中国大气气溶胶辐射特性参数的观测与研究进展

长期系统的气溶胶辐射特性观测资料是定量研究气溶胶辐射和气候效应的重要基础.本文综合介绍中国大气气溶胶辐射特性观测与研究现状和成果,重点包括以下内容:地面太阳光度计联网观测气溶胶光学厚度、单次散射反照率、尺度谱;从全波段太阳辐射反演气溶胶光学厚度、单次散射反照率;浊度计和黑碳仪测量地面气溶胶散射系数和吸收系数;地基/星载激光雷达观测气溶胶(后向散射系数)垂直分布;极轨/静止卫星遥感反演气溶胶光学特性.     

MODIS卫星遥感北京地区气溶胶光学厚度及与地面光度计遥感的对比

介绍MODIS卫星遥感气溶胶的方法,利用北京大学地面多波段太阳光度计的观测进行了对比,二者的相关性比较好.给出了描述北京地区气溶胶光学厚度分布的几幅图片.卫星遥感对于更好地研究空气污染提供了一种新手段,卫星遥感的气溶胶光学厚度弥补了地面观测空间覆盖不足的缺陷.卫星遥感的气溶胶资料不仅对全球和区域气候研究而且对城市污染分析提供了丰富的资料.     

近年来大气遥感研究进展

本文着重介绍中国科学院大气物理研究所2003年以来在大气遥感研究方面的主要进展与成果,内容包括:(1)遥感技术与设备的发展;(2)大气气溶胶遥感;(3)云遥感;(4)大气微量气体遥感;(5)反演方法发展;(6)大气辐射传输算法研究。气溶胶的光学特性遥感研究是近年来热点之一,本文简要论述在气溶胶光学特性地基和卫星遥感反演算法、中国大气气溶胶光学特性时空分布特性、气溶胶辐射强迫遥感研究等方面所取得的成果。     

气溶胶辐射特性的观测研究

利用一个简化的辐射平衡模式,讨论了气溶胶直接辐射强迫和气溶胶辐射特性以及与地面反射率之间的关系。模式分析表明,增加气溶胶层以后,地气系统对太阳辐射的反射率可能增大,也可能减少,取决于气溶胶的单散射反射率~ω0、不对称度因子g与地面反射率αg之间的配置,但与气溶胶光学厚度δ没有直接的关系。气溶胶光学厚度值仅和反射率变化的幅度成正比。从辐射平衡模式的结果可知,为了定量地研究气溶胶直接辐射强迫作用,需要有系统的有关气溶胶辐射特性的观测资料。从地面和空间对中国地区气溶胶的辐射特性开展了观测研究,包括从地面用太阳光度计测量气溶胶的光学厚度、用浊度计测量气溶胶的散射系数、黑碳仪测量气溶胶的吸收系数,并且利用MODIS资料反演气溶胶的光学厚度。地面太阳光度计观测的气溶胶光学厚度用于检验卫星遥感的气溶胶光学厚度值,对中国东部地区,遥感的结果是可以接受的,主要是由于这一地区存在较低的地表反射率;但对中国北方植被条件不很好的地区,在遥感反演时对地面反射率的估计可能偏低,如做适当的修改还有可能提高遥感反演的精度。从地面直接测量气溶胶的散射系数和吸收系数算出的气溶胶单散射反射率在0.8左右,需要有更多的观测,以便进一步查清这一问题。     

大气气溶胶光学厚度遥感研究概况

大气气溶胶是影响气候变化的重要因子之一,利用遥感手段不仅可以获得气溶胶的分布信息,也可以得到相关的气溶胶光学特性参数。本文阐述了国内外气溶胶遥感的发展动态,介绍了气溶胶遥感的基本情况及气溶胶光学厚度反演的几种方法,提出了存在的问题并对今后的研究进行了展望。     

ＣＥ３１８太阳光度计常见故障及排除方法

CE318型太阳光度计,是法国CIMEL公司制造的一种高精度野外太阳和天空辐射测量仪器,主要用来测量大气气溶胶光学厚度。用于卫星遥感产品真实性检验和气溶胶气候研究的大气气溶胶环境监测仪器,在遥感卫星传感器辐射定标中用于大气光学参数测量的重要仪器,同时还在沙尘暴监测中发挥重要作用。     

中国大气气溶胶研究综述

文中综合论述了近 2 0年来中国大气气溶胶研究状况 ,包括对大气气溶胶的直接采样分析 ,地面和卫星的遥感 ,大气气溶胶辐射特性及其气候效应的研究以及沙尘暴的形成、输送及气候效应的研究等。直接采样分析不仅研究了气溶胶的浓度和粒子谱分布等特性 ,而且也对其化学组分做了分析 ,高空气球采样得到了对流层和低平流层的气溶胶样品 ,并用X能谱电子显微镜进行了分析。地面遥感和多种卫星资料 ,包括AVHRR ,SVISSR ,TOMS ,POLDER等 ,被用来研究大气气溶胶的辐射特性 ,并提出了用消光和前向散射相结合和利用天空散射光分布反演粒子谱分布相函数等方法。开展了有关气溶胶气候效应的数值模拟研究 ,并对非球形粒子以及吸湿性粒子的作用做了专门的计算。对沙尘粒子的直接观测为研究其生成条件和输送特性提供了基础数据。文中对不同的研究方法进行了初步评述 ,并对气溶胶的研究提出几点建议。     

GMS卫星遥感中国地区气溶胶光学厚度

讨论了利用GMS卫星遥感湖面上空气溶胶光学厚度的方法,根据在5个湖面附近与多波段光度计遥感结果的比较,对卫星遥感的方法和结果进行了检验,然后利用该方法遥感了中国大陆25个湖面上空气溶胶光学厚度.结果显示,利用卫星反演湖面光学厚度可以提供大陆上空气溶胶的信息,是研究大陆上空气溶胶光学厚度一个可行的方法.     

利用MODIS资料反演北京及其周边地区气溶胶光学厚度的方法研究

基于 6S辐射传输模式 ,文中同时采用暗像元法和结构函数法建立了利用EOS Terra/MODIS 0 .6 6和 0 .4 7μm通道数据反演陆地气溶胶光学厚度的遥感模型 ,用于获取北京及其周边地区的气溶胶光学厚度。同时 ,利用与卫星观测同步的地基太阳光度计观测资料估计的气溶胶光学厚度数据验证卫星资料反演结果。研究结果给出了如何选择算法、卫星通道数据和气溶胶模型的最佳组合获取理想气溶胶光学厚度的方法。采用 4种气溶胶模型供反演计算选择。在研究中发现 ,暗像元法不适用于城市地区气溶胶光学厚度反演 ,这不仅与亮地表条件的限制有关 ,而且具有强吸收特性的城市气溶胶也是重要影响因素。两种算法由相同气溶胶模型假定误差造成的气溶胶光学厚度反演误差方向 (增加或减小 )相反。反演试验获取的气溶胶光学厚度分布指出 ,石家庄—北京—天津一线易出现气溶胶光学厚度高值带。     

从归一化植被指数提取气溶胶光学信息

利用卫星遥感和改进归一化植被指数(NDVI)算法,在最大值合成的MVC-NDVI与监测日NDVI差值中提取气溶胶浑浊度信息,形成新的气溶胶光学指数产品,通过监测珠三角地区细粒子气溶胶扩散过程的验证,表明方法是成功的。基于理论和实例分析,提出气溶胶研究应当从本地区地理环境和气溶胶特征的实际出发,重视细粒子气溶胶作为稳定的胶体系统对空气质量、天气系统和气候变化的影响,重视卫星遥感在气溶胶监测中的不可替代的作用。     

Aircraft observations of the microphysical and optical properties of major aerosol species

We summarise the microphysical and optical parameters of some principal aerosol species obtained by instrumentation on the UK Met Office C-130 aircraft during international field campaigns since 1996. The aerosol species include Saharan dust, biomass burning aerosol, European continental pollution, eastern seaboard USA pollution, and clean maritime aerosol. The typical structure of the aerosol in the vertical from each airmass type is described. Microphysical parameters are described that comprise the mode radius and geometric standard deviation associated with 2–3 lognormal fits to the mean observed aerosol size distributions spanning the accumulation and coarse modes. Optical parameters comprising the aerosol single scattering albedo (which was both measured and derived from Mie theory), specific extinction coefficient, and asymmetry factor (which were derived from Mie theory) are also presented. Where available, evolution of the physical and optical properties of the aerosol has been highlighted. Comparisons with long-term ground-based AERONET aerosol retrievals show reasonable agreement. Our observations provide useful data for validating and improving global circulation models (GCMs) that use physically based aerosol representation and for validating satellite retrievals of the physical and optical properties of aerosols.     

Effect of particle shape on dust shortwave direct radiative forcing calculations based on MODIS observations for a case study

Assuming spheroidal and spherical particle shapes for mineral dust aerosols, the effect of particle shape on dust aerosol optical depth retrievals, and subsequently on instantaneous shortwave direct radiative forcing (SWDRF) at the top of the atmosphere (TOA), is assessed based on Moderate Resolution Imaging Spectroradiometer (MODIS) data for a case study. Specifically, a simplified aerosol retrieval algorithm based on the principle of the Deep Blue aerosol retrieval method is employed to retrieve dust aerosol optical depths, and the Fu-Liou radiative transfer model is used to derive the instantaneous SWDRF of dust at the TOA for cloud-free conditions. Without considering the effect of particle shape on dust aerosol optical depth retrievals, the effect of particle shape on the scattering properties of dust aerosols (e.g., extinction efficiency, single scattering albedo and asymmetry factor) is negligible, which can lead to a relative difference of at most 5% for the SWDRF at the TOA. However, the effect of particle shape on the SWDRF cannot be neglected provided that the effect of particle shape on dust aerosol optical depth retrievals is also taken into account for SWDRF calculations. The corresponding results in an instantaneous case study show that the relative differences of the SWDRF at the TOA between spheroids and spheres depend critically on the scattering angles at which dust aerosol optical depths are retrieved, and can be up to 40% for low dust-loading conditions.     

Identification of Aerosol Types and Their Optical Properties in the North China Plain Based on Long-Term AERONET Data

Characterization of aerosols is required to reduce uncertainties in satellite retrievals of global aerosols and for modeling the effects of these aerosols on climate.Aerosols in the North China Plain(NCP) are complex,which provides a good opportunity to study key aerosol optical properties for various aerosol types.A cluster analysis of key optical properties obtained from Aerosol Robotic Network(AERONET) data in Beijing and Xianghe during 2001-11 was performed to identify dominant aerosol types and their associated optical properties.Five dominant aerosol types were identified.The results show that the urban/industrial aerosol of moderate absorption was dominant in the region and that this type varied little with season.Urban/industrial aerosol of weak absorption was the next most common type and mainly occurs in summer,followed by that strong aerosols occurring mainly in winter.All were predominantly fine mode particles.Mineral dust(MD) and polluted dust(PD) occurred mainly in spring,followed by winter,and their absorption decreased with wavelength.In addition,aerosol dynamics and optical parameters such as refractive index and asymmetry factor were examined.Results show that the size of coarse mode particles decreased with AOD indicating the domination of external mixing between aerosols.     

Retrieval of aerosol optical depth for Chongqing using the HJ-1 satellite data

Aerosol optical depth (AOD) is a common indicator applied in monitoring aerosols in the atmosphere. The hilly landscape and rapid economic growth of the megacity Chongqing have facilitated increased aerosol concentration, and it is meaningful to accurately retrieve AOD over Chongqing. The HJ-1A/B satellite of China carries a sensor/camera called the Charge Coupled Device (CCD), the spatial resolution of which meets the requirement for retrieving high resolution AOD. In this paper, analysis of the AOD retrievals from different methods using the HJ-1 satellite data revealed the most suitable algorithm. Through comparison with the AOD product of Moderate Resolution Imaging Spectroradiometer (MODIS), the AOD retrieval results using enhanced vegetation index (EVI) to estimate dark pixels showed the highest correlation. The continental aerosol model was used to build a lookup table that was able to facilitate a good AOD retrieval for both city and rural areas. Finally, the algorithm that combined dark pixels, buffer areas, and the deep blue algorithm was found to be most suitable for AOD retrieval. The AOD retrieval results based on the HJ-1 data were consistent with MODIS products, and our algorithm yields reasonable results in most cases. The results were also compared with ground-based PM₁₀ measurements synchronized with the overpass time of the HJ-1 satellite, and high correlation was found. The findings are relevant to other Chinese satellite data used for retrieving AOD on the same channels.     

The effect of ozone and aerosols on the surface erythemal UV radiation estimated from OMI measurements

Surface erythemal UV radiation is mainly affected by total column ozone, aerosols, clouds, and solar zenith angle. The effect of ozone on the surface UV radiation has been explored many times in the previous studies due to the decrease of ozone layer. In this study, we calculated the effect of aerosols on the surface UV radiation as well as that of ozone using data acquired from Ozone Monitoring Instrument (OMI). First, ozone, aerosol optical depth (AOD), and surface erythemal UVB radiation measured from satellite are compared with those from ground measurements. The results showed that the comparison for ozone was good with r ² of 0.92. For aerosol, there was difference between satellite measurements and surface measurements due to the insufficient information on aerosol in the retrieval algorithm. The r ² for surface erythemal UV radiation was high (～0.94) but satellite measurements showed about 30% larger values than surface measurements on average by not considering the effect of absorbing aerosols in the retrieval process from satellite measurements. Radiative amplification factor (RAF) is used to access the effect of ozone and aerosol quantitatively. RAF for ozone was 0.97～1.49 with solar zenith angle. To evaluate the effect of aerosol on the surface UV radiation, only clear-sky pixel data were used and solar zenith angle and total column amount of ozone were fixed. Also, RAF for aerosol was assessed according to the single scattering albedo (SSA) of aerosols. The results showed that RAF for aerosol with smaller SSA (< 0.90) was larger than that for with larger SSA (> 0.90). The RAF for aerosol was 0.09～0.22 for the given conditions which was relatively small compared to that for ozone. However, considering the fact that aerosol optical depth can change largely in time and space while the total column amount of ozone does not change very much, it needs to include the effect of aerosol to predict the variations of surface UV radiation more correctly.     

Regional aerosol optical depth characteristics from satellite observations: ACE‐1, TARFOX and ACE‐2 results

Analysis of the aerosol properties during 3 recent international field campaigns (ACE‐1, TARFOX and ACE‐2) are described using satellite retrievals from NOAA AVHRR data. Validation of the satellite retrieval procedure is performed with airborne, shipboard, and land‐based sunphotometry during ACE‐2. The intercomparison between satellite and surface optical depths has a correlation coefficient of 0.93 for 630 nm wavelength and 0.92 for 860 nm wavelength. The standard error of estimate is 0.025 for 630 nm wavelength and 0.023 for 860 nm wavelength. Regional aerosol properties are examined in composite analysis of aerosol optical properties from the ACE‐1, TARFOX and ACE‐2 regions. ACE‐1 and ACE‐2 regions have strong modes in the distribution of optical depth around 0.1, but the ACE‐2 tails toward higher values yielding an average of 0.16 consistent with pollution and dust aerosol intrusions. The TARFOX region has a noticeable mode of 0.2, but has significant spread of aerosol optical depth values consistent with the varied continental aerosol constituents off the eastern North American Coast.     

Assessment of FY-4A and Himawari-8 Cloud Top Height Retrievalthrough Comparison with Ground-Based MillimeterRadar at Sites in Tibet and Beijing

正1Key Laboratory of Middle Atmosphere and Global Environment Observation, Institute of Atmospheric Physics,Chinese Academy of Sciences, Beijing 100029, China2University of Chinese Academy of Sciences, Beijing 100049, China     

A Statistical Algorithm for Retrieving Background Value of Absorbing Aerosol Index Based on TROPOMI Measurements

The ultraviolet aerosol index(UVAI) is essential for monitoring the absorbing aerosols during aerosol events. UVAI depends on the absorbing aerosol concentration, the viewing geometry, and the temporal drift of radiometric sensitivity. To efficiently detect absorbing aerosols with the highest precision and to improve the accuracy of long-term UVAI estimates,the background UVAI must be examined through the UVAI retrieval. This study presents a statistical method that calculates the background val...     

Evaluation of cloud properties in the NOAA/NCEP global forecast system using multiple satellite products

Knowledge of cloud properties and their vertical structure is important for meteorological studies due to their impact on both the Earth’s radiation budget and adiabatic heating within the atmosphere. The objective of this study is to evaluate bulk cloud properties and vertical distribution simulated by the US National Oceanic and Atmospheric Administration National Centers for Environmental Prediction Global Forecast System (GFS) using three global satellite products. Cloud variables evaluated include the occurrence and fraction of clouds in up to three layers, cloud optical depth, liquid water path, and ice water path. Cloud vertical structure data are retrieved from both active (CloudSat/CALIPSO) and passive sensors and are subsequently compared with GFS model results. In general, the GFS model captures the spatial patterns of hydrometeors reasonably well and follows the general features seen in satellite measurements, but large discrepancies exist in low-level cloud properties. More boundary layer clouds over the interior continents were generated by the GFS model whereas satellite retrievals showed more low-level clouds over oceans. Although the frequencies of global multi-layer clouds from observations are similar to those from the model, latitudinal variations show discrepancies in terms of structure and pattern. The modeled cloud optical depth over storm track region and subtropical region is less than that from the passive sensor and is overestimated for deep convective clouds. The distributions of ice water path (IWP) agree better with satellite observations than do liquid water path (LWP) distributions. Discrepancies in LWP/IWP distributions between observations and the model are attributed to differences in cloud water mixing ratio and mean relative humidity fields, which are major control variables determining the formation of clouds.