Sensible Heat and Latent Heat Transfer

The most familiar form of heat storage and transport is known as sensible heat—it's what you feel when you touch a warm object. When we use a thermometer, we are measuring sensible heat. Sensible heat transfer moves heat from warmer to colder objects by conduction when they are in direct contact. Sensible heat is also transferred by convection when a fluid such as the atmosphere or ocean carries heat energy away from a surface.

In contrast, latent heat—or hidden heat—cannot be measured by a thermometer. It is heat that is taken up and stored as molecular motion when a substance changes state from a solid to a liquid, from a liquid to a gas, or from a solid directly to a gas. For example, when liquid water changes to water vapor, or ice changes to liquid water, heat energy is absorbed from the surroundings. This is why sweat cools the skin. Latent heat energy is stored in free fluid motion of the liquid water molecules or in the fast random motion of free water vapor molecules. When the vapor turns back to a liquid or solid, the latent heat is released, warming the surroundings.

In the Earth–atmosphere system, latent heat transfer occurs when water evaporates from a moist land surface or from open water, moving heat from the surface to the atmosphere. That latent heat is later released as sensible heat, often far away, when the water vapor condenses to form water droplets or snow crystals. On a global scale, latent heat transfer is a very important mechanism for transporting large amounts of heat from one region of the Earth to another.