Identification of frequency changes in synoptic circulation types and consequences for glacier mass balance in Norway

Abstract

The cumulative net mass balances of maritime glaciers in Norway display a net surplus during the period 1963–2000. The article seeks to establish the causal mechanisms that resulted in the positive net balances occurring on Norwegian maritime glaciers. To achieve this, a Temporal Synoptic Index (TSI) was derived for a 30-year period for a number of synoptic meteorological stations in Norway. The TSI is derived using Principal Components Analysis (PCA) and subsequent clustering of component scores to classify days for both winter and summer seasons. Findings indicate that the occurrence of ‘warm’ type air masses during the summer months have increased in frequency, particularly since the late 1980s. A reduction in the frequency of ‘cold’ cluster types during the winter months is evident after this period, while the frequency of ‘warm’ types, with an increased moisture carrying capacity, has increased in frequency. The frequency occurrence of these key air mass types is shown to be significantly related to glacier mass balance during both the accumulation and ablation season. Winter air mass types from maritime source regions act to enhance accumulation and suppress ablation, while summer continental source types suppress accumulation and enhance ablation.