There are studies, which propose mechanisms, that are kind of obvious, but haven’t been described that explicitly before. One of these is possibly Gaetani et al. (2011), who show a “West African Monsoon influence on the summer Euro‐Atlantic circulation” (http://dx.doi.org/10.1029/2011GL047150). Based on convection data for July, August and September (JAS) they find Sahel region convection to be “co”-related to a positive NAO or – not stated by the authors – the “Mediterranean Pattern” as described by Hatzaki et al. (2007, http://dx.doi.org/10.1002/joc.1429). That is, a stronger monsoon leads to a more positive NAO phase (a more zonal situation with enhanced westerly winds, that is summers in western Europe are colder, let’s call it “summer is more like autumn). Of course, that’s not the full story, but it’s an interesting take on late summer climate in Europe – especially in relation to the Mediterranean Pattern.
African monsoon “drives” European summer climate