The rate of change of temperature with altitude (\(\frac{\text{d}T}{\text{d}z}\)). The rate of temperature decrease with increase in altitude which is expected to occur in an unperturbed dry air mass is \(9.8\times 10^{3}\ ^{\unicode{x26ac}}\text{C min}^{-1}\). This is called the dry @A00144@. The lapse rate is taken as positive when temperature decreases with increasing height. For air saturated with H₂O, the lapse rate is less because of the release of the latent heat of water as it condenses. The average tropospheric lapse rate is about \(6.5\times 10^{3}\ ^{\unicode{x26ac}}\text{C}\ \min ^{-1}\). The lapse rate has a negative value within an @I03146@ layer.