A new methodology for identifying daughter cyclogenesis: Application for the Mediterranean Basin

This study is the first one to objectively identify 'parent-daughter' relationships between cyclones and to apply it to Mediterranean cyclones (MCs). The methodology includes cyclone detection, tracking and mapping the area of influence of a cyclone; here daughter cyclones are expected to be found. Cyclone detection and tracking is based on standard algorithms, which were modified to cope with irregularities in intensity and trajectory shapes of MCs. We have developed our own algorithm for mapping cyclones' area of influence. Application of our methodology to the ERA-Interim data for 33 mid-winter seasons identified parents for 97.5% of the MCs. While previous studies claimed that most MC parents are situated over Europe, this study found the majority of MCs' parents (56%) positioned over the Mediterranean itself. This disagreement stems from the fine spatial resolution used here (0.75° × 0.75°), which enabled uncovering smaller cyclones than noticed previously, thus revealing earlier stages of cyclogenesis. The parenthood analysis identified two main types of cyclogenesis within the Mediterranean; one driven by parent MCs, the other driven by Atlantic or European cyclones. The latter is manifested either by directly generating a new MC or by intensifying existing weak MCs. Cyclone generations were explored through backtracking chains of parents down to the ninth generation, the longest chain found. The results indicate that the primary source of MCs is the Atlantic (2/3 of the MCs) and then Equatorial Africa and the Red Sea (1/3). The results also imply that although native MCs owe their existence to the Atlantic-European cyclone track, regional cyclogenetic effects, such as topographic, thermal and baroclinic, are even more influential. The innovative methodology for objective identification of cyclone parents can be used to characterize cyclogenetic scenarios, in particular away from main storm tracks and over complex terrain.