AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Using a Global Model Adjoint to Unravel the Footprint of Spatially-Distributed Emissions on Cloud Properties
VLASSIS KARYDIS, Shannon Capps, Daven Henze, Athanasios Nenes, Georgia Institute of Technology
Abstract Number: 400 Working Group: Aerosols, Clouds, and Climate
Abstract Cloud droplets form upon pre-existing atmospheric aerosols, and their modulation has profound impacts on cloud radiative properties, the hydrological cycle and climate. Unraveling the complex relationship of cloud droplet number concentration (CDNC) to aerosol and aerosol precursor emissions is carried out with global climate models, often by activating/deactivating emissions. Although straightforward, this approach neglects the nonlinear dependence of aerosol concentrations on aerosol precursor emissions so that the resulting sensitivity reflects not only the actual CDNC response to an emissions change but also an altered size distribution and composition.
Adjoint modeling eliminates these issues by propagating an infinitesimal perturbation backwards through the model and, thus, elucidating the sensitivity of model output (e.g., CDNC) to the entire field of model parameters (e.g., emissions) without perturbing the model state. In this study, we reveal these relationships by developing the adjoint of the Kumar et al. (2009) CDNC parameterization (which considers the effects of soluble/insoluble particles on cloud droplet formation) and coupling it with the adjoint of the GEOS-Chem chemical transport model. This model framework is then used to determine the impacts of emissions of aerosol precursors on cloud droplet formation through adjoint gradients. Specifically, the adjoint model is applied to quantify the influences of global emissions on the predicted CDNC within the Midwest US, Southest US, California, and Central Europe.
The resulting sensitivity maps display the range of spatial, sectoral and seasonal variability in the susceptibility of CDNC to emissions changes. In particular, over US, SO2 and NOx emissions have a significant impact on CDNC during August, while NH3 emissions are the most important contributor to CDNC during February. Moreover, SO2 and NH3 emissions from East Asia have also a significant impact on CDNC over California. Finally, the CDNC over Central Europe is most sensitive to NH3 and NOx emissions during both seasons.