On the Link Between the Madden‐Julian Oscillation, Euro‐Mediterranean Weather Regimes, and Morocco Winter Rainfall

Abstract

AbstractK‐means cluster analysis of wintertime 500‐hPa geopotential height anomalies allowed identifying seven weather regimes (WRs) describing the atmospheric variability over the Euro‐Mediterranean domain. The study of transitions between those WRs provided consistent results with the westward displacement of the blocking nearby northern Europe before the onset of the negative phase of the North Atlantic Oscillation (NAO−). The onset of the latter is, indeed, preceded by the North Atlantic blocking regime (NABl). In addition, we detected a preferred transition from the Scandinavian Blocking (ScBl) to NAO+ through the European Ridge regime (EuRG), which is modulated by active phases of the Madden‐Julian Oscillation (MJO). The examination of the relationship between WRs and precipitation over Morocco showed that the NAO− (NAO+) regime is accompanied by more (less) rainy episodes. The investigation of the lagged relationships between the MJO and the WRs depicted the role of an active MJO in Phase 2 as a precursor of the ScBl and of an active MJO in Phase 6 as a precursor of the NABl. The exploration of the 10–15 days lagged impact of the MJO on Moroccan rainfall showed an increase (decrease) of wet (dry) conditions 10 to 15 days after the occurrence of an active MJO in Phases 6 and 8 (Phases 2‐3‐4). The MJO modulation of the WRs and rainfall patterns over Morocco constitutes an important source of predictability at the medium‐ and the extended‐range (subseasonal) time scales, with potential use by decision makers in key socioeconomic sectors in the region.