Abstract
In the present study, collocated and simultaneous measurements on meteorological parameters and solar radiation on horizontal surface were obtained from different meteorological sensors and pyranometer sensor over a semi-arid station, Anantapur (14.62° N, 77.65° E and 331 m asl) during January–December 2013. The temperature is usually lower at midnight, decreasing in the early hours of the morning around 08:00 LT (Local Time) (24.71 ± 2.7 °C), and then increasing rapidly until just after midday at 15:00 LT (31.88 ± 3.2 °C). It decreases to 26.70 ± 2.9 °C during the night around 23:00 LT. The relative humidity ranges from 30–76%, 20–65%, 46–80% and 48–90% during winter, summer, monsoon, and post-monsoon seasons respectively. The diurnal variation of soil moisture exhibits slight variations at different depths over the region. The diurnal and monthly variations of solar radiation as well as clearness index (k t ), diffusion index (k d ) were studied in the present study. In diurnal variation, it shows a steady rise in solar radiation received at the surface after 7:30 LT and attains a maximum solar radiation between 12:00 – 13:00 LT. The amount of solar radiation also varies depending on the time of day and the season. The annual mean of daily global, extraterrestrial and diffuse radiation at Anantapur is found to be 202.43 ± 40.45, 408.15 ± 61.63 and 49.33 ± 11.26 W/m 2 . The high global and diffuse solar radiations were observed during March-May (257.67 ± 34.18 W/m 2 , 65.07 ± 11.20 W/m 2 ) whereas low global and diffuse solar radiations during monsoon months (137.66 ± 12.41, 33.47 ± 7.44 W/m 2 ). In the case of extraterrestrial solar radiation was high in the month of December (472.92 ± 0.67 W/m 2 ) and low in the month of June (312.87 ± 2.58 W/m 2 ).
Highlights
The air temperature variation brings about a change in water evaporation and air saturation and leading to the change in air humidity
Based on different meteorological conditions prevailing over the observation site, the months of the year are classified into four seasons namely winter (December-February), summer (March-May), monsoon (JuneAugust) and post-monsoon (September-November)
The minimum temperature of 25.28 ± 3.7 °C was observed during the January 2013 and a maximum of 32.68 ± 3.6 °C during May 2013
Summary
The air temperature variation brings about a change in water evaporation and air saturation and leading to the change in air humidity. Locations will cause air pressure differences, which in turn would produce air movement, thereby wind This variation in humidity and wind speed leads to direction affect on rainfall. The radiation that reflects from surroundings (so-called albedo) is of importance for some angle to the horizontal surface This radiation is mainly diffuse and comes to the receiving surface under different angles. Solar radiation is received at the earth’s surface under different atmospheric conditions, which clearly affect the amount and quality of radiation obtained at the ground. Transparency, air mass, atmospheric water vapor contents layers and distribution of cloud cover have been suggested as the atmospheric conditions that exert influence solar radiation at the earth’s surface through the process of absorption, scattering and reflection of the incoming solar radiation. A frequency distribution of clearness index and diffuse index of global solar radiation are presented and discussed
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