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Cloud and aerosol characteristics during dry and wet days of southwest monsoon over the rain shadow region of Western Ghats, India


In situ measurements of aerosol particle chemistry and cloud microphysics made during the Cloud–Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) in 2015 over the Western Ghats and its rain shadow region are presented in this study. The high ratio of cloud condensation nuclei (CCN) to large sized aerosol (above 0.1 µm) concentrations indicates Aitken mode aerosols as the major contributor towards the observed CCN. Morphology and chemical composition of airborne aerosol samples collected from different altitudes and the warm cloud layers indicated distinct particle chemistry on the dry and wet days. The majority of the particles sampled were heterogeneous and internally mixed with two or more aerosol species indicating multiple sources and atmospheric aging, even during the wet days. Si-rich particles (up to 73%) were the dominant species in samples collected during dry days when the shallow clouds with narrow drop size distribution were observed. A higher concentration of Na-rich particles (up to 50%) was observed on wet days when the clouds were majorly multiple layers of stratus, which had broader cloud droplet spectra. Internally mixed carbonaceous and iron/cobalt-rich aerosols from local pollution sources were found on both wet and dry days suggesting boundary layer venting of aerosols. Large droplets were observed near the cloud base over the Western Ghats compared to those formed over the rain shadow region.

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The Ministry of Earth Sciences (MoES) fully funds the CAIPEEX program and the Indian Institute of Tropical Meteorology (IITM), Govt. of India. The filter sampling was designed and fabricated at IITM and was implemented for aircraft sampling. The authors are grateful to all the CAIPEEX aircraft and ground team for helping with the data collection. The authors from Mahatma Gandhi University (MGU) acknowledge the financial support from Department of Science and Technology (DST), Govt. of India for funding through FIST & PURSE and SAIF schemes and University Grants Commission (UGC), Govt. of India through the SAP-DRS program. The authors are thankful to DST-Nano Mission and MGU for funding the characterization facilities. The authors from MGU gratefully acknowledge IITM for scientific guidance, technical expertise, and financial support for this study. The MERRA-2 model data for dust loading was plotted using the online GIOVANNI platform ( provided by NASA. Back trajectory analysis was produced using the online version of the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT4) model ( The ERA5 reanalysis data used in this study was freely downloaded from!/home. Authors MV and JJ acknowledge Sathy Nair for preparing the meteorological briefings from the daily weather reports of IMD.


The Ministry of Earth Sciences, Govt. of India fully funds the CAIPEEX program and IITM. The HR-TEM and EDS facility of the International and Inter University Centre for Nanoscience and Nanotechnology (IIUCNN), MGU, was funded by the Department of Science and Technology (DST) Nano Mission for the project titled 'Development of Engineered Nanostructured Materials for High-Performance Applications' order No. SR/NM/NS-54/2009, 2708.2010 and 14.07.2011.

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Authors TVP and MV designed the study. PM designed the filter sampling system used in this study. MK, SB, TVP, PM, REA, MV made the aircraft observations used in this study. AAS and JJ performed the single-particle analysis using HR-TEM and EDS under the guidance of NK and ST. MV and JJ did the different analyses and prepared the manuscript. Authors TVP, ST, NK, MK, and SB reviewed the manuscript. All authors read and approved the final manuscript.

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Correspondence to Mercy Varghese.

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Varghese, M., Jose, J., Anu, A.S. et al. Cloud and aerosol characteristics during dry and wet days of southwest monsoon over the rain shadow region of Western Ghats, India. Meteorol Atmos Phys 133, 1299–1316 (2021).

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