利用水平面太阳直接辐射日曝辐量反演大气气溶胶光学厚度的方法研究

本文发展了一个从宽带水平面太阳直接辐射日曝辐量 (总辐射与散射辐射日曝辐量之差) 反演光谱大气气溶胶光学厚度的方法, 包括建立一个 “等效” 的瞬时太阳天顶角模型, 并提出了一个基于气溶胶标高的云影响甄别方法。对该反演方法的数值模拟和误差分析表明: “等效” 瞬时太阳天顶角模型的不稳定性引起的光学厚度反演误差平均为3.66％; 光学厚度日变化对一段较长时间的平均光学厚度的影响不显著; 订正造成的散射辐射误差≤20％时, 光学厚度平均偏差≤4％。通过与AERONET产品的比对验证表明: 本文发展的光学厚度反演方法和云影响甄别方法都是有效的; 晴空反演的0.75 μm光学厚度与AERONET的相关系数超过0.95, 平均误差约0.02; 云甄别方法计算的季节和年平均光学厚度与AERONET具有较好的一致性。     

近10年中国16个台站大气气溶胶光学厚度的变化特征分析

应用宽带消光法从1993～2002年中国16个辐射观测站小时累积太阳直接辐射资料,反演了逐时气溶胶光学厚度值,并统计日、月、年的平均值,用作气溶胶光学厚度变化特征分析.结果表明,16个辐射站总的年平均气溶胶光学厚度在0.32～0.36之间变化,沈阳和郑州两站的气溶胶光学厚度有明显增加的趋势,而哈尔滨、兰州、广州、北京等站气溶胶光学厚度则有明显减弱的趋势.就季节变化而言,一般气溶胶光学厚度最大值出现在春季.月平均气溶胶光学厚度与月平均能见度有较好的负相关关系.     

宽带太阳漫射辐射法反演辐射加权平均的气溶胶一次散射反照率研究

引入了一个辐射加权平均的宽带气溶胶一次散射反照率(SSA)的定义,提出了一个从宽带的漫射信息反演该SSA的方法.数值模拟结果表明,在Junge气溶胶谱分布情形下,对气溶胶光学厚度、(A)ngstr(o)m 指数与气溶胶虚部的通常变化范围,应用该SSA所计算的2160组宽带太阳辐射反射率、漫射透过率、总透过率和吸收率的相对标准误差都在1.107%以内; 绝对标准差在0.00287以内.对非Junge的大陆性和都市工业污染气溶胶模式(由水溶性、沙尘和碳粒子组成),在72组反射率、漫射透过率、总透过率和吸收率计算中,相对标准差都在2.047%以内,绝对标准差在0.0075以内.在Junge气溶胶假设下,作者提出了一个综合应用宽带太阳直射和漫射信息同时反演气溶胶光学厚度与辐射加权平均SSA的方法,并通过模拟反演分析了SSA反演的3个主要误差因子.从反演结果可以看出:(1)如果(A)ngstr(o)m指数误差在±0.2以内,对0.55 μm气溶胶光学厚度大于0.312大陆性气溶胶,SSA误差在±0.0418以内;(2)波长无关的宽带地表反照率适用于SSA反演;(3)气溶胶光学厚度越大,辐射资料误差所引起的SSA解误差越小.当辐射误差在±2%以内以及0.55 μm气溶胶光学厚度大于0.312时,SSA解的误差在±0.0149以内; 辐射误差在±4%以内时,SSA解的误差在±0.0317以内.     

关于中国大气气溶胶光学厚度的一个参数化模式

应用中国 1 6个气象台站探测的 1 990年太阳宽带直射辐射信息 ,反演得到了这些台站大气气溶胶光学厚度资料 ,发展了一个应用地面气象能见度和水汽压信息确定大气柱气溶胶光学厚度的参数化模式 ,它比 Elterman模式更适合中国的广大地区。研究还发现 ,比较 Elter-man气溶胶粒子浓度垂直分布模式 ,中国许多地方气溶胶粒子浓度垂直衰减较慢。     

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。     

敦煌地区大气气溶胶光学厚度的季节变化

讨论了利用太阳直接辐射资料反演大气气溶胶光学厚度的一种方法，并且用1981－1983年敦煌地区太阳直接辐射资料计算了该地区大气气溶胶光学厚度的季节变化特征，结果表明：敦煌地区大气气溶胶光学厚度冬季稳定，变化小，春季不稳定，变化幅度大，夏季次之；秋季较小。     

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。     

中国10个地方大气气溶胶1980～1994年间变化特征研究

作者发展了一个从地面上太阳短波直射辐射和能见度信息综合确定大气柱气溶胶总光学厚度和平流层气溶胶光学厚度的方法，并应用这个方法从气象台站观测资料反演得到北京、昆明、喀什、上海、广州、郑州、沈阳、武汉、格尔木和乌鲁木齐等10个地方从1980到1994年间晴天气溶胶光学厚度资料，分析了这些地方气溶胶光学厚度月变化和年变化特征，并侧重分析了1982年墨西哥厄尔奇琼火山和1991年菲律宾皮纳图博火山爆发对气溶胶光学厚度的影响。     

北京等7个气象台站太阳总辐射观测资料的准确度评估

基于地面太阳短波总辐射对气溶胶光学特性和地表反照率的敏感性, 该文提出了一个评估我国气象台站总辐射资料准确度的方法。该方法选用气溶胶光学厚度和太阳天顶角较小情形下的晴天辐射资料, 从太阳直射辐射反演气溶胶光学厚度, 用于计算宽带透过率, 再从该透过率和总辐射资料反演太阳常数E_{0, P}, 并采用E_{0, P}对世界辐射基准 (WRR) 的偏差表示总辐射资料的不确定性。模拟结果表明:气溶胶折射率虚部和大气柱水汽含量的输入误差是两个主要的评估不确定因子。用于准确度评估的资料越多, 越有利于平滑气溶胶、水汽含量等输入参数随机误差的效应, 评估结果越合理。应用这一方法, 该文评估了2000— 2004年我国沈阳、额济纳旗、北京、乌鲁木齐、格尔木、上海和广州7个气象台站总辐射资料的准确度。7个站共有1161个太阳常数反演值, 都满足太阳天顶角余弦 (μ₀) 大于0.7的条件。这些E_{0, P}值对WRR的最大偏差为7.33%, 97.78%的E_{0, P}值对WRR的偏差小于5%, 总平均E_{0, P}值对WRR偏差只有-1.15 %。依据这些结果, 当μ₀≥0.7时, 这些台站的晴天总辐射资料的不确定度估计为5%。     

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.     

从全波段太阳直射辐射确定大气气溶胶光学厚度 II：实验研究

本文通过比较太阳直射表和太阳光度计探测的大气柱气溶胶光学厚度，分析了从太阳直射表探测的全波段太阳直射光强信息确定大气柱气溶胶光学厚度的误差，并应用北京观象台的太阳直射表观测资料，反演得到了 1990—1993年北京大气柱气溶胶光学厚度，分析了该光学厚度月与年变化规律以及1991年菲律宾皮纳图博火山爆发对北京大气气溶胶含量的影响。本文还提出了关于有效水汽含量的一个经验关系式，用于确定水汽对太阳辐射的吸收率。     

Interpretation of Mauna Loa atmospheric transmission relative to aerosols,using photometric precipitable water amouts

Precipitable water measurements made coincident in time and space with direct broadband solar irradiance measurements are used in conjunction with an atmospheric transmission model to derive a parameter whose major dependence is on total aerosol extinction. Irradiance measurements are used to calculate an atmospheric transmission factor (ATF) that is independent of the instrument calibration and the extraterrestrial solar constant. The dependency of the ATF on precipitable water is determined using LOWTRAN5, an atmospheric transmission model with high spectral resolution. Precipitable water measurements are then used to adjust the measured ATF to correspond to an ATF value obtained for a constant precipitable water amount. The remaining variability in the adjusted ATF is due mostly to aerosol extinction. The technique is applied to a 6-year period (1978–1983) for clear-sky mornings at Mauna Loa, Hawaii (MLO). MLO ATF aerosol residuals are compared with independently measured monochromatic aerosol optical depth. Results show that the ATF aerosol residual is nearly equal to the 500 nm aerosol optical depth prior to the eruption of E1 Chichon, at which time a nonlinear time-dependent relationship between the two quantities is evident. ATF aerosol residuals reflect the spectrally integrated aerosol influence on transmission and, therefore, could indicate better than monochromatic optical depth the radiation balance perturbations due to aerosols. The 6-year precipitable water record for MLO, determined from a dual-channel sunphotometer, has a mean value of 0.3 cm. An annual cycle in precipitable water is evident, as is a 4-month 5-standard-deviation drought from December 1982 through March 1983.     

The effects of the Arctic haze as determined from airborne radiometric measurements during AGASP II

The interaction of the Aretic winter aerosol (Arctic haze) with solar radiation produces changes in the radiation field that result in the enhancement of scattering and absorption processes which alter the energy balance and solar energy distribution in the Arctic atmosphere-surface system. During the second Arctic Gas and Aerosols Sampling Project (AGASP II) field experiment, we measured radiation parameters using the NOAA WP-3D research aircraft as a platform. State-of-the-art instrumentation was used to measure in situ the absorption of solar radiation by the Arctic atmosphere during severe haze events. Simultaneously with the absorption measurements, we determined optical depths, and total, direct, and scattered radiation fields. All optical measurements were made at spectral bands centered at 412, 500, 675, and 778 nm and with a bandpass of 10 nm. With this selection of spectral regions we concentrated on the measurement of the radiative effects of the aerosol excluding most of the contributions by the gaseous components of the atmosphere. An additional measurement performed during these experiments was the determination of total solar spectrum fluxes. The experimentally determined parameters were used to define an aerosol model that was employed to deduce the absorption by the aerosols over the full solar spectrum and to calculate atmospheric heating rate profiles. The analyses summarized above allowed us to deduce the magnitude of the change in some important parameters. For example, we found changes in instantaneous heating rate of up to about 0.6 K/day. Besides the increased absorption (30 to 40%) and scattering of radiation by the atmosphere, the haze reduces the surface absorption of solar energy by 6 to 10% and the effective planetary albedo over ice surfaces by 3 to 6%. The vertical distribution of the absorbing aerosol is inferred from the flux measurements. Values for the specific absorption of carbon are found to be around 6 m²/g for externally mixed aerosol and about 11.7 m²/g for internally mixed aerosol. A complete study of the radiative effects of the Arctic haze should include infrared measurements and calculations as well as physics of the ice, snow, and water surfaces.     

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.     

Absorption properties of urban/suburban aerosols in China

The broadband diffuse radiation method is improved to retrieve the aerosol refractive index imaginary part （AIP） and broadband （400-1000 nm mean） single scattering albedo （SSA）. In this method, four sets of SSA selection criteria are proposed for quality control. The method is used to retrieve AIP, SSA and absorptive optical thickness （AbOT） from routine hourly-exposed pyrheliometer and paranometer measurements over 11 sites （meteorological observatories） in China during 1998-2003. Apart from one suburban site （Ejin Qi）, the other urban sites are all located around big or medium cities. As shown in the retrieval results, annual mean SSA during 1998-2003 changes from 0.941 （Wuhan） to 0.849 （Lanzhou）, and AIP from 0.0054 to 0.0203. The 11-site average annual mean SSA and AIP are 0.898 and 0.0119, respectively. SSA during winter is smaller for most sites. There is an evidently positive correlation between SSA and aerosol optical thickness （AOT） for all sites. There is also a positive correlation between SSA and relative humidity for most sites, but a negative correlation for a few sites, such as Kashi and ǚrǚmqi in Northwest China.     

光学遥感大气气溶胶特性

本文提出一种光学遥感大气气溶胶特性的新方法。由多波段望远光度计观测的太阳直接辐射和太阳所在地平纬圈天空亮度的相对分布值,同时反演出气溶胶散射相函数,整层大气的光学厚度随波长的变化,进而用“库”方法反演出气溶胶粒子的尺度谱和折射率的实部和虚部。对比平行观测的结果表明,光学遥感方法所得的结果是可信的。本文同时也讨论了北京地区大气气溶胶的光学参数在不同季节的变化。     

藏北高原五道梁地区的气溶胶特征

通过对藏北高原五道梁地区的大气气溶胶光学厚度分析发现,该地区气溶胶光学厚度有明显的日变化及季节变化特征,气溶胶光学厚度增大时月平均气温与年平均气温减小。