Description of EERIE idealised atmosphere-only simulations

This report describes a multi-model dataset of idealised atmosphere-only sensitivity experiments, which are designed to complement EERIE reference simulations and help disentangle the impacts of the ocean mesoscale on weather and climate variability. The purpose of these experiments is to evaluate the response of the atmospheric circulation to the direct thermodynamic forcing attributable to extratropical SST anomalies associated with quasi-stationary fronts or transient mesoscale features (e.g. nonlinear eddies). These experiments are conducted with two resolutions of the IFS (~28 km and ~9 km) and HadGEM3 (~60 km and ~20 km) atmosphere models. Ocean and sea-ice boundary conditions are derived from high-resolution satellite-based estimates of daily-mean sea surface temperatures (SST) and sea-ice concentration from the European Space Agency Sea Surface Temperature Climate Change Initiative (ESA CCI SST version 3.0) and the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) Ocean and Sea Ice Satellite Application Facility (OSI-SAF), respectively. Other than the specification of SST boundary conditions, the idealised simulations described here are identical to the EERIE atmosphere-only reference experiments described in EERIE Deliverable 9.3. In these idealised experiments, extratropical SSTs are modified with a physically-informed spatial filter to suppress the influence of either transient mesoscale anomalies (SmoothAnom experiments) or sharp gradients associated with ocean fronts (SmoothClim experiments). A preliminary evaluation of these idealised experiments indicates that transient mesoscale SST anomalies can have a small but systematic impact on the climatological zonal winds and position of the tropospheric jets. However, the vertical and latitudinal structure of the zonal wind response to ocean eddies varies by season, hemisphere, and model configuration. Future work will assess the statistical robustness of these preliminary results and work towards understanding the physical mechanisms associated with the large-scale atmospheric response to transient mesoscale SST anomalies and quasi-stationary fronts in the EERIE simulations.