Chaos, Coupling and Climate: The Oceanic Pathway to Atmospheric Blocking

After establishing the link between Gulf Stream heat transport and subsequent atmospheric blocking in Mathews and Czaja (2024), revealing nearly double the amount of blocking over Greenland during DJF following increased heat transport through the Florida Straits in late summer, and confirming this connection using the ECMWF IFS in Mathews et al. (2024)—where surface latent heat fluxes over the Gulf Stream were suppressed, resulting in a reduction of blocking by up to 30% across the entire northern hemisphere, attributed to the diminished transport of boundary layer air into the upper troposphere along warm conveyor belts—we now adopt a playful exploration of this mechanism through a heuristic model.

This simple three-box model connects a basic slab ocean to an atmospheric boundary layer via heat fluxes, which then connects to the upper troposphere through slantwise convection following Emanuel (1983). Mimicking real-world dynamics, the model shows increased (decreased) ocean heat content before (after) an atmospheric block. Additionally, convection is triggered only when negative potential vorticity is present in the atmospheric boundary layer as theorised by Bennetts and Hoskins (1973).  

By adjusting various feedback parameters the system bifurcates, leading to a series of period doublings before entering a chaotic regime. By utilising the instantaneous dynamical systems properties of the attractor as described by Faranda et al. (2017), we infer the predictability of the system with different arrangements of control parameters.

This simple model underscores the importance of accurately representing the oceanic pathway to atmospheric blocking in more sophisticated climate models for precise predictions of how atmospheric blocking changes in a warmer climate.