The potential impacts of improved MJO prediction on the prediction of MJO teleconnections in the UFS global fully coupled model

The value of Madden-Julian oscillation (MJO) prediction for extratropical subseasonal forecasts hinges on the assumption that reliable MJO simulation translates to reliable simulation of its teleconnections. This study examines the prediction of the MJO and its teleconnections in two recently developed NOAA Unified Forecast System (UFS) coupled model prototypes: Prototype 7 (UFS7) and Prototype 8 (UFS8). The MJO is skillfully predicted at a lead time of 27 days in UFS8, which is a considerable improvement (~ one-week skill increase) compared to UFS7. The potential effect of this improvement on MJO teleconnections via both tropospheric and stratospheric pathways is examined. UFS8 captures the pattern and amplitude of the geopotential height response in the North Pacific reasonably well and its evolution following active MJO events. The dipole response in the storm tracks over the North Pacific after active MJO events is also better captured in UFS8. In addition, the upward wave propagation and subsequent weakening of the polar vortex are better simulated in UFS8, with comparable strength to that in the reanalysis. Despite the notable improvements listed above, some biases remain: too-fast MJO propagation, an underestimation of geopotential height variability in the North Atlantic and Europe, an underestimation of the precipitation response, failure to capture the temperature evolution, and weaker MJO impacts on the NAO. This study suggests the potential of increasing the MJO teleconnection prediction skill, although not in all variables, by improving MJO predictions in dynamical models with more coupled components and upgraded model physics.