Atmospheric Response to North Pacific SST: The Role ofOcean–Atmosphere Coupling*

Atmospheric response to a midlatitude winter SST anomaly is studied in a coupled ocean–atmosphere general circulation model. The role of ocean–atmosphere coupling is examined with ensemble experiments of different coupling configurations. The atmospheric response is found to depend critically on ocean–atmosphere coupling. The full coupling experiment produces the strongest warm-ridge response and agrees the best with a statistical estimation of the atmospheric response. The fixed SST experiment and the thermodynamic coupling experiment also generate a warm-ridge response, but with a substantially weaker magnitude. This weaker warm-ridge response is associated with an excessive heat flux into the atmosphere, which tends to force an anomalous warm- low response and, therefore, weakens the warm-ridge response of the full coupling experiment. This study suggests that the atmospheric response is associated with both the SST and heat flux. The SST forcing favors a warm-ridge response, while the heat flux forcing tends to be associated with a warm-low response. The correct atmospheric response is generated in the fully coupled model that produces the correct combination of SST and heat flux naturally.