Aerosol–Cloud Interaction over South-Central India and Adjoining Coastal Areas

The MODerate Resolution Imaging Spectroradiometer (MODIS) retrieved (2009–2015) aerosol and cloud products over South-Central India, including adjoining coastal areas, were quantitatively analyzed to explore aerosol–cloud interaction and to estimate aerosol indirect effect (AIE). The spatial distribution of aerosol optical depth (AOD) showed high AOD_{550 nm} (~ 0.7) over the northern India and is attributed to the long- and short-range transport of desert dust aerosols, dense population, and industrialization. The mean seasonal AOD_{550 nm} over region decreases from (0.55 ± 0.11) to (0.45 ± 0.05) and to (0.39 ± 0.04) for monsoon, post-monsoon, and winter seasons, respectively. The western Indian regions, particularly Pune and Jaipur, showed higher mean AOD_{500 nm} as compared to other cities. The positive correlation of aerosol indirect effect (AIE) with AOD for Pune and Pondicherry through pre- as well post- monsoon seasons for all cities except Pondicherry is ascribed to hygroscopic aerosol particulate growth. The aerosol size spectra undergo significant transformation from dominant high accumulation-mode during September–February months [with Angström exponent (AE) > 1.0] to dominant augmented coarse-mode (AE < 1.0) through March to June–July period. The AOD_{500 nm}-to-cloud fraction (CF) correlation coefficients range between 0.05 and 0.46 for coastal region, while for Jaipur, Pune, and overall study region, the CFs are 0.53, 0.65, and 0.75, respectively. The pre-monsoon months recorded lower (0.4–0.6 µm) cloud effective radii values than monsoon season (0.8–1.3 µm). The AOD-to-cloud liquid water path correlations for Goa and Pune (0.30–0.48) are higher than other cities (0.01–0.19). The AIE average values for metropolitan, semi-arid, coastal, high-altitude sites, and overall study region were found to be − 0.168, − 0.025, − 0.104, − 0.101, and − 0.128, respectively. There occurs a noticeable negative AIE for three categories (viz., Metropolitan, coastal, and high-altitude station), while for semi-arid category, there exists a prominent Twomey (positive AIE) effect.