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Discussion papers
https://doi.org/10.5194/acp-2019-571
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-571
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 24 Jul 2019

Submitted as: research article | 24 Jul 2019

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This discussion paper is a preprint. A revision of this manuscript was accepted for the journal Atmospheric Chemistry and Physics (ACP) and is expected to appear here in due course.

Altitude profiles of CCN characteristics across the Indo-Gangetic Plain prior to the onset of the Indian summer monsoon

Venugopalan Nair Jayachandran1, Surendran Nair Suresh Babu1, Aditya Vaishya2, Mukunda M. Gogoi1, Vijayakumar S. Nair1, Sreedharan Krishnakumari Satheesh3,4, and Krishnaswamy Krishna Moorthy4 Venugopalan Nair Jayachandran et al.
  • 1Space Physics Laboratory, Vikram Sarabhai Space Centre, ISRO PO, Thiruvananthapuram, India
  • 2School of Arts and Sciences, Ahmedabad University, Ahmedabad, India
  • 3Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bangalore, India
  • 4Divecha Centre for Climate Change, Indian Institute of Science, Bangalore, India

Abstract. Concurrent measurements of the altitude profiles of cloud condensation nuclei (CCN) concentration, as a function of supersaturation (ranging from 0.2 % to 1.0 %), and aerosol optical properties (scattering and absorption coefficients) were carried out aboard an instrumented aircraft across the Indo-Gangetic Plain (IGP) covering coastal, urban and arid environments, just prior to the onset of the Indian summer monsoon (ISM) of 2016, under the aegis of the SWAAMI - RAWEX campaign. In general, the CCN concentration has been highest in the Central IGP, decreasing spatially from east to west above the planetary boundary layer (PBL), which is ~ 1.5 km for the IGP during pre-monsoon. Despite of this, the CCN activation efficiency at 0.4 % supersaturation has been, interestingly, the highest over the eastern IGP (~ 72 %), followed by the west (~ 61 %), and has been the least over the central IGP (~ 24 %) within the PBL. In general, higher activation efficiency is noticed above the PBL than below it. The Central IGP showed remarkably low CCN activation efficiency at all the heights, which appears to be associated with high black carbon (BC) mass concentration there, indicating the role of anthropogenic sources in suppressing the CCN efficiency. First ever CCN measurements over the western IGP, encompassing "The Great Indian desert", show high CCN efficiency, ~ 61 % at 0.4 % supersaturation, indicating hygroscopic nature of the dust. The vertical structure of CCN properties is found to be airmass-dependent; with higher activation efficiency even over the central IGP during the prevalence of marine airmass. Precipitation episodes seem to reduce the CCN activation efficiency below cloud level. An empirical relation has emerged between the CCN concentration and the scattering aerosol index (AI), which would facilitate prediction of CCN from aerosol optical properties.

Venugopalan Nair Jayachandran et al.
Venugopalan Nair Jayachandran et al.
Venugopalan Nair Jayachandran et al.
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