Calibration of a three‐component angular distribution model of sky radiance

Abstract

A three‐component (isotropic, circumsolar and horizon‐brightening) model of the angular distribution of sky (short‐wave) radiance has been tested and validated against a data base of measured sky radiance. The data base encompasses cloud cover 0.0 to 1.0 and solar zenith angles 30 to 80°. Empirical constants have been derived for the model enabling the prediction of sky radiances for any sky condition.     

An approximate expression of the sky radiance in almucantar and its application

An approximate expression of the sky radiance in almucantar is confirmed in this paper. Under the conditions with molecular optical depth<0.3, aerosol (or cloud) optical depth<0.6, solar zenith angle< 75° and scattering angle<30°, the errors of the sky radiance and the aerosol phase function computed from the expression are respectively less than 8 % and 10 %, but the phase functions computed from Box-Deepak formula and single-scattering formula can be 84 % and 260 % more than the exact value, respectively. Furthermore, by use of the expression we have inferred the volume scattering functions of 1°≤θ≤30° for retrieving aerosol size distribution with the conclusion that the distribution information in the range of 0.1相似文献   

Spectral reflectance in an urban area a case study for Tokyo

The spectral reflectance of the surface in an urbanized area was estimated through airborne measurements of the spectral upward flux of visible radiation in the range 475–750 nm. Atmospheric effects due to Rayleigh and Mie scattering were accounted for by using optical parameters to solve the radiative transfer equation. The values for these parameters were derived from measurements of the particle number concentration and size distribution.The results clearly show a difference in reflectance between urban and suburban areas. The difference in spectral reflectance decreases from the suburban to the urban area.In a metropolitan area, the surface reflectance generally decreases with urban development, and the global upward flux of visible radiation has a similar tendency. This trend supports the idea of a decrease in reflectance due to the modification of the surface structure.     

Comparison between experimental and calculated values of sky luminance in the Sun's vertical plane at Seville (Spain)

An attempt has been made to find a satisfactory agreement between calculated and measured values of diffuse skylight luminance in the sun's vertical plane at Seville (Spain). Measurements were carried out at three different wavelengths in the visible region (λ₁ = 632.2 nm, λ₂ = 546.4 nm and λ₃ = 435.6 nm). Data of atmospheric optical thickness was also obtained at these wavelengths.At first, computations dealt only with primary scattering, but the agreement was unsatisfactory.An approximation method which takes into account multiple scattering (aerosol and molecular) was then used with good results. The best agreement between experimental and calculated values is obtained at λ₁ and λ₂.     

A case study of a wave-like cloud and gravity wave in the lower troposphere in Mizuho Plateau,Antarctica

A case study of a gravity wave is carried out with visual observations of cloud and low-level air soundings. The wave is well interpreted by the simple classical theory of a deep water wave. The observed frequency agrees with the Brunt-Väisälä frequency if the Doppler effect is considered.     

Effects of ocean particles on the upwelling radiance and polarized radiance in the atmosphere-ocean system

Based on a vector radiative transfer model of the atmosphere-ocean system, the influence of oceanic components on radiation processes, including polarization effects, was investigated in the wavelength region ranging from 0.380 to 0.865 μm. The components considered were phytoplankton, inorganic suspended material (sediment), and colored, dissolved organic matter. Due to their important roles in oceanic radiation processes, the sensitivity of the bidirectional reflectance to the rough ocean surface, represented by the wind velocity 10 m above the ocean surface, and aerosol, were taken into account. The results demonstrated that both radiance and polarized radiance just below the ocean surface were sensitive to the change of the concentrations of the considered components, while the dependence of polarized radiance on the observation geometry was more sensitive than radiance. Significant differences in the specular plane existed between the impacts of the phytoplankton and sediment on the degree of polarization just above the ocean surface at 670 nm. At the top of the atmosphere (TOA), polarization was relatively insensitive to changing concentrations of ocean particles at longer wavelengths. Furthermore, the radiance at the TOA in the solar plane was more sensitive to the aerosol optical thickness than wind velocity. In contrast, wind velocity strongly influenced the radiance at the TOA in the sun glint region, while the polarization degree showed less dependence in that region. Finally, a nonlinear optimal inversion method was proposed to simultaneously retrieve the aerosol and wind velocity using radiance measurement.     

Long-term Variability of Integral and Spectral Transparency of the Atmosphere at Mirny Observatory,Antarctica

The aerosol optical depth of the atmosphere obtained from spectral sun photometer measurements and the integral optical depth determined from standard actinometric observations of direct solar radiation are the parameters of the optical state of the atmosphere. The quantitative estimates of the integral transparency and aerosol optical depth of the atmosphere in Antarctica are presented, their long-term variability over the entire period of observations is analyzed. The comparison of obtained data with the estimates for other natural regions and conditions revealed that during the periods without the impact of volcanic eruptions, the levels of atmospheric aerosol turbidity in Antarctica over the recent decades are minimal on the planet and can be considered as global background characteristics.     

卫星辐射率资料EnSRF同化及暴雨模拟应用

基于自主构建的WRF—EnSRF（Weather Researchand Forecasting—Ensemble Square—Root Filter）同化系统,同化了ATOVS（Advanced TIROS Operational Vertical Sounder）辐射率资料,以检验该系统同化卫星资料的能力及其在暴雨过程模拟中的效能。对2008年6月6—7日广东地区一次大暴雨过程进行了同化及数值模拟试验,结果表明,同化ATOVS辐射率资料得到的分析场,丰富了对流层高层的大气温度和对流层中低层的大气湿度信息,对风场也有一定的改进。控制试验和同化试验都较好地模拟出了降水的主要落区和发生时段,但控制试验对暴雨、大暴雨的雨区和雨强的模拟效果欠佳;相比而言,同化试验对强降水中心的位置、范围的模拟均有更好的反映,模拟的暴雨强度也与实际降水量级基本一致,同化改进效果明显。     

Climate change and human activities: a case study in Xinjiang, China

We examined both long-term climate variability and anthropogenic contributions to current climate change for Xinjiang province of northwest China. Xinjiang encompasses several mountain ranges and inter-mountain basins and is comprised of a northern semiarid region and a more arid southern region. Climate over the last three centuries was reconstructed from tree rings and temperature series were calculated for the past 50 years using weather station data. Three major conclusions from these analyses are: (1) Although temperature varied considerably in Xinjiang over the last 200 years, it was non-directional until the last 50 years when a substantial warming trend occurred; (2) The semiarid North Xinjiang was representative of the northern hemisphere climate, while the more arid South Xinjiang resembled the southern hemisphere climate, meanwhile, (3) The entire Xinjiang province captured the global-scale climate signal. We also compared human contributions to global change between North and South Xinjiang, including land cover/land use, population, and greenhouse gas production. For both regions, urban areas acted as heat islands; and large areas of grassland and forest were converted to barren land, especially in North Xinjiang. Additionally, North Xinjiang also showed larger increase in population and greenhouse gas emissions mainly associated with animal production than those in South Xinjiang. Although Xinjiang province is a geographically coupled mountain–basin system, the two regions have distinct climate patterns and anthropogenic activities related to land cover conversion and greenhouse gas production.     

The 1983 drought in the West Sahel: a case study

Some drought years over sub-Saharan west Africa (1972, 1977, 1984) have been previously related to a cross-equatorial Atlantic gradient pattern with anomalously warm sea surface temperatures (SSTs) south of 10°N and anomalously cold SSTs north of 10°N. This SST dipole-like pattern was not characteristic of 1983, the third driest summer of the twentieth century in the Sahel. This study presents evidence that the dry conditions that persisted over the west Sahel in 1983 were mainly forced by high Indian Ocean SSTs that were probably remanent from the strong 1982/1983 El Ni?o event. The synchronous Pacific impact of the 1982/1983 El Ni?o event on west African rainfall was however, quite weak. Prior studies have mainly suggested that the Indian Ocean SSTs impact the decadal-scale rainfall variability over the west Sahel. This study demonstrates that the Indian Ocean also significantly affects inter-annual rainfall variability over the west Sahel and that it was the main forcing for the drought over the west Sahel in 1983.     

Short-wave radiation flux divergence in arctic cirrus: a case study

Radiation and particle measurements have been performed with an aircraft in deep cirrus cloud fields near the island of Svalbard. The data of 12 March 1993, when measurements at 10 different levels could be obtained, are used in a comparative study with radiative transfer calculations. In a first analysis, the cirrus cloud field was assumed to be horizontally homogeneous and invariable during the time of measurements (frozen properties). Calculations of the up and downward radiative flux densities showed root mean square differences of 9 Wm⁻² from the measurements. To estimate the possible effect of changes of the optical properties of cirrus with time, the flux densities in the upper part (6000–8500 m) and the lower part (3000–5500 m) of the cirrus cloud were analyzed separately. In these simulations, the optical thickness in the lower (upper) part was increased (decreased) by 50%. By this treatment, most of all calculated flux densities were within one standard deviation of the natural variability in each leg. Finally, the effect of inhomogeneities in the cloud field on the solar flux density has been simulated using a Monte Carlo method, since the upper part of the cirrus field has indeed been very inhomogeneous. This paper is a result of a collaborative effort between the MRI in Tsukuba, Japan, and the GKSS in Geesthacht, Germany.     

天津平流雾过程及其空中微物理特征个例研究

2016/2017冬季在天津开展了平流雾微物理特征观测试验,结合距地66 m高度处雾滴谱和255 m气象塔大气边界层资料,借助突变和趋势一致性非参数检验方法对重度霾后接连发生的两次平流雾过程发展阶段进行客观划分,揭示雾体内部一定高度处雾滴微物理特征和尺度分布特征的观测事实,讨论其生消演变规律。结果表明,伴随西南暖湿平流,饱和层首先在空中出现并向地面扩展,雾过程中成熟阶段观测高度范围内升温,雾层处于中性或弱不稳定层结状态。66 m高度处大雾滴持续存在,微物理特征与地面能见度准同步变化,数浓度高值出现在成熟阶段初期,而含水量、特征直径高值出现在成熟阶段后期,对应成熟阶段后期雾滴数浓度减少、地面能见度小幅跃升。消散阶段各尺度数浓度因雾滴蒸发同步减小。     

Vulnerability and adaptive capacity in forestry in northern Europe: a Swedish case study

Climate change is likely to present new and substantially unpredictable challenges to human societies. The prospect is of particular concern at the local and regional levels, since vulnerability and adaptive capacity are location-specific and many decisions regarding climate-induced risks are made at those levels. In this light, one is compelled to survey stakeholders’ understandings of their situation and perceived problems. Assessments should also include the context of other ongoing changes, such as globalisation, that will impact communities and exacerbate their vulnerabilities. This paper presents an assessment of vulnerability and adaptive capacity in the forestry sector in the Pite River basin in northern Sweden. The study was carried out using a multi-method design encompassing literature surveys, interviews with stakeholders, and stakeholder meetings. The paper concludes that while climate change will have an impact on the region, its effect will be superseded by that of broader socio-economic changes. The results illustrate the need to understand local and regional perceptions of adaptation in formulating appropriate policy measures.     

AgClimate: a case study in participatory decision support system development

Potential economic benefit exists from the use of seasonal climate forecasts in agriculture. To assess potential end user attitudes toward and interests in climate data, and to provide inputs from users to the development of decision support tools, we conducted a series of surveys. Survey results affected the design, development, and enhancement of AgClimate, a web-based decision support system for minimizing climate risks to agriculture. The overall process is an example of how decision makers can participate in the research process, thereby improving the value and relevance of research products such as decision support systems.     

Consumption-based GHG emission accounting: a UK case study

Global GHG emissions continue to rise, with nearly a quarter of it due to trade that is not currently captured within global climate policy. In the context of current trade patterns and limited global cooperation on climate change, the feasibility of consumption-based emissions accounting to contribute to a more comprehensive (national) policy framework in the UK is investigated. Consumption-based emissions results for the UK from a range of models are presented, their technical robustness is assessed, and their potential application in national climate policy is examined using examples of policies designed to reduce carbon leakage and to address high levels of consumption. It is shown that there is a need to include consumption-based emissions as a complementary indicator to the current approach of measuring territorial emissions. Methods are shown to be robust enough to measure progress on climate change and develop and inform mitigation policy. Finally, some suggestions are made for future policy-oriented research in the area of consumption-based accounting that will facilitate its application to policy.

Policy relevance

Emissions embodied in trade are rapidly increasing and there is thus a growing gap between production emissions and the emissions associated with consumption. This is a growing concern due to the absence of a global cap and significant variation in country-level mitigation ambitions. Robust measurements of consumption-based emissions are possible and provide new insights into policy options. This includes trade-related policy (e.g. border carbon adjustments) and domestic policies (e.g. resource efficiency strategies). As climate policy targets deepen, there is a need for a broad range of policy options in addition to production and technological solutions. Consumption-based emissions are complementary to production-based emissions inventories, which are still the most accurate estimate for aggregated emissions at the global level. However, without consumption-based approaches, territorial emissions alone will not provide a complete picture of progress in regional and national emissions reduction.     

大理机场一次晴空大风天气诊断分析

利用常规气象资料、NCEP2.5°×2.5°资料和风廓线雷达资料,分析了2015年2月27日晴空大风天气过程。结果发现:大理机场上空位于高空西风急流轴附近,虽然高空冷平流较弱,但是动量下传是造成大风的主要因子。当高空至机场近地面均为下沉运动时,下沉气流携带高空的动量下传,造成大理机场出现大风天气。相反,当近地面至700 h Pa为上升运动时,上升气流会阻碍高空动量向下传递,机场大风结束。风廓线雷达资料分析也表明动量下传是27日大风的主要动力因子,当高空到地面均为下沉运动时,大于3 m/s的下沉速度到达的高度越低,大风的出现频率越高;同时300~2500 m风向随时间反气旋偏转能使高空动量持续向近地面传送,对大风的产生和维持起作用,相反300~2500 m风向随时间气旋性偏转,则对高空的动量下传起抑制作用。     

Copula based analysis of rainfall severity and duration: a case study

The main objective of this study is to investigate the joint distribution of rainfall severity and rainfall duration in the state of Victoria, Australia, based on monthly rainfall data from selected rain-gauge stations which are located in the north-eastern and south-western parts of the state, during the period from 1950 to 2010. Traditional approach for considering the joint distribution of rainfall characteristics using standard bivariate modeling presents some limitations that can be circumvented by using Copula models. Archimedean and extreme-value copulas will be used to obtain the bivariate distribution of rainfall severity and duration. The Standard Precipitation Index (SPI), which is employed extensively to quantify rainfall severity, will be discussed in detail. Several goodness of fit tests will be performed to find the best fitting copulas and the results will be summarized. The final fitted copulas will then be applied to obtain the joint and conditional return periods from a minimum of two years to one hundred years of rainfall events in Victoria.     

Some methodological questions concerning advection measurements: a case study

A dataset from two campaigns conducted at the Vielsalm experimental site in Belgium was used as a basis for discussing some methodological problems and providing intermediate results on estimating CO₂ advection. The analysis focused on the horizontal [CO₂] gradient and on the vertical velocity w, the variables most affected by uncertainty. The sampling error for half-hourly horizontal [CO₂] gradients was estimated to be 1.3 μmol mol⁻¹. Despite this important random error for half-hour estimations of [CO₂], the mean horizontal [CO₂] gradients in advective conditions were shown to be representative at the ecosystem scale and to extend only to the lowest part of a drainage sub-layer, which developed in the trunk space. By contrast, under daytime conditions, this gradient was shown to be more sensitive to local source heterogeneities. The estimation of the short-term averaged vertical velocity ( was the greater source of error when computing advection terms. The traditional correction methods used to obtain are discussed and a (co)sine correction is tested to highlight the instrumental origin of the offset in w. A comparison of measurements by sonic anemometers placed close together above the canopy showed that the uncertainty on was 0.042 m s⁻¹, which is of the same order of magnitude as the velocity itself. In addition, as the drainage sub-layer is limited to the lowest part of the canopy, the representativeness of is questionable. An alternative computation using the divergence of the horizontal wind speed in the trunk space produced a estimation that was four times lower than the single-point measurement. However, this value gives a more realistic estimate of the vertical advection term and improves the CO₂ budget closure at the site.     

Quantifying internal variability in a regional climate model: a case study for Southern Africa

This study aims at presenting various methodologies to separate the reproducible and irreproducible components of seasonal and intraseasonal climate variability simulated by a regional climate model over Southern Africa (south of 15°S), during an austral summer rainy season representative of the climatology. To that end, a 30-member ensemble simulation is performed using WRF laterally forced by the ERA40 reanalyses. Retained metrics include the analysis of weather regimes, signal-to-noise ratio, inter-member standard deviation and coefficient of variation. At the seasonal timescale, simulated rainfall amounts generally show a strong reproducibility, except in the subtropics and over the southern part of the Mozambique Channel. There, the number of rainy days is roughly similar in all members, while their average intensity varies extensively. At the intraseasonal timescale, the chronology of weather regimes, derived from the 500?hPa geopotential height, is highly reproducible. Rainfall variability is much less reproducible, especially in the central parts of the domain and near its outflow boundaries. Analysis of a South African regional index nonetheless indicates that both wet and dry spells tend to be accurately simulated and occur in phase in most members, demonstrating that they are embedded in large-scale variability patterns. Internal variability is lastly related to the lateral forcings along the domain boundaries. An objective classification of inflow/outflow mass fluxes allows identification of the recurrent synoptic configurations that favor strong or weak regional reproducibility. The main uncertainties concern the basic morphological features of rain-bearing systems (i.e., their spatial extension, location and propagation speed). Consequences for tropical-temperate interactions are then discussed.