The imprint of the Atlantic jet stream and storm track on ocean overturning in the North Atlantic
Prof. Ric Williams, University of Liverpool
- External Supervisors:
Prof. Tim Woollings (University of Oxford)
Dr Doug Smith (Hadley Centre)
Prof. Ric Williams (University of Liverpool), email@example.com
- CASE Partner:
Application deadline: 10 January 2020
The meridional ocean overturning in the North Atlantic is expected to vary with climate change, usually viewed simply in terms of a weakening overturning with reducing surface heat loss. However, this viewpoint ignores the strong imprint of changes in the atmospheric storm track, altering the surface wind stress, as well as the supply of warm or cold air over the ocean, and so altering the air-sea heat exchange.
Anthropogenic greenhouse-gas forcing is leading to the North Atlantic storm track strengthening and extending further east (Woollings et al., 2012), which reduces the frequency of atmospheric blocks and shifts them eastward over Europe (Hoskins and Woollings, 2015). We will examine the connection between the atmospheric storm track and blocking patterns, and changes in the meridional overturning in the North Atlantic Ocean.
The atmospheric storm tracks will alter the wind stress and air-sea buoyancy flux changes, which together drive variations in the meridional overturning (Lozier et al. 2010) and gyre-scale convergence in heat transport, which in turn controls multi-year and decadal changes in ocean heat content (Williams et al., 2015).Project Summary:
The student would examine the effect of atmospheric storm tracks on meridional ocean overturning using two different model data sets:
1. Document how storm tracks and ocean overturning are evolving in climate model projections. In particular, document the changes in the latest UK Earth System Model (UKESM, ukesm.ac.uk) model projections used for Coupled Model Intercomparison Project Phase 6 (CMIP6), as part of the World Climate Research Programme (WCRP).
2. Diagnose the relationships between atmospheric storm tracks, surface density distributions and ocean overturning in large ensemble model data sets that the UK Met Office develop for their decadal forecasts; namely the Met Office decadal prediction system3 & 4 (Dunstone et al. 2016), designed to make global and regional climate predictions over seasonal to decadal timescales. We have already demonstrated how the atmospheric storm tracks control patterns of air-sea heat flux, surface temperature and sea-ice fraction (Ma et al., 2019, in review). We will extend this work to examine the connection to surface density distributions and meridional overturning.
This analysis will consider how the relationship between storm tracks and ocean overturning alters with timescale, varying from seasonal, interannual to decadal.References:
Dunstone, N., D. Smith, A. Scaife, L. Hermanson, R. Eade, N. Robinson, M. Andrews, and J. Knight, 2016: Skilful predictions of the winter North Atlantic Oscillation one year ahead. Nature Geoscience, 9 (11), 809.
Hoskins B.J. and T. Woollings (2015). Persistent extratropical regimes and climate extremes. Current Climate Change Reports, 1,2 115-124.
Lozier, M. S., V. Roussenov, M. S. C. Reed, and R. G. Williams, 2010: Opposing decadal changes for the North Atlantic meridional overturning circulation. Nature Geoscience, 3, 728–734.
Ma, L., T. Woollings, R.G. Williams, D. Smith and N. Dunstone, 2019. How does the winter jet stream affect surface temperature, heat flux and sea ice in the North Atlantic. Journal of Climate, under review.
Williams, R. G., V. Roussenov, M. S. Lozier, and D. Smith, 2015. Mechanisms of heat content and thermocline change in the subtropical and subpolar North Atlantic. Journal of Climate, 28 (24), 9803–9815.
Woollings T. et al. (2012). Response of the North Atlantic storm track to climate change shaped by ocean– atmosphere coupling. Nature Geoscience, 10.1038/NGEO1438.