Radiative transfer to space affected by atmosphere?

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Discussion Overview

The discussion revolves around modeling radiation losses from a flat surface facing the sky at night, particularly focusing on how the atmosphere influences this process. Participants explore theoretical aspects, practical implications, and existing research methodologies related to radiative transfer in the presence of atmospheric conditions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant presents a basic model for heat flux, suggesting that the effective temperature of outer space is 3K, and questions how atmospheric effects alter this model.
  • Another participant notes that the infrared transparency of the atmosphere varies with humidity, indicating that this complicates the modeling process and suggests using satellite data for estimates.
  • A different participant argues that emissivity is wavelength-dependent and relates it to absorption, proposing that the heat transfer equation should be treated as an integral over wavelength.
  • One participant reiterates the initial question about atmospheric effects and mentions that some calculations use a sky temperature of 230K on clear nights, implying variability in the model based on atmospheric conditions.

Areas of Agreement / Disagreement

Participants express differing views on the impact of the atmosphere on radiation losses, with no consensus reached on a unified approach or model. Multiple competing perspectives on how to account for atmospheric effects remain present in the discussion.

Contextual Notes

Limitations include the dependence on specific atmospheric conditions such as humidity and temperature, as well as the variability in emissivity with wavelength. The discussion does not resolve how these factors quantitatively influence the modeling of radiation losses.

Mapes
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I'm trying to model radiation losses from a flat surface facing the sky at night. If we ignore radiative absorption/emission in the atmosphere, the heat flux is the well-known

Q=\epsilon\sigma(T_s^4-T_\infty^4)

where we have the emissivity, the S-B constant, the temperature of the surface, and where I would think T_\infty is the effective temperature of outer space, 3K.

How does the presence of the atmosphere affect this model? How have other researchers dealt with this complication?
 
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The IR transparency of the atmosphere is dependent on humidity. It would be a significant complication. I suppose you could get a reasonable estimate based on the view of Earth down from the top: http://www.goes.noaa.gov/ECIR4.html

With a known surface temperature and a measured temperature through the atmosphere, you can estimate the effect of sky transparency.
 
It's pretty easy: the emissivity is a function of wavelength. Becasue of conservation of energy, the emissivity = absoprtion. The heat transfer equation simply turns into an integral over wavelength.

The atmospheric absoprtion depends on pretty much everything, there's good computational models (LOWTRAN/MODTRAN/HITRAN) out there, some of which are public domain.
 
Mapes said:
I'm trying to model radiation losses from a flat surface facing the sky at night. If we ignore radiative absorption/emission in the atmosphere, the heat flux is the well-known

Q=\epsilon\sigma(T_s^4-T_\infty^4)

where we have the emissivity, the S-B constant, the temperature of the surface, and where I would think T_\infty is the effective temperature of outer space, 3K.

How does the presence of the atmosphere affect this model? How have other researchers dealt with this complication?

On most of the heat transfer calculations I've seen the sky temperature on a clear night was taken as 230K.
 

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