What type of lapse rate is defined as 3°C per thousand feet?

The type of lapse rate defined as 3°C per thousand feet is known as the dry adiabatic lapse rate. This rate describes how the temperature of an unsaturated air parcel decreases as it rises in the atmosphere by expanding due to reduced pressure. For every 1,000 feet (or about 300 meters) of ascent, the temperature of the air decreases approximately 3°C (or about 5.4°F).

This concept is key in understanding how temperature and pressure interact in rising air parcels, which is especially important in meteorology and aviation. The dry adiabatic lapse rate applies strictly to unsaturated conditions, meaning the air does not contain enough moisture to form clouds or precipitation as it rises. If the air becomes saturated, the moist adiabatic lapse rate would come into play, which decreases at a slower rate due to the release of latent heat during condensation.

While the standard lapse rate generally refers to an average atmospheric decrease, the environmental lapse rate varies based on the specific conditions of the atmosphere at a given time and place. Thus, the dry adiabatic lapse rate is a specific measurement relevant under certain conditions, distinguishing it from the other rates described.