Spatiotemporal Characteristics and Possible Causes of the Collapse of the Northern Hemisphere Polar Vortex

Changes in atmospheric circulation can be influenced by the collapse characteristics of the polar vortex, a significant system in the Northern Hemisphere. This study reveals the spatiotemporal evolution and causative mechanisms of the collapse of the Northern Hemisphere polar vortex, as well as the polar vortex collapse criteria, Mann–Kendall test, mutation year extraction, and physical mechanism analyses, based on the fifth-generation European Centre for Medium-Range Weather Forecasts (ECMWF) atmospheric reanalysis of the global climate (ERA5) data for 1980–2024. The main conclusions are as follows: (1) The collapse events, which primarily occurred in spring, and the collapse time exhibited a U-shaped trend. (2) The collapse period exhibited significant spatiotemporal nonuniformity, with shorter periods in 10–100 hPa, larger variations in 100–300 hPa, and longer periods in 300–500 hPa. (3) The collapse mutation propagated downward to lower layers, beginning in 10–30 hPa and concentrating between 1995 and 2005. (4) The momentum flux and heat flux exhibit meridionally concentrated structures in the middle–lower stratosphere. The transition layer forms a region of momentum and energy accumulation. In the lower levels, the heat flux weakens. (5) The polar vortex collapse results from enhanced lower-stratospheric instability, weakened transition-layer disturbances, and upward energy transfer from low-level convergence, together forming a characteristic U-shaped collapse structure.