The Sun is the main source of energy for processes at the Earth's surface and is the driving force behind the weather, climate, life, ocean currents, hydrologic cycle, etc.
9% ultraviolet radiation (not visible to our eyes; causes tanning,
burns and cancer in skin)
41% visible radiation (eyes are sensitive to this form of radiation)
50% infrared radiation (sensible on the skin as heat; used by reptiles for body temperature regulation)
Earth only receives radiation from the Sun on one half of the sphere.
Approximately one third of all incoming radiation is reflected directly back into space.
Infrared and Ultraviolet radiation are absorbed by the Earth and reemitted as infrared radiation
Radiation is lost to space on both the night side and day side of the sphere.
Two major dips in the outgoing radiation curve occur.
Water and carbon dioxide in the atmosphere absorb certain wavelengths of infrared radiation, blocking it from escaping into space.
The amount of incoming solar radiation equals the amount of outgoing radiation.
Not quite a true balance - the Earth's interior is also losing heat which increases the amount of outgoing radiation
Changes in the amounts of incoming radiation vs. outgoing radiation can have dramatic effects on the global climate.
Insolation is Incoming Solar Radiation
The amount of insolation received at a given location is primarily controlled by two factors:
Angle of the incoming radiation and the Exposure Time
Daily variation
- one side of the globe receives radiation while the other does not
- Day vs. Night.
Seasonal Variation
- for areas in the mid- to high latitudes there is a noticable difference in the length of a day in summer vs. a day in winter.
Daily Variation
- at sunrise the angle at which the sun's rays strike the Earth's surface are very low, but a noon the angle is much higher, much more intense radiation is recieved.
Latitude Variation
- During the Equinox, the subsolar point is at the Equator, the intensity of solar radiation is 100%, but north or south the
sun's rays strike the Earth at an angle, thus decreasing the angle at which the rays strike the surface.
Seasonal Variation
- For the northern hemisphere, in the wintertime the sun is always low in the southern sky, a lower angle means lwer intensity of radiation recieved at the surface, but in the summertime it is much higher
- more intense radiation.
Both the variation in exposure time and the angle of the insolation need to be considered together to understand the intensity of insolation being recieved at the surface at any given location.
