- Dona Paula, Goa, India.
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Abstract Submission No. | ABS-2022-07-0409 |
Title of Abstract | INTRA SEASONAL VARIABILITY OF AEROSOLS AND ITS IMPLICATION OVER THE INDIAN SECTOR OF SOUTHERN OCEAN |
Authors | ATIBA A. SHAIKH*, AVIRUP SEN, NEHA SALIM SHAIKH, HARILAL B. MENON |
Organisation | GOA UNIVERSITY |
Address | SCHOOL OF EARTH, OCEAN AND ATMOSPHERIC SCIENCES, GOA UNIVERSITY. PANAJI, GOA, India Pincode: 403206 Mobile: 7767874011 E-mail: atibashaikh123@gmail.com |
Country | India |
Presentation | Poster |
Abstract | To study aerosol characteristics and associated thermodynamics in the Indian Ocean sector of Southern Ocean (35°S to 69°S), experiments were made in the 9th and 10th Indian Southern Ocean Expedition (SOE) during austral summers of 2016-2017 and 2017-18. Along the track measurements of Aerosol Optical Depth (AOD) and Black Carbon (BC) mass concentrations (ng m-3) were carried out and supplemented by Radiosonde launches to understand the atmospheric dynamics. Second order derivative of ÿngström exponent, α˿, Direct Shortwave Aerosol Radiative Forcing (DSARF), Convective Available Potential Energy (CAPE) and Convective Inhibition Energy (CIN) were estimated. The in-situ data were further supplemented by HySPLIT trajectories and fire count data. Additionally, MODIS-AQUA derived Chl-a (mg m-3) surface mass concentration. Monthly averaged surface incoming solar flux (W m-2) along with time-averaged surface mass concentration (ng m-3) products of Dimethyl Sulfide, Black Carbon, and Sulphate and cloud albedo had also been used. On the basis of AOD distribution, the study area is divided into two zones: Zone-1 (35 48°S) and Zone-2 (64 69°S). The study revealed AOD500 to be higher in Zone-1 during SOE 9, while similar values were encountered in Zone-2 during both expeditions. The AOD spectra did not follow Junges power law. More spectral variability was observed in both zones during SOE-9 compared to SOE-10. Moreover, Spectra were much flatter in Zone-2 compared to Zone-1 in both the expeditions. The dominance of fine mode over coarse mode was prominent in January. However, the trend reversed as the season advanced from summer to winter as the source of fine mode decreased. Analysis of decadal satellite data revealed that chl-a concentration increased from September to January and further decreased from February onwards, depicting maxima during November-December. A peak in chl-a mass concentration was observed as the solar insolation reached its optimum level during November-December (onset of austral summer). DMS production during December and January was found to be high, as DMS is produced during the lysis/grazing of Phytoplankton. Hence, a lag was seen between chl-a maxima and DMS maxima. DMS further underwent gas to particle conversion increasing the fine mode particle concentration, depicted as a peak in December-January. Sulphate mass concentration over the region matches with DMS. Since the resultant aerosol particles are hygroscopic, they act as cloud condensation nuclei (CCN) leading to increased cloud formation as the season advanced. The newly formed cloud particles being in liquid state reduces the albedo for the season. The study also revealed the presence of black carbon aerosol in the ambient aerosols due to long-range transport. The average BC concentration was marginally lower in Zone-2 (59.41±28.30 ng m-3) as compared to Zone-1 (61.76±29.71 µg m-3) for SOE-9, while for SOE-10 it was higher in Zone-2 (74.67±16.22 ng m-3) than Zone-1 (72.31±39.53 ng m-3). Composite AOD and MABL height determine the DSARF. The DSARF was 3.27 ± 0.58 W m-2 and 1.84 ± 0.30 W m-2 for SOE-9 and SOE-10 in Zone-1 respectively. Similarly, the DSARF was 1.24 ± 0.23 W m-2 and 1.44 ± 0.19 W m-2 for Zone-2. Average Heating rate (HR) values (~0.020 K day-1) encountered in Zone-2 were much lower compared to Zone-1 for SOE-9; unlike SOE-10 where only slightly lower HR values (~0.004 K day-1) were observed in Zone-2. |