The impact of vertical model levels on the prediction of MJO teleconnections in the UFS global coupled model

This study evaluates the prediction of MJO teleconnections in two versions of the NOAA Unified Forecast System (UFS): prototype 5 (UFS5) and prototype 6 (UFS6). One of the differences between two prototypes with a potential impact on the prediction of MJO teleconnections is the number of vertical layers (127 in UFS6 vs. 64 in UFS5) along with the model top (80 km in UFS6 vs. 54 km in UFS5). We evaluate MJO teleconnections of large scale circulation, extratropical cyclone activity and surface air temperature, as well as the mean biases of the two prototypes since it may modulate the teleconnection. With respect to ERA-Interim, the global teleconnections of the MJO to the Northern Hemisphere 500hPa geopotential height show similar biases over the North Atlantic and European sectors in both prototypes, whereas UFS6 has slightly smaller biases over the North Pacific region. Both prototypes capture the extratropical cyclone activity occurring in week 3-4 over the North Atlantic after the MJO phase 6-7 and over the North Pacific and North America after the MJO phase 4-5. Both prototypes forecast the sign, amplitude, and approximate locations of 2-meter temperature anomalies over the mid-to-high latitude continents occurring in weeks 3-4 after MJO phase 3 but fail to capture the sign reversal of anomalies over North America between weeks 3 and 4 after MJO phase 7. Overall, the two prototypes show similar performance in simulating the tropospheric basic state as well as prediction skill of the MJO and MJO teleconnections.