Introduction
Continuous monitoring of changes of glacier mass balance is based on an imitational model of monitoring of mass balance. The model’s fundament is a supposition of the possibility of a change in correlation between annual values of mass balance, b a, and equilibrium line altitude (ELA) Reference Dyurgerov(Dyurgerov, 1984, 1988).
Verification of the model for the glacierization area was realized by measurements at Tuyksu Glacier (Zailiyskiy Alatau Range). A number of multiannual measurements of changes of b a and ELA a was used from 1957 to 1989. 40 values of b t and ELAt were obtained for the summer periods of 1987 to 1989. It is established that relations of ELAt(bt) conserve changes as the relations of ELAa(ba). The maximum deviations were observed during the extreme positive mass balance. At all altitudes, the relationship between ELAa and b a, as well as ELAt and bt is approximated by the hypsographic curve. With the linear approximation the errors reach 70 g cm−2 in conditions of extreme negative mass balance.
Conclusions
Simultaneous monitoring of mass balance was undertaken for the three glaciers: Tuyuksu, Sary-Tor (in the central Tien Shan) and Glacier No. 1 (in the eastern Tien Shan). During the summer period of 1989, the altitudinal gradient of mass balance db t/dz varied on these glaciers.
Tuyuksu Glacier and Glacier No. 1 showed the maximum differences between the variations of db t/dz. Glacier No. 1 has a positive db t/dz in the initial part of the ablation season, when b t increases with the elevation of ELA t. The most probable reason for the differences lies in the difference in the proportion of annual total precipitation occurring in summer. Because of different altitude gradients of db t/dz and ELA t/db t, the mass balances of the three glaciers do not vary simultaneously during summer, and at the end of the year have different sign magnitudes.
