Collaborative Research: Using Controlled Aerosol Perturbations to Improve Understanding of Cloud Responses for Climate

California Institute Of Technology, Pasadena CA

Investigators

Abstract

Particles in the atmosphere play a key role in cloud formation, acting as nuclei for water droplets. Clouds play an important role in absorbing and reflecting heat, hence they can potentially mitigate or exacerbate global warming. Aerosol-cloud radiative interactions are widely held to be the largest single source of uncertainty in climate model projections of future climate change due to increasing anthropogenic emissions (IPCC, 2007). The underlying causes of this uncertainty among modeled predictions of climate are the gaps in our fundamental understanding of cloud processes. There has been significant progress with both observations and models on these important questions. However, the quantitative representation of these processes is nontrivial and limits our ability to represent them in global climate models (GCMs), resulting in the largest uncertainties in predictions of future climate. Given the timeliness of these questions for advancing GCMs, it is essential to address the unanswered questions in cloud dynamical response to aerosol perturbations. Intellectual merit. This research is a targeted aircraft campaign with embedded modeling studies to inform the experiment planning and to facilitate the interpretation of the results. The study will use the Center for Interdisciplinary Remotely-Piloted Aircraft Studies (CIRPAS) Twin Otter aircraft in July 2011 off the coast of Monterey, California, with a full payload of instruments to measure particle and cloud number, mass and composition distributions. The research is composed of three novel and important additional, climate-focused studies: 1. Controlled release and atmospheric distribution of three different size ranges of particles in flight and on or by a dedicated ship; 2. Large Eddy Simulations and Aerosol-Cloud Parcel modeling studies constrained by the observations to test our ability to quantitatively predict the dynamical response to increases in particle concentrations in the natural atmosphere; 3. Satellite analyses of marine stratocumulus to constrain the radiative properties of the natural, perturbed, and regional cloud systems. Broader impacts. The broader scientific impacts of the research will be the improved understanding of fundamental aerosol-cloud processes that can be incorporated in global climate models to better inform decision makers. The broader educational impacts of the research will be realized through: (1) Promotion of teaching, training and learning through development and piloting of an informal science education program targeting an underserved audience; (2) Broadened participation of underrepresented groups - in this case, retired and elderly people - in research as well as in outreach; (3) Enhancement of infrastructure for teaching through partnerships with an established educational organization (Osher Lifelong Learning Institute); (4) Broad dissemination of results through presentations, peer-reviewed publications and via the web; and (5) Societal benefits in terms of improved understanding of climate science and the related ethical issues.