What condition occurs when the air at ground level is cooler than the air above it?

A temperature inversion occurs when the normal temperature gradient of the atmosphere is reversed, resulting in cooler air at ground level and warmer air above it. In this situation, the cool air near the surface is trapped by a layer of warmer air above, which can lead to various atmospheric phenomena, including fog, smog, and reduced air quality. This condition is significant in the context of herbicide application because it affects the dispersion and movement of pesticide vapors and can result in unintended harm to non-target areas if applications are made under inversions when air is stable and pollutants accumulate near the surface.

This phenomenon is distinct from other weather conditions; for example, high-pressure systems typically bring stable weather and clear skies, low humidity relates to the moisture content of the air rather than temperature stratification, and wind shear refers to changes in wind speed or direction which can cause turbulence but does not directly relate to temperature differences in the atmosphere. Understanding temperature inversions is crucial for safe and effective herbicide application.