Anthropogenic emissions of greenhouse gases and aerosols both influence Earth’s climate via anomalous radiative forcing. However, the climate impact of these forcings is distinct: short-lived aerosols emitted from Northern Hemisphere industrial centers have imparted a consistently hemispherically asymmetric energy forcing on the climate. This work hinges on the question of how hemispheric differences in extratropical radiative forcing can drive coupled ocean-atmosphere interactions and energy transport. Because of the well-known impact of tropical variability on global climate, I pay particular attention to the question of how extratropical aerosol-like forcing impacts the equatorial Indo-Pacific, what pathways communicate this influence, and which climate feedbacks are involved in these pathways. This investigation, however, is complicated by the coupled nature of the climate system. While certain sea surface temperature (SST) anomaly patterns may suggest the importance of a specific local feedback, attributing causality or remote influence is difficult. To this end, I present several model-based decomposition methods to address chicken-or-egg problems common to coupled climate dynamics.
In the first three chapters of this dissertation, I mechanically decouple the oceanic and atmospheric components of a comprehensive global climate model (NCAR CESM1) by overriding surface ocean wind stress. This mechanical decoupling technique disables momentum feedbacks, which allows me to approximately partition a fully coupled climate response into the linear sum of buoyancy-forced and momentum-forced dynamics. In Chapter 1, I explore the SST biases introduced by two discrete wind stress overriding techniques, and I underline the importance of maintaining synoptic variability to create a realistic ocean mixed layer. In Chapter 2, I outline the surface ocean-atmosphere feedback pathway that creates a quasi-steady La Niña-like SST response to aerosol-like forcing. Then, in Chapter 3, I explore the ocean’s cross-equatorial heat transport response to this same aerosol-like forcing. Surprisingly, I find that buoyancy-forced dynamics drive the Indo-Pacific subtropical cells’ heat transport. I explore this adjustment using ocean-only simulations in Chapter 4 and show that subtropical temperature forcing affects the equatorial Pacific via dynamic and thermodynamic mechanisms within a decade and that the cross-equatorial overturning circulation response from Chapter 3 is a basin-scale thermal wind response. I conclude in Chapter 5.