Atmospheric anomalies in NP-DICE act to reinforce SST anomalies underneath also via anomalous mechanical mixing, turbulent heat fluxes (Miller et al. 1994), anomalous driving of the gyres (Sekine 1988), and by altering downward longwave radiation (Fig. 3). A local feedback loop in NP-DICE can be established, if the observed atmospheric anomalies are proven to be maint-ained in response to the midlatitude SST anomalies as simulated in some atmospheric GCMs (Peng et al. 1997).
An important issue still unsolved is what mechanism switches the polarities of anomalies so that the system acts as a delayed-action oscillator. We are not sure at this stage whether the switching is due to the gyre adjustment to the anomalous wind stress curl (e.g., Latif and Barnett 1994) or to the advection of thermal anomalies by the mean gyre circulation. In an attempt to obtain a clue for this issue, the smoothed SST anomaly at each location was correlated with the PC of our first mode while imposing various lags in years. Lag-correlation maps thus-constructed (Fig. 5) indicate significant precursory anomalies in KOIZ that appear 〜3 years in advance of the rapid development of SST anomalies along SAFZ with no tropical significant precursors. They also indicate a tendency of SST anomaly development in STFZ a few years after the maturity of the anomalies in SAFZ, as simulated in several coupled GCMs (e.g., Latif and Barnett 1994; Yukimoto et al. 1996).
