LAUSR

In this study, a quantitative assessment of clear‐sky aerosol direct radiative effects (ADREs) at the surface over the Yangtze River Basin (YRB), China was conducted based on Mesoscale Atmospheric Global Irradiance Code (MAGIC) radiation code (direct method) and ground‐based measurements (indirect method). For the direct method, The ADRE at the surface was calculated using MAGIC radiation code with Moderate Resolution Imaging Spectroradiometer (MODIS) and interim ECMWF Re‐Analysis (ERA‐INTERIM) integrated water vapour as input. Results showed that the multi‐year average ADRE ranged from −39.29 to −1.95 W/m2 with mean values of −18.19 ± 1.44 W/m2. High ADRE (larger than −34 W/m2) occurred in Sichuan Basin, Central Hubei Province and Yangtze River Delta. The seasonal ADRE was high in spring (−23.05 ± 13.48 W/m2) and low in winter (−14.24 ± 8.51 W/m2). Generally, an increasing trend (0.27 W/m2 per year) of ADRE was found from 2001 to 2010 and a decreasing trend (−0.72 W/m2 per year) from 2011 to 2015. The water vapour radiative effect (WVRE) was calculated using MAGIC radiation code and the multi‐year average value was −52.59 ± 1.45 W/m2, which indicated the attenuation of clear‐sky radiation in YRB due to water vapour was stronger than the aerosols. However, the trends of water vapour effects were 0.03 W/m2 per year during 2001–2010 and −0.37 W/m2 per year during 2011–2015, which were much smaller than the trends of ADRE. For the indirect method, the clear‐sky ADRE at sites was calculated using the solar radiation observations. The variations of annual average ADRE obtained by above methods gave good match. An obvious increasing trend (−0.71 W/m2 per year) of aerosol radiative cooling effect was found in Central Hubei Province from 2001 to 2010 and an obvious decreasing trend (3.23 W/m2 per year) in Sichuan Basin from 2011 to 2015. The determination coefficient (R2) between ADRE trends and clear‐sky solar radiation trends is 0.874, indicating that the trends of clear‐sky solar radiation were mainly determined by the trends of ADRE.