MJO Influence on Subseasonal-to-Seasonal Prediction in the Northern Hemisphere Extratropics

Abstract

The impacts of the Madden-Julian oscillation (MJO) on the subseasonal-to-seasonal (S2S) prediction in the Northern Hemisphere extratropics are examined using the reforecasts from the S2S Project and Subseasonal Experi-ment Project (SubX). When forecasts are initialized during an active MJO, extratropical prediction skill becomes signifi- cantly higher at 3-4-week windows compared to inactive MJO. Such prediction skill improvement is evident in the 500-hPa geopotential height over the Pacific-North America region and the North Atlantic and in surface temperature over North America, especially when the model is initialized during the MJO phases 6-7 and 8-1. However, the extratropical predic-tion skill is not modulated by the MJO phases 2-3 and 4-5. This phase dependency is likely determined by the arrival time of the MJO at the Maritime Continent (MC) barrier that substantially enhances the MJO amplitude error. This result sug-gests that only MJO phases whose convection lies east of the MC are a source of wintertime S2S predictability in the extratropics.