Amplification of Winter Stationary Waves Reshaping Hydroclimate Extremes in Western North America

Abstract

This dissertation investigates how global warming amplifies Northern Hemisphere winter stationary waves and how such a change reshapes regional climate patterns. Through analysis of observational data, multi-model simulations, and numerical climate experiments, we establish a comprehensive framework for understanding anthropogenic forcing’s impact on atmospheric circulation. Our research reveals that anthropogenic greenhouse gas-induced warming drives a northward shift of the Asia-Pacific jet, enhancing interactions with the Alaska mountains and strengthening the upper tropospheric ridge over western North America. This process has transformed teleconnection relationships, with the North American Winter Dipole (NAWD) replacing the Pacific North American (PNA) pattern as the dominant mode of variability influencing regional hydroclimate. This dynamic is underpinned by the balance between two distinct mechanisms: tropical ocean warming and Arctic sea ice reduction. Using numerical climate modeling with streamfunction budget analysis, we demonstrate that tropical Pacific warming drives these changes primarily through western tropical warm pool convection generating vorticity divergence, while strengthening mid-latitude westerlies enhances vorticity advection – counter-balanced processes that maintain the amplified wave structure. Arctic sea ice loss operates differently, creating polar high-pressure anomalies that produce anomalous easterly winds and horizontally trapped wave propagation patterns. These amplified waves trigger unprecedented regional climate extremes, particularly in Alaska, where they increase winter precipitation while elevating summer wildfire risk by promoting vegetation growth in the abnormally wet seasons that subsequently serve as fuel during fire-conducive conditions during abnormally dry seasons. These findings reveal how climate change is fundamentally altering atmospheric circulation patterns, creating climate risks with significant implications for predicting and managing regional hydroclimate extremes across North America and potentially worldwide.