Convection-permitting projections of North American low-level jets and their mechanistic responses to climate change

Abstract. This study investigates the response of North American Low-Level Jets (LLJs) to climate warming using a high-resolution (4 km) convection-permitting Weather Research and Forecasting (WRF) simulation driven by the Pseudo-Global Warming (PGW) approach. The simulation reveals that the response of LLJs is highly heterogeneous across seasons and regions. Among the various LLJ systems over North America, the most robust and dynamically distinct responses to climate warming are identified in the Great Plains southerly LLJ and the California coastal northerly LLJ. For the Great Plains southerly LLJ, the research identifies a robust intensification in spring but a muted response in summer. Mechanism analysis indicates that the spring strengthening is driven by a steepened zonal thermal gradient and enhanced nocturnal stability, which amplifies the inertial oscillation. In contrast, increased nocturnal instability in summer suppresses this decoupling mechanism, preventing significant strengthening. Regarding the California coastal northerly LLJ, the simulation projects a weakening trend in summer. This is attributed to a reconfiguration of the land-sea thermal contrast, where enhanced local sea-breeze circulations disrupt the coastal baroclinicity that sustains the jet. These results highlight the necessity of convection-permitting scales in capturing the fine-scale thermodynamic and dynamic adjustments governing future LLJ evolution. The projected seasonal shifts in jet intensity and vertical structure have important implications for other interdisciplinary fields.