Cloud Physics and Cloud Processes

Clouds and aerosols are two important constituents of the atmosphere. Aerosols are microscopic solid or liquid particles that occur naturally or are generated from anthropogenic activities. Aerosols have direct impacts on radiation, can impact human health, and can change the microstructure and precipitation from clouds. Clouds control the Earth’s energy budget and global temperature, power its many storms, and provide the precipitation that sustains life. Understanding cloud, aerosol and radiative processes and their linkage is critical to all aspects of atmospheric science, from numerical weather prediction to global climate change. Clouds and aerosols present scientists with complex research challenges. Scientists must understand natural and human-related aerosol emissions and the resulting effects on atmospheric composition, along with determining effects of these changes on atmospheric processes and on society. Composed of countless water droplets and ice crystals, each formed on an aerosol, clouds cover vast regions of the planet, change constantly, interact with radiation in complex ways and —worst of all for researchers—are above the ground where they can’t be easily reached. We are forced to study clouds with probes mounted on aircraft, or with satellites and radars that sense electromagnetic radiation they either scatter or produce, or with numerical models, that attempt to simulate their many physical and dynamical characteristics.

At the Department of Atmospheric Sciences, we have an exceptionally strong research program focusing on aerosols, clouds and radiation. Illinois students are studying the effects of emissions from aviation on atmospheric chemistry and composition, and resulting impacts on climate. Research is also aimed at understanding the effects of dust storms in China on Asian air quality and nutrient deposition in the ocean, the interactions of this dust with urban and biomass burning air pollutants, its long-range transport and resulting effects on Asia and elsewhere, including effects on the circulations within hurricanes. Students are also using satellites, numerical models and in-situ probes to explore how changes in aerosol concentration and composition affects clouds, precipitation and the radiative budget. All aspects of clouds, from their basic microphysical properties to their role in the global climate system, are studied. A new acquisition to our program is the SCAMP (System for Characterizing And Measuring Precipitation), a mobile suite of instruments comprised of a vertically pointing Doppler radar, particle spectrometer, optical disdrometer, rain/snow gauge, aerosol optical particle sizer, and a weather station. This system is used in field programs and on campus to characterize precipitation from clouds and its effects. Students in the department also work on a wide array of investigations which include field studies of cloud and cloud systems, remote sensing studies of clouds from space, numerical modeling of individual clouds and cloud systems, and development of cloud and precipitation parameterizations for weather prediction and global climate models. Students conduct investigations that are far reaching, including investigations of clouds occurring over every continent and over the oceans, including studies of clouds near the top of the atmosphere, such as polar stratospheric clouds interacting with the Earth’s protective ozone layer and tropical cirrus over 18 km high generated by deep thunderstorms—to low-level boundary clouds over the Arctic Ocean and the fair weather cumulus of the tropics, which feed the Earth’s Hadley cell and subsequently drive the atmosphere’s global heat engine. We need more students to tackle these challenges if we are to solve the pressing environmental problems of the 21st century—are you the right person to take on this effort?

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