DATE2018-05-20 07:01:13
AUTHORSS Qasmi (1), E Sanchez-Gomez (2), C Cassou (3), J Boe (4)
  1. CERFACS/CECI, Toulouse, France
  2. CERFACS/CECI, Toulouse, France
  3. CERFACS/CECI, Toulouse, France
  4. CERFACS/CECI, Toulouse, France
ABSTRACTDuring the last decades, the evolution North Atlantic sea surface temperature (SST) has been affected by both, low frequency intrinsic climate variability and external forcing, both anthropogenic and natural. The low frequency internal climate variability, also known as Atlantic Multidecadal Variability (AMV), has received particular attention in the last years. The SST pattern associated with the AMV exhibits homogeneous basin-wide SST anomalies of the same sign, leading to the warm AMV (AMV+) and cold AMV (AMV-) phases. Observational studies have shown the existence of decadal climate variability in the Mediterranean basin in the period 1850-2009, moreover a great part of this decadal variability can be explained by the AMV. All these studies highlight the importance of better understanding and predicting the AMV and its climate impacts to address the near term future changes in the Mediterranean-European climate. However, the shortness of the historical observational record compared to the AMV period makes it difficult to rigorously isolate the drivers and the impacts of the AMV. In this context, numerical coupled climate models offer a valuable alternative to investigate the AMV climate impacts and associated mechanisms. In this study we investigate the AMV impacts over the Mediterranean basin by using a set of idealized coupled experiments in which the coupled model CNRM-CM5 coupled model is used to carried out two ensembles of 40 members each, with SST restored to both, the warm and cold phases of the AMV. The difference of these two ensembles gives an estimate of the climate response to the AMV forcing. We focus on the AMV impacts and associated mechanism over the Mediterranean basin for two particular seasons: summer and autumn. Preliminary analysis shows that the response of surface temperature (2m) to the AMV SST anomalies is quite consistent with previous studies, with a prominent warming (cooling) over the Mediterranean area for the AMV+ (AMV-). The temperature impact over the Mediterranean area is more prominent in the western part of the basin. The AMV impact on precipitation during summer displays a general drying over the Mediterranean countries. Much less clear is the response of the atmospheric dynamics to AMV anomalies. An assessment of how AMV affect the temperature extremes in summer and cyclogenetic activity in late summer-autumn will be also investigated. Finally, the mechanisms explaining the AMV impacts over the Mediterranean basin are addressed by isolating the role of the atmospheric dynamics from the thermodynamically driven processes.