The ocean’s role in the Climate of the North Atlantic Region

Project Rationale:

The North Atlantic Ocean undergoes multidecadal variations in sea-surface temperature (SST) (Kushnir, 1994) with major impacts on the weather and climate of adjacent land regions, a phenomenon known as Atlantic Multidecadal Variability (AMV). It is therefore important to establish the physical mechanisms governing AMV and to determine whether AMV, and hence regional climate is predictable on decadal timescales. Although there is little consensus on the mechanism, there is evidence that an important part is played by the Atlantic Meridional Overturning Circulation (AMOC),a system of warm northward surface currents and cold southwards deep currents that transports heat poleward.

Moat et al., 2019 developed a simple approach to relate the three key variables of SST, ocean heat content (OHC) and ocean-atmosphere heat exchange in order to understand the drivers of AMV in a state-of-the-art climate model, showing that ocean-atmosphere exchanges in the western subpolar North Atlantic are important in initiating large AMV excursions, and the Atlantic Meridional Overturning Circulation (AMOC) is important for their subsequent evolution.

In this project we aim to apply the diagnostic approach of Moat et al. 2019 to an ensemble of the latest climate model simulations and to observations to understand the mechanisms linking AMOC, OHC and AMV.

Methodology:

Moat et al 2019 developed simple equations for the evolution of the SST and full depth ocean heat content, where the lateral transport, which is difficult to measure accurately, is obtained as the difference between surface heat gain/loss and heat content change in the well-mixed surface layer (for SST) and over the full ocean depth (for heat content). The student will follow Moat et al., 2019 and extend the method to an ensemble of the latest climate model simulations of present day climate as well as observations, observational surface and subsurface ocean temperature datasets, surface heat igain/loss (from atmospheric observations) and recent direct in situ AMOC observations, supplemented by indirect estimates of the AMOC over the past century (e.g. McCarthy et al., 2015). They will identify large excursions of the AMV in both models and observations and form a composite of the AMV cycle and its driving terms, and the AMOC, thus identifying the relative roles of surface fluxes versus lateral transport/AMOC at different points in the AMOC cycle. Finally the student will investigate how the AMV and its driving terms are modified in the future scenarios climate simulations, where Earth’s climate is modified by anthropogenic greenhouse .gas emissions.

Training:

The INSPIRE DTP programme provides comprehensive personal and professional development training alongside extensive opportunities for students to expand their multi-disciplinary outlook through interactions with a wide network of academic, research and industrial/policy partners. The student will be registered at the University of Southampton and hosted at the National Oceanography Centre, Southampton.

Specific training will include:
• Training/experience in conceptual/theoretical models and advanced analysis of observations and climate models.
• Training in the programming languages such as Matlab and Fortran in a linux environment.

The student will join the vibrant NOC modelling team, gain experience analyzing large model/observational datasets and work alongside leading NOC observationalists. S/he will acquire a solid background in ocean circulation and climate research. They will join an active team of postdoctoral researchers and postgraduate students focusing on the role of the ocean in climate. They will be encouraged to present results at national and international conferences.