The rate of decrease of temperature with elevation, −∂T/∂z, or occasionally ∂T/∂p, where p is pressure. The concept may be applied to other atmospheric variables (e.g., lapse rate of density) if these are specified. The environmental lapse rate is determined by the distribution of temperature in the vertical at a given time and place and should be carefully distinguished from the process lapse rate, which applies to an individual air parcel. See autoconvective lapse rate, superadiabatic lapse rate.