Abstract View
Assessing Polarimetric Measurement Sensitivities to Light-Absorbing Aerosol
CHENCHONG ZHANG, William Heinson, Benjamin Sumlin, Michael Garay, Olga Kalashnikova, Rajan K. Chakrabarty, Washington University in St. Louis
Abstract Number: 572
Working Group: Carbonaceous Aerosol
Abstract
Aerosol absorbs and scatters solar radiation, thus affecting the earth’s energy budget through direct and semi-direct radiative forcing. The carbonaceous aerosol is one of the most uncertain drivers of radiative forcing. It is made up of two dominant components: black carbon (BC) and brown carbon (OC). Direct radiative forcing (DRF) due to the light-absorbing carbonaceous aerosol, including BC and a fraction of OC (optically defined as brown carbon (BrC)), is one of the least understood aspects of the climate system. Part of the reason for this uncertainty is optical parameters of importance to climate modelers have a complex dependency on the aerosol’s microphysical properties, including size distribution, shape, and composition (hence, their refractive index). In this study, we apply a successive order of scattering (SOS) code to simulate remote reflectance signals at the top of the atmosphere (TOA) to a variety of aerosol microphysical inputs. The results show that aerosol’s aerosol microphysical properties sensitively affect the polarimetric measurements at TOA. The sensitivity levels are measured by atmospheric reflectance Jacobians to specific aerosol properties. Our quantitative sensitivity analyzes also show that the refractive index of light-absorbing aerosol normally has more significant effects on atmospheric radiative transfer compared to size distribution. This spectral sensitivity of atmospheric reflectance reaches its maximum in the regime where the imaginary refractive index less than 0.1. It implies polarimetric measurements are more effective in tracking the evolution of the absorption capacity of the aerosol which is composed of weakly absorbing material (e.g., BrC). This type of remote sensing technique can be further applied to study the atmospheric aging process of BrC.