01-05 December 2025
INCOIS, Hyderabad, India.
| Abstract Submission No. | ABS-04-0138 |
| Title of Abstract | Oceanic influence on large-scale atmospheric convection during co-occurring La Niña and negative IOD events |
| Authors | Supriya Ovhal*, Mujumdar M, Swapna P, Sreenivas P, Sandeep N, M. Ravichandran |
| Organisation | Indian Institute of Tropical Meteorology |
| Address | IITM COLONY, PANCHWATI, PASHAN, PUNE PUNE, MAHARASHTRA, India Pincode: 411008 E-mail: supriyaovhal@gmail.com |
| Country | India |
| Presentation | Oral |
| Abstract | This study explores the influence of co-occurring La Niña and negative Indian Ocean Dipole (nIOD) on atmospheric convection and rainfall over South Asia, focusing on the often-overlooked role of oceanic subsurface processes. Using observed and reanalysis datasets, we find that the interaction of strong equatorial Pacific easterly wind anomalies during La Niña and equatorial westerly wind anomalies during nIOD results in convergence over the eastern Equatorial Indian Ocean (EIO). This convergence deepens the thermocline and warms sea surface temperatures (SST), intensifying the Indian Ocean equatorial Walker cell with anomalous rising motion over the eastern EIO and subsidence over the western EIO. The subsidence over the western EIO promotes divergence, enhancing northward moisture transport and southerly winds over the northern Arabian Sea. Simultaneously, a westward shift of the Western Pacific Subtropical High (WPSH) induces low-level easterly winds over the Indo-Gangetic Plain. The interaction between nIOD-induced southerlies and WPSH-induced easterlies over the northern Arabian Sea further deepens the thermocline and warms SST over the north Arabian Sea. Ekman pumping from wind stress curl also contributes to this warming. These conditions create a favorable environment for sustained convection and enhanced rainfall over north-west India and adjoining areas. Our findings suggest that recent extreme rainfall events in northwest India and Pakistan are linked to the combined influence of La Niña and nIOD. Climate model projections indicate potential intensification of ENSO and IOD under global warming, which can amplify their combined effects and increase the risk of extreme precipitation events over South Asia. |
| Are you part of IIOE-2 endorsed project | no |
| Keywords | Atmospheric convection, Monsoon, Climate modelling, Ocean subsurface, La Niña, Indian Ocean Dipole |
| For Awards | yes |
| Date Of Birth | 16-04-1992 |
| ECSN Registration Number | IIOE2-ECSN-0255 |