Exploring uncertainty of trends in the lower-tropospheric North Pacific Jet

The underlying dynamics responsible for the climatological position of jet streams are complex. In a warming world, there is mounting evidence from modelling and observational studies that amplified upper‐level tropical warming will have a poleward impact on the latitude of the tropospheric jet streams, which will continue across this century. However, existing research has also created confusion over these exact movements/trends, and as such they remain without consensus at any scale nor in any region. Here, we argue that this is in part due to the wide variety of statistics that have been used to define ‘jet latitude’ – one such method of quantifying the jet position, from which to calculate climatological shifts.

In this talk, trends associated with the latitude of the lower tropospheric jet streams are examined over the North Pacific using seven unique jet latitude statistics, four modern climate reanalysis products and CMIP6 historical simulations and future projections. Using these, we assess the relative importance of various associated uncertainties arising from choice of data, scenario, or statistic. The results show that the winter North Pacific Jet is moving polewards within both the reanalysis and climate models. The climatological trend of the North Pacific jet is found to vary by season in the reanalysis, and is most robust to choice of statistic and reanalysis dataset in winter. Finally, a poleward end-of-century shift of the jet position is shown that is robust to choice of statistic and model for autumn.