Atmospheric Sciences Research Spotlight

Incorporating 3-D Cloud Effects into Weather and Climate Models

Researchers explain how a new radiative scheme can be incorporated into global weather and climate models to better capture the effect of clouds on climate.

Source: Journal of Geophysical Research: Atmospheres


Clouds have a significant but complicated effect on Earth’s climate.  They shield the planet from incoming solar radiation, reflecting sunlight back into space. Clouds also insulate Earth like a blanket, emitting infrared radiation down to the surface while blocking radiation emitted by the surface from escaping to space.

Despite their obvious importance for weather and climate, the complexity of cloud shapes, their ephemeral nature, and the extreme variability in how they form and how long they last make modeling clouds and their interaction with radiation very difficult. Historically, radiation schemes in weather and climate models have ignored the flow of radiation through cloud sides because the only schemes that could accurately capture these  three-dimensional (3-D) effects were much too computationally costly for use in global models.

In a step toward less computationally costly methods, Schäfer et al. present a radiation scheme called the Speedy Algorithm for Radiative Transfer Through Cloud Sides (SPARTACUS). The researchers used an isolated, homogeneous, isothermal, cubic cloud as a benchmark to develop the scheme’s ability to capture infrared radiation emitted from clouds.

Theoretically, 3-D effects within this reference cloud are expected to increase the cloud radiative effect by a factor of 3. SPARTACUS was able to capture this effect, as long as the movement of energy throughout the cloud was accounted for. The authors parameterized the energy fluxes at cloud sides and presented an empirical adjustment to roughly account for the fact that in cloud clusters, neighboring clouds can absorb emitted radiation from each other, influencing the overall cloud radiative effect.

In a companion paper, Hogan et al. further explore the modifications necessary to incorporate SPARTACUS into weather and climate models. To ensure that the SPARTACUS scheme incorporated 3-D effects, the authors modified two-stream equations, which usually assume radiation to flow just up and down, to include horizontal radiative movement as well.

The study revealed that the 3-D radiative effects significantly influence how cumulus clouds influence Earth’s energy budget, but there is still room for improvement in the treatment of cloud clustering. According to the authors, more observations of cloud geometry and clustering in the real world will help researchers determine the effect of 3-D radiative transfer on the solar and infrared radiation on a global scale. (Journal of Geophysical Research, doi:10.1002/2016JD024875, doi:10.1002/2016JD024876, 2016)

—Kate Wheeling, Freelance Writer

Citation: Wheeling, K. (2016), Incorporating 3-D cloud effects into weather and climate models, Eos, 97, Published on 30 August 2016.
© 2016. The authors. CC BY-NC-ND 3.0
  • davidlaing

    So, we vilify carbon dioxide, the basic building block of life on Earth because we couldn’t afford the technology that would allow us to model the effects of clouds on the thermal structure of the atmosphere. What else have we ignored because our emphasis on CO2 gave us a pat answer? We all know that explosive volcanoes cool Earth because they inject long-lasting aerosols into the stratosphere, but how about the effect of NON-explosive (basaltic) volcanoes, like Iceland’s Bardarbunga, whose massive eruption in 2014-2015 was the greatest since Laki in 1783? After that, there was a huge spike in global temperature and an El Nino in 2015 that ended the 17-year “hiatus” of flat temperatures. Non-explosive volcanoes emit chlorine and bromine, which deplete stratospheric ozone, letting more hot, solar UV-B reach Earth’s surface. Humans injected massive amounts of CFCs into the atmosphere in the late 20th century, which released chlorine, and global temperature soared. The Montreal Protocol stopped that, and global warming stopped, too, giving us the “hiatus.” Back in 1900, Knut Angstrom disproved greenhouse warming experimentally. Do we really know what we’re doing with our fancy climate models, or is our methodology far too simplistic to conform to reality?