Atmosphere-ocean feedback processes in the North Atlantic

It is well known that the climate change over the North Atlantic is dominated by coupled patterns of variability of the North Atlantic Oscillation (NAO) in the atmosphere and a tripole in sea surface temperature (SST) anomalies. Results of coupled general circulation model (CGCM) experiments and a linear model diagnosis indicate that a weak positive feedback is at work between the above atmosphere-ocean patterns through the surface heat flux anomalies, which lead to the persistence of one polarity of anomalies during a winter season, against the local thermal damping and the stochastic forcing due to internal atmospheric dynamics. In addition, the SST anomalies in winter tend to recur in the following winters with a help of the so-called reemergence mechanism associated with the seasonal cycle of the ocean mixed layer depth. Because of the two processes, the positive feedback and reemergence, it is expected that the NAO/tripole SST anomalies may be predictable beyond a year. We attempt to discuss the possibility using CGCM simulations.

This abstract was submitted to the special session "On midlatitude air-sea interaction and its linkage to the tropics", organized by Dr. Mike Alexander.