A simplified technique to compute spectral atmospheric radiation

The spectral distribution of longwave atmospheric radiation arriving at the earth's surface is composed of contributions from atmospheric layers which absorb and re-emit longwave radiation. A procedure to estimate this radiation requires, as input, the temperature and pressure variations with altitude and the distribution of absorbing gases in the atmosphere. Such detailed information about the atmosphere at a given location and time is rarely known. However, local variation of the amount of water vapor is generally known, and ozone undergoes known seasonal variations. These two gases along with carbon dioxide are the main emitters of longwave radiation in the atmosphere.A rigorous technique to compute spectral atmospheric radiation is used together with atmospheric data from a Standard Atmosphere to examine the variation of spectral emissivity with the amount of absorbing gases in the atmosphere. A simple spectral correlation is thereby developed which is then applied to the other Standard Atmospheres utilizing their water vapor amount as the only input. Results obtained from this correlation are compared with those obtained from detailed computations for each Standard Atmosphere. Good agreement is observed at all the wavelengths considered except in a 1 μm region wherein the differences are somewhat larger. It is demonstrated that for any geographic latitude and season the spectral longwave atmospheric radiation can be computed from a simple correlation using precipitable water vapor amount as the only input parameter.     

A model for the calculation of solar global insolation

A theoretical model is described that is designed to give the total global insolation falling on the earth's surface and the transmission of the atmosphere. It is compared to a model by Braslau and Dave[1] and found to agree to within a few percent in all cases. Climatogical values of total pricipitable water, turbidity, and surface albedo are required as the model inputs, and the sources of these data are described. The model has been applied to 26 stations in the National Weather Service (NWS) pyranometer network, where measured true solar noon atmospheric transmission values are available, as part of the NOAA program to rehabilitate the old pyranometer observations. For three of these stations where reliable true solar noon irradiance and transmission values are available, the model calculations and observations are compared. At 18 locations the calculated and measured daily mean insolation values are compared for clear days. At one location (Boulder, Colorado) calculated and measured radiation climatologies for all weather conditions are compared. In all comparisons the model and observations differ by no more than 2.7 per cent, which is within the experimental accuracy (±5 per cent) of the pyranometers. Possible sources of errors are discussed.     

Measurements and predictions of solar radiation incident on horizontal surfaces at Santa Fe, Argentina (31° 39′S, 60° 43′W)

Measurements and predictions of solar radiation during a period of 10 years on horizontal surfaces at Santa Fe (31° 39′ S, 60° 43′ W), Argentina, reported as average daily global radiation for each month, are presented. Data are compared to those obtained with a previously published and verified model for computing solar radiation on horizontal planes at the earth's surface for cloudless sky days. Measurements show an important reduction of global radiation with respect to the cloudless sky model predictions for all months of the year. Conversely, averaged daily diffuse solar radiation calculated with Page's formula shows a small increment with respect to the predicted diffuse solar radiation for cloudless sky conditions. When direct solar radiation data, calculated from global and diffuse solar radiation values, are compared to theoretical prediction, a significant decrease is observed. This trend is similar to that obtained for global solar radiation.     

Radiative fluxes in the troposphere from upper air meteorological data in Saudi Arabia

An attempt is made to use the empirical type of parameterization scheme for the calculations of solar radiative fluxes and atmospheric heating or cooling rates in the troposphere by using observed upper air meteorological data. This type of parameterization scheme is useful in calculating the upper air heating/cooling rate for use in planetary boundary layer modelling and in the evaluation of the surface heat budget equation. The results presented in this paper are based on the upper air data collected between 1300 to 1500 Local Standard Time (LST) in Dhahran for the year 1989. The diurnal variation of vertical profiles of radiative fluxes and heating/cooling rates is calculated by changing the solar zenith angle. The diurnal variation of annually averaged solar radiation fluxes reaching the ground is compared with the observed values of solar radiative flux at Dhahran. The calculated values are in excellent agreement with the observed values in the morning and evening times. The scheme used in this paper can be used for obtaining solar radiative fluxes and atmospheric heating or cooling rates above the earth's surface at places where only upper air meteorological data is available.     

A study of ultraviolet solar radiation at Cairo urban area, Egypt

The monthly mean values of global, G, and ultraviolet, UV, solar radiation incident on a horizontal surface at Cairo urban area during the two different periods (1969–1973) and (1993–1997) are presented, analyzed and compared. The effect of urbanization processes on the solar radiation components is investigated and discussed. It was found that the total radiation of the two components, G and UV received at the urban area of Cairo during the period (1969–1973) highly exceeds the radiation received during the period (1993–1997) for all months of the year. The mean relative reduction of G and UV reached 17.4% and 27.4% respectively. A significant correlation between G and UV radiation has been established and the recommended correlation equation has been stated to estimate the values of UV radiation that are difficult to measure at any site in the zone of Lower Egypt. Also, a comparative study of the two radiation components, G and UV, at urban (Cairo) and rural (Bahtim) areas during the period (1993–1997) revealed that the urban area always has values of G and UV radiation distinctly lower than that found in rural area for all months of the year. Urban–rural mean reduction of G and UV reached 7.0% and 17.9% respectively. The ratio of the ultraviolet to global radiation (UV/G) are calculated and compared with other sites in the Arabian Peninsula. The effect of atmospheric dust on the measured solar radiation components is also investigated and discussed.     

POTSOL: Model to predict extraterrestrial and clear sky solar radiation

A model was developed to predict potential and clear sky solar radiation for any latitude. The model (POTSOL) uses the fundamental geometric relationships between the earth and sun to predict the theoretical solar radiation outside the earth's atmosphere, clear sky solar radiation received at the earth's surface after accounting for atmospheric interference, and clear sky solar radiation on a panel with any tilt angle between 0° and 90° from the horizontal. The only model input parameters are latitude (PHI), clearness number (CN), and panel tilt angle (PT). The model was verified using weather data obtained from the National Climatic Center, Asheville, North Carolina for Ely, Nevada.     

夏季晴天不同土壤湿度条件的绿洲辐射特征

利用2005年在甘肃省金塔绿洲开展的"绿洲系统能量与水分循环过程观测试验"所取得的资料,分析了夏季晴天金塔绿洲不同土壤湿度条件下的辐射收支特征。结果表明:向下短波辐射不受土壤湿度的影响;当植被处于同一生长期,土壤湿度越大,向上的辐射就越小,净辐射就越大;当空气中的水汽含量相差不大时,土壤较湿润则大气逆辐射白天较小,夜晚较大。但当水汽含量差别较大时,水汽含水量起主要影响作用,空气越湿润,大气逆辐射越小。     

Night Sky Radiation in Athens During the Summer. Influence of City Pollutants

Night sky radiation measurements have been carried out in June in Athens. Computations of the correlations with the most common type of equations used for sky radiation are performed. Brunt, Brutsaert and Idso type of equations fit well with experimental data. In terms of the zero intercept, equations (of polynomial type) correlating the sixth power of the screen level air temperature and the square of vapour pressure show better behaviour. City pollutants do influence the sky radiation. The equation that best fits to the experimental data is of polynomial type and includes the square of the sum of the partial pressures of four city pollutants as well as the sixth power of screen level air temperature and the square power of vapour pressure.     

干旱地区不同下垫面的辐射收支

利用2000年6月2001年5月在干旱地区敦煌和高原北部的五道梁所获取的太阳辐射观测资料，分析研究了干旱地区不同下垫面的加辐射收支特点。结果表明：虽然两地地理位置和海拔高度不同，但由于两地下垫面条件的差异，使得太阳短波辐射特别是地表吸收辐射在夏季大致相近，冬季则是敦煌小于五道梁；长波辐射(地面向上长波辐射和大气逆辐射)郭煌明显大于五道梁；地表净辐射夏季五道梁比敦煌为大，冬季则两地相近。     

The distribution of global and net radiation over Greece

In the present study an attempt is made to establish the distribution of global and net radiation over Greece, with the help of meteorological data. An empirical formula based on that proposed by Budyko[1] is derived which reproduces satisfactorily the available actual measurements at the National Observatory of Athens. Parameters utilized in the equations were: elevation, absolute humidity, cloud cover, air temperature at the screen height, surface albedo. The results indicate that the main factors which contribute to the distribution of global radiation over Greece are elevation and cloudiness. The extreme values are 4.2 Kly/month over Macedonia during the winter and 18.0 Kly/month over the mountainous regions of Crete during the summer. On the other hand the main factors which contribute to the distribution of net radiation over Greece are the absolute humidity and the air temperature. The extreme values are −0.35 Kly/month over eastern Macedonia during the winter and 7.8 Kly/month over Crete and the western Peloponnesos during the summer.     

Solar radiation correlations for the Athens,Greece, area

In the present study, correlations of the solar radiation for the Athens area are provided, based on hourly measurements over the period 1955–1980. These correlations are of two kinds: The first, which provide the average total radiation incident on a horizontal surface in terms of hour, day, and month of the typical year, is suitable for solar energy collection applications. The correlations of the second kind provide the maximum radiation and are suitable for use in the design of air-conditioning installations or other applications requiring knowledge of maximum values. The correlations of this kind are based on the calculation of the solar constants A, B, and C, i.e. the “apparent solar irradiation at zero air mass,” the “atmospheric extinction coefficient,” and the “diffuse radiation factor,” respectively. These solar constants permit the calculation of the maximum direct normal radiation and of the maximum diffuse radiation as well as of the total radiation on surfaces of various orientations and inclinations. The solar heat gain through fenestration of various orientations (needed in air-conditioning applications) is calculated, as an example of the applications of the solar constants A, B, and C.     

Fuzzy inference systems applied to the daily ultraviolet radiation evaluation (295–385 nm) from daily global radiation

This work presents the results of applying different automatic learning techniques to the calculation of daily ultraviolet radiation from daily global radiation on a horizontal surface. Using the data from three Spanish locations, a zonal study was made, which was finally combined in models for general application. Using the corresponding atmospheric transparency index, three models based on multivariate linear regression, non-linear regression and generation of fuzzy inference systems, respectively, were designed. The results obtained verify the good behavior of the fuzzy inference system calculated.     

SIMULATION OF BROAD-BAND AND SPECTRAL SOLAR ULTRAVIOLET RADIATION

Daily broad-band and spectral measurements of solar ultraviolet radiation reaching the ground at Athens, Greece (38^°N, 24^°E) during 1989-1993 in conjunction with daily total ozone measurements deduced from satellite and ground-based instrumentation were used to investigate their association. Furthermore, employing a new parametric model, the spectral and broad-band solar ultraviolet radiation for die period 1979-1993 were calculated considering the total ozone values, derived from both the satellite Nimbus-7, and the ground-based Dobson spectrophotometer.     

藏北高原典型草甸下垫面与HEIFE沙漠区辐射平衡气候学特征对比分析

利用中日合作“全球能量与水分平衡试验一青藏高原季风试验(GAME—Tibet)”和中日合作“黑河地区地一气相互作用野外观测实验研究(HEIFE)”IOP、FOP资料,计算分析了藏北高原典型草甸下垫面安多站和HEIFE沙漠站的辐射平衡各相关特征量时频变化的气候学特征。结果表明：无论是高原安多站还是黑河沙漠站,夏季均出现超太阳常数现象(只是安多更为明显);总辐射、大气逆辐射、地表长波辐射、地表有效辐射和地表辐射平衡等的日变化(晴天)无论是安多站还是沙漠站均表现为早晚出现最小值而正午附近(地方时)达到最大值,而地表反照率的日变化(晴天)相反表现为早晚大而正午附近小的规律;上述各分量均表现有程度不等的季节变化规律：总辐射、大气逆辐射、地表长波辐射和地表辐射平衡均表现为夏半年增大达到最大值百而冬半年降低量出现最小值;另外,大气长波辐射、地表有效辐射和地表反照率在沙漠站的年际变化的振幅较安多站更为显著和有规律。     

Spectral Solar Irradiance And Some Optical Properties For Various Polluted Atmospheres

Using ground-based spectroradiometric measurements taken over the Athens atmosphere during May 1995, the influence of gaseous pollutants and aerosol on the spectral radiant energy distribution was investigated. It was found that spectral measurements exhibited variations based on various polluted urban atmospheric conditions as determined via gaseous pollutants record analysis. The relative attenuations caused by gaseous pollutants and aerosol can exceed 27%, 17% and 16% in the global ultraviolet, visible and near-infrared portions of the solar spectrum respectively, as compared to “background” values. In contrast, an enhancement of the near-infrared diffuse component by 66%, was observed, while in visible and ultraviolet bands the relative increases reached 54% and 21% respectively. Experimental total Rayleigh-corrected and spectral aerosol optical depths were retrieved, representing differences in polluted air over the Athens atmosphere. The diffuse component accounts for more than 80% of the total radiation field under high polluted atmosphere. The observed differences of solar radiation between the Athens center and at a nearby suburban site are a manifestation of contrasting air properties provided mainly by automotive traffic.     

基于MATLAB的太阳辐射资源计算

运用MATLAB软件编程,计算了太阳辐射穿过大气层后到达地面的强度,综合考虑海拔高度、大气透明度系数的影响,建立了太阳辐射强度数学计算模型。模型计算得到的理论数据与用MS4型太阳能资源测试仪测试获得的数据进行了对比分析,相对误差在0.002%～9.981%之间,验证了计算模型的合理性。     

Correlations for the yearly or seasonally optimum salt-gradient solar pond in Greece

Simple correlations and corresponding nomographs are presented, which express the maximum useful heat received from salt-gradient solar ponds throughout the year or during a specified season of the year, and the corresponding optimum depth of the nonconvective zone in terms of the thickness of the upper convective zone and the temperature under which the maximum useful heat is received. The correlations are valid for the Athens (Greece) area or for regions with a similar climate, because solar radiation and ambient temperature values for Athens have been employed, obtained by a statistical process of hourly measurements over a period of about 20 years. For other climates, it is easy to develop similar correlations using the same methodology. Development of the proposed correlations is based on a method, which simulates the transient operation of the salt-gradient pond using finite-differences, and calculates the useful heat received hourly along the typical year. Thus, the useful heat received during a period or throughout the year is calculated as a sum of hourly values. Calculations of the useful heat are performed for a great number of values of the parameters of the problem, and the combinations of values that maximize useful heat are selected and used for developing correlations and corresponding nomographs. The correlations presented may be employed in the design of the optimum solar pond under the specific requirements of each application.     

Estimating direct, diffuse, and global solar radiation for various cities in Iran by two methods and their comparison with the measured data

Two computational methods for calculating hourly, daily, and monthly average values of direct, diffuse, and global solar radiation on horizontal collectors have been presented in this article for location with different latitude, altitude, and atmospheric conditions in Iran. These methods were developed using two different independent sets of measured data from the Iranian Meteorological Organization (IMO) for two cities in Iran (Tehran and Isfahan) during 14 years of measurement for Tehran and 4 years of measurement for Isfahan. Comparison of calculated monthly average global solar radiation, using the two models for Tehran and Isfahan with measured data from the IMO, has indicated a good agreement between them. Then these developed methods were extended to another location (city of Bandar-Abbas), where measured data are not available. But the work of Daneshyar [1] predicts its monthly global radiation. The maximum discrepancy of 7% between the developed models and the work of Daneshyar [1] was observed.     

Contribution to the study of solar radiation in Burgos, Spain

A series of daily measurements of global solar radiation on horizontal surface realized during the period 1978–1982, in Burgos, Spain, is analysed. The mean decadic values show fluctuations, in the spring and at the beginning of the summer especially. The absolute maximums generally appear in July with values that oscillate between 23 and 26 MJ m⁻², and the minimums in January or December with values between 4 and 5 MJ m⁻². Averaging the analogous months we obtain the maximums in July with a value of 23 MJ m⁻². We have studied the elemental statistic characteristics and we remark that the interquartile range is small in the winter months and increases in the spring and summer. The number of the days in which the radiation has remained inferior to a given value, has been calculated in the frequency analysis, remarking that in the days corresponding to the period of the winter appear radiation values inferior to 10 MJ m⁻² and only 3% of July days are below this value. We have defined and determined the potential radiation and have calculated the extraterrestrial radiation in order to know the attenuation of global radiation in its passage through the atmosphere. We remark that the energy percentage transmitted by the atmosphere increases from winter to summer, a maximum value of 59% is obtained in July and a minimum of 30% in December. The atmospheric transparency without clouds oscillates between 71% in the spring and 62% in the winter.     

Fundamentals and characteristics of solar radiation

The calculation of solar radiation received at a particular place and at a particular time, involves many factors like rotation and revolution of the earth, atmospheric attenuations, atmospheric conditions, time of day and year, geographic location of place, and site location of collector, tilt of collector, type of its variation due to seasonal and atmospheric conditions and show how calculation for horizontal and tilted surfaces may be done based on geometrical and seasonal consideration. Certain angles have been defined for specification of the sun's position in the sky like solar altitude and azimuth angles and the sun's apparent path across the sky found on the celestial sphere. The method of defining position of a point on the earth's surface with respect to the sun's rays by means of latitude, hour angle and declination is also shown. Depletion of extraterrestrial radiation by absorption, scattering etc. is also discussed in detail in this paper.