The adiabatic cooling rate of a rising parcel of air which is saturated (see saturated air), and in which condensation is taking place as it rises, so that the energy release of the latent heat of vaporization moderates the adiabatic cooling. The reduction of the rate of cooling below the dry adiabatic lapse rate of 9.8 °C/km varies with temperature. This results from the greater energy release by condensation from air at higher temperatures. Thus at a given atmospheric pressure, air at 20 °C may have an SALR as low as 4 °C/km, whereas at -40 °C the SALR may be close to 9 °C/km. The stability or instability of the atmosphere at any given time for vertical motion is determined by whether the environmental lapse rate of temperature within it is less than or greater than the adiabatic lapse rate (i.e. less than or greater than the rate of decrease of temperature of rising parcels of air).
Subjects: Earth Sciences and Geography.