Using ERA40 in Cyclone Phase Space to refine the classification of historical tropical storms

Knowledge of cyclone structural evolution during and beyond the tropical stage has increased tremendously over the past fifty years with various satellite-based, model-based, and analysis-based classifications (e.g., Cyclone Phase Space; Hart, 2001). This has brought forward the reanalysis of historical storms in the context of present understanding (Landsea et al 2000, 2002). Using ECMWF Reanlaysis data (ERA40), three parameters that classify a cyclone within a continuum of structure (warm to cold core, shallow to deep, frontal to nonfrontal) can be calculated. By plotting these parameters against each other in three-dimensional space and subsequently taking cross-sections, it is possible to create a more complete description of the life-cycle of any particular cyclone and to refine the structural classification of that cyclone within the best-track dataset. The reanalysis of historical cyclones using this method is vital for the further improvement of cyclone track and structure climatology of tropical and extra-tropical cyclones, and the long-term climate changes implied by them. Several cases of tropical and extratropically transitioning storms are examined here, including Betsy (1965), Carrie (1957), Daisy (1958), Gracie (1959), Donna (1960), Esther (1961), among others. Further, several previously undocumented potential subtropical and tropical cyclones will be discussed. A summary of the comparison to the existing best-track for the period 1957-2002 will be presented.