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Aerosol‐induced changes in cloud microphysical and radiative properties have been studied for the first time using ground‐based and airborne observations over a semiarid rain shadow region. The study was conducted for nonprecipitating, ice‐free clouds during monsoon (July to September) and postmonsoon (October) months, when cloud condensation nuclei (CCN) concentrations over the region of interest increased monotonically and exhibited characteristics of continental origin. A multifilter rotating shadowband radiometer and microwave radiometric profiler were used to retrieve the cloud optical depth and liquid water path (LWP), respectively, from which cloud effective radius (CER) was obtained. CER showed wide variability from 10–18 µm and a decreasing trend toward the postmonsoon period. During monsoon, the estimated first aerosol indirect effect (AIE) increased from 0.01 to 0.23 with increase in LWP. AIE at different super saturations (SS) showed maximum value (significant at 95%) at 0.4% SS and higher LWP bin (250–300 g/m2). Also, statistically significant AIE values were found at 0.6% and 0.8% SSs but at lower LWP bin (200–250 g/m2). The relationship between CCN and CER showed high correlation at 0.4% SS at higher LWP bin, while at higher SSs good correlations were observed at lower LWPs. Data combined from ground‐based and aircraft observations showed dominance of microphysical effect at aerosol concentrations up to 1500 cm−3 and radiative effect at higher concentrations. This combined cloud microphysical and aerosol radiative effect is more prominent during postmonsoon period due to an increase in aerosol concentration.

The important radiative properties of clouds such as cloud optical depth (COD) and droplet effective radii (R e ) are retrieved from the simultaneous measurements by ground-based multifilter rotating shadowband radiometer (MFRSR) and microwave radiometric profiler (MWRP), colocated at Mahabubnagar, a rain shadow region in southern Indian peninsula. Min and Harisson's (1996) retrieval algorithm is used for the first time to derive monsoon cloud properties in India. COD and liquid water path (LWP) retrieved from two independent instruments of MFRSR and MWRP showed reasonably good correlation. During monsoon (July to September) and postmonsoon (October) months, the maximum probability of occurrence of COD for overcast sky is 20. The maximum probability of occurrence of LWP is 100 gm À2 for water clouds during monsoon months, while October showed maximum occurrence at a lower value of 50 gm À2 , where most of the times the cloud bases are above freezing level indicating mixed phase clouds. Maximum R e varied from 14-16 μm (10-12%) to 12 μm (9%) during monsoon to postmonsoon transition with very less probability of occurrence indicating the characteristic feature of this region. A case study showed that the mean R e from ground-based and aircraft measurements are 12.0 ± 3.7 μm and 8.14 ± 1.4 μm, respectively, indicating a fairly good agreement within the experimental constraints. Intercomparison of ground-based and Moderate Resolution Imaging Spectroradiometer (MODIS)-Terra and MODIS-Aqua-derived COD, LWP and R e over the observational site for overcast and warm clouds indicates that on an average, MODIS-retrieved mean COD and LWP are underestimated, while mean R e is overestimated as compared to ground retrievals.

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