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How is ice cloud formation influenced by anthropogenic activities? - Aircraft observations of cirrus cloud formation in global field studies

Speaker: Minghui Diao, Graduate Student
Series: EEWR Brown Bag Seminars
Location: Engineering Quad E225
Date/Time: Friday, October 19, 2012, 12:00 p.m. - 1:00 p.m.

Abstract:

Clouds play important roles in the Earth's climate and weather system. However, they remain one of the largest uncertainties in climate models. The IPCC AR4 report shows that both the magnitude and sign of anthropogenic influences on cloud radiative forcing are highly uncertain. Particularly, the anthropogenic influences on ice cloud formation are still highly debated. Here we use in situ, 1 Hz observations of the Vertical Cavity Surface Emitting Laser (VCSEL) hygrometer on board the NSF Gulfstream-V research aircraft to analyze the formation processes of cirrus clouds (T ? 40°C). Our field studies include nine Pole-to-Pole transects from the year of 2009 to 2011, extending from 87°N to 67°S, and also include samplings over the North America and the Pacific and Atlantic Ocean. We apply the regional comparisons between the Northern and Southern Hemispheres, as well as over land and ocean to examine the differences of cirrus cloud formation. Our findings demonstrate large differences in ice nucleation thresholds between regions with polluted or pristine background, which indicates highly possible influences from the different aerosol loading in the two hemispheres. To quantify their direct causal relationship still requires more in situ, fast observations in future studies for aerosol loadings in the upper troposphere.