Temperature Inversions and Isothermal Layers

Generally, as air rises and expands in the atmosphere, the temperature decreases. However, when the temperature of the air rises with altitude, a temperature inversion exists. Inversion layers are commonly shallow layers of smooth, stable air close to the ground. The temperature of the air increases with altitude to a certain point, which is the top of the inversion. The air at the top of the layer acts as a lid, keeping weather and pollutants trapped below. If the relative humidity of the air is high, it can contribute to the formation of clouds, fog, haze, or smoke resulting in diminished visibility in the inversion layer.

Inversion layers are shallow layers of smooth, stable air close to the ground. Normally, air temperature decreases with an increase in altitude, but during an inversion, the typical temperature profile with altitude is inverted and temperature increases with an increase in altitude.

Surface-based temperature inversions occur on clear, cool nights when the air close to the ground is cooled by the lowering temperature of the ground. The air within a few hundred feet of the surface becomes cooler than the air above it. Frontal inversions occur when warm air spreads over a layer of cooler air, or cooler air is forced under a layer of warmer air. In some cases, a subsidence inversion develops when a widespread layer of air descends. The layer is compressed and heated by the resulting increase in atmospheric pressure, and, as a result, the lapse rate of temperature is reduced.

Isothermal Layers

An isothermal layer is defined as a vertical column of air having a constant temperature with height.