  Teleconnections between the tropical and the extratropical climates are often
considered as a potential source of long-term predictability at seasonal to
decadal time scales in the extratropics. This claim is taken up in the present
work by investigating the predictability of a coupled ocean-atmosphere
extratropical model under a one-way forcing generated by a tropical model. Both
models display a chaotic dynamics, and the dominant variable of the
extratropical model displays a high correlation with the tropical forcing in
the reference simulation, inducing a low-frequency variability signal in the
extratropics.
  Numerical experiments emulating the presence of initial condition errors in
the tropical model are conducted to clarify their impact on the predictability
in the extratropics. It is shown that: (i) The correlation skill of the
dominant observable affected by the forcing is considerably degraded at
interannual time scales due to the presence of initial condition errors in the
tropics, considerably limiting the potential of teleconnections; (ii) averaging
of an ensemble of forecasts -- with a small number of members -- may
substantially improve the quality of the forecasts; and (iii) temporal
averaging may also improve the quality of the forecasts (at the expense of
being able to forecast extreme events), in particular when the forcing affects
weakly the observable under interest.
