HelioClim-3 (HC3) is a database providing time series of the surface downwelling solar irradiance that are computed from images of the Meteosat satellites. This paper presents the validation results of the hourly global horizontal irradiance (GHI) and direct normal irradiance (DNI), i.e., beam irradiance at normal incidence, of versions four and five of HC3 at seven Egyptian sites. The validation is performed for all-sky conditions, as well as cloud-free conditions. Both versions of HC3 provide similar performances whatever the conditions. Another comparison is made with the estimates provided by the McClear database that is restricted to cloud-free conditions. All databases capture well the temporal variability of the GHI in all conditions, McClear being superior for cloud-free cases. In cloud-free conditions for the GHI, the relative root mean square error (RMSE) are fairly similar, ranging from 6% to 15%; both HC3 databases exhibit a smaller bias than McClear. McClear offers an overall better performance for the cloud-free DNI estimates. For all-sky conditions, the relative RMSE for GHI ranges from 10% to 22%, except one station, while, for the DNI, the results are not so good for the two stations with DNI measurements.

McClear, a fast model based on a radiative transfer solver, exploits the atmospheric properties provided by the EU-funded MACC project (Monitoring Atmospheric Composition and Climate) to estimate the surface downwelling solar irradiances for cloud-free instances. This article presents the first validation of the McClear model for the specific climate of the United Arab Emirates where skies are frequently cloud-free but turbid. McClear accurately estimates the global horizontal irradiance measured every 10 min at seven sites. The bias ranges from -9 W m(-2) (-1% of the mean observed irradiance) to +35 W m(-2) (+6%). The root mean square error (RMSE) ranges from 22 W m(-2) (4%) to 47 W m(-2) (8%) and the coefficient of determination ranges from 0.980 to 0.990. Estimates of the direct irradiance at normal incidence exhibit an underestimation that is attributed to the overestimation of the aerosol optical depth in the MACC data set and not accounting for the circumsolar radiation in McClear. The corresponding bias ranges from -57 W m(-2) (-8%) to +6W m(-2) (+1%). The RMSE ranges from 62W m(-2) (9%) to 87W m(-2) (13%) and the coefficient of determination ranges from 0.830 to 0.863. When compared to two other models in the literature, McClear is better able to capture the temporal variability of the direct irradiance at normal incidence. The validation results remain comparable for the global horizontal irradiance. (C) 2015 The Authors. Published by Elsevier Ltd.

Earth observation data and in situ measurements were used to derive a method for the estimation of Air Temperature(AirT) and thereby produce maps. The methodology was developed and validated using data acquired at five stations located in the United Arab Emirates(UAE) during the year 2012. In the first step, the effect of different variables on the estimation of AirT values was investigated and the variables of high importance were used to build the final model. Land surface temperature (LST), relative humidity, global horizontal irradiance, direct normal irradiance, and diffuse horizontal irradiance were identified as the most important inputs for Air Testimation. Models were developed separately for four different cases based on the seasons (Winter/Summer) and the time of the day (Day/Night). The models were evaluated using jackknife validation on the stations resulting in root mean square errors of 2.25°C(Winter/Day), 2.24°C (Winter/Night), 2.56°C (Summer/Day), and 2.69°C (Summer/Night) and an overall average accuracy of 2.44°C. Finally, the model has been applied on a larger scale by assimilating the relevant Earth observation data and in situ measurements for the creation of AirT maps for the entire country. The resulting AirT maps were generated in near real time at a temporal resolution of 15 min from METEOSAT/SEVIRI LST and the above-mentioned in situ measurements. These maps can be considered as important resources for several applications (e.g, climate studies, solar energy applications, thermal comfort studies, etc.).

A database containing the global and diffuse components of the surface solar hourly irradiation measured from 1 January 2004 to 31 December 2010 at eight stations of the Egyptian Meteorological Authority is presented. For three of these sites (Cairo, Aswan and El-Farafra), the direct component is also available. In addition, a series of meteorological variables including surface pressure, relative humidity, temperature, wind speed and direction is provided at the same hourly resolution at all stations. The details of the experimental sites and instruments used for the acquisition are given. Special attention is paid to the quality of the data and the procedure applied to flag suspicious or erroneous measurements is described in detail. Between 88 and 99 % of the daytime measurements are validated by this quality control. Except at Barrani where the number is lower (13 500), between 20 000 and 29 000 measurements of global and diffuse hourly irradiation are available at all sites for the 7-year period. Similarly, from 9000 to 13 000 measurements of direct hourly irradiation values are provided for the three sites where this component is measured. With its high temporal resolution this consistent irradiation and meteorological database constitutes a reliable source to estimate the potential of solar energy in Egypt. It is also adapted to the study of high-frequency atmospheric processes such as the impact of aerosols on atmospheric radiative transfer. It is planned to update regularly the current 2004–2010 database, which has been placed on the PANGAEA repository (doi:10.1594/PANGAEA.848804) and contains the individual meteorological and irradiation data files of the eight stations.