# Western Mediterranean Precipitation Extremes, the Result of Quasi-Resonant Sea-Atmosphere Feedbacks
## 3 Results
### The Western Mediterranean SST Anomaly Is Weak, in Phase with EREs
#### 3.2.1 Partial Clustering of Atlantic and Mediterranean Low-Pressure Systems  
EREs 7, 8, and 9 (Figures 4, S2 and S3) are the outcomes of such a partial clustering of Atlantic and Mediterranean low-pressure systems. In the three cases, the SST anomalies of the western Mediterranean are weak, around 0.3 \({}^{\circ}\)C, in phase with EREs. Strong SST anomalies in phase with EREs occur in the Adriatic, Black, and Baltic Seas, exceeding 0.5 \({}^{\circ}\)C (Figures 4e,f, S2e,f and S3e,f). The eastern Mediterranean and the North Sea off the Scandinavian peninsula are also in phase with ERE 7; the Aegean is in phase with ERE 8; the Central Mediterranean and the North Sea are in phase with ERE 9. Figure 3: Precipitation depth and SST anomalies are related to ERE 3 occurring on 06 September 2005. The time reference is the daily precipitation at 41.7\({}^{\circ}\)N, 4.1\({}^{\circ}\)E (precipitation height = 431 mm/day). In (**a**,**b**), the amplitude of precipitation is represented in two period ranges, i.e., 0.71 to 1.43 days, and 1.43 to 2.9 days; the amplitude (**c**) and the phase (**d**) of precipitation depth and the amplitude (**e**) and the phase (**f**) of SST anomalies are represented in the period range of 11.4 to 42.7 days. The time scale relative to the time reference is the phase within the mean period, that is 21.5 days. In (**d**,**f**), the phase is considered significant only for the 50% highest values of the amplitude in (**c**,**e**). In Figure S2c,d, the clustering of the Atlantic and Mediterranean lows is reflected by the phase homogenization where the amplitude of the precipitation anomalies is peaking. Precipitation anomalies off the Gulf of Lion on one hand and off the southwest coast of France on the other hand are in phase with ERE 7. The clustering of the Atlantic and Mediterranean lows occurs in the same way for ERE 8 (Figure S3c,d). As for ERE 9, a narrow strip that follows the Spanish border links the Mediterranean and the Atlantic lows (Figure 4c,d). In each of these three cases, the Atlantic and Mediterranean depressions result in precipitation anomalies nearly in phase with EREs. These anomalies are more or less disjointed, the gap reflecting the presence of cloud/water vapor. The main precipitation anomalies are essentially concentrated over the Mediterranean, extending very little over the continent (Figures 4c, S2c and S3c). In its paroxysmal phase, the deep convective system of ERE 7 is concentrated off the Gulf of Lion near the Mediterranean coast of France (Figure S2a,b); precipitation height reaches 520 mm/day locally. For ERE 8, the convective system extends in the north-south direction with a strong penetration into French territory, reaching the German border, while zigzagging (Figure S3a,b); precipitation height reaches 288 mm/day locally. For ERE 9, several anomalies are on either side of the southeast coast of France, with a strong penetration to the west into French and Spanish territories along the Pyrenean (Figure 4a,b); precipitation height reaches 260 mm/day locally. 2.2 The Atlantic Ocean Does Not Contribute Significantly to the Co-Evolution of the Extratropical Cyclone  
EREs 2, 4, and 6 (Figures 5, S4 and S5) exhibit these characteristics. In each of the three cases, a phase-shifted precipitation anomaly is interposed between the Mediterranean and Atlantic anomalies, which highlights the absence of continuity and therefore of a link between the two depressions (Figures 5c,d, S4c,d and S5c,d). The SST anomalies of the western Mediterranean are weak, around 0.3 \({}^{\circ}\)C, in phase with EREs 4 or 6 (Figures S4e,f and S5e,f)  
Figure 4: Precipitation depth and SST anomalies related to ERE 9 occurring on 24 November 2016. The time reference is the daily precipitation at 43.1\({}^{\circ}\)N, 5.3\({}^{\circ}\)E (precipitation height is 260 mm/day). (**a–f**) same conventions as in Figure 3.  
or partly out of phase with ERE 2 (Figure 5e,f).