Clouds can both cool Earth by reflecting energy from the Sun and warm it by trapping heat like a blanket. Because traditional climate models lack detailed descriptions of clouds, however, scientists have long struggled to accurately model how clouds will affect, and be affected by, climate change. Now Schwartz et al. present a new technique that could help fill that gap using a simple tool: a $400 digital camera.
Much of what scientists already know about clouds, they’ve learned from satellites. The International Satellite Cloud Climatology Project, for example, found that clouds cover roughly two thirds of the planet and revealed how cloud cover varies over time from region to region, as well as many other cloud properties such as pressure and temperature. Because satellite images are taken from high up and far away, however, they can’t show the fine differences in cloud amount and thickness that affect how much light clouds reflect and thus how much solar radiation reaches Earth’s surface.
Small, low clouds called cumulis humilis, or “fair weather” clouds, are particularly difficult to analyze via satellite, in part because they form and dissipate so quickly. What’s more, they are often so small that they are not detected at all: Even sensitive radar systems sometimes fail to detect them. Despite their diminutive size, however, such clouds can scatter a great deal of light, particularly when they form around high concentrations of aerosolized pollution.
To study these clouds in greater detail, the authors pointed a Fujifilm digital camera up at the sky over north central Oklahoma. Over the course of 7 minutes, they captured a time series as a cluster of small, puffy white clouds passed through the camera’s field of view. Taken from roughly 2 kilometers away, the images achieved 4-centimeter resolution, up to 5 orders of magnitude higher than previous techniques, the team reports.
By examining the images pixel by pixel, the researchers found dramatic variations, of roughly an order of magnitude, in the clouds’ structure within the 30 × 30 meter frames, including shifts in their radiance—how much light the clouds scatter—and their optical depth, a measure of how much light can pass through. The approach could lead to more-accurate climate models by improving scientists’ understanding of fair weather cloud physics. (Journal of Geophysical Research: Atmospheres, https://doi.org/10.1002/2016JD025384, 2017)
—Emily Underwood, Freelance Writer