Shallow cumulus clouds – the cotton-ball clouds that drift overhead on partly cloudy days – are hard to observe and, therefore, hard to model and predict. By deploying a 12-km-diameter ring of cameras, these clouds are now being observed in fine detail using stereo reconstruction.
Shallow cumulus clouds play a large role in cooling the Earth, so even small changes to their abundance as the planet warms could substantially ameliorate or exacerbate the warming. These high-resolution observations will allow scientists to test their theories for the behavior of these important clouds.
Shallow cumulus clouds play a large role in Earth's current radiation balance, and their response to global warming makes a large and uncertain contribution to Earth's climate sensitivity. To develop accurate theories and parameterizations of shallow cloud cover, we need measurements of clouds' horizontal dimensions, their elevations, their depths, the rate at which they are created, the rate at which they dissipate, and how all of these factors vary with changes to the large-scale environment. Only observations that are high-resolution relative to individual clouds in all four dimensions (space and time) can provide these needed data.
Towards this end, we have installed a ring of cameras around the Southern Great Plains (SGP) Atmospheric Radiation Measurement (ARM) site in Oklahoma. Six digital cameras are situated in pairs at a distance of 6 kilometers from the site and with a spacing of 500 meters between cameras in a pair. These pairs of cameras provide stereoscopic views of shallow clouds from all sides; when these data are combined, they allow for a complete stereo reconstruction. The result, called the Clouds Optically Gridded by Stereo (COGS) product, is a 4D grid of cloudiness covering a 6 km x 6 km x 6 km cube at a spatial resolution of 50 meters and a temporal resolution of 20 seconds. This provides an unprecedented set of data on the sizes, lifetimes, and lifecycles of shallow clouds.