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Influences of the clearness index on UV Solar Radiation for Two Locations in the Tibetan Plateau——Lhasa and Haibei

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Advances in Atmospheric Sciences 2008年第5期25卷 885-896页

作者：胡波王跃思刘广仁 State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry (LAPC) Institute of Atmospheric Physics Chinese Academy of Sciences

Ultraviolet （UV） solar radiation has a significant influence on human health, the environment and climate. A series of measurements, including UV radiation （290 400 nm） and global solar radiation （Rs）, were continuously recorded from August 2004 at the Lhasa and Haibei sites on the Tibetan Plateau. Both observation sites＇ altitudes are above 3000 m and have similar meteorological conditions. The data from 2005 2006 was used to identify the varying characteristics of UV radiation. It＇s relation to the clearness index Ks, the relative optical mass mr, and Rs were established. The annual mean values of total daily UV radiation are 0.92 and 0.67 MJ m^-2 at Lhasa and Haibei, respectively. The UV radiation in Lhasa represented 4.6% of the global solar radiation while in Haibei this percentage was 4.2%. In the case of clear days （Ks 〉 0.8）, these percentages ranged between 4.0% and 4.5% in Lhasa and between 5.1% and 5.5% in Haibei. In the case of cloudy days （Ks 〈 0.4）, these percentages ranged from 4.4% to 6.8% in Lhasa and from 5.1% to 5.5% in Haibei. The maximum values of UV radiation for each relative optical mass diminished exponentially with mr. Thus, for Lhasa and Haibei, UV=46.25mr-129, and UV=51.76mr-142, respectively. The results of this study can be used to obtain more UV radiation data for the study of UV climate characteristics, the effects of UV on ecological processes and the feedback of the thinning of the stratospheric ozone, from more routine measurements Rs data.

关键词： ultraviolet radiation clearness index Tibetan plateau

Estimation of monthly global solar radiation over twelve major cities of Libya

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Energy and Built Environment 2024年第1期5卷 46-57页

作者： Alhassan Ali Teyabeen Najeya B.Elhatmi Akram A.Essnid F.Mohamed Libyan Center for Solar Energy Research and Studies TripoliLibya Libyan Authority of Scientific Research TripoliLibya

This study aims to estimate monthly averaged daily horizontal global solar *** climatological data collected at twelve major cities located across Libya’s map were used to establish 7 different empirical *** empirical coefficients of the models were calculated using the least square *** accuracy of the models was evaluated using different statistical criteria such as Taylor diagram,mean absolute percentage error,MAPE,and root mean square error,*** results indicated that the sunshine duration-based models are more accurate than air temperature-based models,and the best performance was obtained by the quadratic regression model for all twelve Libyan ***,this regression model can be used for the prediction of monthly mean horizontal global solar radiation at a specific site across Libya’s regions with minimum ***,the results of the global solar irradiance produced by this method can be used for designing solar systems applications.

关键词： Monthly global solar radiation clearness index Empirical models Performance evaluation Taylor diagram Libya

Estimation of Daily Global Solar Radiation with Different Sunshine-Based Models for Some Burundian Stations

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Energy and Power Engineering 2024年第1期16卷 1-20页

作者： Mathias Bashahu Gratien Ndacayisaba Department of Physics and Technology University of Burundi Bujumbura Burundi Department of Physics Ecole Normale Supérieure Bujumbura Burundi

Sunshine duration (S) based empirical equations have been employed in this study to estimate the daily global solar radiation on a horizontal surface (G) for six meteorological stations in Burundi. Those equations include the Ångström-Prescott linear model and four amongst its derivatives, i.e. logarithmic, exponential, power and quadratic functions. Monthly mean values of daily global solar radiation and sunshine duration data for a period of 20 to 23 years, from the Geographical Institute of Burundi (IGEBU), have been used. For any of the six stations, ten single or double linear regressions have been developed from the above-said five functions, to relate in terms of monthly mean values, the daily clearness index () to each of the next two kinds of relative sunshine duration (RSD): and . In those ratios, G0, S0 and stand for the extraterrestrial daily solar radiation on a horizontal surface, the day length and the modified day length taking into account the natural site’s horizon, respectively. According to the calculated mean values of the clearness index and the RSD, each station experiences a high number of fairly clear (or partially cloudy) days. Estimated values of the dependent variable (y) in each developed linear regression, have been compared to measured values in terms of the coefficients of correlation (R) and of determination (R2), the mean bias error (MBE), the root mean square error (RMSE) and the t-statistics. Mean values of these statistical indicators have been used to rank, according to decreasing performance level, firstly the ten developed equations per station on account of the overall six stations, secondly the six stations on account of the overall ten equations. Nevertheless, the obtained values of those indicators lay in the next ranges for all the developed sixty equations:;;;, with . These results lead to assert that any of the sixty developed linear regressions (and thus equations in terms of and ), fit

关键词： clearness index Two Kinds of Relative Sunshine Duration Ångström-Prescott Linear Model and Four Derivatives Statistical Tests Six Burundian Stations

Overcast sky condition prevails on and influences the biometeorology of the tropical Andean Páramos

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Journal of Mountain Science 2023年第1期20卷 78-86页

作者： Paola MONTENEGRO-DÍAZ Rolando CELLERIALVEAR Galo CARRILLO-ROJAS Departamento de Recursos Hídricos y Ciencias Ambientales Universidad de CuencaCuenca010207Ecuador Facultad de Ingeniería Universidad de CuencaCuenca010207Ecuador Facultad de Ciencias Químicas Universidad de CuencaCuenca010207Ecuador

Clouds play a major role in modulating the biometeorological processes. We studied the influence of cloudiness on four biometeorological variables:daily air temperature(Tair), relative humidity(RH),reference evapotranspiration(ETr),and photosynthetic active radiation(PAR), recorded at four sites of Andean Páramos in southern Ecuador during 2.5 to 5.5 years. First, we quantified both the cloud cover percentage(Cloud%) creating cloud masks over the visible bands of Landsat 7 images and the sky condition(K_(T)) using the records of solar and extraterrestrial radiation. Second, we estimated KTfrom Cloud%. Finally, we quantified T_(air), RH, ET_(r), and PAR under clear, cloudy, and overcast K_(T) and their dependence on KT. The average Cloud% ranged between 65%–76%, and KTcorroborated the prevailing overcast sky(between 55% and 72.5% of the days) over the páramos. The proposed model performed well in the sites of calibration(R^(2)= 0.80;MBE = 0.00;RMSE = 0.05) and validation(R^(2)= 0.74;MBE =-0.07;RMSE = 0.11). The overcast sky diminished T_(air)(≤ 10℃), ET_(r)(≤ 1.6 mm day-1), and PAR(4 MJ m^(-2)day^(-1)) and increased RH(≥ 88%),while the variables showed the opposite behavior during the uncommon clear sky(≤ 5.5% of the days).Thus, mostly the dynamic of RH(R^(2)≥ 0.62), ETr(R^(2)≥ 0.85), and PAR(R2≥ 0.77) depended on K_(T). Hence,the prevailing overcast sky influenced the biometeorology of the páramos.

关键词： Cloudiness indicator clearness index Satellite imagery Tropical Andes

Effects of cloud,atmospheric water vapor,and dust on photosynthetically active radiation and total solar radiation in a Mongolian grassland

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Journal of Arid Land 2012年第4期4卷 349-356页

作者： Tserenpurev BAT-OYUN Masato SHINODA Mitsuru TSUBOn Meiji University Tokyo168-8555Japa Arid Land Research Center Tottori UniversityTottori 680-0001Japan

Photosynthetically active radiation （PAR） is an important input parameter for estimating plant produc- tivity due to its key role in the growth and development of plants. However, a worldwide routine network for sys- tematic PAR measurements is not yet established, and PAR is often calculated as a constant fraction of total solar radiation （SR）. Although the ratio of PAR to SR （PAR/SR） has been reported from many places, few studies have been performed for dry regions. The present study was therefore carried out in an arid region of Mongolia to obtain PAP-JSR and examine its dependency on sky clearness （the clearness index）, water vapor in the atmosphere and aeolian dust. Continuous measurements of PAR and SR were taken every one second using quantum and pyranometer sensors, respectively, and the readings were averaged and recorded at intervals of 30 minutes for a period of 12 months. The lowest monthly mean daily PAR/SR occurred in April （0.420）, while the highest ratio was observed in July （0.459）. Mean daily PAR/SR during plant growing season （May-August） was estimated to be 0.442, which could be useful for modeling plant productivity in the study area. The annual mean daily PAR/SR （0.435） was lower than the values reported in many previous studies. This difference could be explained with the regional variation in climate： i.e. drier climatic condition in the study area. PAR/SR was negatively correlated with the clearness index （r= -0.36, P〈0.001）, but positively with atmospheric water vapor pressure （r=0.47, P〈0.001）. The average PAR/SR was significantly lower （P=0.02） on the dusty days compared to the non-dust days. Water vapor in the atmosphere was shown to be the strongest factor in the variation of PAR/SR. This is the first study examining PAR/SR under a semi-arid condition in Mongolia.

关键词： clearness index dust storm photosynthetically active radiation total solar radiation water vapor pressure

Impact of Cloud on Net Ecosystem CO2 Exchange of Alpine Meadow in Tibetan Plateau

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Chinese Journal of Population,Resources and Environment 2010年第4期8卷 69-75页

作者： Fan Yuzhi Zhang Xianzhou Shi Peili Wu Jianshuang Institute of Geographic Sciences and Resources Research Chinese Academy of Sciences Beijing 100101 China Graduate University of Chinese Academy of Sciences Beijing 100049 China

Meteorological elements and CO2 fluxes over alpine meadow ecosystem were observed continuously from 2004 to 2005 in Damxung Alpine Meadow Flux Station, China Flux Network. Based on the eddy covariance CO2 fluxes and meteorological data obtained, the relationships among the CO2 fluxes, the cloud amount, and the meteorological factors in alpine meadow ecosystem were explored and analyzed. Some conclusions can be drawn from the discussion with previous researches as following: (1) the cloud amount can affect the net ecosystem CO2 exchange (NEE) of alpine meadow on Tibetan Plateau; (2) the soil temperature sensitive to the cloud amount, is a major environmental controlling factor for NEE, and closely relates to the maximum of NEE. In the morning period with large cloud amount, the NEE reaches its maximum when the clearness index ranges from 0.5 to 0.7; yet in the afternoon it comes to the maximum with the index from 0.2 to 0.35. The span of soil temperature covers from 12 to 15°C as the NEE at its highest; (3) the scatterplots between NEE and photosynthetic available radiation (PAR) was a significant inverse triangle in the clear day, two different kinds of concave curves in the cloudy day, and strongly convergent rectangular hyperbola in the overcast day. These differences were controlled by the changes of light radiation and soil temperature. © 2010 Taylor & Francis Group, LLC.

关键词： Alpine meadow ecosystem clearness index Cloud amount Net ecosystem CO2 exchange Tibetan Plateau

Variation characteristics of Ultraviolet radiation derived from measurement and reconstruction in Beijing, China

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Variation characteristics of Ultraviolet radiation derived f...