The earths energy balance MR ASKEW

The unequal heating of the atmosphere  Short wave radiation heats the earths surface.  The heated earth radiates lower energy, long wave, 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 spherical shape of the earth, more insolation received at the equator compared to the poles.

It’s colder at the poles because:  1. The suns rays have to travel through thicker atmospheric layer and more incoming energy lost through absorption, scattering and reflection before 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 more energy is lost as radiated heat  At the equator more insolation is received and less energy lost as radiated heat.

The effects of unequal heating on the earths energy balance  To maintain a balance heat energy is transferred from the tropics to the poles.  Between the tropics the incoming solar rays are high, therefore daytime hours are nearly consistent all year round. More energy is gained 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 hours change with the seasons.  More energy is lost than gained therefore there is an energy deficit.

 The difference between energy gained and lost means there is an imbalance in the radiation budget at the tropics and the poles.  The atmosphere and oceans have more of the surplus heat energy at the tropics and the poles, this maintains the Earths overall energy balance.

The significance of the earths axis in revolution around the sun  Intensity of insolation varies with the seasons of the year.  Seasons result from variations the suns height above the horizon and the changing length of the day.  What causes the seasons?  The earth moves in an elliptical path around the sun called the ecliptic.  Therefore the earths distance from the sun varies each year in a regular way.  Seasonal changes are caused by the earths varying distance from the sun, in combination with a number of factors.

Have a look at table 6 on pg 50

What are the seasonal effects of the energy balance?  Seasons have an effect on temperature.  More heat received in summer.  Earths rotational axis is tilted and the tilt stays the same throughout the annual revolution around the sun.  It is summer in each hemisphere when the hemisphere is tilted towards the sun.  Because the hemisphere tilted towards the sun has longer 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 when the earth is at the equinox ( 21 March and 23 Sept)  The circle of illumination (the boundary between the sunlight and darkness) will pass through both poles.  All places on earth have a 12 hour day and night, both hemispheres share the amount of solar radiation  As the earth moves into the solstice position (21 June ), the N hemisphere is tilted towards the sun.  Therefore the longer days and shorter nights cause the N hemisphere 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 s hemisphere tilts towards the sun and receives more insolation, results in summer conditions.   Complete activity 2 on pg 51