PI: Lynn M. Russell; Lead Institution: University of California San Diego (UCSD) CoPIs and Collaborating Institutions: John H. Seinfeld, California Institute of Technology (CIT) Bruce Albrecht, University of Miami (UM) Armin Sorooshian, University of Arizona (UA)
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, while the qualitative aspects of the Twomey, Albrecht, and Ackerman indirect effects of aerosols on clouds are well known, 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.
Our proposed approach 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. As part of this project, we propose to expand the scope of a meteorology-focused ONR aircraft-based study of marine stratocumulus with three novel and important additional, climate-focused studies:
(1) Controlled release and atmospheric distribution of three different size ranges of particles in flight (Albrecht) and on or by a dedicated ship (Russell) (2) Large Eddy Simulations (LES, Seinfeld) and Aerosol-Cloud Parcel (ACP, Russell) 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 (Sorooshian) of marine stratocumulus to constrain the radiative properties of the natural, perturbed, and regional cloud systems
Russell, Seinfeld, Albrecht, and Sorooshian bring important expertise in the state-of-the-art of these techniques to the proposed collaboration, and their commitment to working collaboratively on this project will enable advances in understanding cloud responses to particles.
The broader scientific impacts of the proposed 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 proposed 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 Ð in this case, retired and elderly people Ð 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 (5) Societal benefits in terms of improved understanding of climate science and the related ethical issues
Figure: The planned ship path for a ship speed of 12 m s-1 is shown on the first (bottom) layer of the horizontal grid. The second (middle) layer shows the resulting spatial distribution of CN in a 300 m deep boundary layer (based on our simple Gaussian puff dispersion model and transverse wind speed of 5 m s-1with blue region indicating <250 cm-3 and red region indicating >1000 cm-3). The third (top) layer shows the associated changes in the relative CDN inferred from the fraction of ship-emitted CN that are estimated to be CCN (with gray region indicating <100 cm-3 and white region indicating >500 cm-3). Overlying the CDN contours of the third (top) layer are the planned Twin Otter flights for sampling in the cloud, including comparable time in the track and the background concentrations. The modeled ship emissions of 1016 s-1are at the low end of previous observations [Hobbs et al., 2000; Frick and Hoppel, 2000].
A one-day test cruise was proposed and approved on the R/V Sproul; this cruise was carried out on 23 February 2011.