Clouds are a significant factor regarding Earth's energy budget. Cloud cover fluctuations have significant impacts on temperature, the water cycle, and incoming solar radiation. The cloud shortwave radiative effect (CRE) quantifies radiation changes due to variable cloud cover. At the surface, this variable is closely related to both macro, or large-scale, and micro, or small-scale physical properties of clouds.
To better understand clouds' influence on incoming and outgoing radiation, collaborators from Chengdu University of Information Technology, Chinese Academy of Sciences (CAS), Institute of Atmospheric Physics (IAP) and Nanjing University of Information Science & Technology evaluated CRE alongside cloud type and cloud fraction (CF). The team published their findings in Advances in Atmospheric Sciences
Researchers studied five years of one-minute surface irradiance, or the flux or radiant energy per unit area, and cloud data at Xianghe—an IAP managed observation station. This location provided an ideal location for radiation measurements, as it is within a frequently heavily polluted region surrounding the North China Plain.
"Our results suggest that the radiative forcing of clouds on irradiance and its components depend on the position of a cloud relative to the sun," said corresponding author, Prof. XIA Xiangao with the IAP.
As Prof. XIA suggests, their research provides reliable quantification of CF variation and corresponding radiative forcing at Xianghe for the first time. Additionally, results indicate that CF is a dominant factor affecting diffuse irradiance, or radiant energy scattered by the atmosphere.
Xianghe Observation Site (Images by IAP)
Overall, this process affects global irradiance, especially under clear sky conditions. Meanwhile, CF affects both direct and diffuse irradiance, resulting in a non-linear relationship between CF and CRE, under sun-obscured conditions, or when clouds are in the sky, but do not block the sun.
"This study will provide future scientific research suggestions for forecasting solar radiation flux and it will improve understanding of cloud-radiation interaction." said Prof. XIA.
Citation: Liu, M. Q., J. Q. Zhang, H. R. Shi, D. S. Fu, and X. A. Xia. 2022: Data-driven estimation of cloud effects on surface irradiance at Xianghe, a suburban site in North China Plain. Adv. Atmos. Sci., https://doi.org/10.1007/s00376-022-1414-x