A methodology to assign atmospheric fronts to extra-tropical cyclones on the Euro-Atlantic and European Sector

The passage of strong extra-tropical cyclones over the Euro-Atlantic and European Sector is typically associated with significant socio-economic impacts namely fatalities, proprieties damages, flooding and landslides. Major disruption typically occurs along the exact path of the storm, referred to as cyclone footprint. Within a cyclonic structure, the fronts location indicates the transition zone between two different air masses where it is more likely for precipitation (and wind) extremes to be recorded. Atmospheric fronts and their related precipitation bands typically develop from the cyclone centers and might extend far away from the cyclone itself, as in case of deep lows.

A recent work from Hénin et al., (2018) shows how to objectively relate precipitation to atmospheric fronts. As a follow-up to this, an objective methodology to assign fronts to cyclones is presented in this study, with the aim to quantify the amount of precipitation ultimately related to a cyclone. At first, it is explained how to manipulate fronts datasets in order to univocally identify frontal features. Therefore, atmospheric fronts are labeled, as clusters of frontal grid points. Afterward, each cluster is co-located with the center of the corresponding cyclone, provided that they are close enough to each other. To obtain this, a search box is used, looking for frontal features in the neighborhood of each cyclone. The optimal size for the search box is investigated and its shape and location are adjusted to fit with different cyclones intensity ranges and latitudes.

Results show that the assignment of fronts to cyclones is not always straightforward and it depends on the different mechanisms driving the overlying weather pattern. For example, when local pressure minima form in the tail of a pre-existing parent cyclone it is ambiguous to automatically co-locate each front to the corresponding cyclones. A few criteria, based on minimum distance and cyclones intensity, are suggested to make the assignment process more objective.

ACKNOWLEDGMENTS

This work is supported by Fundação para a Ciência e a Tecnologia (FCT) through project PTDC/CTA-MET/29233/2017 - WEx-Atlantic. FCT is providing for R. Hénin doctoral grant (PD/BD/114479/2016). A. M. Ramos is supported by the Scientific Employment Stimulus 2017 from FCT (CEECIND/00027/2017).