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Definition:
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A model of mass balance in which surface ablation is estimated as a function of temperature, usually near-surface air temperature measured either on the glacier or at the nearest weather station; temperatures may also be taken from upper-air soundings, meteorological reanalyses or climate models. A leading form of temperature-index model is the positive degree-day model, in which a degree-day factor represents the dependence of ablation on temperature. Temperature-index models are valuable because they require only simple input variables and perform well when suitably calibrated, for example by allowing for the differences in reflectivity between surfaces of ice and snow by choosing a smaller degree-day factor for snow than for ice.
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