Sarah Doherty

Research Scientist

From the ozone hole to climate change and science management

SarahSarah Doherty is a Research Scientist at JISAO, where she is the Executive Officer (EO) of the International Global Atmospheric Chemistry Project (IGAC) of the International Geosphere-Biosphere Programme (IGBP). Since 1990, through a large number of projects and activities, IGAC has created a worldwide community of scientists, enhancing international cooperation towards understanding the role of atmospheric chemistry in the entire Earth System. Sarah joined IGAC as the EO with the transition into the project’s second phase, in 2003. She works with the IGAC Scientific Steering Committee to implement the goals of the organization by helping to initiate and organize research projects, holding workshops on current key issues, holding the biennial IGAC conference, and acting as a hub for multi-national and multi-disciplinary networking within the community. Sarah also produces and edits the IGACtivities newsletter, which features synthesis and overview articles on current issues in atmospheric chemistry.

Much of the first decade of IGAC research was conducted in the context of focused, intensive measurement campaigns, such as the “ACE” series (Aerosol Characterization Experiment; e.g., ACE-1 in the clean southern ocean off Tazmania, ACE-2 off the polluted U.S. east coast, and ACE-Asia off the coast of China/Korea, studying a mix of pollutants and dust). The scope of IGAC in its next phase includes both regional characterization and the extension into issues that cross more expansive boundaries in space, time and discipline. While local and regional-scale atmospheric chemical composition will be a primary focus, it is now clear that issues such as intercontinental transport and transformation of chemically active species and the interactions between atmospheric chemistry and climate must also be addressed in order to better understand atmospheric chemical composition and to provide guidance to the public and policy-making community. It is also clear that atmospheric chemistry must be viewed within an Earth System context, and as such IGAC is collaborating with partner projects, including two new projects of the IGBP, the Integrated Land-Ecosystem Atmosphere Process Study (iLEAPS) and the Surface Ocean Lower Atmosphere Study (SOLAS), and two of the World Climate Research Programme’s (WCRP) projects, Stratospheric Processes and their Role in Climate (SPARC) and the Global Energy and Water Cycle Experiment (GEWEX).

Recently, Sarah – along with IGAC and SPARC chairs Philip Rasch and A.R. Ravishankara – has been instrumental in starting a joint project with SPARC: the Atmospheric Chemistry and Climate Initiative. In the 2006-2009 timeframe this activity will focus on assessing and improving the representation of atmospheric chemistry/climate interactions in models. The results of this effort will contribute to the next WMO Ozone Assessment and the next IPCC Assessment.

While running the IGAC project has fully consumed Sarah’s time for the past two and a half years, as a graduate student, post-doc, and Research Scientist Sarah was very actively involved in research on atmospheric aerosols. Aerosols are small particles suspended in the atmosphere, which interact with sunlight, thereby reducing the amount of sunlight that reaches the surface of the earth and, when the particles are dark (i.e., gray, brown or black), heating the atmosphere. Overall, the particles lead to surface cooling and may also affect cloud properties, such as reflectivity, lifetime and precipitation rates. An understanding of launching balloon-borne instruments to measure ozonethe quantity, distribution and optical properties of these particles is critical to being able to accurately predict global temperatures, such as in a global climate model. Sarah’s research focused on assessing the optical properties of aerosols from both natural and anthropogenic sources.

As a PhD student working with Professors Robert Charlson and Tad Anderson, she developed an instrument to measure 180-degree backscatter by aerosols (photo). This simulates the signal measured by a lidar (light detection and ranging) instrument, which works very much like a radar but at visible wavelengths. Lidars are increasingly being used to study in detail the vertical distribution of aerosol particles. In 2006, a lidar designed to measure atmospheric aerosols was, for the first time, launched on a satellite. The CALIPSO instrument is delivering an information-rich picture of the vertical distribution of clouds and aerosols around the globe. However, the signal measured by the lidars such as CALIPSO must be calibrated using a coefficient called the “lidar ratio”, which varies with the aerosol size and composition. The instrument Sarah helped develop, when used in conjunction with existing instrumentation, allows for measurement of the lidar ratio.

After calibrating and testing the "180-degree backscatter nephelometer" in the lab, Sarah and her colleagues took the instrument in the field and made measurements of the lidar ratio and other aerosol optical properties from both surface sites and the NCAR C-130 aircraft (photo). Her field work took her to a coastal site in Hawaii to study sea salt aerosol; to central Illinois to study regional summertime pollutants from both local and long-range sources; to the Maldives islands to study the pollution plume coming off of the Indian sub-continent; and to Japan to study the mix of pollution and desert dust coming from China, Korea and Japan.

This year Sarah has returned to doing research, joining a project led by Professors Steve Warren (University of Washington Atmospheric Sciences) and Antony Clarke (University of Hawaii, Department of Oceanography) to study the deposition of black carbon (dark particles) onto the Arctic surface. These particles absorb sunlight, Sarah paragliding off Mt. Bakerheating the surface snow and thereby accelerating melt rates. The goal of the project is to better quantify how much black carbon is deposited in the Arctic and whether it is making a significant contribution to the recent acceleration in melt rates in this region.

Sarah has a BA in Physics (1988) from Colby College in Waterville, Maine, and an MS (1998) and PhD (2001) in Atmospheric Sciences from the University of Washington. In the interim between her undergraduate and graduate work, she spent several years doing laser and electro-optic research on adaptive optics systems in Cambridge, Mass. She then spent just over a year at McMurdo Station, Antarctica as the Science Technician, running a dozen experiments, mostly related to the stratospheric ozone hole. After half a year of traveling through Southeast Asia and readjusting to life in the U.S. she decided her future lay in atmospheric science and she applied to the University of Washington.

When she is not working, Sarah enjoys experiencing the weather first-hand from a paraglider, getting into the mountains to rock climb and backcountry ski, and training for triathlons. Most of her free time at the moment is consumed by training for a half-ironman triathlon as a fundraiser for the Leukemia-Lymphoma Society, taking care of her puppy and getting ready for her wedding this Spring.