Earth Albedo

Author: CislunarSpace

Site: https://cislunarspace.cn

Definition

Earth albedo is the reflection and scattering of incoming solar radiation by Earth's atmosphere and surface back into space. The Earth's Bond albedo is approximately 0.30, meaning about 30% of incoming solar radiation is reflected. For stratospheric airships, earth albedo received by the bottom skin is an important directional thermal input.

Albedo Definition

Planetary Albedo

Aplanet=Reflected radiationIncoming radiation=FreflectedFincomingA_{planet} = \frac{\text{Reflected radiation}}{\text{Incoming radiation}} = \frac{F_{reflected}}{F_{incoming}}

Typical Values

Surface TypeAlbedo
Ocean0.05-0.15
Forest0.10-0.20
Desert0.25-0.40
Ice/Snow0.60-0.90
Cloud0.40-0.80
Global average0.30

Effects on Stratospheric Airships

Thermal Input Calculation

Earth albedo radiation received by bottom skin:

Qalbedo=αskin⋅ρearth⋅Isun⋅cos⁡θground⋅AbottomQ_{albedo} = \alpha_{skin} \cdot \rho_{earth} \cdot I_{sun} \cdot \cos\theta_{ground} \cdot A_{bottom}

Nighttime Heat Source

At night, earth albedo is zero, but Earth's own infrared radiation (~240 K) persists:

QIR,earth=εskinσTearth4AprojQ_{IR,earth} = \varepsilon_{skin} \sigma T_{earth}^4 A_{proj}

References

  • Liou K N. An Introduction to Atmospheric Radiation[M]. Academic Press, 2023.
  • Stephens G L, et al. Earth's Climate and Earth's Energy Budget[J]. Journal of Climate, 2024.