Diurnal Energy Budgets Flashcards
factors affecting diurnal energy budget
incoming + reflected solar radiation
albedo
sensible heat transfer
long wave radiation
latent heat transfer
Scattering
Particles send incoming radiation in different directions without changing the wavelength
6% of incoming SW radiation is scattered
preferential scattering of the blue wavelength of light causes the sky’s blue colour
Absorption
Solar radiation is retained by a substance and converted into heat energy
This is then converted into LW radiation emissions that come from the particle (Wien’s Law)
17% of incoming SW radiation is absorbed
94% of terrestrial radiation is absorbed in atmosphere, with some radiated to Earth’s surface (A C-R)
Reflection
Sunlight is redirected by 180 degrees after it strikes an atmospheric particle
This redirection causes a 100% loss of the insolation
Approximately 30% is reflected at the TOA (planetary albedo is 0.3)
Albedo
The earth’s average albedo is 31%
Fresh snow and ice reflect almost all of incoming solar radiation, 95%
Grass and crops reflect 25% and forests reflect 20%
Atmospheric counter-radiation (A C-R)
Greenhouse gases in atmosphere absorb most of the Earth’s emitted LW infrared radiation, which heats the lower atmosphere
In turn, the warmed atmosphere emits LW radiation, some of which radiates toward the Earth’s surface (Atmospheric Counter-Radiation), keeping our planet warm
Diurnal Energy Budget (daytime)
Less LW radiation escapes to space than insolation to the surface - energy surplus
A C-R amplifies positive energy balance
Hottest part of day is around 4pm as ground stores the energy throughout the day so it builds up
Excess heat used to evaporate water to become latent heat
More latent heat stored in water molecules during day
Diurnal Energy Budget (night time)
Energy deficit from 4pm-7am as total outgoing energy greater than incoming energy - energy deficit
This cools Earth’s surface
Water vapour condenses to water or freezes to ice, releasing latent heat from atmosphere
Dew and fog form from condensation of water vapour at night
Causes release of latent heat in form of LW radiation
Equation for net radiation balance at Earth’s surface
(incoming solar radiation + atmospheric counter-radiation) - (reflected solar radiation + outgoing terrestrial radiation)
Latent Heat
Energy used to convert matter into a different state
When evaporation occurs, heat is required to overcome molecular forces of attraction between water particles - heat is stored
Water condensing releases heat (endothermic)
Latent heat takes heat away from body (sweating)
Latent heat from condensation keeps air buoyant, causing clouds to billow up from their own latent heat
Precipitation
Condesnation and rain are most common forms by which latent heat energy is released into atmosphere
This allows clouds to be warmer than surrounding air
One of the key drivers of thunderstorms is this
Sensible Heat
Energy required to change temperature of a substance with no phase change
Occurs mostly by convection when there is a negative temperature gradient (conduction from surface to air above it, then convection)
Diurnal sensible heat transfers
When surface is warmer than air above, heat is transferred upwards into air as a positive sensible heat transfer
Transfer of heat raises air temperature but cools surface
If air is warmer than surface, heat is transferred from air to surface creating a negative sensible heat transfer
This could happen at night when sun goes down and there is no insolation
Here, ground cools due to LW emission and air directly above surface is warmer
Ground Heat Flux (GHF)
Movement of heat from surface to subsurface
There must be a temperature gradient
During day, surface tends to be warmer than subsurface so GHF moves towards subsurface (positive GHF)
At night, subsurface is warmer than surface as surface loses heat from outgoing LW, sensible and latent heat so GHF is negative
