Insolation and Earth's Energy Balance

Insolation and Earth's Energy Balance

• Insolation: Incoming solar radiation reaching Earth's atmosphere or surface.
• Only about 52% of insolation reaches the Earth's surface. The remaining is absorbed or reflected by water, dust, clouds, and the Earth's surface.
• Albedo: The reflectivity of an object. It is the extent to which the object reflects sunlight.
• Greenhouse effect: Reflected heat, in the form of long-wave radiation, is trapped in our atmosphere. This warms the planet.

Energy Balance Variations

• Latitudinal variations: There's a net gain of solar energy in tropical latitudes and a net loss towards the poles.
• Insolation differences: Insolation rises from approximately 50 joules at the poles to 275 joules at the equator. Terrestrial radiation varies less (120 joules at the poles to 200 joules at the equator).
• Energy transfer: Atmospheric circulation transfers energy from lower (surplus) to higher (deficit) latitude areas. Without this transfer, lower latitudes would overheat and higher latitudes would cool.

Tropical vs. Polar Regions

Tropical Regions

• Solar concentration: Sun's rays are more concentrated, higher in the sky.
• Atmospheric passage: Less atmosphere to pass through, less energy loss.
• Vegetation: Dense vegetation absorbs radiation, low albedo.
• Sunlight angle: Sun is directly overhead year-round.

Polar Regions

• Solar concentration: Sun's angle is lower, rays are more spread out and less intense.
• Atmospheric passage: Rays travel further through the atmosphere, more reflection.
• Surface reflection: Snow and ice have high albedo, reflecting a large percentage of solar radiation.
• Solar energy receipt: Six months of no direct solar energy due to Earth's orbit and tilt.