15 December 2010

How do you catch a cloud and pin it down?

Posted by mohi


A complex interaction of particles and air currents shape the way clouds behave. Image courtesy of NOAA

At first glance, fluffy clouds seem innocuous. On lazy summer days, they take on whatever form our imaginations can conjure–morphing from fat little bunnies to fire-breathing dragons as the afternoon fades into evening. But if you’re a climate scientist, that mutability is not so fun. Ever changing, their dynamic nature is the bane of many a modeler’s existence.

In this morning’s poster session A31A: Aerosol Observability and Predictability: From Research to Operations for Chemical Weather Forecasting I Posters, Wanmin Gong from the Science and Technology Branch of Environment Canada talked about her efforts to better understand chemical cycling in clouds and what that means for our planet’s climate.

Clouds are complicated beasts. Their existence depends on finding little nuclei of dust or flecks of pollution for water molecules to cling to. But they won’t take just any particle. Some are easier for water to condense on than others.

Sulfur dioxide, a particulate produced mainly by power plants, dissolves quite readily in water droplets floating around our atmosphere. But Gong adds that sulfur dioxide is also very willing to react with chemicals like hydrogen peroxide to form sulfate particles. The size and distribution of these particles influence how well clouds reflect incoming sunlight. This means that clouds can have a cooling affect or a warming affect on our climate. Such ephemeral conditions make creating equations to describe cloud  behavior incredibly difficult.

Gong is trying to refine computer models of how clouds interact with chemical particles to help improve climate forecasts. By comparing several computer models with observations from an industrially generated particle plume over Chicago, she can get a better idea of the strengths and weaknesses of each model.

Gong found that while the models were able to forecast cloud cover as a result of interactions with the plume, there was still considerable variability in their predictions. “It’s a tough process, trying to get it right,” she said. There will always be limitations, whether it’s in our understanding, in computer power, or something else. But she added that it’s important to gauge how accurate current models are so that scientists know where they need to be improved.

But even knowing the grief that clouds give scientists like Gong, I’m still going to enjoy watching a cloud shaped like the Starship Enterprise as it transforms into a hat.

–Jane Lee is a science communication graduate student at UC Santa Cruz