The Role of the Ocean in Midlatitude, Interannual-to-Decadal-Timescale Climate Variability of a Coupled Model

Abstract Three 1000-yr climate simulations with an atmospheric general circulation model (AGCM) coupled to, respectively, a slab mixed layer model, an ocean GCM, and responding to yearly repeating daily sea surface temperature (SST) and sea-ice coverage climatology derived from the fully coupled run were analyzed and compared. When coupled to a slab mixed layer, surface air temperature (SAT) and SST are strongly coupled and the reddening is significantly larger than in the case of coupling to a dynamically active ocean. A simple one-dimensional stochastic model is developed to explain the different spectra of SAT above land and ocean. It is argued that ocean advection generating SST variability that does not match the principal modes of SAT above the ocean is the main factor in damping SAT variability. The variability of SAT and 800-hPa geopotential height (GEO) and covariability of SST–SAT and SST–GEO have been analyzed, and it is found that coupling does not change the dominant patterns of atmospheric v...