Abstract View
Investigating the Clear Sky Bias: Cloud-Relevant Aerosol Chemistry
MADISON FLESCH, Amy Christiansen, Virendra Ghate, Annmarie Carlton, University of California, Irvine
Abstract Number: 85
Working Group: Aerosols, Clouds and Climate
Abstract
Measurements of aerosol physical, chemical, and radiative properties at cloudy times are critical to accurately understand and predict aerosol-cloud interactions necessary to improve atmospheric models. The uncertainty surrounding aerosol-cloud interactions and their effects on the radiation budget still persists, despite decades of study and improvements in measurement and modeling tools. Low level shallow cumulus clouds interact with boundary layer aerosol, which can serve as cloud condensation nuclei. The fundamental controlling chemistry among inorganic and organic particulate matter constituents and how they affect uptake of aerosol liquid water (ALW) is the same at the surface and at cloud height. Remotely sensed and ground-based measurements of optically-relevant aerosol properties during cloudy periods are often removed from final, quality assured data products due to increased error during such times. This contributes to a clear sky bias in the quantitative understanding of atmospheric aerosol burden, and in particular chemical composition and hygroscopicity that affect water uptake, a controlling factor of particle size and light scattering. Holistic evaluation of optical and physicochemical properties of aerosols can establish a greater understanding of this relationship. We combine surface measurements of Angstrom exponents and particulate matter chemical composition from six co-located AErosol RObotic NETwork (AERONET) and Interagency Monitoring of PROtected Visual Environments (IMPROVE) sites across the U.S. and statistically analyze their relationships as a function of satellite-derived cloud flags in aerosol optical depth (AOD) files. We find aerosols are physically larger and ALW content is enhanced by 20% on cloudy days over clear sky days across the U.S. This suggests that the inability by current atmospheric models to accurately describe aerosol-cloud interactions is caused, in part, by a clear sky bias in the recording of aerosol optical properties.