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| Abstract Submission No. | ABS-2022-07-0318 |
| Title of Abstract | Flux of Dimethyl sulfide from eastern Araabian sea during northeast monsoon; influence on cloud microphysics |
| Authors | Damodara Rao Valavala*, K. Ramu, Anitha Gera, G V M Gupta, V. Ranga Rao |
| Organisation | National Centre for Coastal Research, Ministry of Earth Sciences |
| Address | NCCR, NIOT Campus, Velachery Tambram Main Road, Pallikaranai, Chennai 600100 Chennai, Tamil Nadu, India Pincode: 600100 Mobile: 7588921024 E-mail: damodarv@gmail.com |
| Country | India |
| Presentation | Oral |
| Abstract | Biogenic gases and particles emitted from surface seawater play an important role in atmospheric chemistry. Among the biogenic compounds contributed from oceans Dimethyl Sulfide (DMS) occupies considerable place. DMS is produced biologically from its precursor Dimethyl sulfoniopropionate and removed through various processes such as sea to air flux, microbial consumption and Oxidation of DMS to dimethyl sulfoxide(DMSO). As part of the ongoing MEDAS (Marine Ecosystem Dynamics of eastern Arabian Sea) , samples for DMS have been collected in northeast monsoon (NEM, from 14.01.2019 to 02.02.2019) season onboard FORV Sagar Sampada. Sampling was carried out in the eastern arabian sea (between 6.460N to 22.230N and 67.680E to 77.220E). To understand the distribution of DMS, seven transects have been selected where each transect is covering a distance of approximately 200Kms from coast to open ocean. DMS concentration was measured onboard immediately after collection using purge and trap technique and flux was calculated as a function of sea surface temperature and wind speed. An attempt has been also made to compare the observed DMS flux with empirically calculated DMS flux using DMS concentrations derived from Anderson⿿s model as a function of chlorophyll, shortwave radiation and nitrate. Cloud droplet number concentration (CDNC) and aerosol extinction coefficient have been calculated from cloud parameters (cloud optical thickness (COT) and cloud effective radius of liquid (CER), aerosol optical depth(AOD)) obtained from MODIS satellite. DMSO concentrations showed increasing trend with depth and higher than that of DMS in the deeper waters.This study aims to understand the responsible processes for such high concentrations of DMSO. DMS export to the atmosphere and to the other reduced forms have been discussed. Influence of DMS on cloud microphysics is elucidated by comparing the observed and modelled fluxes of DMS with that of CDNC over the study region during North east monsoon. Surface DMS concentrations ranged from 0.73 to 38.24 nM with an average of 5.74±5.58 nM during January 2019. DMS flux is found to be 28 µmol m⿿2 d⿿1. CERl data obtained from MODIS data suggests that lower atmosphere in the study region contains a homogeneous patch of liquid particles with lower particle size (ranged between 14 and 16.5µ) and high numbers of CDNC (90 to 150 cm-3). Significant correlation (r=0.6) between the DMS flux and CDNC suggest the considerable role DMS in the formation of CDNC during north east monsoon. Keywords: Arabian Sea, DMS export, DMSO, North east Monsoon, cloud microphysics, CDNC |