Intra-seasonal atmospheric variability and extreme precipitation events in the European-Mediterranean region

The low frequency atmospheric variability over the European-Mediterranean region is described by the weather regimes, obtained by using a clustering algorithm applied on the September-December geopotential height at 500 hPa. Links between the European-Mediterranean weather regimes and extremes of precipitation over Europe are examined. We focus on the autumn season, when heavy precipitation episodes are likely to occur over the Mediterranean coasts. In the second part of this paper, we study whether the European-Mediterranean weather regimes can be related to the phases of some intra-seasonal atmospheric oscillation. By using the Multi-Channel Singular Spectrum Analysis (MSSA), we identify a 50-day oscillation over the European-Mediterranean region. The phases of this oscillation are found to be consistent with the preferred weather regimes transitions. This could influence intra-seasonal predictability and suggests that links between the episodic (weather regimes) and oscillatory (intra-seasonal oscillations) approaches may also apply to the regional scale.