# Western Mediterranean Precipitation Extremes, the Result of Quasi-Resonant Sea-Atmosphere Feedbacks
## 3 Results
### SST Anomalies in Western Mediterranean out of Phase with EREs  
EREs 1, 12, 5, and 11 (Figures 6 and S6-S8) exhibit these characteristics. The extension of SST anomalies in the western Mediterranean varies significantly from one ERE to another. Anomalies exceeding 0.5 \({}^{\circ}\)C are located off the French coast for EREs 1, 5, and 11, and are more extensive for ERE 12 (Figures 6e,f and S6e,f-S8e,f). They are all out of phase, behind EREs 1, 12, and 5 or ahead of ERE 11 (this phase shift mainly concerns the Adriatic, the central Mediterranean, and the Mediterranean off the Spanish coast). This phase shift also concerns the Adriatic Sea, either in its northern part (EREs 1, 12, 5) or as a whole (ERE 11).  
As for ERE 1, SST anomalies exceed 0.5 \({}^{\circ}\)C off the southwestern coast of Turkey and in the Black Sea. The southern part of the Adriatic, the central part of the Mediterranean, and the Black Sea are in phase with EREs. However, the Baltic is out of phase and the anomaly in the Atlantic off the southwestern coast of France as well. These same characteristics apply to ERE 12 with the exception of the Baltic Sea, which is in phase with EREs.  
Figure 5: Precipitation depth and SST anomalies related to ERE 2 occurring on 3 December 2003. The time reference is the daily precipitation at 41.7\({}^{\circ}\)N, 4.5\({}^{\circ}\)E (precipitation height is 678 mm/day). (**a–f**) same conventions as in Figure 3.  
The Adriatic, the Atlantic off the southwestern coast of France, and the Black Sea are partially out of phase with ERE 5. However, the Aegean, the Baltic, and the North Sea off the Scandinavian coast are in phase with ERE 5.  
Like the Adriatic and the central Mediterranean, the Atlantic anomaly off the southwestern coast of France is out of phase with ERE 11 (ahead of the ERE). However, the Mediterranean off the Gulf of Lion, the Black Sea, the Baltic, and the North Sea off the Scandinavian peninsula are in phase with EREs.  
Due to the phase shift of the SST anomaly, the western Mediterranean is not involved in the sea-atmosphere quasi-resonance. In this way, mainly depressions resulting from baroclinic instabilities induced by SST anomalies of closed and semi-closed seas intervene in the clustering of lows, which is shifted to the east. This is clearly displayed in Figures 6c,d and S6c,d, referring to EREs 1 and 12, respectively. As for EREs 5 and 11, homogenization of the phase is not complete (Figures S7c,d and S8c,d). For ERE 5, the clustering of lows occurs over two distinct regions, in southeastern France on one hand and in southern Italy and western Croatia on the other. For ERE 11, the clustering of lows occurs off the eastern coast of Spain, off the southeastern coast of France, and off the west coast of Italy; the phase of the anomaly shifts from west to east.  
It follows that the deep convective system is moved towards the north of Italy, Corsica and Sardinia for EREs 1 and 12 (Figures 6a,b and 6a,b); precipitation height reaches 222 and 259 mm/day locally, respectively. For ERE 5, the deep convective system moves in 3 days from the southeast of France towards the south of Italy while intensifying (Figure S7a,b). The anomaly exceeds 60 mm/day in Italy for both the daily and bi-daily period ranges (precipitation height reaches 256 mm/day locally). For ERE 11, the deep convective system moves in 2 days from the coasts of the northeastern Spain and the southeast of France towards Sicily while mitigating (Figure S8a,b). The anomaly in the Gulf of Lion exceeds 60 mm/day for both the daily and bi-daily period ranges (precipitation height reaches 283 mm/day locally). Such a shift in the deep convective system has only occurred in the two cases studied during the 22 years of observation.  
Figure 6: Precipitation depth and SST anomalies related to ERE 12 occurring on 14 September 2006. The common time reference is the daily precipitation time series at 42.1\({}^{\circ}\)N, 9.7\({}^{\circ}\)E (precipitation height is 259 mm/day). (**a–f**) same conventions as in Figure 3.