Global mass balance and the length-of-day variation

AbstractUntil now, an assumption of surface-parallel glacier flow has been used to express the vertical velocity component in terms of the horizontal velocity vector, permitting all three velocity components to be determined from synthetic aperture radar interferometry. We discuss this assumption, which neglects the influence of the local mass balance and a possible contribution to the vertical velocity arising if the glacier is not in steady state. We find that the mass-balance contribution to the vertical surface velocity is not always negligible as compared to the surface-slope contribution. Moreover, the vertical velocity contribution arising if the ice sheet is not in steady state can be significant. We apply the principle of mass conservation to derive an equation relating the vertical surface velocity to the horizontal velocity vector. This equation, valid for both steady-state and non-steady-state conditions, depends on the ice-thickness distribution. Replacing the surface-parallel-flow assumption with a correct relationship between the surface velocity components requires knowledge of additional quantities such as surface mass balance or ice thickness.

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Can the mass balance of the entire glacier area of the Tien Shan be estimated?

Annals of Glaciology ◽

10.3189/1992aog16-1-173-179 ◽

1992 ◽

Vol 16 ◽

pp. 173-179

Author(s):

M.B. Dyurgerov ◽

M.G. Kunakhovitch ◽

V.N. Mikhalenko ◽

A. M. Sokalskaya ◽

V. A. Kuzmichenok

Keyword(s):

Mass Balance ◽

Vertical Profile ◽

River Basins ◽

Annual Runoff ◽

Snow Accumulation ◽

Tien Shan ◽

Exponential Dependence ◽

Glacier Area ◽

Equilibrium Line Altitude ◽

Boundary Area

The total area of glacierization of the Tien Shan in the boundary area of the USSR is about 8000 km2. The computation of mass balance was determined for this area in 12 river basins.In computation procedure, the vertical profile of snow accumulation in these regions and exponential dependence of variation of ablation with altitude are used. Thus the mass balance in each basin, bn, was calculated on the basis of these curves and represented in its relation with the equilibrium line altitude (ELA). It is shown that the relation ELA = f(bn) is linear when the range of bn values is close to zero, and in all altitude intervals this relation can be described by hypsographic curves, in all basins bn positive up to an ELA elevation of 3450 to 3500 m a.s.l. For average annual altitude of ELA, bn is negative for all regions. So the glaciers of these mountains add about 4 km3 of water to the total annual runoff.

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