Amplitude: Amplitude is a parameter characterizing the annual or diurnal fluctuation of soil temperature around an average value. An annual amplitude is half the difference between maximum and minimum daily average temperatures in a year. While a daily amplitude is half the difference between maximum and minimum temperatures in a day.

Damping depth: Damping depth is a constant characterizing the decrease in amplitude with an increase in distance from the soil surface. It is defined as (2D_h/w )^1/2, where D_h is the thermal diffusivity and w is the frequency of a temperature fluctuation. For annual fluctuation w =2p /365 d^-1, while for diurnal fluctuation w =1 d^-1.

Thermal diffusivity: Thermal diffusivity is the change in temperature produced in a unit volume by the quantity of heat flowing through the volume in unit time under a unit temperature gradient. It can be calculated from thermal conductivity and volumetric heat capacity.

Time lag: Time lag is the number of days from an arbitrary starting date to the occurrence of the minimum temperature in a year.