01-05 December 2025
INCOIS, Hyderabad, India.
| Abstract Submission No. | ABS-03-0383 |
| Title of Abstract | Stagnation of atmospheric circulation leads to historically prolonged extreme rainfall event over northwestern India in August 2024 |
| Authors | Mahendra Nimmakanti*, Matthew Huber, Lei Wang, Kieran M R Hunt, Nagaraju Chilukoti, Jasti S. Chowdary |
| Organisation | Purdue University |
| Address | Department of Earth, Atmospheric, and Planetary Sciences West Lafayette, Indiana, United States Pincode: 47907-2051 E-mail: mnimmaka@purdue.edu |
| Country | United States |
| Presentation | Poster |
| Abstract | Northwestern India (NWI) received anomalously heavy rainfall from August 21-30, 2024, despite the monsoon being in a break phase. This study reveals how mid-latitude dynamics triggered this unusual event. Using reanalysis, we perform a moisture budget analysis and Local Wave Activity (LWA) diagnostics and find that the enhanced mid-tropospheric baroclinic instability greater than 1.1 per day (1.34 Ͽ) peaked during August 13-17 in the North Atlantic, 7-10 days before the NWI rainfall event. This instability fueled the north Atlantic westerly jet and reinforced an "Ω" shaped blocking high over the Ural Mountains ("Ural block") that developed over August 21-22. This block initiated a wave train that propagated eastward with increasing amplitude over subsequent days. The downstream distorted Rossby waves broke, triggering a pronounced Caspian Sea trough that deepened by August 25-26, strengthening a subtropical jet streak north of the Tibetan Plateau, with maximum geostrophic wind speeds exceeding 120 m²s⁻². The NWI was in the jet streak's right entrance region, where upper-level divergence and compensatory upward motion intensified a low-pressure system that had been steered northwestward into the region. Despite monsoon break conditions, the elevated mid-tropospheric humidity allowed sustained deep convection, which combined with the quasigeostrophic ascent arising from the jet streak entrance region, led to extreme rainfall over NWI. Our analysis provides a case study showing the importance of the growing influence of mid-latitude circulation changes traceable to alterations in the North Atlantic for Indian Monsoon variability. The physical linkages demonstrated here may be crucial for improving monsoon behaviour in changing climate. |
| Are you part of IIOE-2 endorsed project | no |
| Keywords | Local Wave Activity,Tibetan Plateau,atmospheric circulation |
| For Awards | no |