The adiabatic lapse rate and the environmental lapse rate are terms used in meteorology to describe the change in temperature with increasing altitude in the Earth's atmosphere. The major difference between the two lies in the mechanisms that drive the temperature changes.
- Adiabatic Lapse Rate: The adiabatic lapse rate refers to the rate at which the temperature changes with increasing altitude for a parcel of air that expands or compresses without exchanging heat with its surroundings. There are two types of adiabatic lapse rates:
Dry Adiabatic Lapse Rate (DALR): The dry adiabatic lapse rate applies to a parcel of unsaturated air, meaning its relative humidity is less than 100%. As the unsaturated air parcel rises or descends, it expands or compresses due to changes in atmospheric pressure. The dry adiabatic lapse rate is approximately 9.8°C per kilometer (or 5.5°F per 1,000 feet) and represents the rate at which the air temperature changes solely due to the expansion or compression of the air parcel.
Moist Adiabatic Lapse Rate (MALR): The moist adiabatic lapse rate applies to a parcel of saturated air, where the relative humidity is 100%. When saturated air rises or descends, it undergoes adiabatic processes while also experiencing condensation or evaporation of water vapor. The rate of temperature change is slower in saturated air due to the release or absorption of latent heat during condensation or evaporation. The moist adiabatic lapse rate varies but is typically around 6°C per kilometer (or 3.3°F per 1,000 feet).
- Environmental Lapse Rate: The environmental lapse rate refers to the actual rate at which the temperature changes with increasing altitude in the surrounding atmosphere. It represents the observed vertical temperature profile and is influenced by various factors such as solar radiation, heat transfer, advection, and local weather conditions. The environmental lapse rate can vary widely and is typically around 6.5°C per kilometer (or 3.6°F per 1,000 feet) on average.
The major difference between the adiabatic lapse rate and the environmental lapse rate is that adiabatic lapse rates describe the temperature change of rising or descending air parcels assuming no heat exchange with the environment, while the environmental lapse rate describes the actual temperature change in the surrounding atmosphere. The environmental lapse rate takes into account various processes and factors that affect temperature changes at different altitudes, including radiation, convection, and advection, among others.