Abstract View
Laboratory Exploration of the Effect of Mean and Fluctuations in Saturation Ratio on Activation in a Turbulent Cloud
ABU SAYEED MD SHAWON, Prasanth Prabhakaran, Gregory Kinney, Jesse C. Anderson, Raymond Shaw, Will Cantrell, Michigan Technological University
Abstract Number: 250
Working Group: Aerosols, Clouds and Climate
Abstract
The aerosol indirect effect is notably dependent on the inextricable interaction between aerosol and cloud. The prerequisite to form a cloud droplet is the preexistence of an aerosol in the atmosphere. This cloud forming process (i.e. aerosol activation) is also the primary removal mechanism for the accumulation mode aerosol (diameter ranges from 0.1 to 1 μm). From a conventional point of view, the possibility of an aerosol to become a cloud droplet depends on its size, chemical composition, and the ambient supersaturation. However, field campaigns, laboratory measurements, and simulation results suggest that the knowledge of only size and chemical composition does not provide enough information to predict which particles (or fraction of particles) will activate. The knowledge of fluctuations in the saturation ratio, induced by turbulence, is also necessary to get a complete picture of the activation process.
We report a series of targeted experiments, performed in the controlled environment of Michigan Tech’s cloud chamber to better perceive how the mean saturation ratio and its fluctuations affect the activation process. A protocol was developed and implemented to study the effect of mean and fluctuations independently. In steady state conditions, measurements from the chamber show coexistence of monodisperse aerosols with homogeneous chemical composition in both interstitial and cloud droplet residual distributions, suggesting the absence of one to one correspondence of size, chemistry, and activation. Different regimes of activation were achieved only by changing the saturation ratio which suggests that the fluctuation in saturation ratio can mimic the effect of heterogeneity in size and chemical composition on the aerosol activation process.