Modulation of Polar Low Activity by the Madden-Julian Oscillation

The impacts of the Madden-Julian Oscillation (MJO) on polar low (PL) activity are examined. We found that PL frequency increases over the Irminger Sea and decreases over the Norwegian-Barents Seas following the MJO Phases 2–4, and nearly opposite changes are found for Phases 6–8. Further analysis reveals significant anomalies of static stability and low-level baroclinicity for different MJO phases, which have opposing effects on PL activity in many regions. The diagnosis of the PL genesis potential index agrees well with the observed PL activity. The agreement confirms the robustness of the MJO impacts on PL activity and suggests that such impacts can be largely explained by background environmental conditions. Significant anomalies of PL activity are also found over the North Pacific but with a weaker magnitude, which can be attributed to the comparatively lower PL frequency and the larger cancellation between static stability and low-level baroclinicity anomalies in that basin.