A theoretical approach to glacier equilibrium-line altitudes using meteorological data and glacier massbalance
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Based on a close exponential relationship between mean ablation-season temperature and winter precipitation at the equilibrium-line altitude (ELA) of 10 Norwegian glaciers, three equations are derived. The first equation enables calculation of the minimum altitude of areas climatically suited for glacier formation, and is termed the altitude of instantaneous glacierization (AIG). Equation (2) is derived based on the ‘principle of terrain adaptation’, enabling quantification of the glacial buildup sensitivity (GBS) in presently non-glaciated areas. The theoretical climatic temperature-precipitation ELA (CTP-ELA) in presently non-glaciated areas is calculated in equation three by combining GBS with terrain altitude. Mass-balance records from four modern glaciers (Ålfotbreen, Nigardsbreen, Storbreen and Gråsubreen) situated in maritime to continental climate regimes in southern Norway are used to test these equations. Correlation between AIG and net balance measurements (bn) yielded correlation coefficients of r = –0.80 to r = –0.84. Calculated AIGs correspond well with observed ELAs on Ålfotbreen, Nigardsbreen and Gråsubreen, while it deviates from the observed ELA on Storbreen; the latter is probably due to leeward accumulation of wind-blown snow on this cirque glacier. Based on this approach, regional representative climatic ELAs can be calculated for non-glaciated areas with instrumental records of ablation-season temperature and winter precipitation.