What is an isothermal lapse rate?

An isothermal lapse rate is characterized by the temperature remaining constant with increasing altitude. This means that as you ascend through the atmosphere, the temperature does not change; it stays the same at different levels. This scenario often occurs when a layer of warm air traps cooler air below it, leading to a stable atmosphere where no temperature gradient exists.

When considering temperature behavior in the atmosphere, an isothermal lapse rate is distinct compared to other lapse rates where temperature typically decreases with altitude in the troposphere due to adiabatic cooling or increases due to specific thermal inversions. In simpler terms, in situations described by the isothermal lapse rate, there is no typical decrease in temperature with height, which is common in most atmospheric layers. This condition is important for meteorological phenomena and understanding atmospheric stability.