What is indicated by a relative increase in temperature with height in the lower part of the atmosphere?

A relative increase in temperature with height in the lower part of the atmosphere is indicative of a temperature inversion. In a typical atmospheric profile, temperature decreases with height due to the cooling of air as it rises. However, during a temperature inversion, a layer of warm air traps cooler air near the ground. This can happen under specific meteorological conditions, such as during stable weather when the ground cools quickly at night, leading to warmer air above cooler air.

Temperature inversions are important because they can significantly impact weather patterns and air quality. Since the cooler air near the surface does not rise, it can prevent pollutants from dispersing, leading to increased pollution levels and affecting local climates. Additionally, inversions can cause unusual weather phenomena, such as fog or low clouds, due to the increased humidity levels at the surface.

The other options relate to different atmospheric phenomena but do not accurately describe the situation where temperature increases with height. The environmental lapse rate typically describes the normal decrease in temperature with altitude, while the pressure gradient and thermal expansion do not directly relate to temperature changes with height.