Chapter 9 - Midlatitude Mesoscale Ocean-Atmosphere Interaction and Its Relevance to S2S Prediction

Abstract

Mesoscale eddies in the ocean are the dynamical analog of atmospheric weather. Satellite observations have identified significant correlations between mesoscale sea surface temperature (SST) anomalies and near-surface atmospheric flow. A hierarchy of mechanistic simulations is carried out using high-resolution regional climate models to assess the impact of mesoscale SST anomalies in the North Pacific on atmospheric circulation above the boundary layer. By comparing ensembles of simulations using high-resolution SST boundary conditions at the surface to those using smoothed SST, it is demonstrated that oceanic mesoscale eddies in the Kuroshio Extension Region (KER) have both local and remote influences on the atmospheric storm track. The local influence is associated with increased vertical moisture flux in the presence of oceanic eddies, leading to enhanced diabatic heating and intensified baroclinic cyclogenesis. The remote influence manifests itself as a shift in the Pacific storm track that affects winter rainfall patterns over the West Coast of the United States. As oceanic mesoscale eddies persist and evolve on sub-seasonal to seasonal (S2S) timescales, it is argued that their interaction with atmosphere can contribute to S2S predictive skill. This highlights the need for increased horizontal resolution to represent this mode of air-sea interaction adequately in S2S forecast models.