2.1 Diurnal Energy Budgets Flashcards
(22 cards)
Energy Budgets
Models which help analyse the heating & cooling of the atmosphere
Scale
- can be global
- local
Time
- day vs night
- seasonality
Different type of Radiation?
Shortwave
- Incoming solar radiation from the sun
- provides input during daytime energy budget
Longwave
- Outgoing radiation, re-radiated from the earth’s surface after it has been absorbed
- usually happens at night
- longwave radiation can be trapped by gases on the way out
What happens to incoming short wave
Reflected before ground 29% - so only 71% in system
Absorbed by Atmosphere 23% - so only 48% reaches ground
Absorbed 48%
What then happens to the 48% of absorbed energy
Reradiated 12% (LW) leaves space window
Sensible 5% vertically conduction & convection
Latent 25% vertically (evaporation)
Reradiated then reabsorbed is 6% (LW)
Latent Heat
Transfer of energy with a change in state
Sensible Heat
Transfer of energy without a change in state
Role of Clouds in Energy Budget
Reflection
- Reflect back into space, dependant on albedo and cover
- higher albedo = more reflection higher coverage = more reflection
- Cumulonimbus 92% albedo vs stratos 65%
Absorption
- They also play a big role in absorbing incoming heat
Reflecting LW
- can heat by reflecting re-radiated LW
- back to earth
Also vary temporally - over the year - more in autumn
And specially more over equator
Role of Ash, Smoke & Dust particles
Reflect & Scatter
- so less incoming radiation
- cooler earth
Episodic, wild fires & volcanos
Role of Albedo
- Higher = more reflection
Sea 10%, grass 25% snow 80%
Role of GHGs
More GHGs = more absorption
- water vapour CO2 etc
What are the 6 daytime energy budgets
- Incoming SW
- Absorption
- Reflection
- Latent Heat Transfer
- Sensible Heat Transfer
- Re-radiated heat LW
Evaluation of the role of incoming solar radiation in the daily energy budget?
- atmosphere’s only input
- therefore directly impacts all other inputs in the system
- variations over space & time; spacially - latitude, temporally - seasonally
Space
- strongest levels of insolation at equator
- when 90 degrees overhead, although shifts throughout the year with tilt
Evaluation of the role of reflected solar radiation in daytime energy budget?
Big
Effects
- how much radiation reaches the surface
- how much is absorbed
- how much is transferred by latent & sensible heat
- how much is re-radiated
overall decides how much the atmosphere warms
How?
Depends on Albedo;
- the proportion of sunlight reflected by a surface - due to colour
- clouds; thickness type etc - thicker = more - cumulonimbus 92% vs 65% stratus - coverage as well
- Ocean; varies - 4% during height of the day can go up to 80% when sun is low
- snow; 80% grass 24%
Evaluation of the role of Surface Absorption in daytime energy budget?
Effects
- amount of reflection
- amount of re-radiation as LW
Very important in nightime energy budget - less in day
How?
Albedo / Nature of surface:
- example; dark granite - low albedo & good conductor so high absorption vs limestone - lighter colour, so higher albedo poor conductor
Moisture
- moisture helps conductivity;
- e.g. wet sand is a very good conductor
Urbanisation
- materials used for building with have very high thermal capacities vs agricultural land (6x higher); so can absorb a lot more heat
- urban areas have many surfaces which can absorb - more surface area
- overall leads to more absorption in urban areas
Evaluation of the role of latent heat in daytime energy budget?
What does it do
- vertical transfer of energy from the surface to the upper atmosphere back out to space; change in state - evaporation
Effects
- high energy usage as turn water to liquid requires a lot of energy
- 25% of absorbed energy due due to this
- requires moisture
Evaluation of the role of sensible heat transfers in daytime energy budget?
What does it do
- Heat transferred vertically by convection or conduction
- doesn’t require a change in state
- 5% of absorbed energy (small)
Effects
- removal of heat energy from the surface during the day
- replaces it with cooler air
- explain convection; air is heated rises and cools in atmosphere - cooler air sinks and replaces it at the surface
- depends on the amount of energy at surface
Evaluation of the role of longwave radiation in the daytime energy budget?
Terrestrial radiation - radiation which has been absorbed by the earth’s surface and is re-radiated later on.
- responsible for the removal of heat
- can also be trapped by clouds etc
Night time Energy Budget Factors?
- Absorption - released as conduction
- Longwave radiation
- Sensible heat
- latent heat
Evaluate role of absorption in night time energy budget?
How?
- Energy absorbed during the day is re-released at night as conduction
- this is the only input of energy into the night time energy budget
- Effected by urbanisation due to higher surface area and greater thermal capacities = increase absorption so increased re-radiation
Evaluate role of latent heat transfers in night time energy budget?
(Radiation cooling)
Causes a gain due to radiation cooling:
Radiation cooling;
- The cold surfaces will cool the air above them
- if the air is cooled to the dew point temperature any water vapour will condense
- leads to condensation at the surface without the need for the air to rise up
- leads to deposition of moisture at the surface (dew)
- when the water vapour condenses it releases heat energy (latent heat) = gain in energy
Evaluate the role of sensible heat in the night time energy budget?
Very little sensible heat due to the lack of insolation which causes convection
However;
- some convection if due to advection (the heating and cooling due to wind) - warm wind will heat vice versa
Evaluate the role of longwave radiation in the night time energy budget?
Depends on clouds;
- Cloudless = energy escapes
- Cloudy = reradiation back to earth and warmer temps, depends on cloud type, coverage, thickness & albedo
