Radiation Balance Flashcards
Radiation Balance
The balance between incoming and outgoing radiation that determines mean climate on Earth
What makes up the radiation balance?
Solar flux, terrestrial flux and circulation of the atmosphere and ocean
What is solar flux?
The amount of shortwave radiation hitting the earth from the sun.
What is terrestrial flux?
The amount of longwave radiation leaving Earth
What gases absorb longwave radiation in our atmosphere?
H2O, CO2, CH4, N2O, CFCs, with H2O vapour being very important.
What determines how much radiation is received by Earth?
Solar output (solar constant varies from sunspot minima to maxima), varying distance for sun due to orbital parameters, sun’s altitude, albedo.
Influences of geographical variation of radiation budget: Sun’s Altitude
- Influences insolation: has more spread at lower altitude.
- Longer path lengths through the atmosphere scatter more
- Longer path length also increases albedo.
Influences of geographical variation of radiation budget: Albedo
- Ice and snow covered poles are very reflective whereas oceans are not.
- Clouds have a massive effect on global albedo related to the types and properties of cloud.
What determines longwave radiation emission?
Temperature. Hotter thing emit more radiation, hence most is emitted at lower latitudes where we see warmer temperatures.
Geographical distribution of radiation balance
There are massive imbalances of energy across earth, with a net annual loss at the poles and net gain in the tropics. It is the atmosphere and ocean that act to redistribute this imbalance.
Forces in Atmosphere: Gravity
Constant downward acting force.
Forces in Atmosphere: Coriolis Force
Occurring due to Earth’s rotation, it is an apparent force occurring when there is movement relative to a rotating frame.
Forces in Atmosphere: Centrifugal Force
Experienced by a rotating fluid as an outward apparrent force, and is balanced by a real inward, centripetal force.
Forces in Atmosphere: Pressure Gradient Force
Present where regions have different pressures, moving from high pressure to low pressure.
Forces in Atmosphere: Frictional Force
Friction is a retarding force due to its ‘rubbing’ against neighbouring parcels, occurring when bodies in contact move with different velocities. It is greatest near the ground for air or sea floor for water.
Dimensions of Forces on Earth
As the earth is 3D we have to consider forces in all dimensions:
u = zonal wind velocity, east to west.
v = meridional wind velocity, north to south
w = vertical wind velocity
Coriolis Force: General Form
This force is proportional and acts at a right angle to velocity, being stronger for faster moving things. It increases with latitude and is 0 at the equator.
In the N hemisphere it deflects to the right, and left in the S hemisphere (always east), and occurs only if there is motion relative to a rotating frame (earths spin).
Gravity vs Centrifugal Force
- Gravity pulls us to the central mass of Earth, and centrifugal force opposing the centripetal force pulls us out to space due to rotation.
- The centrifugal force pulls us away from Earth’s rotating axis, rather than central mass, meaning they are not acting in opposite directions.
- Earth has adjusted to this imbalance by bulging at the equator which is around 21km wider.
Pressure Gradient Force
All systems want to equilibriate, hence high pressure moves to low pressure to balance out.
Stronger gradient means stronger force, higher density means weaker force.
This is the key driving force for movement of air.
What contributes to the motion of air?
Relative Acceleration = coriolis force + pressure gradient force + gravitational force + frictional force.
This determines if there is a net force in action that would cause an air parcel to accelerate
