Gulf Stream Ocean Conditions Influence on Atmospheric Rivers

Extreme precipitation and wind events in Western Europe are driven by Atmospheric Rivers (ARs) developing over the North Atlantic Ocean. While extensive research has been conducted on the atmospheric dynamics of ARs in this region and their connection with the North Atlantic Storm Track, gaps persist in understanding how oceanic variability influences AR activity, particularly in the eddy-rich environment of the Gulf Stream extension. The enhanced ocean heat supply and high mesoscale eddy activity over these western oceanic currents increase the surface latent heat flux in the area, thereby increasing moisture availability in the lower atmosphere and potentially facilitating AR genesis.

This study focuses on evaluating the status of mesoscale eddies and oceanic heat flux within the Gulf Stream extension and their downstream impact on AR activity. To achieve this, we employ a high-pass Fourier Filter Transformation to isolate and then quantify the mesoscale eddy activity (smaller than ~500 km) of the Gulf Stream extension region in two high-resolution (0.25º) observational products for sea surface height and temperature. Additionally, we utilize heat transport data from the RAPID dataset to quantify the oceanic heat supply to the Gulf Stream extension region. Finally, we identify and track Atmospheric Rivers in the ECMWF reanalysis ERA5 dataset and calculate their intensity over the North Atlantic, including their landfall on the European West Coast.

Our analysis provides a spatial and temporal cross-correlation analysis between the Gulf Stream state (high and low pass eddy variance) and the AR activity downstream. Furthermore, we investigate temporal lags between various oceanic conditions and their impact on ARs, thereby identifying oceanic precursors for AR genesis. Consequently, our study establishes a novel statistical relationship between Gulf Stream state and AR activity, with a particular emphasis on the role of mesoscale features. This includes a comprehensive characterization of mesoscale eddy activity within the region, contributing to a deeper understanding of the mechanisms driving AR formation and propagation in Western Europe.