2025/01/04 by W. Yao, Yao, Wuqiushi, Jianhua Lü +3
Biochemistry, Genetics and Molecular Biology · Earth and Planetary Sciences · Physics and Astronomy · #Atmospheric and Oceanic Physics (physics.ao-ph) #FOS: Physical sciences #Geomagnetism and Paleomagnetism Studies #Geophysics and Gravity Measurements #Solar and Space Plasma Dynamics
paper · pdf · doi:10.48550/arxiv.2501.02326
openalex publication_date 2025/01/04 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
The seasonality of the tropical meridional circulation evolves differently across different regions, governs the onset and retreat of monsoons and migration of tropical precipitation, thereby influencing agricultural productivity and disaster preparedness in the tropics and subtropics. By defining a pseudo meridional overturning streamfunction (Ψpseudo) and defining a new vector-type, dual-component index (ASCI), we diagnose zonally asymmetric abrupt seasonal change (ASC) of tropical meridional circulation. Ψpseudo converges to traditional, meridional overturning streamfunction (Ψm) after being averaged over a zonal circle around any latitude. By applying the Helmholtz decomposition to horizontal velocity fields so as to decompose Ψpseudo into rotational and divergent components, we quantitatively compare the contributions of horizontally rotational and divergent flows to the abrupt seasonal change. We find that the zonal sectors associated with strong deep convection exhibit the most pronounced ASC of tropical meridional circulation, and all of subregions exhibiting ASC contain landmass with low heat inertia. Particularly, in contrast to the case of zonally symmetric Hadley cell, rotational flow, rather than the thermal-direct divergent flow, dominates the zonally asymmetric ASC in the tropics, although the divergent flow also contributes to the ASC over the zonal sectors associated with deep convection. We suggest that the interplay between tropical Rossby-type eddies with extratropical eddies and tropical circulation is essential to the zonally asymmetric ASC of tropical Hadley circulation.