Date of Award

Spring 1-1-2015

Document Type


Degree Name

Doctor of Philosophy (PhD)


Atmospheric & Oceanic Sciences

First Advisor

Peter A. Pilewskie

Second Advisor

Odele Coddington

Third Advisor

Dan Marsh

Fourth Advisor

Mark Rast

Fifth Advisor

Cora Randall


Assessing and distinguishing between natural climate variability and anthropogenic forcing, and quantifying their relative contributions to climate change is a formidable challenge. Understanding how variations in the Sun and natural modes of variability affect the climate system will aid future climate projections. The Sun is Earth's primary source of energy, providing a global average irradiance that is four orders of magnitude greater than the largest secondary energy source, Earth's interior heat flux. Variations in the Sun occur both in the total solar irradiance and solar spectral irradiance (SSI), impacting the ocean, troposphere, and stratosphere via atmospheric winds, temperature, and planetary waves. Yet one of the difficulties in assessing the solar response is the fact that several internal modes of variability are present which can prevent accurate detection. The response of the stratosphere to the combined interaction of the Quasi-Biennial Oscillation (QBO) and the solar cycle was investigated using the Whole Atmosphere Community Climate Model (WACCM). Transient and fully coupled simulations that included observed greenhouse gases, varying SSI, and an internally generated QBO, were analyzed. A persistent wintertime solar response in the polar vortex when stratifying by QBO phase was not found. Results contradict conclusions drawn from observational data over the period 1953-2012. The Pacific Decadal Oscillation (PDO) is defined as the leading mode of sea surface temperature variability in the North Pacific, oscillating on decadal timescales. Changes in the PDO are linked to changes in precipitation, temperature, sea-level pressure, and sea-level height changes. Here we show in WACCM that the PDO also influences the stratosphere, with a weaker polar vortex in the positive PDO phase, which has implications for decadal prediction. Some evidence also points to possible modulation of the PDO by the solar cycle, which may provide an additional pathway for the Sun to impact decadal climate.