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Linearity of Outgoing Longwave Radiation: From an Atmospheric Column to Global Climate Models

Author(s): Zhang, Yi; Jeevanjee, Nadir; Fueglistaler, Stephan

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Abstract: The linearity of global‐mean outgoing longwave radiation (OLR) with surface temperature is a basic assumption in climate dynamics. This linearity manifests in global climate models, which robustly produce a global‐mean longwave clear‐sky (LWCS) feedback of 1.9 W/m2/K, consistent with idealized single‐column models (Koll & Cronin, 2018, https// However, there is considerable spatial variability in the LWCS feedback, including negative values over tropical oceans (known as the “super‐greenhouse effect”) which are compensated for by larger values in the subtropics/extratropics. Therefore, it is unclear how the idealized single‐column results are relevant for the global‐mean LWCS feedback in comprehensive climate models. Here we show with a simple analytical theory and model output that the compensation of this spatial variability to produce a robust global‐mean feedback can be explained by two facts: (1) When conditioned upon free‐tropospheric column relative humidity (RH), the LWCS feedback is independent of RH, and (2) the global histogram of free‐tropospheric column RH is largely invariant under warming.
Publication Date: 25-Aug-2020
Citation: Zhang, Yi, Nadir Jeevanjee, and Stephan Fueglistaler. "Linearity of outgoing longwave radiation: From an atmospheric column to global climate models." Geophysical Research Letters 47, no. 17 (2020). doi:10.1029/2020GL089235.
DOI: doi:10.1029/2020GL089235
ISSN: 0094-8276
EISSN: 1944-8007
Type of Material: Journal Article
Journal/Proceeding Title: Geophysical Research Letters
Version: Final published version. Article is made available in OAR by the publisher's permission or policy.

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