Impact of the Gulf Stream front on atmospheric rivers and Rossby wave train in the North Atlantic

Abstract

The Gulf Stream (GS) ocean front exhibits intense ocean-atmosphere interaction in winter, which has a significant impact on the genesis and development of extratropical cyclones in the North Atlantic. The atmospheric rivers (ARs), closely related with the cyclones, transport substantial moisture from the North Atlantic towards the Western European coast. While the influence of the GS front on extratropical cyclones has been extensively studied, its effect on ARs remains unclear. In this study, two sets of ensemble experiments are conducted using a high-resolution global Community Atmosphere Model forced with or without the GS sea surface temperature (SST) front. Our findings reveal that the inclusion of the strong GS front leads to approximately 25% enhancement of water vapor transport and precipitation associated with ARs in the GS region and a more pronounced downstream response in Western Europe, characterized by up to 60% (40%) precipitation increases (reductions) around Spain (Norway). The influence of the GS front on ARs is mediated by both thermodynamic and dynamic factors. The thermodynamic aspect involves an overall increase of water vapor in both the GS region and Western Europe, promoting AR genesis. The dynamic aspect encompasses changes in storm tracks and Rossby wave train, contributing to downstream AR shift. Importantly, we find the co-occurrence of ARs and the GS front is crucial for inducing deep ascending motion and heating above the GS front, which perturbs the deep troposphere and triggers upper-level Rossby wave response. These findings provide a further understanding of the complex interaction between the oceanic front in the western boundary current regions and extratropical weather systems and the associated dynamics behind them.

The Gulf Stream Front Amplifies Large-Scale SST Feedback to the Atmosphere in North Atlantic Winter

“…The contours in Figure 1d,f show the winter season mean SST in CTRL and in FLTR, respectively. For a detailed description of the model settings, please refer to our recently submitted paper [21]. By smoothing, the SST gradient was weakened by approximately 40% in the middle of the GS extension region (72 • W-47 • W), resulting in greatly reduced ocean-atmospheric interaction in the GS region [2,22].…”