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。     

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。     

中国遥感卫星辐射校正场气溶胶光学特性观测研究

1999年6月28日~7月19日在敦煌场, 7月25日~7月31日在青海湖水面场进行了一次大规模综合野外测量试验, 其中采用3台先进的法国CIMEL太阳辐射计对两个场地大气光学特性进行了系统全面测量, 获得大量晴空天气条件下的大气光学数据。利用Langley法处理气溶胶通道数据得到气溶胶光学厚度及其光谱变化。测量结果显示550 nm波长平均气溶胶光学厚度分别为0.12、0.18, 由气溶胶光学厚度的波长变化得到气溶胶Junge参数分别为2.6、3.0, 并与几种典型气溶胶类型比较。结果表明两地在晴空天气里, 气溶胶含量较小, 符合遥感卫星传感器辐射定标的大气条件。     

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。     

CE318太阳光度计基本结构与安装使用

CE31 8自动跟踪太阳光度计是由法国CIMEL公司研制生产、用于气溶胶光学特性和大气质量监测的自动测量仪器 ,它不仅能自动跟踪太阳作太阳直射辐射测量 ,而且可以进行太阳等高度角天空扫描、太阳主平面扫描和极化通道天空扫描。CE31 8能自动存储测量数据 ,并可自动传输到计算机保存及发送。 CE31 8测得的直射太阳辐射数据可用来反演计算大气透过率、消光光学厚度、气溶胶光学厚度、大气水汽柱总量和臭氧总量。其天空扫描数据可以反演大气气溶胶粒子尺度谱分布及气溶胶相函数。 CE31 8可用于卫星遥感产品检验和气溶胶气候研究 ,在大气光…     

青藏高原纳木错站地表反照率观测与MODIS资料的对比分析

利用中国科学院纳木错多圈层相互作用综合观测研究站内太阳光度计观测的大气气溶胶光学厚度和整层气柱水汽总量,作为大气辐射传输模式的输入参数,模拟计算了2007年5月—2008年8月无雪期晴空条件下,正午时段该站的太阳总辐射和散射辐射,得到两者的比例S。基于MODIS发布的MCD43B3产品中的短波段黑空和白空反照率以及比例S,计算得到实际大气条件下地表反照率的卫星反演值,进而与地面观测值进行对比分析。结果显示,两者没有显著差别,可以满足气候模式对地表反照率绝对偏差为0.02的精度要求,且均方根偏差约为0.0156,最大偏差为0.046。雨季纳木错站的土壤含水量增加,使得该站晴空时观测的5 min平均地表反照率呈线性下降。     

由卫星资料估算晴空大气太阳直接辐射和散射辐射

根据光的多次散射理论 ,对水汽、气溶胶、臭氧、混合气体等实行辐射参数化处理 ;利用中国探空站资料和诺阿 ( NOAA)气象卫星垂直业务探测器 ( TOVS)资料反演的探空资料 ,由离散纵标法计算了大气各高度上的太阳直接辐射和散射辐射 ,并与此同时的和同站点位置的卫星可见光、红外测值进行统计回归拟合 ,建立卫星测值与大气中太阳直接辐射和散射辐射的计算模式 ,据此可以利用卫星资料估算太阳直接辐射和太阳散射辐射 ,这对于大气环境光学特性和大气环流、气候变化的研究有重要意义。     

北京地区大气气溶胶光学特性监测研究

该文依据气溶胶光学厚度测量原理,利用CE318太阳光度计,于2000年7月～2001年7月期间对北京地区大气气溶胶光学厚度进行观测试验,计算得到约50天的气溶胶光学厚度和Junge参数等大气光学特性数据,给出了北京地区气溶胶光学特性分布特征.计算统计得到北京城区晴空条件下的Junge参数为3 15、2001年3月份沙尘天气状况下急剧下降为2.28,而北京郊区顺义县的测量结果介于二者之间为2.65.分析表明,由试验获得的气溶胶光学特性数据对于分析和监测北京地区大气污染、改善北京地区空气质量具有一定的意义.     

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。     

用卫星资料计算我国东部地区晴空太阳辐射

根据光的多次散射理论的离散纵标法，利用我国东南沿海地区探空站的资料，计算出不同高度上分谱段的太阳直接辐射和向上，向下散射辐射，与相应时刻的卫星测值（可见光，红外通道S－VISSR计数值）进行逐步回归拟合，建立晴空状况下卫星测值与大气中各高度太阳直接辐射和攻射辐射的统计模式，并将拟合方法进行稳定性检验，据此可以利用卫星资料计算各高度分谱段的太阳直接辐射和散射辐射。     

Influence of Clouds on UV Irradiance at Ground Level and Backscattered Exittance

The influence of various cloud parameters and the interactions with the ground albedo and the solar zenith angle have been studied by means of model simulations. The radiative transfer model suitable for a cloudy atmosphere as well as for a clear atmosphere has been developed on the basis of the Discrete Ordinate Method. This study leads to a general understanding for cloudy atmospheres: in the presence of a uniform cloud, the cloud scattering is dominant to molecular and aerosol scattering, and it is also wavelength-independent; the ratio of transmitted irradiance in a cloudy atmosphere to that in the background clear atmosphere is independent of cloud height and solar zenith angle. That’s to say, the radiation downwelling out of a cloud is quite isotropic; it decreases approximately exponentially with the cloud optical depth at a rate related to the ground albedo; the reflected irradiance at the top of the atmosphere is dependent on cloud optical depth as well as on solar zenith angle, but not on ground albedo for clouds of not very thin optical depth.     

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。     

Influence of the total atmospheric optical depth and cloud cover on solar irradiance components

Broadband solar irradiance data obtained in the spectral range 400–940 nm at Kwangju, South Korea from 1999–2000 have been analyzed to investigate the effects of cloud cover and atmospheric optical depth on solar radiation components. Results from measurements indicate that the percentage of direct and diffuse horizontal components of solar irradiance depend largely on total optical depth (TOD) and cloud cover. During summer and spring, the percentages of diffuse solar irradiance relative to the global irradiance were 5.0% and 4.9% as compared to 2.2% and 3.0% during winter and autumn. The diffuse solar irradiance is higher than the direct in spring and summer by 24.2%, and 40.6%, respectively, which may largely be attributed to the attenuation (scattering) of radiation by heavy dust pollution and large cloud amount. In cloud-free conditions with cloud cover ≤2/10, the fraction of the direct and diffuse components were 66.0% and 34.0%, respectively, with a mean daily global irradiance value of 7.92±2.91 MJ m⁻² day⁻¹. However, under cloudy conditions (with cloud cover ≥8/10), the diffuse and direct fractions were 97.9% and 2.2% of the global component, respectively. The annual mean TOD under cloudless conditions (cloud cover≤2/10) yields 0.74±0.33 and increased to as much as 3.15±0.67 under cloudy conditions with cloud amount ≥8/10. An empirical formula is derived for estimating the diffuse and direct components of horizontal solar irradiance by considering the total atmospheric optical depth (TOD). Results from statistical models are shown for the estimation of solar irradiance components as a function of TOD with sufficient accuracy as indicated by low standard error for each solar zenith angle (SZA).     

A study of aerosol particle sizes in the atmosphere of Athens,Greece, retrieved from solar spectral measurements

This work aims at determining the aerosol particle radii in the atmosphere of Athens. Such a work is carried out in Athens for the first time. For this purpose, solar spectral direct-beam irradiance measurements were used in the spectral range 310–575 nm. To estimate the particle radius from aerosol optical depth retrieval, a minimization technique was employed based on the golden-section search of the difference between experimental and theoretical values of the aerosol optical depth. The necessary Mie computations were performed based on the algorithm LVEC.In this study, the mean particle radius of a given distribution was calculated every 30 min during cloudless days in the period November 1996 to September 1997. The largest particles were observed in the summer and the smallest during winter. The result was verified by the increased values of the aerosol optical depth and the turbidity factors calculated in the summer. The differences in the diurnal variation from season to season are attributed to the prevailing wind regime, pollutant emission and sink rates in the atmosphere of Athens.     

Aerosol optical properties during Asian dust storm episodes in South Korea

Summary ¶Aerosol optical depth (_a) is the most comprehensive variable to characterize aerosol, assess atmospheric pollution and make atmospheric corrections to satellite remotely sensed data from ground-based instruments. The aerosol optical properties in Korea peninsula observed at both Kwangju and Anmoyondo during the Asian dust period (March–May) have been presented in this study. Aerosol optical depths at all wavelengths showed a sharp increase during major dust outbreak in spring when compared with the average for the season. For example at Kwangju, aerosol optical depths increase from the spring average value of 0.43±0.02 at 501nm to values >0.70 during major dust event days in 1999 and 2001. Daily mean Ångström exponents () computed at both sites show dramatic changes from high values to low values on dust day periods with a sharp increase in the single scattering albedo. The study also revealed that the observed direct normal solar irradiance and diffuse horizontal irradiance during days with increased dust pollution levels is capable of reducing direct solar radiation by as much as 28% and a corresponding increase of 14% in diffuse solar irradiance during cloudless and windless days.     

A study of aerosol particle sizes in the atmosphere of Athens, Greece, retrieved from solar spectral measurements

This work aims at determining the aerosol particle radii in the atmosphere of Athens. Such a work is carried out in Athens for the first time. For this purpose, solar spectral direct-beam irradiance measurements were used in the spectral range 310–575 nm. To estimate the particle radius from aerosol optical depth retrieval, a minimization technique was employed based on the golden-section search of the difference between experimental and theoretical values of the aerosol optical depth. The necessary Mie computations were performed based on the algorithm LVEC.In this study, the mean particle radius of a given distribution was calculated every 30 min during cloudless days in the period November 1996 to September 1997. The largest particles were observed in the summer and the smallest during winter. The result was verified by the increased values of the aerosol optical depth and the turbidity factors calculated in the summer. The differences in the diurnal variation from season to season are attributed to the prevailing wind regime, pollutant emission and sink rates in the atmosphere of Athens.     

Evaluation of solar irradiance at the surface—inferences from in situ and satellite observations and a mesoscale model

Accurate information about the solar irradiance at the soil surface is essential for many agricultural, hydrological and environmental models that take into account the surface energy balance. The main goal of present study was to evaluate the solar irradiance predictions from the Advanced Research Weather Research and Forecasting (ARW) model for both clear sky and cloudy conditions. An extended observational dataset from the Georgia Automated Environmental Monitoring Network (AEMN) provided hourly solar irradiance at the surface and other collocated surface level measurements. The radiation bias (determined from the difference between the ARW predictions and AEMN observations) showed a linear relationship with the cloud optical depth and the cirrus cloud amount from the moderate resolution imaging spectroradiometer (MODIS). For cloud-free days, the ARW model had a positive radiation bias that exceeded 120 W m^?2 over coastal and urban areas of Georgia. The model radiation and air temperature bias increased with increasing aerosol optical depth derived from the MODIS observations during the cloud-free days, attributed to fire events that lasted intermittently throughout the study period. The model biases of temperature, mixing ratio, wind speed, and soil moisture were linearly dependent on the radiation bias.     

Nephelometer derived and directly measured aerosol optical depth of the atmospheric boundary layer

The aerosol optical depth of the atmospheric boundary layer was determined both from direct solar irradiance measurements and from vertical extrapolation of ground-based nephelometry, during a period with cloudless skies and high aerosol mass loadings in the Netherlands. The vertical profile of the aerosol was obtained from lidar measurements. From humidity controlled nephelometry at the ground and humidity profiles from soundings, the scattering aerosol extinction as a function of height was assessed. Integration of the extinction over the aerosol layer gave the aerosol optical depth of the atmospheric boundary layer. This optical depth at the narrow band of the nephelometer was translated to a spectrally integrated value, assuming an Angstrom wavelength exponent of 1.5, a typical value for The Netherlands.It was found that scattering by the boundary layer aerosol contributed on average 80% to the total atmospheric aerosol optical depth. The uncertainty in this value is estimated to be of the order of 13%. Ammonium nitrate dominated the light scattering. This is an anthropogenic aerosol component.The radiative forcing caused by the light scattering of the anthropogenic aerosol was calculated assuming an upward scattered fraction of 0.3. An average value of − 12 W m ⁻² was found (with an estimated uncertainty of 20%). This corresponds to an absolute increase in the planetary albedo of 0.03, which is equivalent to a 15% increase in the local planetary albedo of 0.2.     

Investigation about the dependence of spectral diffuse-to-direct-beam irradiance ratio on atmospheric turbidity and solar zenith angle

Summary The modifications of the solar spectral diffuse and direct-beam irradiances as well as the diffuse-to-direct-beam ratio, E_dλ/E_bλ, as a function of the aerosol optical depth, AOD, and solar zenith angle, SZA, is investigated. The E_dλ/E_bλ ratios decrease rapidly with wavelength and exponential curves in the form E_dλ/E_bλ = aλ^−b can be fitted with a great accuracy. These curves are strongly modified by the solar spectrum distribution, which is affected by the aerosol loading, aerosol optical properties and SZA. The spectral dependence of the above E_dλ/E_bλ ratios in logarithmic coordinates does not yield a straight line, while a significant departure from the linearity is revealed. The reasons for this departure are investigated in detail and it is established that the aerosol physical properties such as single scattering albedo and size distribution along with the effect of SZA are responsible. These parameters strongly affect the scattering processes in the atmosphere and as a consequence the diffuse spectral distribution. The E_dλ/E_bλ ratio, which is an indicator of the atmospheric transmittance (King, 1979), exhibits a strong wavelength and aerosol-loading dependence. The observed differences between turbid and clear atmospheres constitute a manifestation of contrasting air properties and influence solar irradiance spectra. The present work aims at investigating the effect of atmospheric turbidity and SZA on the E_dλ/E_bλ ratio. For this reason, two distinct cases are examined: one having different atmospheric turbidity conditions but same SZA and a second having different SZAs and same atmospheric turbidity levels.