Education: Ph.D., Pennsylvania State University
The mechanisms through which clouds and aerosols interact with the Earth's incoming and outgoing radiation streams are the focal point of my research. These mechanisms are one of the largest sources of uncertainty in global and regional climate simulations, which are the medium for projecting the impacts of climate change. I use data collected using remote and in situ sensors to improve our understanding of these mechanisms and thereby increase confidence in simulations of our future climate.
Much of my research is based upon data collected by the Department of Energy's (DOE) Atmospheric Radiation Measurement (ARM) Program. The ARM program operates long-term climate research facilities in three primary locations: the United States Southern Great Plains (SGP), the Tropical Western Pacific (TWP), and the North Slope of Alaska (NSA). It also operates an ARM Mobile Facility (AMF), which is deployed for periods of up to one-year in remote and under sampled regions. Each of these sites is equipped with a comprehensive suite of sensors that enable the atmospheric structure and its affect on incoming and outgoing radiation to be measured in great detail. Included in this suite are specialized radars that can detect small cloud droplets, along with other sensors that measure many other aspects of the cloud field.
One current research interest of mine is the interaction between aerosols and the Earth's cloud structure. Under typical conditions each cloud droplet forms on the surface of on an aerosol particle known as cloud condensation nuclei (CCN), which originates from natural (pollen) or anthropogenic (fossil fuel combustion) sources. The nature of these CCN can, in theory, alter the manner in which a given cloud interacts with sunlight and outgoing terrestrial radiation. The processes through which aerosols of anthropogenic origin may alter cloud structure are collectively known as aerosol indirect effects. Many aerosol indirect effects have been proposed and the two most important are termed the first and second aerosol indirect effects. The first aerosol indirect effect is a reduction in the average size of the cloud droplets when the underlying CCN are of anthropogenic origin. This reduction in droplet size enables the cloud to reflect more incoming solar radiation, so clouds that form in a polluted environment tend to reflect more sunlight, according to the theory. The second aerosol indirect effect entails a theoretical reduction in the amount of precipitation that is formed by a particular type of cloud with underlying CCN that are of anthropogenic origin (pollution). This type of cloud is likely to exist for a longer period if it cannot loose cloud water through precipitation. Thus, the second aerosol indirect effect impacts the lifetime of clouds.
Aerosol indirect effects are potentially important components of the Earth' cloud system, though the exact amount of their influence is still uncertain. My research aims to quantify these effects and to understand their role in climate change.
More recently, I have become interested in the mechanisms through which the land surface, biosphere, and clouds communicate. These mechanisms are integrally involved in regional climate change and must be thoroughly understood so that they can be correctly characterized in regional and global climate models.