Predictability of seasonal precipitation in the Nordic region

Abstract

Predictability of seasonal precipitation in the Nordic countries (Denmark, Finland, Iceland, Norwayand Sweden) is investigated using a nine-member ensemble of atmospheric general circulation modelsimulations with prescribed sea-surface temperature from October 1950 until March 1999. The simulationsand corresponding observations from 65 stations in the Nordic countries are used to identifylarge-scale patterns of seasonal precipitation, the predictability of which is investigated. Subsequently, the identified large-scale patterns are used in a statistical downscaling of the model simulated precipitation.The downscaling, which is of the model output statistics type, yields seasonal predictions for theindividual stations. The model simulations of precipitation are compared to predictions of precipitationdirectly from observed sea-surface temperature using a statistical prediction method and no dynamicmodel. The two different methods give consistent results. It is demonstrated that seasonal precipitationin the Nordic region contains a weak predictable signal in several seasons. The most skilful predictionscan be made in spring, especially in the April’June season when precipitation appears to be influencedboth by tropical and North Atlantic sea surface temperature. In particular, the North Atlantic Oscillationin winter appears to influence the North Atlantic sea-surface temperature in spring, which in turn hasan effect on precipitation in Scandinavia.