Key role of western boundary currents in wintertime Euro-Atlantic blocking
In this study, we aim to identify the sources of the atmospheric heat and moisture involved in wintertime Euro-Atlantic blocking events using a Lagrangian approach based on NCEP CFSR. Using an atmospheric dispersion model, we track atmospheric particles backward in time from the blocking centres located at 500 hPa, and estimate the associated turbulent heat fluxes whenever the particles fall within the planetary boundary layer over the ocean. Our results indicate that approximately half of the particles released from the blocking centres has undergone moist processes over the course of 10 days before arrival at the blocking centres. These particles influenced by moist processes acquire lower potential vorticity compared to the dry counterpart, implying the central role of the moist processes in blocking events. We found that approximately 70% of these particles receive heat and moisture locally from the Atlantic basin and about 25% of them from the Pacific, before swiftly ascending and thus undergoing latent heating. In particular, our results point towards the importance of the western boundary currents and their extensions in both basins in providing substantial amount of heat and moisture to these particles that make up of the central part of the atmospheric blocking.