[SLS Pre-Defense] Phadtaya Poemnamthip

“Influence of El Niño–Southern Oscillation (ENSO) on Hydrodynamic Variability in a Coral Atoll Lagoon”

The El Niño–Southern Oscillation (ENSO) drives substantial interannual variability in atmospheric and oceanic conditions across the central equatorial Pacific. This study examines how ENSO-related changes in sea surface temperature, precipitation, and wind forcing affect the hydrographic structure and circulation of Kanton Island’s coral atoll lagoon using a high-resolution three-dimensional numerical model. Four 100-day periods representing contrasting ENSO phases were analyzed: the 2002/2003 El Niño (EN02), the 2015/2016 El Niño (EN15), the 2016/2017 La Niña (LN16), and the 2003/2004 ENSO-neutral period (NT03).
Lagoon temperature is primarily controlled by large-scale open-ocean sea surface temperature near the lagoon channel, but local air–sea heat exchange significantly modulates temperature in the shallow Line Reef and Back Lagoon regions. During both El Niño events, enhanced precipitation and cloud cover reduced incoming shortwave radiation, producing synoptic-timescale cooling episodes when lagoon temperatures became temporarily lower than adjacent open-ocean temperatures. Elevated El Niño rainfall also reversed lagoon salinity and density gradients relative to non–El Niño conditions, altering stratification and reversing the direction of baroclinic flow tendency.
Near-surface circulation reflects the superposition of wind-driven and baroclinic exchange flows. Scaling analysis using the Wedderburn number indicates baroclinic dominance at seasonal timescales, with wind forcing contributing more comparably during non–El Niño periods but weakening during El Niño events. Differences between EN02 and EN15 demonstrate that lagoon response depends not only on open-ocean warming but also on precipitation magnitude and wind variability. These findings provide a process-based framework for assessing ENSO impacts on coral atoll lagoon hydrodynamics.

Sack Lunch Seminar Series —
Informal seminar series within PAOC (Program in Atmospheres, Oceans, and Climate) that focuses on more specialized topics than the PAOC Colloquium. The presentations are either given by an invited speaker or by a member of PAOC and can focus on new research or discussion of a paper of particular interest.

Contact: sacklunch-committee@mit.edu