Atmospheric Energy

Atmospheric Energy

1. Primary source of energy- the Sun

   • sheds part of its mass as it radiates waves of electromagnetic energy and high energy particles into space.
   • Long term - accounts for all energy available to Earth.
   • Amount we receive into the atmosphere is controlled by four things.

2. Solar Output

   • Sun = black body = radiates and absorbs lights at the maximum rate possible
   • 1368 Wm-2 Is our solar constant (energy received at the top of the atmosphere)
     • can be affected by up to 0.1% due to sunspots (cooler spots on the sun) which have an 11-year cycle.
   • 53% near infra-red - 39% visible light - 8% ultraviolet

3. Distance from the Sun

   • The eccentricity of the Earth's orbit changes in length over time over a period of about 100,000 years. From near circular to an ellipse.
     • the eccentricity causes only minor variations to the total insolation budget but can have significant seasonal effects.
       • if the orbit was perfectly circular there would be no seasonal variation in solar radiation there is a difference of more than 6%.

4. Altitude of the Sun

   • Affects the amount of radiation received
     • The more directly overhead the more energy received per unit area.
     • At the equator Sun's rays are concentrated, at the poles the rays spread over a wider area.
   • affected by the season, time of day and latitude

5. Day Length

   • The tilt of the Earth's axis produces seasonality by varying day length in both hemispheres
     • E.g. Daylight at the poles can vary from 0-24 hours depending upon the season.
   • In summer, Earth is tilted towards the Sun (it also appears higher in the sky) giving more than 12 hours of sunlight making it warmer
     • The tilt has been shown to vary between 21.8 degrees to 24.4 degrees over a period of 41,000 years.