Sea ice concentration anomalies as long range predictors of anomalous conditions in the North Atlantic basin

Abstract

Long-range empirical forecasts of North Atlantic anomalous conditions are issued, using seaice concentration anomalies in the same region as predictors. Conditions in the North Atlanticare characterized by anomalies of sea surface temperature, of 850 hPa air temperature and ofsea level pressure. Using the Singular Value Decomposition of the cross-covariance matrixbetween the sea ice field (the predictor) and each of the predictand variables, empirical modelsare built, and forecasts at lead times from 3 to 18 months are presented. The forecasts of theair temperature anomalies score the highest levels of the skill, while forecasts of the sea levelpressure anomalies are the less sucessful ones.

To investigate the sources of the forecast skill, we analyze their spatial patterns. In addition, we investigate the influence of major climatic signals on the forecast skill. In the case of the airtemperature anomalies, the spatial pattern of the skill may be connected to El Ninño SouthernOscillation (ENSO) influences. The ENSO signature is present in the predictor field, as shownin the composite analysis. The composite pattern indicates a higher (lower) sea ice concentrationin the Labrador Sea and the opposite situation in the Greenland’Barents Seas during the warm(cold) phase of ENSO. The forecasts issued under the El Nino conditions show improved skillin the Labrador region, the Iberian Peninsula and south of Greenland for the lead timesconsidered in this paper. For the Great Lakes region the skill increases when the predictor isunder the influence of a cold phase. Some features in the spatial structure of the skill of theforecasts issued in the period of the Great Salinity Anomaly present similarities with thosefound for forecasts made during the cold phase of ENSO. The strength of the dependence onthe Great Salinity Anomaly makes it very difficult to determine the influence of the NorthAtlantic Oscillation.