Yu Zhao Dissertation Defense

Title: Multi-Year Marine Heatwaves in the North Pacific: Two Variants, Formation Mechanisms, and Climate Impacts

Abstract: This dissertation investigates the emergence of multi-year marine heatwaves (MHWs) in the extratropical North Pacific—an increasingly prominent phenomenon with significant climate impacts. Two distinct variants are identified: one centered in the Gulf of Alaska and another off the Coast of Japan. Despite similar large-scale dynamics, each variant is linked to unique atmospheric wave patterns and trans-basin interactions that sustain warming across seasons and years. The Gulf of Alaska events are driven by trans-basin wave trains and Pacific–Atlantic feedbacks, while the Japan events are linked to a summer circumglobal wave pattern and seasonal interactions with the North Atlantic. These mechanisms explain the persistence and recurrence of MHWs under global warming. The study also demonstrates how these MHWs, together with El Niño and subtropical Pacific warming, contributed to the unusual U.S. winter precipitation in 2023–24. Findings highlight the importance of atmospheric wave train dynamics and trans-basin interactions in shaping marine heat extremes and their broader climate consequences.