Cosmic ray-aerosol-cloud interactions in the atmospheric environment: Theoretical aspects

The microphysical and radiative processes involved in the interaction of cosmic radiation with the aerosol particulates in the atmosphere aggravate the ion-induced formation of aerosol particles that can act as cloud condensation nuclei (CCN). This may in turn affect the cloud droplet distribution and optical properties of clouds and enhance the process of rising global temperature depending upon the microphysical mechanism. Major observational information about the abundance of aerosols in the tropical atmosphere are obtained from the Indian Ocean experiment (INDOEX) field experiments and about the solar activity and solar cycle from the satellite observations. It has been noticed that when solar activity is less, more cosmic rays pass through the atmosphere, which activate the aerosols already present in the tropical atmosphere. The fluctuations in the cosmic rays due to variations in the solar activity can produce significant changes in the atmospheric environment.     

Modeling of chemical tracer transport in the atmospheric environment and its impact on the global climate

Continental regions are experiencing rapid environmental changes due to expansion of industrial activities and land uses in different types of agricultural productions, burning of fossil fuels, etc., which lead to the emanation of huge amount of smog aerosol particulates and chemicals in the atmosphere. Information about these chemical tracers has been found from Indian Ocean Experiment (INDOEX), Intergovernmental Panel for Climate Change (IPCC) assessment reports as well as from other sources. The results of these computations may be interpreted by the chemical tracer transport model. In this paper, we have used a global atmospheric model in which the optical properties and the concentrations of the chemical tracers and aerosols have been incorporated. The aerosols and chemicals are transported in the atmospheric environment by the model cumulus convection and through the model semi-Lagrangian advection process . Thus, they are globally distributed along with the wind flow. The model has been used in studying the impact of the tropospheric chemical perturbations on the global environment.     

Radiative forcing of aerosols and gases over tropical ocean and its impact on the global atmospheric environment: GCM investigations during INDOEX campaigns

Radiative forcings due to aerosols and the pollutant gases accumulated as haze which are transported from nearby continent to the tropical ocean are essentially important elements of the world climate system. Vertical transport of aerosols and gaseous species takes place within the deep convective cloud clusters of the inter-tropical convergence zone and subsequently these are distributed by the upper atmospheric zonal wind flow, thereby have impact on the global atmospheric environment. The comprehensive global atmospheric models have shown capability of simulating the climate of the atmosphere with proper forcing. We have deduced the radiative forcing, optical depth and the global energy balance components by a global atmospheric model. The results are validated well with INDOEX and other available observational findings.     

Influence of the vertical profile of Saharan dust on the visible direct radiative forcing

The vertical profile of Saharan dust in the atmosphere is generally characterized by a large aerosol concentration in the mid troposphere, differently from the climatological distribution of other types of particles, that show a peak at the surface and a rapid decrease with height. Saharan dust is also characterized by particles of relatively large size of irregular shape, and variable values of the single scattering albedo (the ratio between radiation scattering and extinction). The dust's peculiar vertical distribution is expected to produce an effect on the calculation of the direct aerosol radiative forcing at the surface and at the top of the atmosphere. This effect is investigated by comparing estimates of aerosol direct visible radiative forcing at the surface and at the top of the atmosphere for dust vertical profiles measured in the Mediterranean, and for the climatological profile. The radiative forcing is estimated by means of an accurate radiative transfer model, and for the ocean surface. The sensitivity of the results on the solar zenith angle, aerosol optical depth, and aerosol absorption is also investigated. The aerosol radiative forcing at the surface shows a very small dependency on the aerosol vertical profile. At the top of the atmosphere, the radiative forcing is weakly dependent on the vertical profile (up to 10% variation on the daily average forcing) for low absorbing particles; conversely, it shows a strong dependency (the daily radiative forcing may vary up to 100%) for absorbing particles. The top of the atmosphere visible radiative forcing efficiency produced by dust having single scattering albedo <0.7 is higher by 4 W m⁻² when the observed vertical profile instead of the standard profile is used in the calculations (i.e. it produces a lower cooling). For values of the single scattering albedo around 0.67, the sign of the forcing depends on the vertical profile. The influence of the vertical distribution on the radiative forcing is largest at small values of the solar zenith angle, and at short wavelengths.     

Transmission of radiation through an aerosol medium

The properties of radiation through an aerosol medium have been achieved. This has been done by employing Mie scattering theory to calculate the radiation transfer scattering parameters in the form of extinction, absorption and scattering efficiencies. The equation of radiative transfer for the heat flux through a plane parallel atmosphere of aerosol has been solved. The aerosol size distributions are found in practical systems. Average efficiencies over size distribution for spherical particles of complex refractive index are calculated. Therefore, the radiative properties of stratospheric aerosols have been done. The obtained results found to be in a good agreement with the previous work.     

大气辐射传输模型的比较研究

 讨论了三种通用的大气辐射传输模型的特点和使用限制，用辐射传输定律作了数值检验，并与实验测量资料作了比较。结果表明，氧碘激光和氟化氢泛频20P4激光谱线大气透过率的计算值与实验测量值吻合，氟化氢泛频20P5却出现严重偏差。还研究了大气气溶胶种类对大气透过率计算和测量的严重影响。     

海洋气溶胶多角度偏振辐射特性研究

海洋气溶胶是对流层气溶胶的重要组成部分,对全球的辐射收支平衡及气侯变化均有重要的影响。评价气溶胶的直接与间接辐射效应需要对气溶胶的性质进行深入的研究。多角度偏振为气溶胶光学物理性质研究提供了新的方法。在对可见光550 nm和近红外860 nm波段处海洋气溶胶的光学性质的研究基础上,采用矢量辐射传输模型模拟了TOA（top of atmosphere）反射率和偏振反射率与下垫面性质、观测方位角、气溶胶光学厚度之间的敏感性。模拟结果表明,海洋型气溶胶的多角度偏振信息可以有效地体现气溶胶的光学性质,可以利用多角度偏振遥感信息进行海洋气溶胶的反演,为利用多角度偏振遥感数据进行海洋气溶胶提供了理论基础。     

低太阳高度角条件下的天空偏振模式模拟及大气折射影响研究

为模拟低太阳高度角条件下的天空偏振模式,自主开发了考虑大气球形几何及大气折射效应的辐射传输模式VSPART,并将其运用于漫射光偏振特性仿真.在模式中,基于射线追踪法实现了光线传播轨迹的追踪和入射光偏振态及透过率的计算,基于矩阵算法实现了辐射传输方程的求解.将VSPART模拟结果与基准值、SPDISORT模拟值进行了比较,验证了模型的准确性.在瑞利散射大气和含气溶胶大气条件下,模拟并分析了漫射光偏振度及偏振方向的分布特征,讨论了大气球形几何及折射效应对天空偏振度的影响.结果表明,低太阳高度角条件下,随着波长增加,瑞利散射大气对应的偏振度整体随之增强,中性点向大天顶角方向移动;气溶胶的存在并不改变天空偏振度分布特征,但对偏振方向影响显著,随着光学厚度的增加,天空偏振度值迅速降低;中性点的偏移可能与低阶散射过程紧密相关;大气球形几何和折射效应的主要影响区域为地平线区域、两中性点附近及天顶区域;瑞利散射大气条件下,随着波长增加,大气球形几何及折射效应的影响逐步减弱,特别在中性点附近及天顶区域,其影响逐步消失;随着气溶胶光学厚度的增加,其影响随之增强.     

Systematic tracking of boundary layer aerosols with laser radar

Atmospheric aerosols exhibit a high degree of variability in their properties and their spatial and temporal distribution. Mapping atmospheric aerosols is of great importance for monitoring the effects of anthropogenic activities and natural processes upon local air quality, as well as for producing accurate input for radiative transfer models. To help enhance our understanding of radiative, physical, chemical, and dynamic processes in the atmosphere, laser radar is used to provide systematic monitoring of the temporal evolution of the aerosol rich boundary layer. The Micro Pulse Lidar (Light Detection and Ranging) System is capable of long-term autonomous mapping of vertical aerosol structure. We present a new automated method for tracking boundary layer height from Micro Pulse Lidar data and show the results of this method for a continuous 16 h study conducted on the east coast of the United States.     

Some problems relating to the vertical profile of the aerosol attenuation coefficient in the atmosphere for wavelengths of 0.5–6μ

A calculation of the aerosol attenuation coefficients based on optical measurements along horizontal and inclined direction paths in the atmosphere is discussed. The spectral characteristics of the aerosol attenuation coefficients at various heights in the atmosphere so obtained are compared with the results of calculations based on the microphysical characteristics of an aerosol. Various conclusions are drawn as to the possibilities of simulating the vertical profile of the aerosol attenuation coefficient.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 98–103, May, 1972.     

A single-scattering approximation for infrared radiative transfer in limb geometry in the Martian atmosphere

We present a single-scattering approximation for infrared radiative transfer in limb geometry in the Martian atmosphere. It is based on the assumption that the upwelling internal radiation field is dominated by a surface with a uniform brightness temperature. It allows the calculation of the scattering source function for individual aerosol types, mixtures of aerosol types, and mixtures of gas and aerosol. The approximation can be applied in a Curtis-Godson radiative transfer code and is used for operational retrievals from Mars Climate Sounder measurements. Radiance comparisons with a multiple scattering model show good agreement in the mid- and far-infrared although the approximate model tends to underestimate the radiances in realistic conditions of the Martian atmosphere. Relative radiance differences are found to be about 2% in the lowermost atmosphere, increasing to ∼10% in the middle atmosphere of Mars. The increasing differences with altitude are mostly due to the increasing contribution to limb radiance of scattering relative to emission at the colder, higher atmospheric levels. This effect becomes smaller toward longer wavelengths at typical Martian temperatures. The relative radiance differences are expected to produce systematic errors of similar magnitude in retrieved opacity profiles.     

Radiative transfer in finite participating atmospheric aerosol media

The properties of radiation transfer through a plane-parallel atmospheric aerosol medium has been studied. It has been done by employing Mie theory to calculate the radiation transfer scattering parameters of the medium in the form of extinction, scattering, and absorption efficiencies. Then, the equation of radiative transfer through a plane-parallel atmosphere of aerosol has been solved for partial heat fluxes using two different analytical techniques, namely, the Variational Pomraning -Eddington approximation and Galerkin technique. Average efficiencies over log-normal and modified gamma size distributions are calculated. Therefore, the radiative properties of Carbon, Anthracite, Bituminous, Lignite, and Fly ash have been calculated. The obtained numerical results show very good agreement with each other in addition to the previous published work.     

Wavelength selection of bidirectional laser transmission based on Monte Carlo method

The laser detection technology in uncertain and dynamic environments is of utmost importance in many fields. A model of transient radiative transfer of bidirectional path laser based on Monte Carlo method is developed to investigate the optimum wavelength of active detector at complex atmospheric conditions. The radiative parameters of atmosphere are calculated by HITRAN database and Mie theory at several typical atmospheric conditions including the standard atmosphere, urban aerosol, and radiation fog. Transmission characteristics for five spectral bands at the above atmospheric conditions are calculated by this model. The optimal transmission ability occurred in bands 0.2–0.5, 1.4–1.6, and 0.75–1.25 μm on the condition of standard atmosphere, urban aerosol, and radiation fog, respectively. All results provide effective reference and basic support for choosing the optimal spectral band for active detection.     

A new approach to the retrieval of surface properties from earthshine measurements

Instruments such as the MODIS and MISR radiometers on EOS AM-1, and POLDER on ADEOS have been deployed for the remote sensing retrieval of surface properties. Typically, retrieval algorithms use linear combinations of semi-empirical bidirectional reflectance distribution function (BRDF) kernels to model surface reflectance. The retrieval proceeds in two steps; first, an atmospheric correction relates surface BRDF to top-of-atmosphere (TOA) reflectances, then regression is used to establish the linear coefficients used in the kernel combination. BRDF kernels may also depend on a number of physical or empirical non-linear parameters (e.g. ocean wind speed for a specular BRDF); such parameters are usually assumed known. A major source of error in this retrieval comes from lack of knowledge of planetary boundary layer (PBL) aerosol properties.In this paper, we present a different approach to surface property retrieval. For the radiative transfer simulations, we use the discrete ordinate LIDORT model, which has the capability to generate simultaneous fields of radiances and weighting functions in a multiply scattering multi-layer atmosphere. Surface-atmosphere coupling due to multiple scattering and reflection effects is treated in full; the use of an atmospheric correction is not required. Further, it is shown that sensitivities of TOA reflectances to both linear and non-linear surface BRDF parameters may be established directly by explicit analytic differentiation of the discrete ordinate radiative transfer equations. Surface properties may thus be retrieved directly and conveniently from satellite measurements using standard non-linear fitting methods. In the fitting for BRDF parameters, lower-boundary aerosol properties can either be retrieved as auxiliary parameters, or they can be regarded as forward model parameter errors. We present examples of simulated radiances and surface/aerosol weighting functions for combinations of multi-angle measurements at several different wavelengths, and we perform some examples of self-consistent non-linear fitting to demonstrate feasibility for this kind of surface property retrieval.     

Multi-coupled single scattering method of solving vector radiative transfer equations

<正>A new method of multi-coupled single scattering(MCSS) for solving a vector radiative transfer equation is developed and made public on Internet.Recent solutions from Chandrasekhar’s X-Y method is used to validate the MCSS’s result,which shows high precision.The MCSS method is theoretically simple and clear,so it can be easily and credibly extended to the simulation of aerosol/cloud atmosphere’s radiative properties,which provides effective support for research into polarized remote sensing.     

Lunar eclipse theory revisited: Scattered sunlight in both the quiescent and the volcanically perturbed atmosphere

The residual brightness of the shadowed Moon during a lunar eclipse is attributed to unscattered sunlight rays refracted in the Earth's atmosphere. The classical theory of lunar eclipses is built on the premise that the sunlight scattered by the gases and particles in the atmosphere contributes negligibly to the brightness of the eclipsed Moon. The current work revisits the lunar eclipse theory, extending it to accommodate spectrally resolved observations and addressing the role of scattered sunlight. Predictions of both direct and diffuse sunlight are produced by integrating the radiative transfer equations over the Earth's disk. The investigation contemplates scenarios of normal aerosol loading as well as conditions representative of the months and years following a major volcanic eruption. It is shown that omitting scattered sunlight is an acceptable approximation for low and moderate aerosol loadings at visible and longer wavelengths. However, towards the ultraviolet, or at times when the atmosphere contains elevated aerosol amounts, the relative significance of direct and diffuse sunlight may reverse. Spectra of the sunlight that reaches the shadowed Moon during the eclipse are presented to illustrate the distinct contributions from both components. It is also shown that lunar eclipse spectra obtained up to 4-5 years after a major volcanic eruption, such as Mt. Pinatubo's in 1991, will reveal that the stratosphere remains perturbed above background aerosol levels.     

高分五号卫星多角度偏振相机最优化估计反演:角度依赖与后验误差分析

多角度偏振相机(directional polarimetric camera, DPC)随高分五号卫星已经成功发射并持续获取全球观测数据.针对DPC在陆地气溶胶反演领域的应用需求,本研究基于多参数最优化估计反演框架,引入信息量和后验误差分析工具,讨论了DPC观测信息量对角度的依赖,给出了地表和气溶胶参数的后验误差,并分析了后验误差的影响因素.研究表明:1)卫星观测信息量随观测角度个数的增加显著提升, DPC多角度观测比单角度观测的总DFS(degree of freedom for signal)平均提高了5.45; 2)气溶胶反演比地表更依赖于卫星观测几何,散射角覆盖范围越大,观测包含的气溶胶信息量越多; 3)反演参数的后验误差随观测角度个数的增加显著降低,而气溶胶模型误差对后验误差的影响并不显著.总体来说,观测误差是影响反演结果不确定性的主要因素.本研究对DPC多角度偏振观测的反演能力以及反演不确定性进行了系统的定量评估,为DPC在轨测试及反演算法开发提供参考.     

Fernald前向积分用于机载激光雷达气溶胶后向散射系数反演的理论研究

初步反演结果表明,Fernald前向积分法(FFIM)能够用于机载大气探测激光雷达气溶胶后向散射系数的反演,但相应的理论解释没见国内外相关文献报道.根据合肥地基大气探测激光雷达2008年2月27日的探测数据模拟得到的机载激光雷达数据,对FFIE用于机载大气探测激光雷达气溶胶后向散射系数的反演结果进行了定量分析,分析表明:当反演标定点的高度选在10 km左右时,FFIM能够用于机载大气探测激光雷达气溶胶后向散射系数反演的主要原因有3个:1)Fernald前向积分方程(FFIE)分母中两项的差值一般远大于零, 关键词： 大气光学 Fernald前向积分法 机载大气探测激光雷达 气溶胶后向散射系数     

Simultaneous retrieval of aerosols and ocean properties: A classic inverse modeling approach. I. Analytic Jacobians from the linearized CAO-DISORT model

In this paper and the sequel, we investigate the application of classic inverse methods based on iterative least-squares cost-function minimization to the simultaneous retrieval of aerosol and ocean properties from visible and near infrared spectral radiance measurements such as those from the SeaWiFS and MODIS instruments. Radiance measurements at the satellite are simulated directly using an accurate coupled atmosphere-ocean-discrete-ordinate radiative transfer (CAO-DISORT) code as the main component of the forward model. For this kind of cost-function inverse problem, we require the forward model to generate weighting functions (radiance partial derivatives) with respect to the aerosol and marine properties to be retrieved, and to other model parameters which are sources of error in the retrievals.In this paper, we report on the linearization of the CAO-DISORT model. This linearization provides a complete analytic differentiation of the coupled-media radiative transfer theory, and it allows the model to generate analytic weighting functions for any atmospheric or marine parameter. For high solar zenith angles, we give an implementation of the pseudo-spherical (P-S) approach to solar beam attenuation in the atmosphere in the linearized model. We summarize a number of performance enhancements such as the use of an exact single-scattering calculation to improve accuracy. We derive inherent optical property inputs for the linearized CAO-DISORT code for a simple 2-parameter bio-optical model for the marine environment coupled to a 2-parameter bimodal atmospheric aerosol medium.     

Radiative temperature dissipation in a finite atmosphere—II. The inhomogeneous case

In this paper, solutions to the problem of the radiative relaxation of temperature perturnations in an inhomogeneous, optically finite atmosphere are obtained. The properties of these indicate that there are only certain perturbations that decay at constant rates without changing their shape. These elementary perturbations constitutive the radiative eigenfunctions for the atmosphere and can be utilized to represent perturbations of arbitrary initial shape, whose relaxation can be studied following the relaxation of its expansion in radiative eigenfunctions. The basic solutions for the inhomogeneous atmosphere (i.e., an atmosphere in which the mixing ratio, temperature or band width varies with height) are found in terms of the radiative eigenfunctions for a homogeneous model atmosphere in which the variable parameters have been replaced by averages. The solution for arbitrary initial perturbations is applied to a model of stratospheric warming (for the decaying phase). It is found that there is no perturbation in the stratosphere that can last longer than 30–35 days.