First-of-a-Kind Measurements Help Atmospheric Radiation Measurement (ARM) Scientists Better Understand Effects of Aerosols on Climate Change


Using new measurements, scientists funded by the Office of Science’s Atmospheric Radiation Measurement (ARM) Program have discovered new insights into the effect of pollution on clouds, and, in turn, the heating and cooling of the earth’s atmosphere. This question, known as the aerosol indirect effect, has been studied by scientists for thirty years. One of the fundamental theories is that by increasing the number of particles in the atmosphere upon which cloud droplets can form, clouds will have more, but smaller, droplets. Since smaller droplets are more reflective, clouds affected by pollution may cool the earth more than clouds unaffected by pollution. Researchers recently presented the first measurements of this effect using ground-based instruments located at the ARM Southern Great Plains site. The scientists studied seven cases in which the aerosol amount changed significantly over a day and calculated the aerosol indirect effect by quantifying how much the cloud droplet size changed in response to the changing aerosol amount. Unlike previous studies using satellite observations, the use of ground-based measurements allows scientists to directly observe and quantify the number and size of aerosol particles underneath the clouds at the same time they observe the cloud itself. These simultaneous measurements of cloud droplet size and aerosol amount provide a direct link between the properties of the measured aerosol particles and their effect on the cloud droplets. The new measurement strategy will provide new data for the development of new model parameterizations.