The theoretical rate of decrease of temperature with increasing height in the atmosphere. If heat is neither gained nor lost from the air parcel under consideration, then the lapse rate is said to be adiabatic. For air parcels of differing water content this value is different. [Atmospheric Change: An Earth System Perspective, T.E. Graedel and Paul J. Crutzen, W.H. Freeman and Co., New York, 1993, p.431.]