Abstract
Abstract. Aerosol and cloud properties over southern China during the 10-year period 2006–2015 are analysed based on observations from passive and active satellite sensors and emission data. The results show a strong decrease in aerosol optical depth (AOD) over the study area, accompanied by an increase in liquid cloud cover and cloud liquid water path (LWP). The most significant changes occurred mainly in late autumn and early winter: AOD decreased by about 35 %, coinciding with an increase in liquid cloud fraction by 40 % and a near doubling of LWP in November and December. Analysis of emissions suggests that decreases in carbonaceous aerosol emissions from biomass burning activities were responsible for part of the AOD decrease, while inventories of other, anthropogenic emissions mainly showed increases. Analysis of precipitation changes suggests that an increase in precipitation also contributed to the overall aerosol reduction. Possible explanatory mechanisms for these changes were examined, including changes in circulation patterns and aerosol–cloud interactions (ACIs). Further analysis of changes in aerosol vertical profiles demonstrates a consistency of the observed aerosol and cloud changes with the aerosol semi-direct effect, which depends on relative heights of the aerosol and cloud layers: fewer absorbing aerosols in the cloud layer would lead to an overall decrease in the evaporation of cloud droplets, thus increasing cloud LWP and cover. While this mechanism cannot be proven based on the present observation-based analysis, these are indeed the signs of the reported changes.
Highlights
The role of atmospheric aerosols in climate change has been studied widely in the past
According to the latest terminology (Boucher et al, 2013), the semi-direct effect is described as a “rapid adjustment” induced by aerosol radiative effects, and along with the direct effect it is grouped into the “aerosol–radiation interactions” (ARIs) category, whereas the indirect effects are termed “aerosol–cloud interactions” (ACIs)
Moderate Resolution Imaging Spectroradiometer (MODIS), Multiangle Imaging SpectroRadiometer (MISR) and CloudAerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) total aerosol optical depth (AOD) are in relatively good agreement in most months, with the largest differences occurring in March and April, when CALIPSO deviates from the other two data sets
Summary
The role of atmospheric aerosols in climate change has been studied widely in the past. According to the latest terminology (Boucher et al, 2013), the semi-direct effect is described as a “rapid adjustment” induced by aerosol radiative effects, and along with the direct effect it is grouped into the “aerosol–radiation interactions” (ARIs) category, whereas the indirect effects are termed “aerosol–cloud interactions” (ACIs). Observations of these mechanisms and their effects on climate have been elusive, and the uncertainties associated with them remain high (Boucher et al, 2013).
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