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1.
Summary The aim of this study is the evaluation of models that estimate daily global solar radiation on tilted surfaces from that measured on horizontal surfaces. Global solar radiation incident on a tilted plane consists of three components: beam radiation, diffuse radiation and reflected radiation from the ground. The Klein (1977) method, modified by Andersen (1980), was used for estimating direct solar radiation incident on tilted surfaces and an isotropic model was used for estimating reflected solar radiation incident on a tilted plane. In contrast models for the diffuse radiation component show major differences, which justifies a validation study which has been done. Eight models for derivation of daily slope diffuse irradiance from daily horizontal diffuse irradiance were tested against recorded slope irradiances at Karaj (35°55′ N; 50°56′ E), Iran. The following models were included: Badescu (2002), Tian et al. (2001), Reindl et al. (1990), Skartveit and Olseth (1986), Koronakis (1986), Steven and Unsworth (1980), Hay (1979) and Liu and Jordan (1962). All the models use the same method for calculating beam radiation as well as ground reflected radiation. However, only diffuse component of radiation was compared. Statistical indices showed that Reindl’s model gives the most accurate prediction for the south-facing surface and Koronakis’s model performs best for the west-facing surface. The Relative Root Mean Square Errors (%RMSE), except for Steven and Unsworth’s model that has unacceptable results, for whole data range from 1.02 to 10.42%. In general, Reindl’s model produces the best agreement with the measured tilted data.  相似文献   

2.
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).  相似文献   

3.
Summary ¶Global, diffuse, and horizontal direct (beam) irradiances have been evaluated for 13 stations in Germany where the time series vary between 11 and 48 years. Global irradiance has decreased significantly at two stations and increased at four stations. The mean trend in global is an increase of 1.94Wm–2 or 1.83% per decade. Diffuse irradiance has decreased at five stations, with a mean reduction of 2.44Wm–2 or 3.46% per decade, while horizontal direct irradiance has increased an average of 4.86Wm–2 or 10.40% per decade at five stations. Increases in global and direct are most common at stations in the southwest region of Germany, decreases in global were observed in the southeast, and there was an absence of spatial homogeneity in the diffuse trends. Spatial variability in irradiance over Germany is higher in the direct component compared to variability in global and diffuse.Trend analyses of concomitant time series of radiation, bright sunshine duration, and modeled estimates of Ångströms turbidity coefficient suggest that long-term decreases in aerosols are the most likely cause of increases in global irradiance observed at Mannheim, Norderney, and Trier; decreases in diffuse at Hohenpeissenberg, Kassel, Mannheim, and Trier; and increases in direct irradiance at Bocholt, Kassel, Mannheim, and Trier. An increase in sunshine duration at Freiburg likely contributed to an increase in global and direct irradiance observed at that station.  相似文献   

4.
Summary At the high-mountain station Jungfraujoch (3576 m a.s.l., Switzerland), measurements of the radiation fluxes were made during 16 periods of six to eight weeks by means of a Robertson—Berger sunburn meter (UVB data), an Eppley UVA radiometer and an Eppley pyranometer. Cloudiness, opacity and altitude of clouds were recorded at 30-minute intervals. A second set of instruments was employed for separate measurement of the diffuse radiation fluxes using shadow bands. The global and diffuse UVA- and UVB radiation fluxes change less with cloudiness than the corresponding total radiation fluxes. When the sun is covered by clouds, the global UVA- and UVB radiation fluxes are also affected less than the global total radiation flux. The roughly equal influence of cloudiness on the UVA- and UVB radiation fluxes suggests that the reduction is influenced more by scattering than by ozone. Also, the share of diffuse irradiance in global irradiance is considerably higher for UVA- and UVB irradiance than for total irradiance. At 50° solar elevation and 0/10 cloudiness, the share is 39% for UVB irradiance, 34% for UVA irradiance and 11% for total irradiance. The increased aerosol turbidity after the eruptions of El Chichon and Pinatubo has caused a significant increase in diffuse total irradiance but has not produced any significant changes in diffuse UVA- and UVB irradiances.With 7 Figures  相似文献   

5.
Summary This paper deals with fractal analysis of daily solar irradiances measured with a time step of 10 minutes at Golden and Boulder located in Colorado. The aim is to estimate the fractal dimensions in order to perform classification of daily solar irradiances. The estimated fractal dimension and the clearness index KT are used as classification criteria. The results show that these criteria lead to three classes: clear sky, partially covered sky and overcast sky. The results also show that the evaluation of the fractal dimension of the irradiance signal based on a data set with 10 minutes time step is possible.  相似文献   

6.
Abstract

This study analyzes changes in solar ultraviolet (UV) irradiances at 305 and 325?nm at selected sites located at high latitudes of both hemispheres. Site selection was restricted to the availability of the most complete UV spectroradiometric datasets of the past twenty years (1990–2011). The results show that over northern high latitudes, between 55° and 70°N, UV irradiances at 305?nm decreased significantly by 3.9% per decade, whereas UV irradiance at 325?nm remained stable with no significant long-term change. Over southern high latitudes (55°–70°S), UV irradiances did not show any significant long-term changes at either 305 or 325?nm. Changes in solar UV irradiances are discussed in the context of long-term ozone and other atmospheric parameters affecting UV variability at ground level.  相似文献   

7.
Summary Radiometric ground truth data from seven Norwegian stations (58–64° N), and from five other European stations (38–61° N), are compared to satellite-derived data in the present paper. Hourly global irradiance at ground level is estimated by the Heliosat procedure from the “visible” channel of the geostationary satellite METEOSAT. With increasing latitude this satelllite sees the earth’s surface at an increasingly unfavourable angle. Nevertheless, in this paper, global irradiance estimates reproduce high latitude ground truth data with negligible Mean Bias Deviations (MBD) and only minor deviations regarding frequency distributions. Moreover, the Root Mean Square Deviations (RMSD) are comparable to those typically seen between ground truth stations some 20–30 km apart. Using a number of auxiliary models, a multiplicity of ground level solar radiation data is obtained from satellite-derived global irradiance data, and made available at the SATEL-LIGHT www server. The accuracy of the half-hourly data thus derived from Heliosat global irradiances, using models for diffuse fraction, luminous efficacy and slope/horizontal ratios, is successfully verified against ground truth data. Received August 31, 2000/Revised January 31, 2001  相似文献   

8.
Trend analysis of rainfall time series for Sindh river basin in India   总被引：1，自引：1，他引：0  
The main goal of this paper is to estimate a set of optimal seasonal, daily, and hourly values of atmospheric turbidity and surface radiative parameters Ångström’s turbidity coefficient (β), Ångström’s wavelength exponent (α), aerosol single scattering albedo (ωo), forward scatterance (Fc) and average surface albedo (ρg), using the Brute Force multidimensional minimization method to minimize the difference between measured and simulated solar irradiance components, expressed as cost functions. In order to simulate the components of short-wave solar irradiance (direct, diffuse and global) for clear sky conditions, incidents on a horizontal surface in the Metropolitan Area of Rio de Janeiro (MARJ), Brazil (22° 51′ 27″ S, 43° 13′ 58″ W), we use two parameterized broadband solar irradiance models, called CPCR2 and Iqbal C, based on synoptic information. The meteorological variables such as precipitable water (uw) and ozone concentration (uo) required by the broadband solar models were obtained from moderate-resolution imaging spectroradiometer (MODIS) sensor on Terra and Aqua NASA platforms. For the implementation and validation processes, we use global and diffuse solar irradiance data measured by the radiometric platform of LabMiM, located in the north area of the MARJ. The data were measured between the years 2010 and 2012 at 1-min intervals. The performance of solar irradiance models using optimal parameters was evaluated with several quantitative statistical indicators and a subset of measured solar irradiance data. Some daily results for Ångström’s wavelength exponent α were compared with Ångström’s parameter (440–870 nm) values obtained by aerosol robotic network (AERONET) for 11 days, showing an acceptable level of agreement. Results for Ångström’s turbidity coefficient β, associated with the amount of aerosols in the atmosphere, show a seasonal pattern according with increased precipitation during summer months (December–February) in the MARJ.  相似文献   

9.
A simple form of solar radiation model was analysed for cloudless days for Goose, Nfld., Port Hardy, B.C., and Edmonton, Alta. Performance for daily values of total solar radiation was satisfactory; however, data for Goose indicated that the model over‐and under‐estimated the direct and diffuse components of solar radiation, respectively. Modifications, including solving for an aerosol parameter k and substituting 0.6 forward scattering instead of the more commonly used 0.5, improved model performance for direct and diffuse radiation.  相似文献   

10.
Summary An approach is proposed to estimate the net radiation load at the surface in mountain areas. The components of the radiation balance are derived using a radiative transfer model combined with remotely sensed and digital terrain data. Integrated shortwave (0.28–6.00 µm) and longwave irradiances (3.00–100.00 µm) are computed using a modified version of the Practical Improved Flux Method (PIFM) of Zdunkowski et al. (1982) which makes use of digital topographic data in order to account for slope, aspect, and shading effects. Surface albedo and thermal exitance estimates are obtained using Landsat Thematic Mapper (TM) and digital terrain data combined with the LOWTRAN 7 atmospheric model (Kneizys et al., 1988). LOWTRAN 7 is utilized together with a set of terrain modeling programs to compute direct and diffuse sky irradiance for selected TM bands, and to remove atmospheric effects within the visible, near-infrared, mid-infrared, and thermal infrared bands of Landsat TM. Model testing in the Colorado alpine show a generally good correspondence between estimated values and field measurements obtained over comparable tundra surfaces during several field campaigns. The method is finally used to produce 1) maps of the components of the radiation balance at the time of Landsat TM overflight and 2) maps of daily totals of shortwave irradiance and net shortwave radiation on a typical summer day in the Colorado Rocky Mountains (i.e. including cloud cover effects). The results indicate that the proposed approach is particularly suitable for obtaining estimates of net radiation at the surface from the toposcale to the regional scale.With 6 Figures  相似文献   

11.
A method is proposed to provide measurement of direct normal solar irradiance of bands with wavelength ranges (315?C400?nm, 400?C700?nm) from measurements of global horizontal band irradiance for cloudless sky conditions in Valencia. Global and normal direct irradiance data for every air mass were obtained by applying the SMART2 model to the atmosphere of Valencia. The direct normal to global irradiance ratio was parameterized versus the relative optical air mass. A measurement campaign of global horizontal and diffuse irradiance of UVA and PAR bands was carried out in Valencia, after which, the inferred direct normal irradiance was compared with those provided by the method. The result of the comparison shows that the method is acceptably accurate. The proposed model tends to underestimate the direct normal irradiance of the UVA band by 6%, although for values below 25?W/m2 the model overestimates the direct irradiance by 6%, while for values above 25?W/m2 the model underestimates it by 10%. The other two error estimators used ranging from 11% to 15% are similar in the defined interval measurements in relation to the whole UVA band. Regarding the PAR band, the model overestimates the direct normal irradiance of the PAR band by only 2.2%. With this, the results of the PAR band are more conclusive, as it has been found that for direct normal irradiance values higher than 280?W/m2 the MBE error is almost zero and the other two estimator errors are small, about 5%.  相似文献   

12.
Summary In this paper, we analyze global, direct and diffuse solar radiation data on a horizontal surface observed at stations in Shanghai, Nanjing and Hangzhou for the period of 1961 to 2000. The data include monthly averages of the daily clearness index (G/G0: the ratio of global to extraterrestrial solar radiation) and the diffuse fraction (D/G: the ratio of diffuse to global solar radiation. The present study has processed and analyzed the data, including variables or statistics of mean, and annual monthly and daily total, the diurnal variation and the frequency of daily totals of global solar radiation. A correlation between daily values of clearness index and diffuse fraction is obtained and recommended correlation equations were calculated. The annual variations and trend of yearly series are analyzed for daily global, direct and diffuse radiation on a horizontal surface, as well as for daily clearness index and diffuse fraction in Shanghai, Nanjing and Hangzhou. The results show: 1) the east China is characterized by a decrease in global and direct radiation and a little increase in diffuse radiation and a negative linear relationship was obtained between clearness index and diffuse fraction. 2) The annual variations of global, direct and diffuse radiation for Shanghai, Nanjing and Hangzhou are similar with relative low values of global and direct radiation in June due to the Meiyu period. 3) The acceleration of air pollution and decrease of relative sunshine are the possible causes for the decrease of global and direct radiation.  相似文献   

13.
Measured Spectra of Solar Ultraviolet Irradiances at Athens Basin, Greece   总被引：1，自引：0，他引：1  
Summary From a data archive of spectral energy distribution of global and diffuse solar irradiances measured in Athens during a field experiment, the impacts of changes in solar zenith angle, site altitude, and gaseous-aerosol pollutants loading, on spectral composition of ultraviolet (UV) radiation reaching the ground, has been determined for cloudless conditions. Measurements of spectral energy distribution of ultraviolet irradiance showed that in urban atmospheres there is a significant altitude effect on spectral UV irradiances which is more pronounced on shorter wavelength UVB than on longer wavelength UVA. In particular the largest attenuation in the UVB band, produced by the altitude effect, between the non-urban site of Mt. Hymettus and the urban site of Athens Museum, was about 27%; while the corresponding attenuation in the UVA band reached 20%. Correspondingly, the respective attenuation caused by altitude effect in the diffuse UVB band was 12%; whereas the altitude effect increases UVA band to as much as 9% between the summit of Mt. Hymettus and the urban site of Athens Museum. Depletion of UV irradiances by the urban atmosphere of downtown Athens was strongly related to aerosol-gaseous pollutants loading. The spectral UV measurements were found to be sensitive to both, changes in solar zenith angle and atmospheric turbidity. The spectral ratio of diffuse-to-direct irradiance critically depends on both solar zenith angle and aerosol-gaseous pollutants loading, increasing rapidly toward the shorter wavelengths. Finally, the hypothesis that the increased levels of aerosol-gaseous pollutants may act as a filter to the transfer of UV energy to the ground is supported, by the limited set of spectral measurements used in the present work. Received June 16, 1996 Revised April 18, 1997  相似文献   

14.
Abstract

The Geosat radar altimeter data from ～60 repeat cycles of the Exact Repeat Mission (ERM) over the period November 1986 to September 1989 have been analysed to show the annual variations of the sea‐surface slopes, corrected for ocean tides, over the Scotian Shelf and the Grand Banks. A coastal tidal model developed at the Bedford Institute of Oceanography, combined with the global tidal model of Schwiderski, is employed to remove the tidal signals from the sea‐surface heights over those regions. Linear regression is used to estimate the sea‐surface slopes over the inner shelf region, the outer shelf region, or a combination of the two along the Geosat ground tracks. Harmonic analysis is applied to the time series of sea‐surface slopes to derive the annual signals, showing that amplitudes are of order of 5 × 10‐7 (5 cm/100 km) with onshore slopes positive in winter and negative in summer.

The largest annual cycles occur over the outer portion of the Laurentian Channel and the southern Grand Banks. The annual cycles differ between the eastern and western portions of the Scotian Shelf: in the east, the signal is synchronized with that of the Laurentian Channel, whereas in the west, the phase of the signal is advanced by 2–3 months. The annual signals over the eastern Scotian Shelf are comparable and consistent with historical hydrographie data along the Halifax Hydrographie Section. The amplitude and phase over the western Scotian Shelf are consistent with the adjusted sea level at the Halifax Station. The annual variability of the sea‐surface slopes over the Scotian Shelf and the Grand Banks is thought to be induced by the seasonal outflow from the Gulf of St Lawrence through Cabot Strait, and possibly by an annual cycle in the Slope Water current.  相似文献   

15.
D.G. Steyn 《大气与海洋》2013,51(3):254-258
Abstract

Two soil water models, the Versatile Soil Moisture Budget and the Aridity Index Model were used to investigate differences in modelling results as a consequence of using as input mean‐daily data, derived from historical monthly values, instead of actual daily data. Four different available water‐holding capacities, six different initial soil water contents and 30‐year precipitation and potential evapotranspiration data from 16 climate stations across Canada were used as input to the models. Using mean‐daily data as opposed to daily data resulted in model predictions that underestimated deep drainage and aridity indices and overestimated actual evapotranspiration. The differences in model output decreased when the available water‐holding capacity increased and the initial soil water content decreased. The use of mean‐daily data in the soil water models investigated is not recommended, until improved techniques that retain the characteristics of the highly variable weather conditions can be ascertained.  相似文献   

16.
Abstract

Diurnal changes in the local atmospheric moisture budget over the Canadian Prairies are computed using sequential radiosonde soundings from the 1991 Regional Evaporation Study (RES‐91). Previous attempts to estimate evapotranspiration with radiosonde data have used either similarity theory or a moisture budget, but have been confined to the boundary layer in either case. These studies, as well as semi‐empiric operational techniques which use surface‐based data, exclude the effects of moisture advection and energy exchanges between the boundary layer and the free atmosphere, assuming negligible effects on evapotranspiration. The moisture budget method adopted here includes horizontal advection explicitly, and treats vertical fluxes implicitly through a total tropospheric moisture budget.

Comparison of the evapotranspiration estimates with those of other techniques are positive only when results are averaged over several days to weeks. While the advection estimates are a major source of error for the “daily” estimates in this particular study, it is shown that neither advection nor moisture flux through the boundary layer can be ignored in estimating daily evapotranspiration, regardless of the technique used. The results also suggest that evapotranspiration is more variable on a daily basis than other techniques have indicated. With an improved synoptic database now available for advection estimates, the moisture budget technique may provide an excellent ground‐truth method for fine‐tuning techniques for remote sensing of evapotranspiration, and could lead to improved parametrization schemes for both NWP models and GCMs.  相似文献   

17.
A simple model is developed which estimates daily global radiation at the floor of a non-homogeneous Eucalyptus forest. Model input parameters are easily derived from field measurements and consist of individual tree location, tree height, maximum canopy width and its corresponding height, height of the lowest branch and trunk thickness. In addition, the model requires values for global and diffuse irradiance in the open. The tree canopy is represented as a series of spheres containing leaves which are homogeneously spaced but are oriented in the vertical plane. This configuration closely approaches that of actual eucalyptus trees. A Monte-Carlo approach is used to estimate the albedo of the unit sphere as a function of solar zenith angle. At a given combination of solar zenith and azimuth angle, the model estimates the solar irradiance at a specific forest floor location.The model, when tested against pyranometer measurements, predicted daily solar irradiance with a correlation of 0.98 and a standard error of 0.98 MJ m-2 day-1. This good performance is attributed to the spatial averaging of the radiation fluxes over the entire day, and the relatively low sensitivity of the calculated solar irradiance to sphere albedo.  相似文献   

18.
Long-term data from diffuse and global irradiances were used to calculate direct beam irradiance which was used to determine three atmospheric turbidity coefficients (Linke T L , Ångström β and Unsworth–Monteith δ a ) at seven sites in Egypt in the period from 1981 to 2000. Seven study sites (Barrani, Matruh, Arish, Cairo, Asyut, Aswan and Kharga) have been divided into three categories: Mediterranean climate (MC), desert Nile climate (DNC) and urban climate (UC, Cairo). The indirect method (i.e., global irradiance minus diffuse irradiance) used here allows to estimate the turbidity coefficients with an RMSE% ≤20 % (for β, δ a and T L ) and ~30 % (for β) if compared with those estimated by direct beam irradiance and sunphotometeric data, respectively. Monthly averages of T L , β and δ a show seasonal variations with mainly maxima in spring at all stations, due to Khamsin depressions coming from Sahara. Secondary maxima is observed in summer and autumn at DNC and MC (Barrani and Arish) stations in summer due to dust haze which prevails during that season and at UC (Cairo) in autumn, due to the northern extension of the Sudan monsoon trough, which is accompanied by small-scale depressions with dust particles. The mean annual values of β, δ a , and T L (0.216, 0.314, and 4.6, respectively) are larger in Cairo than at MC stations (0.146, 0.216, and 3.8, respectively) and DNC stations (0.153, 0.227, and 3.8, respectively). Both El-Chichon and Mt. Pinatubo eruptions were examined for all records data at MC, UC and DNC stations. The overburden caused by Mt. Pinatubo’s eruption was larger than El-Chichon’s eruption and overburden for β, and T L at DNC stations (0.06, and 0.58 units, respectively) was more pronounced than that at MC (0.02, and 0.26, respectively) and UC (0.05 and 0.52 units, respectively) stations. The annual variations in wind speed and turbidity parameters show high values for both low and high wind speed at all stations. The wind directions have a clear effect on atmospheric turbidity, and consequently, largest turbidities occur when the wind carries aerosols from the main particle sources, such as industrial particle sources around Cairo or to some extent from the Sahara surrounding all study stations.  相似文献   

19.
Abstract

A 12‐station network located in and around Vancouver, B.C. has been used to define the local (mesoscale) variations in solar energy. Numerical models are used to convert the horizontal data to inclined surface irradiances which, along with temperature, are the inputs required by the simulation models used to assess the significance of these variations on the performance and economics of both active and passive solar heating systems.

Solar radiation differences over the study area have a marked influence on the operation of a domestic hot water heating system while the temperature variations between the same stations have a comparatively small impact. For both active and passive space heating the situation is reversed because temperature has a large impact on the energy demand and hence on the extent of solar energy utilization. The results suggest that local variations of solar radiation should be incorporated in solar domestic hot water design studies while spatial variations in temperature should receive relatively more attention in space heating studies.  相似文献   

20.
Summary  We investigate in the present paper the relationship between satellite count, global irradiance and other solar and illumination resource components, bringing a particular attention to low solar elevation situations (below 20 °) which are very important in northern latitudes. Our investigation is based on data from two geostationary satellites, METEOSAT and GOES, backed by ground measurements in Switzerland and the northeastern USA. The study of different clear sky normalizations lead to the conclusion that a linear correlation between the global clearness index and the irradiance (like the heliosat method) would be inaccurate for low solar elevations, and therefore for high latitude regions. We developed a model that directly relates an elevation dependent clearness index to the could index. This methodology presents a definite advantage because it can be generalized to address the clearness index of other solar radiation components, besides global irradiance, such as direct irradiance, diffuse illuminance, etc. The correlations described in this paper were developed on the data from Geneva (in the frame of the EC program “Satellight”) and evaluated on two other independent data sets (Albany, USA and Lausanne, Switzerland). Their precisions, on a hourly basis, are respectively 30%, 40% and 60% for the global, diffuse and beam components) (90,55 and 95 W/m2). The use of independent data for thederivation and the validation of the models shows thatthose can be used in a wide range of locations, even if the applicability has to be assessed for very different climates. Received June 27, 1998 Revised February 26, 1999  相似文献   

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