Supercomputer models cloud microphysics

An international group of researchers have for the first time accurately calculated the effects of aerosols on clouds in a climate model.

The team lead by researchers from the Advanced Institute for Computational Science (AICS) in Japan used the powerful K computer, combined a model that simulates the entire global weather over a year, at a horizontal resolution of just 14 kilometers, with a simulation of how the aerosols behave within clouds.

Yosuke Sato from the Computational Climate Science Research Team at RIKEN AICS and Nagoya University said: “It was very gratifying to see that we could use a powerful supercomputer to accurately model the microphysics of clouds, giving a more accurate picture of how clouds and aerosol behave in the real world.”

The action of aerosols is an important element of research on climate change, as they partially counteract the heating action of greenhouse gases. Aerosols provide cloud condensation nuclei that allow clouds to form and affect their life cycle. The water in the air condenses onto the tiny particles, and gradually grow into droplets and finally into raindrops that precipitate.

It was previously thought increasing aerosol density would always lead to more clouds, but recent satellite observations showed that this is not necessarily true. Temperature differences between the top and bottom layers of clouds lead to a delicate balance of evaporation and condensation, with aerosols in the lower parts of the clouds promoting cloud formation, but those in the upper parts allowing the water to evaporate.

Unlike conventional models, which show a uniform increase in clouds over the earth when there is an increase in aerosols, the high-resolution model, which takes into account the vertical processes inside clouds, accurately depicted how large areas experience a drop in cloud cover.

The work, which was published in Nature Communications is the start of what the researchers hope will be a push for greater accuracy in climate models. “In the future, we hope to use even more powerful computers to allow climate models to have more certainty in climate prediction,” said Sato.