{"id":3076,"date":"2020-02-17T15:20:32","date_gmt":"2020-02-17T14:20:32","guid":{"rendered":"http:\/\/klima-fakten.net\/?page_id=3076"},"modified":"2021-10-13T08:54:26","modified_gmt":"2021-10-13T07:54:26","slug":"downwelling-ir-how-real-is-it","status":"publish","type":"page","link":"https:\/\/klima-fakten.net\/?page_id=3076&lang=en","title":{"rendered":"Downwelling IR – what is it?"},"content":{"rendered":"
\"image_print\"<\/a><\/div>\n\n\n

Radiation budget<\/h4>\n\n\n\n

In climate science we usually find a „radiation budget“ in order to display the energy fluxes that determine the climate: <\/p>\n\n\n\n

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Radiation Budget of earth<\/a><\/figcaption><\/figure>\n\n\n\n

For a long time I have been wondering about the extremely high value \"333 \frac{W}{m^2}\" of a downwelling radiation called „Back Radiation, absorbed by the surface“, which appears to be (over-)compensated by the „Surface Radiation“ of a comparable value ( \"396 \frac{W}{m^2}\" ), which is split into the „Atmospheric window“ and an upwelling radiation of \"356 \frac{W}{m^2}\" into the atmosphere. Both downwelling and upwelling radiations are significantly larger than both the incoming SW radiation absorbed by the atmosphere (\"78 \frac{W}{m^2}\" ) as well as the outgoing LW radiation (\"169 \frac{W}{m^2}\"). <\/p>\n\n\n\n

Furthermore I was wondering about the strange phenomenon that there should be a radiation through the atmosphere apparently transporting thermal energy from higher altitude to lower altitude<\/strong>, which – in an atmosphere with lapse rate, where temperature decreases with altitude – is physically not possible because it would break the 2nd law of thermodynamics<\/strong>, which forbids spontaneous heat transport from a cold system to a warm system. So I questioned whether „downwelling radiation“ is in fact a real radiation at all – if it was real, then why would I not use it for heating my house instead of burning fossil fuels<\/strong> — catching downwelling radiation on an area of \"18 m^2\" would be enough to provide \"6 KW\" of permanent Energy supply. <\/p>\n\n\n\n

A thought experiment<\/h4>\n\n\n\n

So for myself I came to the conclusion, that the downwelling radiation must be a model artefact and the real energy transport must be associated with the difference between upwelling and downwelling radiation<\/strong>, which in fact moves heat from the warmer surface to the colder atmosphere. At best the downwelling radiation can „slow down“ the energy dissipation from the warmer body.
To clarify matters I made this thought experiment: There are 2 air parcels, a cold one \"p_1\" with temperature \"T_1\" and a hot one \"p_2\" with temperature \"T_2\" (\"T_1 < T_2\"), and they can „see“ each other – the light path is reversible. They both emit radiation, \"p_2\" emits more at all wavelengths due to Planck’s law, therefore losing more heat than \"p_1\" in the process of emission. The received radiation is only a part of what was emitted, and even if the full radiation from \"p_1\" was absorbed, \"p_2\" can never receive more radiation than it has lost by emission. Therefore the temperature of \"p_2\" must necessesarily be smaller after the observed radiation process. <\/p>\n\n\n\n

Sharing this conviction on Twitter quickly raised critical responses. But I was lucky in several ways: Most responses were polite and respectful, yet very clear that they would not accept the „denial“ of downwelling radiation<\/strong>. As a „proof“ they provided links to instruments that can actually measure downwelling radiation. <\/p>\n\n\n\n

Instruments for measuring downwelling IR<\/h4>\n\n\n\n

The typical instrument to measure downwelling IR is a pyrgeometer<\/a>. From its description we find the following features:<\/p>\n\n\n\n