Lecture 7: Earth's energy budget/balance

Question 1

INSOLATION = INCOMING SOLAR RADIATION

Answer 1

• Incoming solar radiation is mostly at an oblique angle and not vertical.
• As a result the same amount of radiative energy is being distributed over a
larger surface area.
• On average the incoming solar radiation, distributed over the whole surface of
the Earth, equals to one quarter of the solar constant.

Question 2

SOLAR RADIATION PATHWAYS

Answer 2

• Absorption:
Radiative energy converted to other forms of energy by gases or particles in the atmosphere
• Reflection:
Radiative energy is reflected back into space when hitting a surface
• Scattering:
Radiative energy is
(at least partly) redirected by air molecules and particles
• Transmission: Radiative energy passes through the atmosphere

Question 3

SCATTERING OF INCOMING SOLAR RADIATION

Answer 3

• Light that bounces off a surface at the same angle at which it strikes is reflected.
• In the atmosphere, light from the sun is deflected in all kinds of directions. This process is called scattering (diffuse light).
• Depending on the size of the object the sunlight falls on, we distinguish between geometric scattering, Mie scattering, and Rayleigh scattering.
• Clouds are made of water droplets that deflect light by geometric scattering.
• Dark clouds have large cloud droplets which absorb light, with rain likely.
• When particle size becomes smaller a process called selective scattering begins, where different wavelengths are scattered more or less efficiently.
• Pollutants often scatter daylight resulting in a brownish haze

Question 4

RAYLEIGH SCATTERING

Answer 4

Air molecules (e.g. N2) result in Rayleigh scattering. In this process the shorter (blue) wavelengths are scattered more efficiently than the long (red) wavelengths.