What is the wet-bulb depression?

The wet-bulb depression is defined as the difference between the dry-bulb temperature (the regular air temperature) and the wet-bulb temperature, which is the lowest temperature that can be attained by evaporating water into the air at a constant pressure. This concept is critical in meteorology and thermodynamics as it helps to assess the humidity level in the atmosphere.

When the wet-bulb temperature is lower than the dry-bulb temperature, it indicates that the air is capable of evaporating moisture, hence providing insights into the moisture content and cooling potential of the air. The larger the wet-bulb depression, the drier the air; conversely, a smaller or zero wet-bulb depression suggests higher humidity. Understanding this difference is vital for various applications, including weather forecasting, comfort levels in environments, and agricultural practices.

The other choices pertain to different concepts in meteorology and atmospheric science. The measure of total moisture in the air relates to humidity measures, pressure altitude and density altitude involve different calculations of altitude in the atmosphere, and the rate of evaporation pertains to the specific processes of water transitioning from liquid to vapor, but does not encapsulate the relationship described by the wet-bulb depression.