Speaker: Matt Luongo, University of Washington & NOAA Pacific Marine Environmental Lab
Title: The Tropical Pacific's Response to Hemispheric Energy Forcing: Subsurface Adjustment & Heat Transport"
Abstract: Changes in cross-equatorial ocean heat transport (OHT) damp hemispheric asymmetries in anomalous extratropical radiative forcing. Prior studies have suggested that these OHT changes occur due to wind-driven changes in the Indo-Pacific’s shallow subtropical cells (STCs) and buoyancy-driven changes in the deep Atlantic meridional overturning circulation. Here, I introduce a method of overriding surface ocean wind stress in a coupled global climate model (CGCM) to linearly partition the ocean’s response to anomalous extratropical forcing into surface buoyancy-driven and surface momentum-driven responses. In contrast with prior expectations, buoyancy-driven changes in the STCs are the primary driver of cross-equatorial heat transport in the Indo-Pacific’s response to Northern Hemisphere aerosol-like cooling. This buoyancy forced STC response arises from extratropical density perturbations that are amplified by the low cloud feedback in the Northeast Pacific marine stratocumulus regime.
While prior studies have explored the important role of surface ocean-atmosphere pathways in connecting the extratropics and tropics, I mechanistically explore the subsurface teleconnection (the so-called “oceanic tunnel”) further by using an ocean-only general circulation model forced by subtropical SST anomalies. Cooling in the Northeast Pacific low cloud deck dynamically adjusts the subtropical thermocline through baroclinic wave activity; within ten years the equatorial Pacific features a shoaled thermocline and La Niña-like cooling. This dynamically driven hemispheric temperature asymmetry drives an equatorially asymmetric subtropical cell adjustment, which transports heat to the cooled hemisphere and qualitatively matches our CGCM results. This overturning is a result of a basin-scale thermal wind response. I find similar equatorial responses when forcing is applied in the Northwest Pacific or the Southeast Pacific, highlighting the importance of wave activity for understanding this adjustment. These results provide a clearer understanding of how the tropical ocean adjusts to hemispheric energy forcing, which has important implications for climate sensitivity, tropical basin interactions, and historical observations of the tropical Pacific.
Bio: Matt Luongo is a CICOES Postdoctoral Research Fellow at the University of Washington and NOAA Pacific Marine Environmental Laboratory. He studies large-scale climate dynamics through the lens of physical oceanography and coupled ocean-atmosphere interactions. He received his PhD from Scripps Institution of Oceanography, UCSD in 2024.
Event details: In-person seminars are only available to CU ID holders.
