Atmospheric Chemistry Program Seminar

Better Understanding Climate and Atmospheric Chemistry by Understanding the Formation of Mixed Phase Clouds by Prof Dan Cziczo, MIT

Abstract:
"Field and laboratory measurements using cloud chambers have been used to understand the atmospheric abundance of droplet and ice nucleating particles and to, in turn, construct parameterizations for mixed-phase and completely glaciated clouds in weather and climate models. This seminar investigates measurements of which particles act as the nuclei for droplets and ice crystals and how we can then mimic those particles in the laboratory to understand how clouds form in our atmosphere. We show here that assumptions about the source of the particles as well as uncertainty in the laboratory and field measurements propagate into uncertainty in our understanding of the Earth’s climate and the chemistry of our atmosphere.
When we consider cloud chambers, uncertainty is likely inherent to varying degrees in all instruments and is caused by a variety of factors including exposure of particles to different humidities and/or temperatures than predicated from theory. This can result in a variable underestimation of reported droplet and ice concentrations. This is a critical issue for models which relay on these data for correct parameterizations of cloud formation. For ice clouds in particular, we find that simulated long wave ice-bearing cloud forcing in a global climate model can vary up to 0.8 W/m2 and can change sign from positive to negative within the experimentally constrained bias range.
We’ll conclude with a discussion of possible instrument improvements and how these can improve our understanding of climate, precipitation and atmospheric chemistry."

ANALYTICAL & ENVIRONMENTAL CHEMISTRY DIVISION and
ATMOSPHERIC CHEMISTRY PROGRAM SEMINAR
Jointly sponsored by the Department of Chemistry and Biochemistry, CIRES, and the Environmental Program