental implementation.The Tauc-plot is based on a single-particle theo⁃ry that neglects the many-electron effects.Modulation spectroscopy analyzes the spectroscopy features in the derivative spectrum,typically,of the reflectance and transmission under an external perturbation.Empirically,the bandgap ener⁃gy derived from the three approaches follow the order of E_(ex)>E_(MS)>E_(TP),where three transition energies are from exci⁃tonic absorption,modulation spectroscopy,and Tauc-plot,respectively.In principle,defining E_(g) as the single-elec⁃tron bandgap,we expect E_(g)>E_(ex),thus,E_(g)>E_(TP).In the literature,E_(TP) is often interpreted as E_(g),which is conceptual⁃ly problematic.However,in many cases,because the excitonic peaks are not readily identifiable,the inconsistency be⁃tween E_(g) and E_(TP) becomes invisible.In this brief review,real world examples are used(1)to illustrate how excitonic absorption features depend sensitively on the sample and measurement conditions;(2)to demonstrate the differences between E_(ex),E_(MS),and E_(TP) when they can be extracted simultaneously for one sample;and(3)to show how the popular⁃ly adopted Tauc-plot could lead to misleading results.Finally,it is pointed out that if the excitonic absorption is not ob⁃servable,the modulation spectroscopy can often yield a more useful and reasonable bandgap than Tauc-plot.
