Observed multi-decadal trends in North Atlantic storm track dynamics: baroclinic diagnostics from ERA5 (1945–2024)

The dynamical properties of the North Atlantic storm track, and their response to ongoing climate change, remain far less constrained than the thermodynamic aspects of the climate system. The evolution of the North Atlantic storm track over recent decades shows an unclear picture. Previous observational studies have largely examined isolated diagnostics, over shorter periods, or within modelbased frameworks; to the best of our knowledge, a combined assessment of the storm track diagnostics and the associated mean flow over an observational record of this length remains lacking.

This study investigates trends in North Atlantic storm track dynamics, focusing on meridional heat fluxes and baroclinicity, variables that are coupled through the baroclinic life cycle of mid-latitude cyclones and collectively describe the state of the upstream storm track. The analysis uses ERA5 data, which now spans more than 80 years with a homogeneous data assimilation system, enabling multidecadal trend detection.

The analysis reveals a pronounced non-stationarity in North Atlantic storm track baroclinicity over the full examined timescale, with periods of enhanced and suppressed Eady growth rate and heat flux that do not conform to a monotonic forced trend. The degree of co-variability among the two dynamically relevant diagnostics differs substantially between sub-periods, indicating that the storm track’s variance structure does not evolve uniformly on decadal timescales but undergoes phases of dynamical reorganisation. These results are consistent with a substantial role of internal variability in modulating storm track variance on multi-decadal timescales.

Our results suggest that projected trends in the dynamics of the North Atlantic storm track may well be non-uniform and difficult to disentangle from apparent decadal internal variability.

This research was funded by the Polish National Agency for Academic Exchange (NAWA) under the Bekker Programme (grant no. BPN/BEK/2024/1/00180). It was further supported by the Department of Meteorology, University of Reading.