| Term: | Specific mass balance |
| Definition: |
Mass balance expressed per unit area, that is, with dimension [M L-2] or [M L-2 T-1]; see specific. The prefix 'specific' is not necessary in general. The units in which a quantity is reported make clear whether or not it is specific. Specific mass balance may be reported for a point on the surface, a column of unit cross-section, or a larger volume such as an entire glacier or a collection of glaciers. In the latter two cases the term 'mean specific mass balance' has been used, although the adjective 'mean' is also not necessary. The definition of 'specific' apparently offered by Meier (1962) has led to some confusion. He wrote... Quantities measured at a point will first be discussed. [They] should all be prefaced by the word specific ...Specific budget terms have dimensions of [length] or [length]/[time]. The confusion arises because of the primacy given by Meier to water-equivalent dimensions ('[length]'). The adjective 'specific' indicates that the quantity has dimension [M L-2] or [M L-2 T-1], not that it is being measured at a point. The adjective 'point', as in point mass balance, should be used when clarity is needed. The unit of area lies in the horizontal plane, not a plane parallel to the glacier surface. For mass-balance purposes this rule applies even when the surface is vertical. For example, at a calving front the frontal ablation is equal to the mass of the entire volume lost by calving, melting and sublimation. If quoted as a specific quantity it is divided by the horizontal area over which the balance is to be stated, such as that of the entire glacier for a glacier-wide mass balance. The glaciological usage is not that which prevails in some other sciences, where often a specific quantity is either a dimensionless ratio of the value of a property of a given substance to the value of the same property of some reference substance, or is a quantity expressed per unit mass. IHPGlacierMassBalance
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