FASTEX IOP17 cyclone: Introductory synoptic study with field data

This paper introduces the study of the early development phase of the IOP17 frontal cyclone of the FASTEX field experiment (Fronts and Atlantic Storm‐Track EXperiment). With the support of observations from FASTEX observing platforms a synoptic description highlights the development of mesoscale features of interest in the operational Météo‐France ARPEGE (Action de Recherche Petite Echelle Grand Echelle) analysis cycle, i.e. cloud head, dry wedge and upper‐level jet outflow. A discussion attempts to isolate two significant differences of the present cyclone life cycle compared with previous well‐known conceptual models of maritime cyclone life cycles: (i) the indirect role of an upper‐level precursor in triggering the surface low; (ii) the existence of a diabatic regime taking over from the baroclinic development to sustain the deepening rate of the cyclone. These two mechanisms are the subject of two companion papers.