Historical changes in wind-driven ocean circulation drive pattern of Pacific warming.

Area of Science:

• Oceanography
• Climate Science
• Atmospheric Science

Background:

• The tropical Pacific warming pattern since the 1950s features distinct warming centers in the western Pacific (WP) and eastern Pacific (EP).
• This pattern includes equatorial central Pacific (CP) cooling and hemispheric asymmetry in the subtropical eastern Pacific.
• The precise mechanisms driving this observed warming pattern are still under scientific debate.

Purpose of the Study:

• To investigate the role of wind-driven ocean circulation in the observed tropical Pacific warming pattern.
• To decompose ocean heat changes and attribute them to different forcing mechanisms.

Main Methods:

• Utilized ocean heat decompositions.
• Analyzed two coupled model large ensembles.
• Simulated scenarios with suppressed wind changes to isolate radiative forcing effects.

Main Results:

• Historical radiative forcing, without wind changes, generates subtropical northeastern Pacific warming, creating hemispheric asymmetry extending to the tropical western Pacific.
• Tropical eastern Pacific warming is driven by cross-equatorial winds linked to hemispheric asymmetry.
• Southward warm Ekman advection from off-equatorial westerly wind anomalies near 5°N is the primary driver, not thermocline adjustment.

Conclusions:

• Wind-driven ocean circulation significantly influences the tropical Pacific warming pattern.
• Climate models' inability to replicate observed central Pacific cooling highlights deficiencies in simulating equatorial oceanic processes.
• Further research is needed to improve the simulation of equatorial oceanic processes and thermal structures in climate models.