Mechanisms of North Pacific Jet on Winter North American Temperature Dipole

To understand the causes of extreme temperature dipoles in North America during winter, we analyse atmospheric circulation, the westerly jet stream, and the sea surface temperature (SST) background based on reanalysis data. Our study reveals the role of the positive Pacific-North American pattern (PNA⁺) in driving sub-seasonal temperature dipoles on North America. The results indicate that a weakened North Pacific jet favors the formation of the temperature dipole. Additionally, North Pacific SSTs can modulate the structure and strength of the temperature dipole by influencing the jet stream. Specifically, during the positive phase of the Pacific decadal oscillation (PDO) in winter, a meridionally oriented wave train structure related to PNA⁺ events is more easily formed, with the North Pacific westerly jet stream shifting southward. This structure contributes to a "warm northwest-cold southeast" temperature anomaly pattern on North America. Conversely, during the positive phase of the Victoria SST pattern, the mid-latitude jet stream is weakened. As a result, the high-pressure system associated with PNA⁺ shifts westward, while the eastern low-pressure system persists. This forms a horizontal wave train structure, which strengthens the intensity of the "west warm-east cold" surface air temperature dipole anomaly on North America associated with PNA⁺.