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| Abstract Submission No. | ABS-2022-02-0308 |
| Title of Abstract | FOOTPRINTS OF SOUTHERN ANNULAR MODE ON INDIAN OCEAN WAVES |
| Authors | Meenakshi Sreejith*, Remya P G, B Praveen Kumar, TMB Nair |
| Organisation | INCOIS, Hyderabad |
| Address | 201, Lakshmi Sai Nilayam, Manjeera tank road, Pragathi Nagar Bachupally, Telangana, India Pincode: 500090 Mobile: 8921077723 E-mail: meenakshi.s@incois.gov.in |
| Country | India |
| Presentation | Poster |
| Abstract | The annular modes are hemispheric scale patterns of climate variability as part of internal atmospheric dynamics in the middle latitudes. On riveting our attention to Indian Ocean, the potential imprints of tropical-extra tropical teleconnection of Southern Annular Mode (SAM) through sequential changes of Hadley cell on the North Indian Ocean (NIO) wave parameters are investigated in the present study. The SAM index (SAMI) that captures the variability of mean sea level pressure (MSLP) over the midlatitudes of the southern hemisphere is constructed. Marshall SAMI values are taken for the present study which was carried out from December 1979 to February 2018 (Marshall et al,2018). In which the Marshall SAMI is computed using (Gong and Wang, 1999) method. The positive and negative phase of SAM changes with the low or high pressure anomaly over the pole and a shift in mid-latitude westerly jet from to pole to equatorward respectively. ERA5(ECMWF ReAnalysis) model data were used for analysing the variables under study, with data coverage from January 1979 to within 5 days of real time. It is the fifth generation atmospheric reanalysis from ECMWF, ERA5-hourly data at 31km horizontal resolution with 137 levels up to 0.01 hPa. The Multiple Linear Regression analysis of Significant wave height( SWH), Swell wave height (SHTS), mean wave period (MWP), and wind sea height (SHWW )for SAM years reveal that the JJA (June, July and August) season is most susceptible to other seasons. The anomalies of SWH, SHTS, MWP, and SHWW are stark opposites during the positive and negative phases of SAM and band-wise in the different IO regions. The southwest monsoon and the strengthening of SAM during the negative phase contribute to IO's highest mean wind fields during JJA. Wind speed is maximum (10m/s-14m/s) between 40°S-60°S. The dominance of wind seas during this period is visible from the lowest MWP fields of JJA. The swell fields are also indicative of this, with the highest swells during JJA. The signature of SAM is evident in the atmospheric signals linked to the change in wave parameters due to the altering wind as a result of modified Hadley cell over this region. A positive SAM event corresponds to a widespread downdraft and intense updraft of Hadley cell. For a negative SAM event, the cells are more constricted and less severe. These changes are a direct consequence of the poleward and equatorward shift of wind during SAM phases. The study establishes the relevance of SAM as a persuasive factor towards wave climate and the covarying atmospheric counterparts in the IO. |