Abstract
ABSTRACTAerosol-cloud interaction is the subject of considerable scientific research, due to the importance of clouds in controlling climate. In the present study, three years (2011–2013) satellite observations are used to investigate the aerosol indirect effect (AIE) over Dehradun. The low values of Angstrom exponent (α) during March–July are attributed to the loading of dust-like coarse particles in the atmosphere, whereas the analysis of aerosol type and Spectral Radiation Transport Model for Aerosol species (SPRINTARS) simulated aerosol species variation supports the fact. Moderate Resolution Imaging Spectroradiometer (MODIS) derived AOD data are associated to the cloud product to examine the dust impact on properties of liquid cloud and ice cloud. The positive values of aerosol cloud interaction effect (ACI) for ice cloud during pre-monsoon (March–May) and monsoon (June–August) seasons reveal the significant impact of dust on ice clouds over Dehradun, which is maximum during May (~0.24 ± 0.05). The present study shows that ice cloud effective radius (ICER) decrease with AOD during dust period. The increase in ice water path (IWP) and ice cloud optical depth (ICOD) reveals the impact of dust on heterogeneous ice generation in low level clouds. However, there is no relation between dust and liquid water cloud during dust period. It is difficult to provide definite conclusions that the dust and cloud changes are driven by the same meteorological conditions. Cloud and the Earth’s Radiant Energy System (CERES) derived flux data are used to examine the associated changes in TOA cloud radiative forcing. The diminution in effective size of ice crystal due to aerosol first indirect effect traps more longwave radiation and reflects more solar radiation. Both first and second indirect effects enhance cloud cooling, whereas the dust induced cloud warming is mainly the result of the semi-direct effect.
Highlights
Aerosols have a crucial role in the life cycle of clouds by acting as cloud condensation nuclei (CCN) or ice nuclei (IN), and can modulate the distribution of radiative heating indirectly
The present study shows that ice cloud effective radius (ICER) decrease with AOD during dust period
The small values of α indicate the loading of coarse mode particles in the ambient atmosphere, while the higher absorption of fine-mode particles lead to the large α values
Summary
Aerosols have a crucial role in the life cycle of clouds by acting as cloud condensation nuclei (CCN) or ice nuclei (IN), and can modulate the distribution of radiative heating indirectly. Concerning the four major terrestrial sources of aerosols are biomass burning, desert dust, anthropogenic aerosol and biogenic aerosol, dust aerosols are responsible for significant climate forcing through their direct effect on radiation (Sokolik and Toon, 1996; Patel and Kumar, 2015) and their indirect/semi-direct effect on clouds and precipitation (Huang et al, 2010; Min and Li, 2010). Patel and Kumar, Aerosol and Air Quality Research, 16: 1820–1831, 2016 due to significant spatiotemporal variations in aerosol and cloud characteristics. According to climate model simulations, dust induced heating of the atmosphere over West Asia and North Africa rapidly modulate monsoon rainfall over central India (Vinoj et al, 2014). Dust induced heating may cause significant changes in regional scale processes in the absence of large-scale processes during monsoon breaks. The present study helps to understand the impact of dust on cloud and radiation
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