Abstract
Lakshmi. N. Sridhar
Chemical Engineering Department
University of Puerto Rico
Mayaguez, PR 00681
*Corresponding author: Lakshmi. N. Sridhar.
Abstract
The El Niño–Southern Oscillation (ENSO) is a dominant driver of interannual climate variability, strongly influencing global weather patterns, tropical cyclone activity, and extreme climate events. This study develops and analyzes a reduced-order nonlinear ocean–atmosphere model that captures the essential mechanisms underlying ENSO dynamics, focusing on the interaction between sea surface temperature anomalies and thermocline depth anomalies in the tropical Pacific. The model incorporates positive feedback between ocean and atmosphere, delayed negative feedback through ocean adjustment processes, and nonlinear saturation effects that constrain system growth. These interactions give rise to self-sustained oscillations representing El Niño and La Niña cycles. A key feature of the system is the emergence of a Hopf bifurcation, marking the transition from a stable climate state to periodic climate variability. This transition is characterized through analytical and numerical Jacobian analysis, confirming the onset of oscillatory behavior. The resulting limit cycles provide a simplified representation of ENSO-driven climate oscillations that modulate global weather extremes, including variations in rainfall, drought patterns, and tropical cyclone activity across multiple ocean basins. The framework further highlights how small changes in ocean–atmosphere coupling strength can significantly alter climate stability, emphasizing the sensitivity of the tropical climate system. Overall, the model provides a physically interpretable and mathematically tractable description of ENSO dynamics, offering insight into the mechanisms governing climate variability and its far-reaching impacts on global weather and extreme events.
