AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Assessing Top of Atmosphere Polarization Sensitivity to Aerosol Emissions Using the GEOS-Chem Chemical Transport Model Adjoint
BRIAN MELAND, Xiaoguang Xu, Daven Henze, Jun Wang, Univesity of Colorado, Boulder
Abstract Number: 90 Working Group: Source Apportionment
Abstract Atmospheric aerosols play important roles in determining the radiative balance of the earth’s atmosphere and in heterogeneous chemical reactions with trace atmospheric gases. However, there is still a great deal of uncertainty in the temporal and spatial distribution of atmospheric aerosols. This can lead to errors in radiative transfer calculations as well as in chemical transport models which both rely on accurate estimates of aerosol concentrations or emissions as inputs.
Recent studies have found that measurements of the full Stokes vector, rather than just the intensity component, of light scattered from atmospheric aerosols can provide additional information on aerosol physical and chemical properties. Since atmospheric aerosols can have lifetimes on the orders of days or weeks, they can be transported over intercontinental scales and impact radiative forcings far from their source regions. Using a vectorized radiative transfer model (VLIDORT) in conjunction with the adjoint of the GEOS-Chem chemical transport model, we seek to quantify the sensitivity of top of atmosphere (TOA) polarization to aerosol emissions, chemical composition, and assumed microphysical properties.
The GEOS-Chem forward model is used to calculate aerosol concentrations of 13 aerosol species on a 47 layer grid over North America. These concentrations are used as inputs for the VLIDORT radiative transfer model which calculates the full Stokes vector and its Jacobian matrix of scattered light at the TOA. The Jacobian matrix then serves as the adjoint forcing terms in the GEOS-Chem Adjoint model which steps backwards in time to determine the contributions of previous (non-local) emissions on polarization. These results help to show the utility of development and application of polarimetric measurements from remote sensing platforms.