Date of Award

Spring 1-1-2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Atmospheric & Oceanic Sciences

First Advisor

Owen B. Toon

Second Advisor

Cora E. Randall

Third Advisor

Andrew Gettelman

Abstract

I have developed a three-dimensional coupled microphysical-climate-radiation model based on the National Center for Atmospheric Research (NCAR) Community Atmospheres Model (CAM3.0 and CAM5.0) and the University of Colorado/NASA Community Aerosol and Radiation Model for Atmospheres (CARMA2.3 and CARMA3.0). The model has been used to investigate the sources, removal processes, transport, optical properties, and radiative effects of Asian dust aerosols on climate. In the initial project, a A Weibull distribution is implemented to estimate the sub-grid scale wind speed variability. The dust AOD agrees well with AERONET data and the timing of dust events is comparable to the National Institute for Environmental Studies (NIES) lidar data in Beijing and Nagasaki. In the second project, the simulated properties of atmospheric dust from the Saharan deserts and the Asian deserts are compared using data from CALIPSO and AERONET during 2006 and 2007. In my model the yearly horizontal dust flux just downwind of the African dust source is about 1088 Tg (10S-40N, 10W) and from the Asian dust source it is about 355 Tg (25N-55N, 105E) in 2007. I find the difference in dust flux is mainly due to the larger area over which dust is lifted in Africa than Asia. However, Africa also has stronger winds in some seasons. Some previous studies suggested that the observed descent of Saharan dust is due to sedimentation of the particles, but my work and satellite data show instead it is dominated by meteorology. I find the size distributions of Asian and African dust are similar when the dust is lifted, but the mode size can differ and secondary size modes can develop probably due to differences in vertical wind velocities during transport. The importance of the uncertainty in the single scattering albedo (SSA) to the radiative effects of dust on the climate of China is explored in my final project through two case studies based on the modeled and observed solar diffuse fluxes/irradiances at the surface. We employ Mie theory and the refractive indices of Shi et al. (2005) as an initial case, but then scale the refractive indices to consider more absorbing aerosols as suggested in Ge et al. (2011). The different SSA based on the scattering theory over East Asia are derived, which directly result in negative (case-Shi) or positive (case-Ge) shortwave fluxes at the Top of the Atmosphere (TOA). The shortwave heating rates in the atmosphere are also different due to dust radiative forcing. The integrated three-dimensional microphysical-climate-radiation model used in this study allows us to consider interactions with the local surface albedo and emissivity, evolution of the size distribution in time, the vertical distribution of the dust as well as transport of dust aerosols vertically and horizontally.

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