Date of Award

Spring 1-1-2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Atmospheric & Oceanic Sciences

First Advisor

Jeffrey P. Thayer

Second Advisor

Brian Toon

Third Advisor

Susan Solomon

Fourth Advisor

R. Michael Hardesty

Fifth Advisor

Cora Randall

Abstract

The variability in stratospheric aerosol from 2000 to 2010 is described. This period is unique because it is the first opportunity to observe decadal variability of stratospheric aerosol unperturbed by colossal volcanic eruptions. Analyses of observations from lidars located in Lauder, NZ, Mauna Loa, HI and Boulder, CO show an increase in aerosol above 20 km that is modulated by a strong annual cycle with a wintertime peak; but observations alone are unable to conclusively partition the source of this increase between volcanic and anthropogenic emissions. Thus, a version of the Whole Atmosphere Community Climate Model coupled to the Community Aerosol and Radiation Model for Atmospheres, structured for sulfate aerosol and meteoritic smoke, is used to help attribute the sources of variability.

Comparisons of baseline simulations, using anthropogenic emissions of sulfur dioxide from 2000, with observations show agreement above 20 km. The comparison also reveals a bias in lidar retrievals that are due to the presence of meteoritic smoke. The bias results from the assumption that the region around 35 km is aerosol free in order to estimate the molecular component of the total observed backscatter. Meteoritic smoke is identified as a major source of extinction above 30 km and needs to be considered in the scattering properties for lidar retrievals.

To explore the decadal trends, increases of sulfur dioxide from known anthropogenic sources and volcanic eruptions were added to the model. Comparisons of simulation results and observations suggest that from 2000 to 2010, above 20 km, volcanic injections are the principle driver of stratospheric aerosol variability. Trends in anthropogenic emissions are found only to increase stratospheric aerosol annually in the late summer and fall in the northern hemisphere in the region near the tropopause.

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