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Keywords:

  • Atlantic variability;
  • North Atlantic oscillation–Arctic oscillation;
  • storms;
  • Labrador Sea;
  • sea ice

Abstract

The wintertime atmospheric response to imposed sea-surface temperature and sea-ice extent changes in the Labrador Sea has been investigated by means of ensemble simulations with an atmospheric general circulation model. Low temperatures and heavy ice conditions in the Labrador Sea produce a statistically significant (at 95% confidence) negative North Atlantic oscillation–Arctic oscillation (NAO–AO) response. Conversely, reduced sea-ice extent in the Labrador Sea produces a positive NAO–AO response. The two simulations with opposite sea-ice conditions in the Labrador Sea exhibit a maximum mean wintertime difference of 4–5 hPa in sea-level pressure corresponding to a substantial and statistically significant change in the NAO–AO index of 0.7 standard deviations. The large-scale response to a local perturbation of sea-ice conditions is associated with marked changes in the transient eddies (synoptic storms). Changes in the sea-ice cover cause changes in low-level baroclinicity that perturb the travelling baroclinic disturbances, which then bring the signal downstream to manifest a non-local Atlantic-wide response. The atmospheric response suggests that the sea ice in the Labrador Sea is able to provide an important negative feedback on long-term NAO–AO variations. Copyright © 2004 Royal Meteorological Society