Can Coastal Kelvin Waves Drive a Basin-Wide Intermediate Circulation With a Semi-Annual Cycle?

Abstract

Ocean circulations are essential for global climate, redistributing heat and water across ocean basins. The Andaman Sea (AS), a key semi-enclosed sea connecting to the Bay of Bengal, has lacked sufficient observational data to understand its intermediate circulation. Based on advanced reanalysis data sets, for the first time, we here report a very interesting natural phenomenon, that is, the basin-wide intermediate circulation of the AS changes its direction twice yearly between cyclonic and anticyclonic, somewhat like a YOYO being played by a kid. A further insightful analysis based on numerical experiments demonstrates that it is the Kelvin waves propagating from the equatorial Indian Ocean that drive basin-wide intermediate circulation with a semi-annual cycle under the constraint law of the potential vorticity conservation. This finding highlights the critical role of equatorial Kelvin waves in driving the AS intermediate circulation, advancing our understanding of circulation dynamics in a marginal sea like the AS.