What is it about?

High clouds can warm the atmosphere by absorbing and backscattering the surface emitted electromagnetic radiation. However, the backscattering contribution is often neglected for speeding up climate simulations. This study performs a climate simulation with the backscattering contribution included. Inclusion of the backscattering contribution causes (1) additional atmospheric warming over the tropics and surface warming over polar areas and the Tibetan Plateau, (2) increased east‐west wind speeds in the lower and upper troposphere over the tropical Pacific, and (3) poleward shift of the midlatitude westerly winds in Southern Hemisphere summer. The long‐lasting equatorward biases of the midlatitude westerly winds in climate simulations may be reduced if the backscattering contribution is taken into account.

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Why is it important?

The study highlights the importance of cloud greenhouse effect in shaping atmospheric circulations over both tropics and midlatitudes.

Perspectives

Previous studies showed correlations between wet and dry spells over midlatitudes and tropical sea surface temperatures, such as those studies from the Lamont-Doherty Earth Observatory at Columbia University. However, to the best of my knowledge, the dynamic link between tropical sea surface temperatures and droughts and floods over midlatitudes has not been made clear. The correlation between the midlatitude westerly winds and the cloud greenhouse effect found in this study, as also found in some previous studies, suggests the upper-level cloud heating gradient between low and high latitudes may link surface temperatures of tropical oceans to rainfall over middle latitudes.

Tong Ren
Texas A&M University System

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This page is a summary of: Global impact of cloud longwave scattering in an atmosphere‐only general circulation model simulation, Journal of Geophysical Research Atmospheres, January 2021, American Geophysical Union (AGU), DOI: 10.1029/2020jd033968.
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