Aerosol control on depth of warm rain in convective clouds

• Published in: Journal of Geophysical Research: Atmospheres Vol. 117; no. D13; pp. 1U - n/a
• Main Authors: Konwar, Mahen, Maheskumar, R. S., Kulkarni, J. R., Freud, E., Goswami, B. N., Rosenfeld, D.
• Format: Journal Article
• Language: English
• Published: Washington, DC Blackwell Publishing Ltd 16.07.2012; American Geophysical Union
• Subjects: aerosol indirect effect; Aerosols; Air masses; cloud condensation nuclei; Clouds; convective cloud; Earth sciences; Earth, ocean, space; Exact sciences and technology; Geophysics; giant CCN; Rain; warm rain depth; Water content; Arabian Sea; Indian Ocean; Asia; India; ISW, Arabian Sea; ISW, India; experimental studies; altitude; rainfall; Water drop; atmospheric precipitation; aerosols; Convective cloud; concentration; rain water; air; isotherms; Condensation nucleus; pollution; depth; Effective radius; Cloud base; extreme value; raindrops; Aircraft observation; plains; temperature; water content; particles; monsoons
• ISSN: 0148-0227; 2169-897X; 2156-2202; 2169-8996
• DOI: 10.1029/2012JD017585

Aircraft measurements of cloud condensation nuclei (CCN) and microphysics of clouds at various altitudes were conducted over India during CAIPEEX (Cloud Aerosol Interaction and Precipitation Enhancement Experiment) phase I and II in 2009 and 2010 respectively. As expected, greater CCN concentrations gave rise to clouds with smaller drops with greater number concentrations (Nc). The cloud drop effective radius (re) increased with distance above cloud base (D). Warm rain became detectable, i.e., rain water content >0.01 g/Kg, at the tops of growing convective clouds when re exceeded 12 μm. The re is determined by the number of activated CCN, Nad, and D. The Nad can be approximated by the maximum measured values of Nc. Higher Nc resulted in greater D for reaching the re threshold for onset of warm rain, re*, denoted as D*. In extreme cases of highly polluted and moist air that formed the monsoon clouds over the Indo‐Gangetic plains, D* exceeded 6 km, well above the 0°C isotherm level. The precipitation particles were initiated there as supercooled raindrops at a temperature of −8°C. Giant CCN reduced re* and D*, by initiating raindrops closer to cloud base. This effect was found mainly in dusty air masses over the Arabian Sea. Besides, the aerosol effect on D*, D* was found to decrease with increase in cloud water path. Key Points Aerosols push depth for warm rain to deeper height Giant CCN accelerates the warm rain formation process Non‐linear relationship between CCN and Nc