The Experts below are selected from a list of 315 Experts worldwide ranked by ideXlab platform
K.k Gopinathan - One of the best experts on this subject based on the ideXlab platform.
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Month–hour distributions of Zenith luminance and diffuse illuminance in Madrid
Energy Conversion and Management, 2003Co-Authors: Alfonso Soler, K.k Gopinathan, L. M. Robledo, Enrique RuizAbstract:Abstract Month–hour equal mean Zenith luminance contours are obtained from one year of data of Zenith luminance measurements for cloudless, overcast and partly cloudy skies and also when the combined data for all sky types are considered. For many hours in different months, the overcast sky luminance values are roughly about three times the cloudless sky luminance values and one and a half times the partly cloudy sky values. The dependence of month–hour equal mean Zenith luminance contours on the ratio of global to extraterrestrial illuminance on a horizontal surface is also given. From equal mean Zenith luminance contours, the approximate values of the mean Zenith luminance for different sky conditions and different hours and months of the year can be easily obtained. Month–hour equal mean diffuse illuminance contours are obtained from diffuse illuminance measurements performed during the period 1992–1998. The dependence on solar altitude of the monthly average hourly values of diffuse illuminance is given and compared to the corresponding one obtained from data for Bet Dagan (Israel).
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Analysis of Zenith luminance data for all sky conditions
Renewable Energy, 2001Co-Authors: Alfonso Soler, K.k GopinathanAbstract:Abstract Two different procedures are explored in the present work to estimate the Zenith luminance at the International Daylight Measurement Program station in Madrid, when all the data available are used independently of the sky type. On the basis of the results obtained, correlations for the seasonal dependence of the Zenith luminance on solar elevation are reported. However, it is observed that polynomials obtained for different ranges of the luminous clearness index, the ratio of global to extraterrestrial illuminance, can predict the Zenith luminance with a more reasonable accuracy. The results show that the luminous clearness index is an important parameter for Zenith luminance characterization, to be used when global illuminance values on horizontal surfaces are available, but diffuse illuminance is not measured
Alfonso Soler - One of the best experts on this subject based on the ideXlab platform.
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Month–hour distributions of Zenith luminance and diffuse illuminance in Madrid
Energy Conversion and Management, 2003Co-Authors: Alfonso Soler, K.k Gopinathan, L. M. Robledo, Enrique RuizAbstract:Abstract Month–hour equal mean Zenith luminance contours are obtained from one year of data of Zenith luminance measurements for cloudless, overcast and partly cloudy skies and also when the combined data for all sky types are considered. For many hours in different months, the overcast sky luminance values are roughly about three times the cloudless sky luminance values and one and a half times the partly cloudy sky values. The dependence of month–hour equal mean Zenith luminance contours on the ratio of global to extraterrestrial illuminance on a horizontal surface is also given. From equal mean Zenith luminance contours, the approximate values of the mean Zenith luminance for different sky conditions and different hours and months of the year can be easily obtained. Month–hour equal mean diffuse illuminance contours are obtained from diffuse illuminance measurements performed during the period 1992–1998. The dependence on solar altitude of the monthly average hourly values of diffuse illuminance is given and compared to the corresponding one obtained from data for Bet Dagan (Israel).
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Analysis of Zenith luminance data for all sky conditions
Renewable Energy, 2001Co-Authors: Alfonso Soler, K.k GopinathanAbstract:Abstract Two different procedures are explored in the present work to estimate the Zenith luminance at the International Daylight Measurement Program station in Madrid, when all the data available are used independently of the sky type. On the basis of the results obtained, correlations for the seasonal dependence of the Zenith luminance on solar elevation are reported. However, it is observed that polynomials obtained for different ranges of the luminous clearness index, the ratio of global to extraterrestrial illuminance, can predict the Zenith luminance with a more reasonable accuracy. The results show that the luminous clearness index is an important parameter for Zenith luminance characterization, to be used when global illuminance values on horizontal surfaces are available, but diffuse illuminance is not measured
Yushu Zhou - One of the best experts on this subject based on the ideXlab platform.
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Effects of diurnal variation of solar Zenith angle on a tropical coupling system: A two‐dimensional coupled ocean‐cloud resolving atmosphere modeling study
Geophysical Research Letters, 2008Co-Authors: Shouting Gao, Yushu ZhouAbstract:[1] The effects of diurnal variation of solar Zenith angle on tropical atmospheric and oceanic variability are investigated with a two-dimensional coupled ocean-cloud resolving atmosphere model. The experiment with a time-invariant solar Zenith angle is compared to the control experiment with a diurnally-varied solar Zenith angle. In both experiments, the model, with imposed large-scale vertical velocity and zonal wind derived from Tropical Ocean Global Atmosphere Coupled Ocean Atmosphere Response Experiment (TOGA COARE), is integrated over a 30-day period. The control simulation shows a good agreement with the observations in terms of atmospheric temperature, specific humidity, and mixed-layer temperature and salinity. The experiment with the time-invariant solar Zenith angle produces a colder and drier atmosphere and a colder and saltier ocean mixed layer than the experiment with the diurnally-varied solar Zenith angle does. The atmospheric temperature and precipitable water budgets and oceanic mixed-layer temperature and salinity budgets are analyzed. Compared to the experiment with the diurnally-varied solar Zenith angle, the experiment with the time-invariant solar Zenith angle has smaller solar heating, consumes more atmospheric water vapor through more condensation, and generates smaller thermal forcing through deeper mixed layer and more saline entrainment. The results indicate the importance of the inclusion of diurnal variation of solar Zenith angle in coupled model simulations to avoid atmospheric and oceanic cooling biases and atmospheric drying bias.
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effects of diurnal variation of solar Zenith angle on a tropical coupling system a two dimensional coupled ocean cloud resolving atmosphere modeling study
Geophysical Research Letters, 2008Co-Authors: Shouting Gao, Yushu ZhouAbstract:[1] The effects of diurnal variation of solar Zenith angle on tropical atmospheric and oceanic variability are investigated with a two-dimensional coupled ocean-cloud resolving atmosphere model. The experiment with a time-invariant solar Zenith angle is compared to the control experiment with a diurnally-varied solar Zenith angle. In both experiments, the model, with imposed large-scale vertical velocity and zonal wind derived from Tropical Ocean Global Atmosphere Coupled Ocean Atmosphere Response Experiment (TOGA COARE), is integrated over a 30-day period. The control simulation shows a good agreement with the observations in terms of atmospheric temperature, specific humidity, and mixed-layer temperature and salinity. The experiment with the time-invariant solar Zenith angle produces a colder and drier atmosphere and a colder and saltier ocean mixed layer than the experiment with the diurnally-varied solar Zenith angle does. The atmospheric temperature and precipitable water budgets and oceanic mixed-layer temperature and salinity budgets are analyzed. Compared to the experiment with the diurnally-varied solar Zenith angle, the experiment with the time-invariant solar Zenith angle has smaller solar heating, consumes more atmospheric water vapor through more condensation, and generates smaller thermal forcing through deeper mixed layer and more saline entrainment. The results indicate the importance of the inclusion of diurnal variation of solar Zenith angle in coupled model simulations to avoid atmospheric and oceanic cooling biases and atmospheric drying bias.
K. Clémer - One of the best experts on this subject based on the ideXlab platform.
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intercomparison of slant column measurements of no 2 and o 4 by max doas and Zenith sky uv and visible spectrometers
Web Science, 2010Co-Authors: Howard K. Roscoe, C. Fayt, N. Abuhassan, C. Adams, M. Akrami, A. Cede, J. Chong, Van M Roozendael, Du A Piesanie, K. ClémerAbstract:Abstract. In June 2009, 22 spectrometers from 14 institutes measured tropospheric and stratospheric NO2 from the ground for more than 11 days during the Cabauw Intercomparison Campaign of Nitrogen Dioxide measuring Instruments (CINDI), at Cabauw, NL (51.97° N, 4.93° E). All visible instruments used a common wavelength range and set of cross sections for the spectral analysis. Most of the instruments were of the multi-axis design with analysis by differential spectroscopy software (MAX-DOAS), whose non-Zenith slant columns were compared by examining slopes of their least-squares straight line fits to mean values of a selection of instruments, after taking 30-min averages. Zenith slant columns near twilight were compared by fits to interpolated values of a reference instrument, then normalised by the mean of the slopes of the best instruments. For visible MAX-DOAS instruments, the means of the fitted slopes for NO2 and O4 of all except one instrument were within 10% of unity at almost all non-Zenith elevations, and most were within 5%. Values for UV MAX-DOAS instruments were almost as good, being 12% and 7%, respectively. For visible instruments at Zenith near twilight, the means of the fitted slopes of all instruments were within 5% of unity. This level of agreement is as good as that of previous intercomparisons, despite the site not being ideal for Zenith twilight measurements. It bodes well for the future of measurements of tropospheric NO2, as previous intercomparisons were only for Zenith instruments focussing on stratospheric NO2, with their longer heritage.
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Intercomparison of slant column measurements of NO2 and O4 by MAX-DOAS and Zenith-sky UV and visible spectrometers
Atmospheric Measurement Techniques, 2010Co-Authors: Howard K. Roscoe, Michel Van Roozendael, C. Fayt, A. Du Piesanie, N. Abuhassan, C. Adams, M. Akrami, A. Cede, J. Chong, K. ClémerAbstract:In June 2009, 22 spectrometers from 14 institutes measured tropospheric and stratospheric NO2 from the ground for more than 11 days during the Cabauw Intercomparison Campaign of Nitrogen Dioxide measuring Instruments (CINDI), at Cabauw, NL (51.97° N, 4.93° E). All visible instruments used a common wavelength range and set of cross sections for the spectral analysis. Most of the instruments were of the multi-axis design with analysis by differential spectroscopy software (MAX-DOAS), whose non-Zenith slant columns were compared by examining slopes of their least-squares straight line fits to mean values of a selection of instruments, after taking 30-min averages. Zenith slant columns near twilight were compared by fits to interpolated values of a reference instrument, then normalised by the mean of the slopes of the best instruments. For visible MAX-DOAS instruments, the means of the fitted slopes for NO2 and O4 of all except one instrument were within 10% of unity at almost all non-Zenith elevations, and most were within 5%. Values for UV MAX-DOAS instruments were almost as good, being 12% and 7%, respectively. For visible instruments at Zenith near twilight, the means of the fitted slopes of all instruments were within 5% of unity. This level of agreement is as good as that of previous intercomparisons, despite the site not being ideal for Zenith twilight measurements. It bodes well for the future of measurements of tropospheric NO2, as previous intercomparisons were only for Zenith instruments focussing on stratospheric NO2, with their longer heritage.
Joseph C. Lam - One of the best experts on this subject based on the ideXlab platform.
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An analysis of all-sky Zenith luminance data for Hong Kong
Building and Environment, 2003Co-Authors: Joseph C. LamAbstract:Sky luminance distribution data are of great importance to estimate internal daylight illuminance for building energy modelling. Sky luminance of a particular sky patch is always expressed as a ratio of the corresponding Zenith luminance. For places where measured Zenith luminance is not available, generating the required data from conversion models would be an appropriate alternative. This paper describes the sky luminance measurements made in 1999 at the City University of Hong Kong and reports the findings. A simple model relating Zenith luminance and horizontal diffuse illuminance has been proposed. An evaluation of the proposed model and the Perez Zenith luminance model has been carried out. It has been found that the proposed model gives reasonably good agreement with the measured data and outperforms the Perez model. The simplicity nature of the proposed model provides a convenient and reliable approach for building designers in estimating the Zenith luminance as well as the whole sky luminance distribution.
