Northeast Pacific Marine Heatwave Mechanism Inferred from Adjoint Sensitivities

• DOI: 10.1175/jcli-d-24-0274.1
• Publication Date: 2025-04-04T14:13:21Z
• Authors: Xiaoxue Wang; Armin Köhl; Detlef Stammer

Abstract A classic example of a marine heat wave (MHW) was the 2014 – 2016 warm event that spread across northeastern Pacific (NEP) Ocean. We use an adjoint sensitivity approach to shed new light on potential causes for such reoccurring NEP MHW events. The study is based Massachusetts Institute Technology general circulation model (MITgcm) and its adjoint, which mean top 100 m temperature during different target years set as objective function, separately two regions (145°∼ 160°W, 48°∼ 56°N) (130°∼ 145°W, 40°∼ 48°N). Resulting sensitivities show years, local turbulent surface flux dominant atmospheric driver, with air temperature, specific humidity longwave radiation leading up 80% anomaly NEP; normal this only about 60%. In contrast, increased wind typically does not lead occurrence it associated deepening mixed layer. find horizontal advection, i.e., impact basin-wide ocean circulation, be less important year; but could act preconditioning through role in climate oscillations. Response analysis shows forcing anomalies occurring within 3 months (from October December) prior year play critical driving MHW. reconstruction using various periods suggests 6-month conditions should have predictive skill next year. Reconstruction includes 36-month performs better than persistence.