On entering the Earth's atmosphere, a large amount of solar radiation gets absorbed and scattered by aerosols, clouds, atmospheric gases, and Earth's surface. In this context, we discuss an approach to characterize the sky conditions...
moreOn entering the Earth's atmosphere, a large amount of solar radiation gets absorbed and scattered by aerosols, clouds, atmospheric gases, and Earth's surface. In this context, we discuss an approach to characterize the sky conditions using ground-based observations of solar radiation. The proposed approach is applied to the measured solar radiation for the duration 16 October 2018 to 31 December 2019, at Himalayan Clouds Observatory (HCO), which is situated at Swami Ram Tirtha (SRT) Campus (30°34 0 N, 78°41 0 E) Badshahithaul, Tehri Garhwal, Uttarakhand, India. The present work demonstrates the variation in Clearness Index (K T) associated with Global Horizontal Radiation (H a), Extraterrestrial Horizontal Radiation (H o) and associated variability of Aerosol Optical Depth (AOD), Angstrom Exponent (AE) and fine particles (PM 2.5 (lg m-3)) in different sky conditions. Most of the period of 2018 shows clear sky (81.82%) as compared to partially cloudy (4.29%) and cloudy (3.9%) days. Whereas only 20.89% days having clear sky, 38.38% as partially cloudy sky and 34.73% as cloudy sky conditions were observed during 2019. From the variance of H a and K T , we obtained minimum values in the monsoon and winter from which we get cloudier condition in these seasons. AOD and PM 2.5 remains lower in clear sky condition and highest in cloudy condition due to several atmospheric factors. Also, the AE of cloudy cases is marginally lower, implying larger particles, most likely due to swelling in humid conditions. Finally, we observed that the negative correlation between AOD and AE which indicates the swelling particles nearby cloudy region. Similarly, a positive correlation between AOD and PM 2.5 indicates the sources of air pollution can influence aerosol loading for all sky conditions.
