Detecting Lifecycles of Atmospheric Fronts: Characteristics and Climatology

Previous studies have shown that condensational heating along trailing cold fronts can yield an increase in baroclinicity and can thus lead to secondary cyclogenesis and cyclone clusters. We assess the importance of this mechanism for secondary cyclogenesis and cyclone clustering by detecting and analysing the life cycles of atmospheric fronts. To compile such a climatology of frontal life cycles, we introduce a new tracking algorithm for fronts. We detect and track fronts as local gradient maxima of equivalent potential temperature using a four-dimensional watershedding algorithm. We demonstrate the suitability of our algorithm for tracking the spatio-temporal evolution of individual fronts. We present a selection of cases of extratropical cyclone development and their affiliated frontal lifecycles. We also highlight the added benefit of our method for climatological studies. The frequency of tracked frontal lifecycles provides a more insightful measure of front activity than conventional frontal detections. Based on our tracking algorithm, we can connect the position of each front to its total life time as well as its momentary age. This provides a better understanding of regionally characteristic frontal life cycles. Fronts in the mid latitudes typically move along west-east trajectories in the storm track regions on weekly time scales. They can thus be distinguished from stationary fronts in lower latitudes which occur on sub-seasonal or diurnal time scales. We find that life cycles of fronts can be classified with respect to their dynamic and diabatic evolution as well as in relation to the development of cyclones and cyclone clusters.