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Abstract
Abstract. We present and validate a set of minimal models of glacier mass balance variability. The most skillful model is then applied to reconstruct 7735 individual time series of mass balance variability for all glaciers in the European Alps and Scandinavia. Subsequently, we investigate the influence of atmospheric variability associated with the North Atlantic Oscillation (NAO) on the glaciers' mass balances. We find a spatial coherence in the glaciers' sensitivity to NAO forcing which is caused by regionally similar mechanisms relating the NAO forcing to the mass balance: in southwestern Scandinavia, winter precipitation causes a correlation of mass balances with the NAO. In northern Scandinavia, temperature anomalies outside the core winter season cause an anti-correlation between NAO and mass balances. In the western Alps, both temperature and winter precipitation anomalies lead to a weak anti-correlation of mass balances with the NAO, while in the eastern Alps, the influences of winter precipitation and temperature anomalies tend to cancel each other, and only on the southern side a slight anti-correlation of mass balances with the NAO prevails.
Highlights
The North Atlantic Oscillation (NAO) is the most prominent mode of atmospheric variability over the North Atlantic Ocean and Northwestern Europe (Visbeck et al, 2001; Wanner et al, 2001; Hurrell et al, 2003)
Where the subscript clim denotes the monthly mean climatological values, the subscript NAO denotes monthly anomalies associated with NAO variability and the prime denotes all other anomalies
The NAO influence is strongest in winter, with positive NAO anomalies leading to above-average temperatures all over Europe, while the precipitation anomalies tend to be positive in northern Europe, and negative around the Mediterranean (Fig. 1, see Hurrell et al, 2003, for a detailed discussion of the impacts of the NAO on European climate)
Summary
The North Atlantic Oscillation (NAO) is the most prominent mode of atmospheric variability over the North Atlantic Ocean and Northwestern Europe (Visbeck et al, 2001; Wanner et al, 2001; Hurrell et al, 2003). I.e., stronger than normal pressure gradient between Iceland and Azores, stronger than normal westerlies, above normal precipitation and mild temperatures prevail across the eastern North Atlantic and northwestern Europe. By influencing precipitation and temperature anomalies, the NAO exerts control over glacier mass balances. Pohjola and Rogers (1997) find that positive mass balances of Scandinavian glaciers during the 80s and 90s were caused by strong westerlies over the northeastern Atlantic, which are linked to the NAO. Reichert et al (2001) find that for Nigardsbreen, an eastern outlet glacier from the Jostedalsbreen ice cap, the impact of winter precipitation overrules the impact of positive temperature anomalies, leading to a correlation of mass balance and NAO. By influencing precipitation and temperature anomalies, the NAO exerts control over glacier mass balances. Pohjola and Rogers (1997) find that positive mass balances of Scandinavian glaciers during the 80s and 90s were caused by strong westerlies over the northeastern Atlantic, which are linked to the NAO. Reichert et al (2001) find that for Nigardsbreen, an eastern outlet glacier from the Jostedalsbreen ice cap, the impact of winter precipitation overrules the impact of positive temperature anomalies, leading to a correlation of mass balance and NAO. Nesje et al (2000) show that the control of the NAO over the glacier mass balance in Scandinavia gradually decreases with increasing continentality (i.e., towards the east), and Rasmussen and Conway (2005) find correlations between the Arctic Oscillation and mass balances of 12 Scandinavian glaciers to be stronger than between NAO and mass balances
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