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 conditions 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 quantify the mesoscale eddy activity (smaller than ~500 km) of the Gulf Stream extension region in a high-resolution (0.125º) satellite product for the sea surface height. Additionally, we utilise different observational products (OAFlux, ARGO and RAPID) to quantify the surface heat fluxes, the ocean heat content in the Gulf Stream extension region and the oceanic heat supply through the Florida Straight. Finally, we identify and track Atmospheric Rivers in the ECMWF reanalysis ERA5 dataset over the North Atlantic.

Our analysis provides a spatial and temporal cross-correlation analysis between the Gulf Stream state 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 characterisation of mesoscale eddy activity within the region, contributing to a deeper understanding of the mechanisms driving AR formation and propagation in Western Europe.