03-23-25, 10:26 AM
From HERE
“What we do have, via satellite spectroscopy, are measurements showing CO₂ absorbing and re-emitting infrared radiation. We measure the “back radiation” impinging on ground stations.”
Curtis and Goody (1956) Thermal Radiation in the Upper Atmosphere discuss the decay rates of vibrationally excited CO2 (CO2*), following absorption of a 15u photon.
Radiative decay lifetime is 0.43 sec. In the lower troposphere at 220 K and 1 atm, collisional lifetime is 15 usec. This means, at the surface, CO2* decays by collision 28,667 times faster than it decays radiatively. This disparity in rates is not controversial.
At the surface, then, 99.997% of CO2* decays by collision. Not radiatively. Collisional decay transfers K.E. into the atmosphere. This is the GHE of CO2.
The question then is how the energetic water cycle of evaporation, convection, condensation responds. That response determines the effect of the extra K.E. on sensible temperature.
15u phonons deliver 7975.1 J/mole. At 288 K, the Boltzmann fraction of thermally excited CO2* is 3.6%. At 1 atm, 99.997% of thermally excited CO2* will decay by collision. Not radiatively.
The density of dry air (STP) is 1.29 kg/m^3. MW is 28.96 gm/mol.=> 44.96 mol/m^3 => 2.71E25 molecules/m^3.
Of these 420E-6 are CO2 => 1.14E21 molecules/m^3. Of these, if all become CO2*, 1.14E22 decay by collision – the same number as the total, at 2 sig figs past the decimal.
The 3.6% of CO2 thermally excited at 288 K is 4.10E20 molecules/m^3. Of these, 99.997% decay by collision at STP.
The radiative decay flux is 0.00035% of the thermally excited CO2* => 1.4E16 photons/sec/m^3. Half of this is “back radiation” namely, 7.1E15 photons/sec/m^3.
First order, the numbers scale with atmospheric pressure. The collision/radiative decay rate disparity also scales with atm. pressure.
Curtis & Goody note that the collision/radiative rate ratio = 1 at 74 km. Collisional decay severely dominates CO2* decay throughout the entire troposphere.
That’s it for “back radiation.” K.E. by radiative transfer from CO2* to the atmosphere is negligible. “Back radiation” contributes nothing to the GHE.
The 288 K atmosphere will generally maintain a thermal radiation bath of intensity set by that temperature. This bath radiation propagates randomly in all directions.
It seems likely that the IR detected and assigned to “back radiation” is just the thermal bath representing the 288 K thermal background IR.
“What we do have, via satellite spectroscopy, are measurements showing CO₂ absorbing and re-emitting infrared radiation. We measure the “back radiation” impinging on ground stations.”
Curtis and Goody (1956) Thermal Radiation in the Upper Atmosphere discuss the decay rates of vibrationally excited CO2 (CO2*), following absorption of a 15u photon.
Radiative decay lifetime is 0.43 sec. In the lower troposphere at 220 K and 1 atm, collisional lifetime is 15 usec. This means, at the surface, CO2* decays by collision 28,667 times faster than it decays radiatively. This disparity in rates is not controversial.
At the surface, then, 99.997% of CO2* decays by collision. Not radiatively. Collisional decay transfers K.E. into the atmosphere. This is the GHE of CO2.
The question then is how the energetic water cycle of evaporation, convection, condensation responds. That response determines the effect of the extra K.E. on sensible temperature.
15u phonons deliver 7975.1 J/mole. At 288 K, the Boltzmann fraction of thermally excited CO2* is 3.6%. At 1 atm, 99.997% of thermally excited CO2* will decay by collision. Not radiatively.
The density of dry air (STP) is 1.29 kg/m^3. MW is 28.96 gm/mol.=> 44.96 mol/m^3 => 2.71E25 molecules/m^3.
Of these 420E-6 are CO2 => 1.14E21 molecules/m^3. Of these, if all become CO2*, 1.14E22 decay by collision – the same number as the total, at 2 sig figs past the decimal.
The 3.6% of CO2 thermally excited at 288 K is 4.10E20 molecules/m^3. Of these, 99.997% decay by collision at STP.
The radiative decay flux is 0.00035% of the thermally excited CO2* => 1.4E16 photons/sec/m^3. Half of this is “back radiation” namely, 7.1E15 photons/sec/m^3.
First order, the numbers scale with atmospheric pressure. The collision/radiative decay rate disparity also scales with atm. pressure.
Curtis & Goody note that the collision/radiative rate ratio = 1 at 74 km. Collisional decay severely dominates CO2* decay throughout the entire troposphere.
That’s it for “back radiation.” K.E. by radiative transfer from CO2* to the atmosphere is negligible. “Back radiation” contributes nothing to the GHE.
The 288 K atmosphere will generally maintain a thermal radiation bath of intensity set by that temperature. This bath radiation propagates randomly in all directions.
It seems likely that the IR detected and assigned to “back radiation” is just the thermal bath representing the 288 K thermal background IR.
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