Preprints
https://doi.org/10.5194/acp-2020-1233
https://doi.org/10.5194/acp-2020-1233

  29 Dec 2020

29 Dec 2020

Review status: this preprint is currently under review for the journal ACP.

Measurement report: Altitudinal variation of CCN activation across the Indo-Gangetic Plains prior to monsoon onset and during peak monsoon periods: Results from the SWAAMI field campaign

Mohanan R. Manoj1, Sreedharan K. Satheesh1,2, Krishnaswamy K. Moorthy2, Jamie Trembath3, and Hugh Coe4 Mohanan R. Manoj et al.
  • 1DST-Centre of Excellence in Climate Change, Divecha Centre for Climate Change, Indian Institute of Science, Bangalore, India
  • 2Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bangalore, India
  • 3FAAM Airborne Laboratory, Cranfield MK43 0AL, U.K.
  • 4Centre for Atmospheric Science, School of Earth and Environmental Sciences, University of Manchester, Manchester, UK

Abstract. Vertical distributions (altitude profiles) of condensation nuclei (CN) and cloud condensation nuclei (CCN) and their spatial variations across the Indo-Gangetic Plain (IGP) have been investigated based on air-borne measurements carried out during the SWAAMI field campaign (June to July, 2016) capturing the contrasting phases of the Indian monsoon activity in 2016; just prior to its onset and during its active phase. Prior to the monsoon onset, high concentrations of CN and CCN prevailed across the IGP and the profiles revealed frequent occurrence of elevated layers (in the altitude range 1–3 km). Highest concentrations and elevated peaks with high values occurred over the central IGP. The scenario changed dramatically during the active phase of the monsoon, when the CN and CCN concentrations dropped (CN by 20 to 30 % and CCN by 6 to 25 %) throughout the IGP with more pronounced changes at altitudes higher than 3 km where decreases as high as > 80 % were observed. These reductions have an east to west decreasing gradient; being most remarkable in the eastern IGP and very weak over the western IGP where the CN concentrations above 3 km increased during the monsoon. The activation ratios (AR) showed contrasting features, increasing with increase in altitude, prior to the onset of monsoon, reversing the trend to decrease with increase in altitude during the active phase of the monsoon. The supersaturation spectrum became flatter during the active phase of the monsoon indicating an increase in the hygroscopicity of aerosols, following the mixing of surface-based emissions with the advected marine airmass.

Mohanan R. Manoj et al.

 
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Mohanan R. Manoj et al.

Mohanan R. Manoj et al.

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Short summary
Vertical distributions of atmospheric aerosols and the ability of aerosols to form clouds has been studied across the Indo-Gangetic Plain based on air-borne measurements carried out during the SWAAMI field campaign studying the Indian monsoon. The ability of the aerosols to act as cloud forming nuclei showed contrasting features, increasing with increase in altitude, prior to the onset of monsoon, reversing the trend to decrease with increase in altitude during the active phase of the monsoon.
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