Characteristics of longwave radiation through the statistical analysis of downward and upward longwave radiation and inter-comparison of two sites in Cyprus (original) (raw)
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Comparison of models for calculating daytime long-wave irradiance using long term data set
Agricultural and Forest Meteorology, 2007
Twenty simple and widely used models for calculating clear sky daytime long-wave irradiance were tested against measured long-wave irradiance data. As input the models required only air temperature or air temperature and water vapour pressure, all measured at screen height. Meteorological data and long-wave irradiance measurements from 32 consecutive years at the Climate and Water Balance Station at Taastrup in eastern Denmark and from 7 consecutive years at the Agrometeorological Station at Foulum in western Denmark were used. The long time series of the data sets ensured all weather conditions and extreme events were captured. Clear sky conditions were assumed when the ratio of measured global radiation at the surface to the extraterrestrial exceeded approximately 0.75. A set of statistical procedures was used to evaluate the performance of the models. The mean bias errors ranged from À23 to +12 W m À2 and À18 to +15 W m À2 and root mean square errors from 39 to 45 W m À2 and 30-36 W m À2 in Taastrup and Foulum, respectively. Model performance improved when using average daily daytime clear sky data and a more strict definition of clear sky conditions. No improvements were found when the data sets were subdivided by season or upwind surface cover type. Four of the clear sky models were superior to the other models tested. These models were combined with two all sky daytime long-wave irradiance models and compared to actual all sky daytime long-wave irradiance data included in the Foulum and Taastrup data sets. The mean bias errors ranged from À8 to +5 W m À2 and À6 to +8 W m À2 and root mean square errors from 29 to 30 W m À2 and 23-24 W m À2 in Taastrup and Foulum, respectively. Based on the results of this study and the fact that the Prata and Brutsaert clear sky models were founded on a physical basis these models were recommended for use with the Crawford and Duchon all sky model when calculating daytime long-wave irradiance in a temperate climate. #
Journal of Atmospheric and Solar-terrestrial Physics, 2003
This paper evaluates models for the estimation of downward longwave atmospheric irradiance at a lowland location and a mountain location under clear and cloudy skies. The multiyear (1992)(1993)(1994)(1995) data sets utilized for the study were recorded in southwest Germany during the REgio KLIma Projekt (REKLIP). Annual mean of downward atmospheric irradiance I↓ ranged from 315 to 328 W m −2 at the lowland site and from 282 to 290 W m −2 at the mountain site. Inter-annual variability of I↓ at the sites was less than 2%. Six existing downward longwave clear-sky irradiance models were assessed in this study. In addition, this study proposes a new parameterization for estimating downward longwave clear-sky irradiance at the surface. The new parameterization, which is validated with data from the Oklahoma-based U.S. Department of Energy Atmospheric Radiation Measurement (ARM) program, performed better than the other six models. It produced estimates, which agree with measurements more closely (within 5% for lowland and 7% for mountain locations). The incorporation of quadratic cloud terms in the parameterization allows for the estimation of I↓ under variable sky conditions.
Applied Sciences, 2021
In this study, two years of hourly longwave downward and upward irradiance measurements at Athalassa, an inland location, are used to analyze and compare them. A detailed quality control process was followed according to the suggested tests proposed by the Baseline Surface Radiation Network (BSRN) group. The criteria involved are based on physically possible, extremely rare and climatological limits. Furthermore, comparison tests were also applied between the two longwave components as well as with air and ground surface temperatures. Additionally, time consistency and persistency tests were applied. All the suspect data were excluded from the analysis. The data showed that the frequency distribution of downward longwave irradiances follows a normal distribution function, while the upward longwave follows an almost normal distribution but with a long positive tail. The annual mean daily downward longwave irradiation is 27.3 MJ m−2 and the annual mean daily upward longwave irradiatio...
Renewable Energy, 2016
Routine measurements of irradiance are valuable for many research fields such as energy applications. However, ground data of solar global radiation can present questionable values. In this study, a set of check procedures is used to test the quality of shortwave and longwave radiation measurements taken at two actinometric stations in Cyprus (Athalassa-inland location and Larnaca-coastal location), during the period November 2012eJuly 2014. The testing procedures include physically possible limits for all the radiation components and comparisons between global radiation and the sum of direct and diffuse radiation. The quality process is implemented to both the 10-min averaged irradiances, hourly irradiation and the respective daily values. This paper reviews the currently available procedures for quality assessment of the solar shortwave and longwave irradiation data. In the present study, the first level of test includes physical possible limits which are determined by the Daylight Research Group and the Baseline Surface Radiation Network of the World Meteorological Organisation (WMO). The second level of test is a semi-automated procedure that is based on the creation of an envelope in the clearness index and the diffuse to global irradiance ratio. The third level of test is based on the comparison of various radiation parameters including comparison of measured extreme values with theoretical estimations from clear sky-models. The fourth level of test of the quality control procedure refers to the analysis of daily and annual variations of the radiation parameters.
IOSR Journals , 2019
Knowledge of downward atmospheric radiation in the range λ= 4-100 μm is vital for several applications. In this study, longwave (LW) radiation datafrom desert (Riyadh, Saudi Arabia) and Mediterranean (Adelaide, Australia) climates are used to characterize seasonal and daily variations. At both sites, the LW radiation shows a maximum in summer and a minimum in winter. The monthly changes in the LW radiation were about 22% for Adelaide, and 36% for Riyadh. When considering these seasonal variations, it was found that during winter and summer, the variations inLW radiation were confined to between 2% and 4%. However, during the transition seasons (spring and autumn) the LW radiation varies considerably. In Adelaide, spring and autumn change by about 8% and 10% respectively. In Riyadh, the LW radiation varies by about 12% in both seasons. At both sites, the LW radiation has aminimum value in the early morning, around 06:00 local time, and reaches its maximum at around 13:00. The daily changes in the LW radiation were 13.5% for Riyadh and 10% for Adelaide. Obviously, the monthly and diurnal variations of the LW radiation closely follow the temperature variations rather than the water content. The influence of screen temperature (T) and atmospheric moisture on LW radiation are examined for each site. The screen level water vapour pressure (e) and the precipitable water vapour (PWV) areusedas two different representative measuresof the atmospheric water contents. PWV is calculated using radiosonde observations from both sites. It is clear thatthe LW radiation correlates better with T than e, and better correlation between LW and e was apparent in Adelaide than in Riyadh. When using the PWV as a measure of thetotal atmospheric water content, the correlation between LW radiation and this variable improves significantly for both sites. Regression analyses are carried out between LW radiation and temperature and water vapour pressure at screen level (T, e), LW radiation and screen temperature and PWV (T, PWV) for eachsite individually, and data arecombined from both sites. Statistical indicators such as mean bias error (MBE), root mean square error (RMSE), mean percentage error (MPE), and student t-tests are used to assess these regressions. Both schemes give good predictions for the measured data, although the model containing(T, PWV) shows better statistics (better predictions) for the three datasets in comparisons with the model using (T, e). For instance, the model containing (T, e) gives a RMSE of 19.38 Wm-2 for Riyadh, 20.52 Wm-2 for Adelaide, and 22.419 Wm-2 for the combined data from both sites. Using the scheme comprising (T, PWV) reduces the RMSE values by 16% for Adelaide, 34% for Riyadh, and 14% for the combined data. Finally, several previously developed models areused to calculate the LW radiation for the three datasets (Adelaide, Riyadh, and the combined data from both sites). Nineteen models with different functional forms and different meteorological variables areselected and used. We find that the predictability of these models varies from one dataset to another. While some models show adequate prediction forone site, they fail forthe other. However, some models give reasonable estimates when the measured data from both sites are combined.
This study aims at assessing the differences induced in the Global Horizontal Irradiance (GHI) predictions by the mesoscale atmospheric Weather Research and Forecasting (WRF) model when using different shortwave radiation. Model predictions are compared with GHI measurements at 12 stations of the Hellenic Network of Solar Energy (HNSE) for January, April, July and October 2013. The shortwave radiation schemes that were evaluated are: the Dudhia, the updated Rapid Radiative Transfer Model (RRTMG), the updated Goddard and the Goddard Fluid Dynamics Laboratory (GFDL) schemes. All schemes perform better under cloudless conditions due to limited ability of the WRF model to simulate cloudy conditions. The Dudhia scheme performs best with mean relative difference of 2.2 ± 15% for clear-skies, while the differences for the other schemes range between 5 and 12% with similar standard deviations. For all-skies, the model-derived hourly GHI is overestimated for all schemes (~40e70%). For the daily averages, the model predictions are in better agreement with the measurements, mainly under all-sky conditions, with deviations of about half those of the hourly data and smaller standard deviations. There are strong indications that the differences of the model predictions from the measurements depend on the solar zenith angle and the amount of aerosols at each station.
Practical models to estimate horizontal irradiance in clear sky conditions: Preliminary results
Renewable Energy, 2010
The Argentinean Northwest (ANW) is a high altitude region located alongside Los Andes Mountains. The ANW is also one of the most insolated regions in the world due to its altitude and particular climate. However, the characterization of the solar resource in the region is incomplete as there are no stations to measure solar radiation continuously and methodically. With irradiance data recently having been measured at three sites in the Salta Province, a study was carried out that resulted in a practical model to quickly and efficiently estimate the horizontal irradiance in high altitude sites in clear sky conditions. This model uses the altitude above sea level (A) as a variable and generates a representative clearness index as a result (k t-R) that is calculated for each site studied. This index k t-R is then used with the relative optical air mass and the extraterrestrial irradiance to estimate the instantaneous clearness index (k t). Subsequently, the index k t-R is corrected by introducing the atmospheric pressure in the definition of relative optical air mass proposed by Kasten. The results are satisfactory as errors in the irradiance estimations with respect to measured values do not exceed 5% for pressure corrected air masses AM c < 2. This model will be used in a feasibility study to locate sites for the installation of solar thermal power plants in the ANW.
EVALUATION OF AN ALL-SKY METEOROLOGICAL RADIATION MODEL AGAINST LONG-TERM MEASURED HOURLY DATA
With the proliferation of cheap, high performance desktop computers, the building services profession is demanding detailed (hourly or sub-hourly) weather data for simulation, optimum plant sizing and design of buildings which may use passive solar and/or natural ventilation features. Even in a developed country, such as the United Kingdom, there is a dearth of measured long-term solar radiation and daylight data. Herein, a simple and precise meteorological radiation model (MRM) is presented, which enables computation of horizontal beam and diffuse solar radiation to be accomplished, given four basic meteorological parameters-hourly dry-and wet-bulb temperatures, atmospheric pressure and bright sunshine duration. These data are available worldwide for very many locations. The present model is of a semi-general nature as demonstrated by its applicability to ten widespread locations in the United Kingdom. The model enables computation of hour-by-hour insolation. Statistical analysis of 100 station-years hourly data indicates that the MRM can compute insolation with an average error of 9% for clear skies and 25% for overcast conditions. On a monthly-averaged hourly and daily basis, this error reduces to 3%.
Empirical modeling of hourly direct irradiance by means of hourly global irradiance
Energy, 2000
A very important factor in the assessment of solar energy resources is the availability of direct irradiance data of high quality. Nevertheless, this quantity is seldom measured and thus must be estimated from measures of global solar irradiance, a quantity that is registered in most radiometric stations. In this work we analyze the results provided by different models in the estimation of hourly direct irradiance values. We have selected several models proposed by Orgill and Hollands, Erbs et al., Reindl et al., Skarveit and Olseth, Maxwell, and Louche et al. With the exception of the model from Louche et al. that estimates direct irradiance values from direct transmittance values, all of the models estimate direct irradiance from the diffuse fraction. The data set used in this study comprises 25 000 hourly values of global and diffuse irradiance. These values were registered in six Spanish locations with different climatic conditions. The results provided by the model depend on the clearness index, k t , and the solar elevation. The best results are obtained for cloudless skies and higher solar elevation. In those conditions we can estimate the direct irradiance with a root square mean error close to 14% of the average measured value. We have estimated the direct irradiance under cloudless sky conditions using a parametric model proposed by Iqbal. In order to analyze the effect of turbidity on the estimation of direct irradiance we have compared the results obtained by the parametric model when using hourly values of the Angstrom turbidity parameter b with those obtained when using monthly means of hourly values of b.