Using outputs from the SNAPSI (Stratospheric Nudging and Predictable Surface Impacts) project, a new model intercomparison protocol, we assess models’ performance in representing the negative Pacific-North American (PNA) pattern in February 2018. Findings indicate that models initialized on January 25 struggled to reproduce the negative PNA pattern, while models initialized on February 8 initially matched the observed PNA pattern closely but later significantly underrepresented it. Our analysis delves into the potential factors influencing the representation of the negative PNA, emphasizing the importance of mid-latitude atmospheric processes in early February. Specifically, the Ural blocking coupled with a strengthened East Asian trough initiated the propagation of Rossby waves towards the North Pacific, crucial for developing the necessary positive anomalies for the negative PNA. Nevertheless, models initialized on January 25 struggled to capture the strengthened East Asian trough and subsequent Rossby wave propagation. Additionally, unusually warm sea surface temperatures (SSTs) over the mid-high latitude North Pacific in late February appear to be a response rather than a causal factor for the negative PNA. Stratospheric conditions had varying impacts on the PNA representation depending on the initialization dates. While the development of the negative PNA in the January 25 initialization appears independent of the stratospheric state, nudging the stratosphere towards observation for the February 8 initialization led to a positive trend in the PNA index around February 24. Factors like the Madden-Julian Oscillation and SST anomalies over the western Pacific and the Niño-3.4 region had limited influence on the negative PNA representation.

平流层对流层耦合、PNA模态、SNAPSI模式比较计划