Early-winter North Atlantic low-level jet latitude biases in climate models: implications for simulated regional atmosphere-ocean linkages

Abstract Climate model biases in the North Atlantic (NA) low-level tropospheric westerly jet are a major impediment to reliably representing variability of NA climate system and its wider influence, particular over western Europe. A aspect is occurrence prominent early-winter equatorward bias Coupled Model Inter-comparison Project Phase 5 (CMIP5) models that has implications for atmosphere-ocean coupling. Here we assess whether this reduced new CMIP6 representation linkages, sub-polar gyre (SPG) region. Historical simulations from CMIP5 datasets were compared against reanalysis data period 1861–2005. The results show remains present models, although with an approximately one-fifth reduction CMIP5. mainly associated weaker-than-observed frequency poleward excursions northern position. potential explanation provided through identification strong link between latitude systematically too-weak model-simulated baroclinicity eastern America early-winter. CMIP larger exhibit weaker correlations temporal speed sea surface conditions (sea temperatures turbulent heat fluxes) SPG. imply could partially explain other known biases, such as seasonal-decadal predictability system.