Ultraviolet radiation in overcast sky at the surface

Based on the analysis of one year of observation data of solar radiation at the ground in Beijing in 1990, a simple empirical formula for calculating UV radiation in overcast sky is established. The formula is Qlw/Quvo = A1S Ao, where Quv and Quvo are monthly mean daily sums of UV exposure in overcast sky and clear sky, respectively. S is the daily sunshine hours. The calculated results agree well with the observed. The maximum and minimum relative biases are 9.9% and 0.1%, respectively, and the yearly relative bias is 2.9%. The ratio of ultraviolet radiation of overcast sky to clear sky in 1990 is between 44.6% and 61.8%, and the yearly average is 53.9%. Thus, almost half of the UV energy is lost in the atmosphere in overcast sky in 1990.     

Performance validation of the Gueymard sky radiance model

Abstract

The Gueymard model of short‐wave sky radiance has been validated against sky radiance date measured in the Rocky Mountain foothills of Alberta. Except for sky points within the circumsolar region in clear skies and for low sun positions in near overcast skies the model performs as well as other current sky radiance models.     

Luminous efficacy of global solar radiation on a horizontal surface for overcast and intermediate skies

Summary  In the first part of this research two models for the luminous efficacy of global solar radiation on horizontal surfaces and overcast skies have been developed. The first of these models is developed using a method similar to that proposed by Littlefair (1988). The second model has been obtained from the corresponding illuminance and irradiance models in an, apparently, new approach to the subject. In the second part of this research, a model for the luminous efficacy of global solar radiation for intermediate skies and horizontal surfaces is developed from the corresponding illuminance and irradiance models. The model for intermediate skies is given by the same mathematical function as that of the analogous model for overcast skies, and only the empirical constants change. In all the cases the only independent variables used are the solar altitude and the brightness index. The models proposed in the present paper have been statistically tested, and their prediction accuracy compared with other models available in the scientific literature. Received June 26, 2000 Revised December 9, 2000     

Spectral radiance and sky luminance in Antarctica: a case study

Summary Sky luminance and spectral radiance has been characterised at Neumayer, Antarctica for selected situations during the austral summer 2003/04. Luminance has also been measured at Boulder, Colorado, USA in June 2003. The high reflectivity of the surface (albedo) in Antarctica, reaching values up to 100% in the ultraviolet (UV) and visible part of the solar spectrum due to snow cover, modifies the radiation field considerably when compared to mid-latitudes. A dependence of luminance and spectral radiance on solar zenith angle (SZA) and surface albedo has been identified. For snow and cloudless sky, the horizon luminance exceeds the zenith luminance by as much as a factor of 8.2 and 7.6 for a SZA of 86° and 48°, respectively. In contrast, over grass this factor amounts to 4.9 for a SZA of 86° and a factor of only 1.4 for a SZA of 48°. Thus, a snow surface with high albedo can enhance horizon brightening compared to grass by a factor of 1.7 for low sun at a SZA of 86° and by a factor of 5 for high sun at a SZA of 48°. For cloudy cases, zenith luminance and radiance exceed the cloudless value by a factor of 10 due to multiple scattering between the cloud base and high albedo surface. Measurements of spectral radiance show increased horizon brightening for increasing wavelengths and generally confirm the findings for luminance. Good agreement with model results is found for some cases; however there are also large deviations between measured and modelled values especially in the infrared. These deviations can only partly be explained by measurement uncertainties; to completely resolve the differences between model and measurement further studies need to be performed, which will require an improvement of modelling the spectral radiance. From the present study it can be concluded that a change in albedo conditions, which is predicted as a consequence of climate change, will significantly change the radiation conditions in polar regions as well.     

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   

山东省设施农业生产季连阴天时空演变特征及其影响

利用山东省59个国家级气象观测站1961—2018年逐日日照时数及32个设施农业小气候观测站2008—2018年逐日气温观测资料,采用线性回归法、Mann-Kendall突变检验法及反距离权重插值法等分析了设施农业生产季连阴天时空分布和变化规律及其对设施内气温条件的影响。结果表明,时间上,过去58 a山东省连阴天年总发生次数和总连阴天数分别以1.7次·a-1和6.5 d·a-1的趋势增加,且年总发生次数在1999年发生突变;空间上,过去58 a连阴天总发生次数和总连阴天数均呈“东北—西南”向增多分布,聊城和德州地区的增加较其他区域更为明显,单站年发生次数和连阴天数增加超过0.06次·a-1和0.2 d·a-1,且变化趋势在聊城等15个和13个站点通过显著性水平为0.05的显著性检验;随着连阴天数增加,设施内气温降温幅度会增大;相同连阴天数时,平均气温和最低气温降幅春秋季大于冬季,分析其原因可能是春秋季基础温度高于冬季,从而更容易引起温度的剧烈变化所导致。研究结果可为有关部门研究设施农业种植布局和指导设施农业生产及防灾减灾提供理论支持。     

Investigation of sea radiance fluctuation

Abstract

The fluctuation of remotely sensed sea radiance is investigated and comparatively simple expressions for the average value and the variance of radiance are derived. Possible causes for this fluctuation are sea waves and the angular gradient of sky radiation. The influence of oil films on the average radiance is also estimated.     

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.     

The albedo of snow for partially cloudy skies

The albedo of snow for different cloudiness conditions is an important parameter in the Earth's radiation budget analysis and in the study of snowpack's thermal conditions. In this study an efficient approximate method is derived to calculate the incident spectral solar flux and snow-cover albedo in terms of different atmospheric, cloud, and snow parameters. The global flux under partially cloudy skies is expressed in terms of the clear sky flux and a coefficient which models the effect of scattering and absorption by cloud patches and multiple reflections between the cloud base and snowcover. The direct and the diffuse components of the clear sky flux are obtained using the spectral flux outside the atmosphere and the spectral transmission coefficients for absorption and scattering by molecules and aerosols.The spectral snow reflectance model considers both specular surface reflection and volumetric multiple scattering. The surface reflection is calculated by using a crystal-shape-dependent bidirectional reflectance distribution function; the volumetric multiple scattering is calculated by using a crystal-size-dependent approximate solution in the radiative transfer equation. The input parameters to the model are atmospheric precipitable water, ozone content, turbidity, cloud optical thickness, the size and shape of ice crystals of snow and surface pressure. The model yields spectral and integrated solar flux and snow reflectance as a function of solar elevation and fractional cloudcover.The model is illustrated using representative parameters for the Antarctic coastal regions. The albedo for a clear sky depends inversely on the solar elevation. At high elevations the albedo depends primarily upon the grain size; at low elevation the albedo depends on grain size and shape. The gradient of the albedo-elevation curve increases as the grains become larger and faceted. The albedo for a densely overcast sky is a few percent higher than the clear-sky albedo at high elevations. A simple relationship between grain size and the overcast albedo is obtained. For a set of grain size and shape, the albedo as a function of solar elevation and fractional cloud cover is tabulated.     

Prediction of downward flux of atmospheric radiation from clear skies

At present, there are two approaches to the prediction of downward flux of atmospheric radiation at the earth's surface. One can use either empirical correlations or radiation charts. The empirical correlations, being very elementary, do not always agree with observations made under different conditions. The radiation charts on the other hand require detailed knowledge of temperature and water vapour profiles. In the present paper, a semi-empirical approach is advocated. The emissivity of water vapour measured in the laboratory is used to predict the atmospheric downward radiation. Since the laboratory data are based on a homogeneous atmosphere, suitable pressure scaling is employed to take into account the non-homogeneity in the earth's atmosphere. The atmospheric downward radiation is obtained as a function of local temperature, water vapour scale height, and temperature lapse rate. It is shown that the resulting predictions agree somewhat better with observations than do the predictions based on empirical correlations.     

On the estimation of long-wave radiation flux from clear skies

Summary Data from measurements of long-wave radiation at Barcelona were used to test the validity of several methods for computing this component of the radiation balance in clear sky conditions.Two types of formulae, the analytically derived formulae of Swinbank and Brutsaert 1 and 2 and the empirically obtained formulae of Brunt, Idso and Jackson and Idso 1 and 2 were used in the test.Most of these methods are derived for a particular location and utilize local empirical coefficients. However, there are several which have been considered more universal.Estimates by the two methods give approximately the same value when the screen level air temperature is above 0°C.In addition, the test for temperatures below 0°C shows several discrepancies between the observed and estimated values of long-wave atmospheric radiation. This fact suggests that modifications may be needed for both analytical and empirical formulae. However, since we have few measurements in the temperature regime below 0°C, this statement cannot be justified as a conclusion of this study.

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Zusammenfassung Es werden Daten der langwelligen atmosphärischen Strahlung bei Barcelona herangezogen, um verschiedene Methoden zur Bestimmung dieser Komponente der Strahlungsbilanz bei klarem Himmel zu vergleichen. Dazu werden zwei unterschiedliche Formeltypen, die analytischen nach Swinbank und Brutsaert (1 und 2) und empirische nach Brunt, Idso und Jackson sowie Idso (1 und 2) benützt.Von diesen Methoden wurden die meisten für einen bestimmten Ort entwickelt und verwenden daher lokale empirische Koeffizienten. Allerdings gibt es einige, die als allgemein verwendbar angesehen werden.Für beide Typen der Abschätzung ergeben sich für Lufttemperaturen über 0°C im Hüttenniveau ähnliche Werte. Bei Lufttemperaturen unter 0°C zeigen sich jedoch einige Unterschiede zwischen den beobachteten und geschätzten Werten der langwelligen atmosphärischen Strahlung. Das legt nahe, die Koeffizienten sowohl für die analytischen als auch die empirischen Formeln anzupassen. Leider war das auf Grund des geringen Datenmaterials bei Temperaturen unter 0°C innerhalb dieser Untersuchung nicht möglich.

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On the measurement of sky radiation

Summary Equipment for the continuous registration, at the earth's surface, of the vertical flux of short-wave sky radiation of solar origin was first introduced into South Africa in 1951. This radiation is the energy component which is scattered out of the solar beam and diffused downwards by gaseous molecules, water droplets and solid particles. A contribution to the radiation from cloudless portions of the sky is also provided by the reflection of sunlight at the surfaces of cloud masses.In this paper the techniques of instrumental measurement and reduction of the records, which have been originated in the Radiation Service of the Union Weather Bureau, are described. In particular, a section is devoted to the problem of correcting for radiation intercepted when shadow bands are employed to screen off the direct solar component. Tabular values of this corrective factor are presented, for a specific screening ring and three standard categories of cloudiness, on a world-wide basis.At present nine radiation stations (soon to be increased to eleven) in Southern Africa are equipped with the type of sky pyranograph described in the paper; in the Belgian Congo, three more stations are operated with equipment which is very similar. The general method outlined here has been adopted by the joint session of the Radiation Commission of the International Union of Geodesy and Geophysics with the Working Group on Radiation of the World Meteorological Organization (Rome 1954) as a basic principle for the introduction of such measurements within national weather services.

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Zusammenfassung Eine Einrichtung für die Dauerregistrierung des Vertikalstroms der kurzwelligen Himmelsstrahlung solaren Ursprungs am Erdboden wurde in Südafrika 1951 eingerichtet; es handelt sich dabei um die Strahlungsenergiekomponente, die aus dem Sonnenstrahl gestreut und durch Gasmoleküle, Wassertröpfchen und feste Partikel abwärts diffundiert wird. Ein Beitrag zu der Strahlung der wolkenlosen Partien des Himmels wird auch durch die Reflexion des Sonnenlichts an den Wolkenoberflächen geleistet.In der vorliegenden Untersuchung wird die Technik der instrumentellen Messung und der Reduktion der Registrierungen beschrieben, die im Strahlungsdienst des Unions-Wetterdienstes entwickelt wurde. Ein spezieller Abschnitt ist dem Problem gewidmet, wie die Strahlungswerte zu korrigieren sind, wenn die direkte Sonnenstrahlung durch einen Beschattungsring abgeschirmt wird. Es werden Tabellenwerte dieser Korrektionsgröße für die ganze Erde und für einen speziellen Abschirmungsring und drei typische Bewölkungszustände vorgelegt.Zur Zeit sind 9 Strahlungsstationen (die in Kürze auf 11 erhöht werden) in Südafrika mit dem hier beschriebenen Modell eines Himmelspyranographen ausgestattet; im Belgischen Kongo werden weitere 3 Stationen mit ganz ähnlichen Einrichtungen betrieben. Die hier skizzierte Methode wurde 1954 in Rom an der gemeinsamen Sitzung der Strahlungskommission der U. G. G. I. und der Arbeitsgruppe für Strahlung der W. M. O. als Grundprinzip für die Einführung solcher Messungen in Landeswetterdiensten angenommen.

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Résumé On a installé en 1951 en Afrique du Sud un dispositif d'enregistrement continu du flux vertical de rayonnement céleste à courte longueur d'onde; il s'agit de la composante de l'énergie radiative solaire diffusée par les molécules gazeuses, les gouttelettes d'eau et les particules solides en suspension. Le ciel serein participe également à ce rayonnement par réflexion de la lumière solaire à la surface des nuages.On décrit ici l'appareillage de mesure et la réduction de celles-ci développée par le Service du rayonnement du Service météorologique de l'Union de l'Afrique du Sud. On s'applique en particulier à la correction des valeurs de rayonnement dans le cas où le rayonnement solaire direct est arrêté par un anneau protecteur. Des tableaux de cette correction ont été calculés pour la Terre entière et pour un anneau déterminé ainsi que pour trois états typiques de la nébulosité.Il existe actuellement 9 stations de mesure (11 sous peu) en Afrique du Sud équipées du pyranographe céleste ici décrit; en outre trois stations travaillent au Congo belge avec un appareillage analogue. La présente méthode a été adoptée en 1954 à Rome lors de la session de la Commission du Rayonnement de l'U.G.G.I. et du Groupe de Travail du Rayonnement de l'O.M.M. comme principe de base pour l'introduction de telles mesures dans les services météorologiques nationaux.

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2005年10月秋季连阴雨中暴雨天气特征分析

利用常规气象观测资料、FNL再分析资料和FY-2C气象卫星资料,应用天气学原理和方法对2005年9月28日—10月2日陕西中南部秋季连阴雨中暴雨过程的天气特征进行了分析。结果表明:暴雨发生在500 hPa稳定的东高西低形势下,乌山阻高、巴湖横槽和副高为连续暴雨产生提供了有利的环流背景条件。低空急流、切变是暴雨产生的主要影响系统。暴雨系统的动力和能量空间结构与盛夏暴雨相比有明显差异:涡度、垂直速度中心随高度升高向北倾斜明显;涡度、散度中心绝对值及垂直速度的数值偏小;降雨强度偏弱,持续时间长,具有中-α尺度系统特征。在暴雨过程中,共有2个中-α尺度系统生成发展,每个中-α尺度系统都是由多个中-β尺度系统发展加强、有规律移动、最后合并生成。     

A new model of thermal diffusion in a translucent medium

The thermal diffusion equation is solved analytically for an ideally translucent and homogeneous medium with an internal, distributed heat source given by the penetration and absorption of solar radiation. The mean annual temperature profile has the coldest values at the surface; the mean annual flux of sensible heat out of the medium balances the internally absorbed solar radiation for the case of constant mean annual temperatures. A new formula is developed for the evaluation of the true thermal diffusivity of a non-homogeneous conductor from the Fourier components of the waves of insolation and temperature; a constant extinction coefficient is assumed. The new model is applied with moderate success to data from the coastal plateau ice at Mawson, Antarctica.National Research Council Postdoctoral Resident Research Associate. Present Affiliation: Stanford Research Institute, Menlo Park, California 94025.     

关中初夏一次连阴雨过程的天气学特征分析

对2007—06—16—22陕西关中连阴雨天气过程的天气动力学分析,认为：500hPa乌拉尔山稳定的长波脊和东北到鄂霍茨克附近的长波脊、贝湖低槽和高原上低值系统的维持是造成陕西连阴雨的主要天气系统;中低层青藏高原东南侧到河套有西南气流发展并维持,为阴雨天气提供充沛的水汽和能量;700hPa切变线是连阴雨期间降水形成的动力和辐合机制;当关中处于高能舌和湿舌区时,降水明显;地面上四川到陕西有倒槽生成时,对应的降水强度大。当东路冷空气减弱消失只有西路冷空气影响时,相应的降水也减小。