Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
© Author(s) 2016. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
11 Nov 2016
Review status
A revision of this discussion paper is under review for the journal Atmospheric Chemistry and Physics (ACP).
Effects of 3D Thermal Radiation on Cloud Development
Carolin Klinger1, Bernhard Mayer1, Fabian Jakub1, Tobias Zinner1, Seungbu Park2, and Pierre Gentine2 1Ludwig Maximilians-Universität München, Fakultät für Physik, Meteorologisches Institut München, Germany
2Department of Earth and Environmental Engineering, Earth Institute, Columbia University, New York, New York, USA
Abstract. We investigate the effects of thermal radiation on cloud development in an idealized setup in large-eddy simulations with the UCLA-LES model. We investigate single convective clouds (driven by a warm bubble) and a large cumulus cloud field at 50 m horizontal resolution. We compare the newly developed 3D "neighboring column approximation" with the independent column approximation and a simulation without radiation and their respective impact on clouds. Thermal radiation causes strong local cooling at cloud tops accompanied by a modest warming at the cloud bottom, and in the case of a 3D scheme, also cloud side cooling. 3D thermal radiation causes systematically larger cooling when averaged over the model domain. In order to investigate the effects of local cooling on the clouds and to separate these local effects from a systematically larger cooling effect in the modeling domain, we apply the radiative transfer solutions in different ways. The direct effect of heating and cooling at the clouds is applied (interactive thermal radiation) in a first simulation. Furthermore, a slab-averaged applications of the 1D and 3D radiation is used to study the effect of local cloud radiation as opposed to the domain averaged effect. These simulations exhibit a cooling profile, with stronger cooling in the cloudy layers. In a final setup, we replace the radiation simulation by a uniform cooling of 2.6 K/d.

For the simulations of isolated single cloud, or the cumulus cloud field with interactive radiation, we find that thermal radiation changes cloud circulation, by causing stronger updrafts and stronger subsiding shells.

In our cumulus cloud field simulation we find that interactive radiation, acting locally on clouds enhances the circulation compared to the averaged radiation applications. In addition we find that thermal radiation triggers the organization of clouds. Comparing the effects of 3D and 1D thermal radiation, we find that organization effects of 3D thermal radiation are usually stronger than the 1D counterpart (either interactive or averaged). Interactive radiation leads to an earlier onset of the organization both in 1D and 3D compared to the averaged radiation application. Applying a constant cooling to the simulations leads to a similar development of the cloud field as in the case of averaged radiation, but less water condenses overall in the simulation. Generally, clouds contain more liquid water if radiation is accounted for. Furthermore, thermal radiation enhances turbulence and mixing as well as the size and lifetime of clouds. Interactive thermal radiation produces larger clouds with longer lifetimes.

Citation: Klinger, C., Mayer, B., Jakub, F., Zinner, T., Park, S., and Gentine, P.: Effects of 3D Thermal Radiation on Cloud Development, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-896, in review, 2016.
Carolin Klinger et al.
Carolin Klinger et al.
Carolin Klinger et al.


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Short summary
Radiation is driving weather and climate. Yet, the effect of radiation on clouds is not fully understood and often only poorly represented in models. Better understanding and better parameterizations of the radiation-cloud interaction are therefore essential. Using our newly developed fast "neighboring column approximation" for 3D thermal heating and cooling rates, we show that thermal radiation changes cloud circulation, and causes organization and a deepening of the clouds.
Radiation is driving weather and climate. Yet, the effect of radiation on clouds is not fully...