The exchange of energy between the earths surface and overlying atmosphere involves four important processes which are (1) absorption and emission of natural electromagnetic radiations by the surface, (2) thermal conduction of heat energy within the ground, (3) turbulent transfer of heat energy towards or away from the surface within the atmosphere and (4) evaporation or water stored in the soil or condensation of atmospheric water vapour onto the surface (The Surface Energy Balance, n.d.). Everything that has a temperature gives off radiation. The sun is extremely hot and emits an extreme amount of radiation. Shortwave radiation, which the sun gives off, contains a higher intensity of radiation. The Earth also emits radiation, but is much cooler than the sun so emits long wave radiation, as it is less intense (Penn State University, 2013).
Shortwave radiation (visible light) contains a lot of energy; long wave radiation (infrared light) contains less energy. Solar energy enters our atmosphere as shortwave radiation in the form of ultraviolet (UV) rays and visible light. The ground heats up and re-emits energy as long wave radiation in the form of infrared rays. Latent heat is the energy absorbed by or released from a substance during a phase change from a gas to a liquid or solid, whilst sensible heat is the energy required to change the temperature of a liquid, gas or solid with no phase changes involved (The Surface Energy Balance, n.d.).
H = Sensible heat flux represents the loss of energy by the surface by heat transfer to the atmosphere. The temperature of the surface and atmosphere controls sensible heat flux.
?E = Latent heat flux is loss of energy from the surface due to evaporation (The Surface Energy Balance, n.d.).
The processes of evaporation, condensation, sublimation, freezing and melting control the conversion of latent heat to sensible forms of heat and vice versa. The temperature of a ground, water or ice surface and the air above the surface varies depending on the time of day, year and latitude of the earth, controlling these heat fluxes (Guest, 2017). Internal heat from the deep interior can affect the surface temperature. Soil temperature also varies throughout the year due to soil type, the temperature of the air above it, rainfall and radiation. This affects the variability of the surface temperature (Reysa, 2015). Downward ground heat flux. This is the loss of energy by heat conduction through the lower boundary. Ground heat flux rates depend on the time of day as during daylight hours, more heat may be absorbed by the surface. During warmer seasons, more radiation is available, therefore there is more potential for the ground to saturate heat. The nature of the surface also affects ground heat flux, for example an icy surface has a high albedo of around 80%, meaning the radiation will be transmitted away from the surface, resulting in a negative ground heat flux (Bretherton, 2017).These components make up the overall surface energy balance equation:Rn = Net surface radiationRn = H + ?E + G This equation represents the gain of energy by the surface from radiation; it will be a positive number when the radiation is towards the surface.