Department of Environmental Sciences

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Seminar Abstracts
Environmental Sciences Seminar Abstract            

  When clouds should be present but are not: The puzzle of ice supersaturation
Mark Zondlo
Princeton University

Cirrus clouds play a critical role in the Earth's climate by efficiently trapping infrared radiation emitted from Earth. Unlike low or middle altitude clouds, cirrus clouds also transmit significant amounts of solar radiation to the surface. The net effect of these two processes is a warming at the Earth's surface. Cirrus clouds cover about 10-20% of the Earth's surface at any given time, and thus accurate predictions of cirrus cloud formation are needed for weather and climate.

In most weather and climate models, cirrus cloud ice particles are predicted to form at relative humidities with respect to ice of 100%. However, recent field studies have shown that large areas of ice supersaturation exist in the upper troposphere. The frequency, magnitude, and horizontal and vertical extent of these layers are not well known. Ice supersaturated regions also have significant impacts on the distribution and trends of water vapor in the upper troposphere, the most important greenhouse gas. Recent aircraft-based field measurements from the Arctic to the Antarctic will be shown that provide new insights into how cirrus clouds form, and the implications for predicting future climate will be discussed.

Last updated: 09/03/2009