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Oceanic strike-slip earthquakes occur on transform faults and fracture zones that cut across thousands of kilometers of seafloor. The largest of these events often rupture a considerable portion of their associated fault and can provide a comprehensive look at seismic slip across the entire fault plane as well as constraints on the depth extent of seismic slip. It is generally accepted that seismic and aseismic slip along oceanic transform faults is thermally controlled, however composition and geometry have been proposed as significant controls on some faults. High strain rates are a mechanism to achieve greater rupture depths, such as the unusually deep centroids reported for the largest strike-slip earthquake recorded to date, the 2012 MW 8.6 Indian Ocean earthquake. Detailed studies of notable earthquakes and a scattering of well-known faults have been of great use in elucidating oceanic strike-slip rupture. Determining if observed behavior is characteristic of all oceanic strike-slip faults requires a different approach. To resolve how seismic and aseismic slip are controlled with depth and along strike, well-constrained depths of many earthquakes along oceanic strike-slip faults are determined by modeling teleseismic body waves. Finite-fault slip inversions are calculated for the largest, most recent, and best-recorded oceanic strike-slip events. The constrained depth and along-strike location of slip for numerous oceanic earthquakes on strike-slip faults illuminates the distribution of seismic rupture on these faults in detail, as well as in unprecedented breadth through the examination of oceanic faults in a range of spreading rates and lithosphere ages. These well-constrained depths are within the expected limit to brittle failure (600-800ºC) and show that seismic rupture extends throughout the upper mantle to the crust. Observations of seismic rupture along an oceanic strike-slip fault also provide a comparison to the behavior of continental strike-slip faults that pose a far greater hazard to population centers, such as the San Andreas Fault in the Western United States and the North Anatolian Fault in Turkey.

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The indirect effects of anthropogenic aerosols—through their interactions with clouds—are currently one of the most uncertain perturbations to the radiative energy balance at the top of the atmosphere. A crucial link between aerosol and cloud is that aerosols can act as cloud condensation nuclei (CCN). This microphysical process must be parameterised if the large-scale effects are to be represented in a general circulation model (GCM). Theoretical work presented in this thesis highlights the importance of incorporating the kinetic limitations on droplet formation in aerosol activation parameterisations. HadGEM-UKCA is a GCM, capable of representing the chemical and microphysical aerosol processes required to model CCN accurately. The author has incorporated a Köhler theory based parameterisation of aerosol activation into HadGEM-UKCA, to facilitate quantitative predictions of the indirect aerosol effects. This thesis presents an estimate of the range of uncertainty in such predictions attributable to the choice of parameterisation of the sub-grid-scale variability of vertical velocity. Results of simulations demonstrate that the use of a characteristic updraught velocity cannot replicate results derived with a distribution of vertical velocities, and is to be discouraged in GCMs. Consequently, work focuses on the effect of the variance (<var>σ</var>_w²) of a Gaussian pdf of vertical velocity. Fixed values of <var>σ</var>_w and a configuration in which <var>σ</var>_w depends on turbulent kinetic energy are tested. Results from the mid-range fixed <var>σ</var>_w and TKE-based configurations both compare well with vertical velocity distributions and cloud droplet number concentrations measured in situ. However, the sparse set of available measurements does not provide enough of a constraint to recommend one or the other as the best configuration globally. The radiative flux perturbation (RFP) due to the total effects of anthropogenic aerosol is estimated at −1.7Wm⁻² for the TKE-based configuration. To the extent that it is valid to decouple the individual aerosol effects, the direct effect accounts for approximately −0.6Wm⁻² of the total, the cloud albedo effect −0.8Wm⁻² and the cloud lifetime effect −0.3Wm⁻², indicating that these effects are additive within HadGEM-UKCA. Total aerosol RFP ranges from −1.4Wm⁻² from simulations with <var>σ</var>_w=0.1ms⁻¹, up to −2.0Wm⁻² for <var>σ</var>_w=0.7ms⁻¹. This range of 0.6Wm⁻² corresponds to almost a third of the total estimate of −1.9Wm⁻², obtained with the mid-range value of <var>σ</var>_w=0.4ms⁻¹. Reducing the uncertainty in the parameterisation of <var>σ</var>_w is therefore an important step towards reducing the uncertainty in estimates of the indirect aerosol effects.

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