Atmospheric particles change in a wide area around clouds

March HighlightsAtmospheric particles change in a wide area around clouds

April 1, 2011Click on image to enlarge.

How do aerosol particles change in the vicinity of clouds?  Figure 1 shows that areas near clouds occupy a large segment of all clear-sky regions, which implies that understanding aerosols near clouds is essential for understanding the role of aerosols in our climate. Comparison of the two panels in Figure 2 reveals that NASA’s CALIPSO lidar observes both stronger light scattering and increased particle size near clouds.  (Particle size is closely related to color ratio.) The increases arise from processes such as aerosol particles swelling up in the humid air that surrounds clouds. Figure 3 shows that the increase in particle scattering is substantial and typically exceeds 40% within 5 km of clouds.  The finding that particle changes in the transition zone are sufficiently prevalent to impact even global statistics highlight the importance of better understanding of these changes, and considering them both in the interpretation of satellite data and in climate simulations.  The ultimate goal is to help reduce some of the largest sources of uncertainties in understanding human impacts on climate: aerosol-cloud inter-actions and aerosols reflecting or absorbing sunlight.