One half of the difference between winter mass balance and summer mass balance, (Bw Bs)/2. Summer mass balance is generally negative because ablation dominates in the summer season. A more general definition, (Ca Aa)/2 or one half of the Annual exchange, could be offered in terms of Annual accumulation and Annual ablation, but these quantities are so seldom measured that a calculation from seasonal balances is more practicable. The balance amplitude tends to be large in maritime climates, in which accumulation is large, and small in continental climates, in which accumulation is small. In consequence the mean balance amplitude is well correlated with the interannual variability of Annual mass balance, and, when it can be estimated from climatological information, has been used as an estimator of the magnitude of the Annual mass balance itself.