Surface Energy Balance Flashcards
(9 cards)
Interpret diurnal cycles of Q*, latent heat and sensible heat fluxes in terms of location & surface characteristics
Q* = QH + QE + QG
Net all-wave radiation = sensible heat flux + latent heat flux + ground heat flux
Latent heat flux, Qe, is the energy involved in phase changes of water; this can be either evaporation (surface to air transfer) or condensation (air to surface transfer). The moisture gradient, turbulence and plant control through the process of transpiration influence it.
What are the three ways of energy flow?
Conduction = transfer of heat by electrons (QG)
Convection = transfer of heat by conduction in a moving medium, such as a fluid (QH and QE)
Radiation = transfer of heat by electromagnetic radiation (K↑ and L↑)
Explain the surface exchanges of latent heat (Qe) and sensible heat (Qh)
Latent heat flux, Qe, is the actual exchange of moisture between the surface and the atmosphere. It determines the moisture content of the atmosphere. It strongest during the day (e.g. puddle drying) and weakly positive at night (e.g. dew).
Sensible heat flux, Qh, is the actual exchange of heat between the surface and the atmosphere. It determines the temperature of the atmosphere. It warms (Qh is positive) during the day and cools (Qh is negative) at night.
Why is the Surface Energy Balance important?
Because it is the fundamental determinant of microclimates, particularly their thermal and moisture characteristics. The partitioning of Q* into QH and QE is determined by the relative abilities of the soil and atmosphere to transport heat.
How is QE and QH partitioned by a surface?
Q* is largely determined by the availability of water at the surface and the gradient between the surface and the atmosphere.
Energy always goes into latent heat first (i.e. evaporation occurs). Any water available at the latent heat flux will be cause it to be positive. Negatives values are usually and generally occur at night (i.e. condensation at surface). A peak in latent heat,QE, is variable and dependent on water and energy availability. A peak in sensible heat is more strongly related to Q* but can be affected by heat storage.
Latent heat describes . . .
The flow of water vapour away from (positive) or towards (negative) the surface
Sensible heat describes . . .
The flow of heat energy away from (positive) or towards (negative) the surface
Convection is the principle means of . . .
Transporting surplus daytime energy away from the surface
What does the Bowen ratio tells us about how QE and QH are partitioned by a surface?
β = QH / QE
Bowen ratio = sensible heat flux / latent heat flux
It is governed by the availability of water, however, the atmospheric temperature and atmospheric water content are also important.
β = 0.1 tropical oceans β = 0.1 – 0.3 tropical wet jungles β = 0.4 – 0.8 temperate forests & grasslands β= 2.0-6.0 semi-arid β = 10 deserts
