Year ELA AAR b_n sigma SIGMA b_n 1956 1530 0.89 1.15 0.5 1.15 1957 -1.34 1.0 -0.19 1958 2100 0.28 -1.90 0.5 -2.09 1959 1725 0.56 -0.30 0.5 -2.39 1960 1730 0.56 -0.28 0.5 -2.67 1961 1675 0.64 0.47 0.5 -2.20 1962 1700 0.59 0.21 0.5 -1.99 1963 1900 0.42 -0.58 0.5 -2.57 1964 1645 0.70 0.63 0.5 -1.94 1965 1950 0.40 -0.56 0.5 -2.50 1966 1655 0.68 0.34 0.5 -2.16 1967 1675 0.64 0.34 0.5 -1.82 1968 1850 0.45 0.03 0.5 -1.79 1969 1660 0.67 0.71 0.5 -1.08 1970 1825 0.47 -0.39 0.5 -1.47 1971 1580 0.83 1.15 0.5 -0.32 1972 1600 0.80 0.40 0.5 0.08 1973 1730 0.56 -0.14 0.5 -0.06 1974 1505 0.91 2.00 0.5 1.94 1975 1620 0.75 0.67 0.5 2.61 1976 1.42 1.0 4.03 1977 -1.24 1.0 2.79 1978 0.51 1.0 3.30 1979 1970 0.39 -1.15 0.5 2.15 1980 2020 0.36 -1.61 0.5 0.54 1981 2030 0.35 -1.31 0.5 -0.77 1982 1645 0.70 0.75 0.5 -0.02 1983 1610 0.77 1.34 0.5 1.32 1984 1660 0.67 0.49 0.5 1.81 1985 1665 0.66 0.42 0.5 2.23 1986 1910 0.41 -0.92 0.5 1.31 1987 1750 0.53 -0.79 1.0 0.52 1988 1625 0.74 0.22 1.0 0.74 1989 1725 0.56 -0.64 1.0 0.10 1990 1850 0.45 -1.18 1.0 -1.08 1991 1750 0.53 -0.79 1.0 -1.87 1992 1850 0.45 -1.18 1.0 -3.05 1993 1900 0.42 -1.35 1.0 -4.40 1994 2050 0.34 -1.75 1.0 -6.15 1995 1650 0.69 -0.01 1.0 -6.16 1996 1750 0.53 -0.79 1.0 -6.95 1997 1700 0.59 -0.49 1.0 -7.44 1998 1825 0.47 -1.11 1.0 -8.55 1999 1500 0.92 1.09 1.0 -7.46
ELA is the late season altitude of the equilibrium line in meters above the National Geodetic Vertical Datum of 1929, AAR is the fraction of the glacier area above that altitude, b_n is the net balance in water equivalent meters, sigma is its estimated standard error, and cumulative values SIGMA b_n are since the end of the 1955 ablation season.
Values for 1956-1997 are from Conway et al (1999), which adjusted b_n given by Armstrong (1989) to be consistent with measured volume changes of the glacier; it also extended the record to later years by applying to late-season observations of the ELA the relation (in terms of the AAR) obtained in earlier years when both b_n and the ELA were measured. That relation was also used to get values for 1998 and 1999.
Although large sigma are ascribed to b_n in individual years, cumulative values over selected periods (between measurements of volume change) are more closely constrained: 1.9 m over 1957-87, 2.8 m over 1987-95, 3.2 m over 1957-95. Years when b_n was measured have sigma = 0.5, others 1.0.
Values here reflect the best judgment of H. Conway and L. A. Rasmussen. The mass balance program was suspended in 1999.