The earths energybalance
MR ASKEW
The unequal heating of theatmosphere
Short wave radiation heats the earths surface.
The heated earth radiates lower energy, longwave, infrared energy back into the atmosphere
This heats the atmosphere
Eventually the heat is lost to space.
The incoming solar radiation which reaches the Earths surface is called insolation.
Insolation does not reach the earths surface equally because of the sphericalshape of the earth, more insolation received at the equator compared to thepoles.
It’s colder at the poles because:
1. The suns rays have to travel through thickeratmospheric layer and more incoming energylost through absorption, scattering and reflectionbefore reaching the earths surface.
2.Insolation is spread over a larger area
3. Albedo effect: reflection off the ice
Therefore
At the poles less insolation is absorbed and moreenergy is lost as radiated heat
At the equator more insolation is received andless energy lost as radiated heat.
The effects of unequal heating onthe earths energy balance
To maintain a balance heat energy is transferred from the tropics tothe poles.
Between the tropics the incoming solar rays are high, thereforedaytime hours are nearly consistent all year round. More energy isgained than lost, therefore there is an energy surplus.
In the polar regions the angle of incoming solar radiation is low,therefore more heat is reflected into space. The day time hourschange with the seasons.
More energy is lost than gained therefore there is an energy deficit.
The difference between energy gained and lost meansthere is an imbalance in the radiation budget at thetropics and the poles.
The atmosphere and oceans have more of the surplusheat energy at the tropics and the poles, this maintainsthe Earths overall energy balance.
The significance of the earths axis inrevolution around the sun
Intensity of insolation varies with the seasons of the year.
Seasons result from variations the suns height above the horizon andthe changing length of the day.
What causes the seasons?
The earth moves in an elliptical path around the sun called theecliptic.
Therefore the earths distance from the sun varies each year in aregular way.
Seasonal changes are caused by the earths varying distance fromthe sun, in combination with a number of factors.
Have a look at table 6 on pg 50
What are the seasonal effects ofthe energy balance?
Seasons have an effect on temperature.
More heat received in summer.
Earths rotational axis is tilted and the tilt stays the samethroughout the annual revolution around the sun.
It is summer in each hemisphere when the hemisphere istilted towards the sun.
Because the hemisphere tilted towards the sun haslonger day time hours and receives more insolation.
In winter receives less insolation and therefore cooler.
Twice a year the sun is directly overhead the equator = this is whenthe earth is at the equinox ( 21 March and 23 Sept)
The circle of illumination (the boundary between the sunlight anddarkness) will pass through both poles.
All places on earth have a 12 hour day and night, both hemispheresshare the amount of solar radiation
As the earth moves into the solstice position (21 June), the Nhemisphere is tilted towards the sun.
Therefore the longer days and shorter nights cause the Nhemisphere to receive more insolation and experience summer.
The S hemisphere is tilted away from the sun and results in winter,shorter days and longer nights.
21 December the earth moves into a solstice position again, the shemisphere tilts towards the sun and receives more insolation, resultsin summer conditions.
Complete activity 2 on pg 51