分层均匀旋转椭球体对偏振电磁波的散射理论及数值计算

本文在旋转椭球坐标系中求解麦克斯韦方程,得到了二层旋转椭球体对偏振电磁波的散射解,并利用所得公式,给出了扁旋转椭球状表面附水冰粒对雷达波散射的数值计算结果。     

扁旋转椭球状冰水混合粒子对偏振雷达波的散射

本文借助于旋转椭球矢量波函数和平均场的理论,得到了非均匀扁旋转椭球粒子对偏振电磁波散射的准解析解,并利用所得理论公式给出了雷达气象上极为重要的在平行和垂直入射条件下,非均匀扁旋转椭球状海绵冰粒对雷达波的后向散射截面数值计算结果。在计算中认为海绵冰粒分二层,内核为纯冰扁旋转椭球,外层由冰水混合构成。     

椭球和圆柱形大粒子的光散射相矩阵

基于射线光学原理,本文提出了处理弯曲表面大粒子散射问题的一种数值方法;计算了空间随机取向的旋转椭球形和有限长圆柱形大粒子的散射相矩阵。该计算结果可用于大气辐射传输和大气遥感。     

大气散射相函数的计算

从实际天空亮度分布推算大气散射相函数必须扣除由于多次散射所造成的影响.利用逐次迭代法,可以算出天空各点多次散射与一次散射的比值,进一步扣除多次散射的影响,从而计算出大气散射相函数.本文提出一个逐次迭代的方案并进行了数值试验。其结果表明这一方案是可行的.     

扁椭球雨滴后向散射的Gans理论和T矩阵差异对雷达探测释义的影响

非球形粒子的散射特性研究是双偏振雷达探测数据处理和释义的基础,非球形状同样会影响常规雷达探测数据的处理和释义。在利用雷达进行降水观测的过程中,需要考虑旋转扁椭球雨滴的散射特性。Gans理论和T矩阵法是常用于计算椭球粒子散射特性的算法,但其算法差异会对雷达探测反演带来不同的结果。利用Gans理论和T矩阵法的数值计算,分析旋转扁椭球雨滴的后向散射截面,同时对比常用雷达波段（S、C、X和Ku）内两种算法的后向散射截面的相对差别,以相对差别的阈值得到Gans理论可适用于计算旋转扁椭球雨滴后向散射截面的最大等效半径和尺度参数。在常用雷达波长处对该差异造成的雷达反射率因子Zh和差反射率因子ZDR的影响进行分析。结果表明,在MP雨滴谱下,X波段处Zh的算法差异可达1.66 dBZ,在C波段处ZDR的算法差异可达0.75 dBZ,其他各波长处也有差异。      

六角柱冰晶的光散射函数的计算

六角柱冰晶是卷云中粒子的基本形态。本文着重讨论了利用作者已发展的模式,对有吸收的红外波段冰晶的散射矩阵的计算结果。对比了可见光的计算结果,也对比了长六角柱、扁六角柱以及球状、旋转椭球状冰晶的散射。发现吸收的影响主要造成冰晶的侧向和后侧向散射能量减小以及因折射和多次内反射引起的晕峰和“雨虹峰值”减弱。不同形状冰晶的散射函数虽然总的情况颇一致,但与六角柱冰晶相比,球状冰晶的侧向散射较弱,而椭球状冰晶则表现出后向和后侧向散射较弱。这些特征无疑地都将影响激光探测卷云和光传输过程。     

分层旋转椭球散射场准解析解级数系数的确定

推导了计算分层旋转椭球散射场准解析解级系数的线性方程组，并采用将各区中椭球角波函数展环境区角汉函数之级数的方法解决了不同区中角波函数不具正交的问题。     

随机取向沙尘气溶胶激光雷达线退偏比特性研究

利用离散偶极子近似法,数值计算分析了随机取向旋转椭球体沙尘气溶胶粒子在尺度参数为0.1~23时（波长0.55 μm对应有效半径为0.01~2 μm）的激光雷达线退偏比特性,通过比较其不同旋转椭球体轴半径比下的差别,研究了粒子非球形性程度对单分散和多分散沙尘气溶胶激光雷达线退偏比特性的影响.单分散旋转椭球体沙尘气溶胶的激光雷达线退偏比对粒子的轴半径比和尺度参数有很强的依赖性;对于长旋转椭球体,沙尘激光雷达线退偏比较小值出现在瑞利散射区,而较大的值出现在米散射区;对于扁旋转椭球体,在米散射区较大沙尘粒子也可以产生较小的激光雷达线退偏比,例如,轴半径比为1/16,尺度参数为3时的沙尘激光雷达线退偏比仅为0.1%.就随机取向旋转椭球体沙尘粒子而言,对于单分散系,仅当尺度参数小于0.5时,非球形特征越明显,其激光雷达线退偏比越大;而对多分散系,非球形特征越明显,其激光雷达线退偏比越大.     

参数化的多次散射激光雷达方程和它的反演理论 Ⅰ:方程

本文提出了一个参数化的多次散射激光雷达方程,该方程基于本文引出的四个因子,即几何消光因子、消光分布因子、前向散射因子和后向散射因子.前两个因子表征多次散射成分对大气消光系数分布、激光的发散角和接收视场角以及接收孔径的依赖关系,后两个因子表征多次散射成分对散射相函数的依赖关系.这个参数化多次散射雷达方程在241个数值试验中得以检验,这些试验包含很宽的大气条件和雷达几何参数,包括14个大气散射相函数,均匀和不均匀的大气消光系数分布,0.5至1之间变化的一次散射反照率,地基和空间站激光雷达两种情形.数值试验表明,在小于4的光学厚度内参数化的解和Monte-Carlo解之间的标准偏差小于27％,而本模式的计算时间比Monte-Carlo方法偏小4个数量级左右.本模式不仅适合于研究多次散射对激光回波信号和激光大气遥感的效应,而且对于考虑多次散射的激光大气探测而言,是一个合适的应用模式.     

对流层与平流层大气气溶胶粒子的若干散射特性

本文应用Ｍｉｅ散射理论，采用简洁方案计算了ＩＡＭＡＰ提出的大气气溶胶主要粒子的散射效率因子及散射相函数，结果表明，大颗粒的散射能力以７５％硫酸液滴最强，其次是水滴，冰晶，沙尘性粒子；小粒子的散射能力仍以７５％硫酸滴最强，其次是沙尘性粒子，小颗粒相函数的前向后向基本对称；大粒相函数随Ｘ值增大而不对称加大；折射率实部不同，则相函数最小值出现在不同的散射角，折射率虚部较大的煤烟，相函数起伏较小，约在１０     

An Improved Atmospheric Vector Radiative Transfer Model Incorporating Rough Ocean Boundaries

The radiative transfer model (RT3), a vector radiative transfer (VRT) scheme in a plane-parallel atmosphere, was bounded by a rough ocean surface in this study. The boundary problem was solved using a Fourier series decomposition of the radiation field as a function of the azimuth. For the case of a rough ocean surface, the decomposition was obtained by developing both the Fresnel reflection matrix and the probability distribution of the water facet orientation as Fourier series. The effect of shadowing by ocean surface waves was also considered in the boundary condition. The VRT model can compute the intensity and degree of polarization of the light at the top of the atmosphere (TOA), the ocean surface, and any level of the atmosphere in the ocean-atmosphere system. The results obtained by our model are in good agreement with those computed by Ahmad’s model. The simulated results showed that the shadow effects of wave facets on the intensity and the degree of polarization are negligible except at the ocean surface near the grazing angle, possibly because we did not consider the effect of white caps.     

雾对光偏振态影响的实验研究

测量了不同人土雾浓度下垂直偏振入射光的透射光强。利用实验数据，分析了垂直、平行方向上透射光强的变化趋势。得出平行偏振分量透射光强大致呈指数下降的趋势，垂直偏振分量透射光强先略微上升而后下降。由退偏振度随雾浓度的变化讨论了退偏产生的原因，指出雾浓度较低时，雾滴可近似视为球形。基于光的偏振特性，从理论上分析并计算得到光在雾中传输时透射、散射光强。实验结果对研究光在雾中传输及分析大气中雾对透射光偏振态的影响有一定的参考价值。     

大气短波辐射传输研究中的辐射函数

研究大气短波辐射传输问题时,必需考虑多次散射,在计算各次散射光的递推方程中存在一个对光学厚度的特殊积分.为此,本文定义了“辐射函数”,并研究了它的数学性质,从而使得平面平行大气中散射光的逐次计算既准确又简便.     

STUDY OF THE POLARIZATION CHARACTERISTICS OF SKYLIGHT OVER BEIJING

One of the significant characteristics of the sky is the polarization of light,which is formedthrough the multi-scattering process of atmospheric molecules,aerosols and earth's surface,andthus contains information on these three factors.It has recently been paid more attentions toretrieve the characteristic parameters of the aerosol and surface of the earth from the skylightpolarization information.Observation of the skylight polarization over Beijing has been conductedwith a multi-wavelength polarimeter developed by LAGEO(Laboratory for Middle Atmosphereand Global Environment Observation),IAP(Institute of Atmospheric Physics)since November1995.With these observation data,both the seasonal variations of the maximum degree ofpolarization of the skylight and the effect of the surface situation are studied in this paper.AMonte Carlo code for the vector radiative transfer calculation is used to simulate and compare withobservation.     

Impact of the moisture transport formulation on the simulated tropical rainfall in a general circulation model

The impact of numerical modeling of moisture transport on the simulation of the seasonal mean pattern of precipitation in the tropics is studied. The NCAR CCM2 with spectral and semi-Lagrangian moisture transport has been used for this purpose. The differences in the numerical modeling of moisture transport are found to have a significant impact on the simulation of the seasonal mean patterns. The major differences while using the spectral method (vis-a-vis the semi-Lagrangian method) are (1) a decrease in rainfall over the Indian monsoon region, (2) a decrease in rainfall over the west Pacific region and (3) an increase in rainfall over the central and east Pacific regions. There are substantial differences in the amount of precipitable water vapor simulated by the two moisture transport techniques. It is shown that the difference in precipitable water vapor between the two simulations is associated with changes in the vertical moist static stability (VMS) of the atmosphere, and differences in the simulated precipitation patterns. Received: 7 August 1998 / Accepted: 15 October 1999     

近红外波段凝结核性质对雨滴散射特性的影响

用M ie散射理论,在已知大气气溶胶粒子的折射率基础上,计算并讨论大气气溶胶以及在其上凝结形成的雨滴的散射相函数、散射效率因子等散射特性。结果表明,对流层中气溶胶粒子的散射能力依次为水滴,冰晶,海洋性粒子,沙尘性粒子,水溶性粒子,煤烟。对于在可溶性核上凝结形成的雨滴,海洋性核的散射能力强于水溶性核的散射能力。由不可溶性核凝结形成雨滴的散射能力依次为煤烟核、冰晶核和沙尘性核。纯水雨滴的散射能力介于沙尘性核和冰晶核之间,强于海洋性核。该结论可以为光学测雨仪器在不同地区条件下的参数设置提供依据。     

Numerical simulation of the scattering indicatrix,linear polarization rate,and depolarization factor in the developing convective cloud for millimeter and centimeter wavelengths

Carried out is the numerical modeling of the scattering indicatrix, linear polarization rate, and depolarization factor in the developing convective cloud based on the convection jet model using the Mi functions for millimeter and centimeter wavelength ranges. The analysis of the results demonstrated that the values of these parameters depend strongly on the scattering angle for any wavelength and at any height of the convective cloud. It is shown that these characteristics vary significantly if there is increase in the droplet size in the spectrum and decrease in the wavelength. Revealed is the inverse dependence between the scattering indicatrix values and the polarization (depolarization). At such scattering angles where the scattering indicatrix is maximal, polarization and depolarization are minimal.     

Calculation on the light scattering function of hexagonal ice crystals

Hexagonal ice crystal is a basic form of the particles in cirrus. The emphasis in this paper is on discussing the computational results of scattering phase matrices for infrared absorptive band by making use of the model developed by the authors. Comparisons have been made between infrared and visible light as well as between hexagonal columns and plates and equivalent spheriods and spheres. It is found that the effects of light absorption on phase function may cause the decreases of scattering energy in side direction and the directions near backscattering, and weaken halo and rainbow peaks which are induced by the refractions and internal reflections. There is a general agreement in the phase functions for ice crystals with different shapes. However, the scattering intensity in side direction for spheres and in backward and backside directions for spheroids is weaker as compared with hexagons. It is believed that these features would, doubtless, have influences on the detection of cirrus by laser and radiation transfer in the atmosphere.     

The solution of the vector radiative transfer equation using the discrete ordinates technique: Selected applications

The paper is devoted to the presentation of a newly developed radiative transfer code SCIAPOL_1.0 for a plane-parallel turbid slab illuminated by the monodirectional wide beam. The SCIAPOL_1.0 is based on the discrete-ordinates solution of the vector radiative transfer equation.The code is applied to a number of problems, including studies of the applicability of the scalar approximation for the calculation of light reflectance from aerosols, clouds, and molecular atmospheres. We also study the accuracy of the single scattering approximation as applied to the calculation of light reflection from molecular and cloudy atmospheres and propose new approximations for the calculation of the reflection function and the degree of light polarization under unpolarized light illumination conditions.     

层状云微物理参数反演及其辐射效应的个例研究

利用毫米波云雷达、微波辐射计联合反演方法,对2015年11月11日安徽寿县的一次层状云过程的云参数进行了反演,将所得云参数加入到SBDART辐射传输模式中,进行辐射通量计算,并将计算的地面辐射通量与观测的地面辐射通量进行了对比分析。研究表明:1)利用毫米波雷达和微波辐射计数据联合反演的云参数比较可靠;2)利用SBDART模式并结合反演的云参数,可以准确实时地计算地面及其他高度层的长短波辐射通量;3)在反演的云参数中,光学厚度对地面各种辐射通量的影响是最大的,云层的光学厚度越大,到达地面的太阳短波辐射越小,地面反射短波辐射也越小。另外云底温度越高,云体向下发射的红外长波辐射越大。地面向上的长波辐射是地面温度的普朗克函数,随地面温度而变;4)云对地面的短波辐射强迫为负值,对地面有降温的作用。云对地面的长波辐射强迫是一个正值,对地面有一个增温的作用;5)云对地面的净辐射强迫随时间变化很大,它的正负与太阳高度角和云参数有关。