The diffuse component of the global solar radiation at Qena / Egypt

Diffuse solar radiation on horizontal surfaces is estimated at Qena / Egypt. The basic procedure is to develop relationships of the widespread use Liu & Jordan types between the daily global horizontal radiation (G) and its diffuse component (D) using measured values of these two quantities. An error analysis has been done for the results of diffuse radiation calculated using the regression models obtained in this paper and those estimated from other known ones of the Liu & Jordan type, According to statistical evaluation of the various relationships, it is seen that our models provide the best estimation of the diffuse radiation, Effect of climatic conditions was considered in the discussion.

Aerosol-light interactions reduce the carbon budget imbalance

Current estimates of the global land carbon sink contain substantial uncertainties on interannual timescales which contribute to a non-closure in the global carbon budget in any given year. This budget imbalance (BIM) partly arises due to the use of imperfect models which are missing or misrepresenting processes. One such omission is the separate treatment of downward direct and diffuse solar radiation on photosynthesis. Here we evaluate and use an improved high-resolution (6-hourly), gridded dataset of surface solar diffuse and direct fluxes, over 1901-2017, constrained by satellite and ground-level observations, to drive two global land models. Results show that tropospheric aerosol-light interactions have the potential for substantial land carbon impacts (up to 0.4 PgCyr-1 enhanced sink) at decadal timescales, however large uncertainties remain, with models disagreeing on the direction of change in carbon uptake. On interannual timescales, results also show an enhancement of the land sink (up to 0.9 PgCyr-1) and subsequent reduction in BIM by 55% in years following volcanic eruptions. We therefore suggest global carbon budget assessments include this dataset in order to improve land sink estimates.

Quantifying the Effect of Building Shadowing and Cloudiness on Mean Radiant Temperature in Singapore

Improving the quality of life in urban areas has become a major concern in the last few decades. With a constantly increasing urban population and in a climate change context, detailed knowledge of the impact of urban elements on the outdoor thermal environment is relevant. In this work, we present the results of several climatic campaigns carried out in Singapore aiming to evaluate local urban climate variables. Sensors were deployed simultaneously in different sites. The effect of building shadowing in the diurnal cycle of mean radiant temperature (Tmrt) is evaluated in different seasons. Although during the Inter-Monsoon season, mean Tmrt reduction due to building shadow is ≈19 °C, during clear skies days, it can be reduced by ≈30 °C. The Tmrt difference between sites is analyzed based on the weather conditions, the sky view factor (SVF), and the type of surrounding urban elements. Under building shadow conditions, higher SVF showed higher Tmrt values, although no correlation was found between Tmrt and diffuse solar radiation (measured above the urban canopy). The results suggest a relevant contribution of other radiation components (e.g., longwave radiation). The quantitative analysis of the Tmrt provided in this work is relevant for outdoor thermal comfort strategies in tropical areas such as Singapore.

Theoretical study of Linke's Turbidity at Some Iraqi Sites Based on Solar Radiation

Turbidity was calculated by solar irradiance (Linke's Turbidity) for sixteen Iraqi sites. These sites were distributed among middle, north and south of Iraq. We have updated these results of turbidity by depending on direct solar radiation, diffuse solar radiation, total solar radiation, and solar constant as inputs for mathematical models in computer programs. The latter calculations taking into account the hours of actual sun shine, hours of theoretical sun shine of the sun, the angle of the sun's rays, and the angle of the sun during the months of the year. The results showed that turbidity in the Iraqi sites which considered in this research depends mainly on the months of the year regardless of the fact that this site is located in the north, middle or south of Iraq. The amount of turbidity is at its greatest value during the winter season, specifically the month of December, where the average turbidity varied for those sites. In latter month the turbidity was ranged from (4.85 to 5.73), while in January it ranged from (4.75 to 5.72), then it began to decrease until the value of turbidity in most sites reached its lowest level in September, where the average turbidity of the studied sites varied (except for the site of Najaf) in this month (2.82 - 3.10) While the Najaf site was unique in registering the lowest average amount of turbidity in June by (3.25). The results showed that the turbidity in all sites included in this research ranges between (2.82 - 5.73) during the year.