Radiative and climate impacts of absorbing aerosols

• Main Author: Zhu, Aihua
• Format: Doctoral or Postdoctoral Thesis
• Language: unknown
• Published: eScholarship, University of California 2010
• Subjects: UCSD Dissertations; Academic Earth sciences. (Discipline); Arctic; Indian; Pacific; black carbon
• Online Access: http://www.escholarship.org/uc/item/3bk0k42h; http://n2t.net/ark:/20775/bb7134409j

By integrating experimental data, radiative transfer theory, and numerical modelling, this dissertation aims to improve our understanding of the radiative and the climate impacts of the major absorbing aerosols: mineral dust, black carbon (BC) and brown carbon. The research presented here combines existing surface, satellite and aircraft measurements and develops self-consistent models for aerosol mixing state, global and regional radiative forcing of absorbing aerosols and their climate effects. The first part of this dissertation presents the climatology and radiative impacts of dust plumes over the Pacific, the Indian and the Atlantic Oceans using multiple satellite datasets in conjunction with MACR (Monte Carlo Aerosol-Cloud-Radiation) model. A core-shell internally mixed aerosol model has been developed using the microphysical, chemical, and radiative observations as constraints. It is shown that internal mixing enhances the aerosol absorption and contributes to over 20% increase of radiative forcing. The aerosol mixing model is validated by comparing model simulated spectrally-resolved irradiance with observations. The results show that aerosol induced forcing is mainly confined in the visible band and the largest forcing occurs in the blue channel. distribution of the spectral radiative forcing is obtained. The aerosol forcing is used to drive a general circulation model (GCM) with prescribed sea surface temperature to investigate the impact of absorbing aerosols on regional climate. One of the main model findings is that heating of the atmosphere by absorbing aerosols can contribute to significant reductions in low level clouds, which in turn amplifies the warming. The simulated cloudiness reduction is particularly strong over the Arctic and China and the simulated warming over the Arctic exceeds 1.5°C. The findings of cloud reduction over China and the warming over the Arctic are consistent with observations. The above effects are relatively weak or negligible when absorbing aerosols are treated as externally mixed which is used as the assumption by most GCM studies thus far. This study reveals the fundamental importance of accounting for the observed chemical and physical properties of absorbing aerosols