Glacier Mass Balance and Regime: Data of Measurements and ...

w, bs, ac(AAR), aa(1-AAR), mm/yr30002500200015001000500bwac*AARbsaa*(1-AAR)0Fig. 2.31986 1987 1988 1989 1990Fig.2.3. Storglaciären (Sweden), seasonal mass balance components: winter (b w), summer (bs),net accumulation (ac) and net ablation (aa); ac and aa recalculated as averages for the entire area of theglacier. The coefficients of regression between b w and ac*(AAR), and bs vs aa*(1-AAR) are both 0.96.components. Thus, strictly speaking, mass balance measured by the glaciological method is notnecessarily equal to volume change, but may be nearly identical to it for many glaciers, where thesecomponents are relatively small. Annual (b a) and net (b n) balances (Mayo et al., 1972) may differfrom year to year, although the difference is not likely to be substantial for longer-term averages.2.1.4. Definition of equilibrium-line altitude (ELA).By definition, the line separating the ablation area of a glacier from the accumulation areais the equilibrium line (Meier, 1962). Thus the equilibrium-line altitude (ELA) marks the area on theglacier where accumulation is balanced by ablation. ELA is usually defined by direct measurementsin the field, at the end of a hydrological year (at the end of a summer). It is clear that ELA is aproduct of climate, or the weather conditions, of this particular year, and changes annually in close26