12 Jan 2023
12 Jan 2023
Status: this preprint is currently under review for the journal WCD.

A composite approach to produce reference datasets for extratropical cyclone tracks: Application to Mediterranean cyclones

Emmanouil Flaounas1, Leonardo Aragão2, Lisa Bernini3, Stavros Dafis4,5, Benjamin Doiteau6,21, Helena Flocas7, Suzanne L. Gray8, Alexia Karwat9, John Kouroutzoglou7,10, Piero Lionello11, Florian Pantillon6, Claudia Pasquero3, Platon Patlakas7, Maria Angels Picornell12, Federico Porcù2, Matthew D. K. Priestley13, Marco Reale14,15, Malcolm Roberts16, Hadas Saaroni17, Dor Sandler17, Enrico Scoccimarro18, Michael Sprenger19, and Baruch Ziv17,20 Emmanouil Flaounas et al.
  • 1Institute of Oceanography, Hellenic Centre for Marine Research, Athens, Greece
  • 2Department of Physics and Astronomy "Augusto Righi", University of Bologna, Bologna, Italy
  • 3Università di Milano - Bicocca, Milano, Italy
  • 4National Observatory of Athens, Institute of Environmental Research and Sustainable Development, Athens, Greece
  • 5Data4Risk, Paris, France
  • 6Laboratoire d’Aérologie, Université de Toulouse, CNRS, UPS, Toulouse, France
  • 7Department of Physics, National and Kapodistrian University of Athens, Athens, Greece
  • 8University of Reading, Reading, UK
  • 9Meteorological Institute, University of Hamburg, Hamburg, Germany
  • 10Hellenic National Meteorological Service, Hellinikon, Greece
  • 11University of Salento, Lecce, Italy
  • 12Agencia Estatal de Meteorología, AEMET, Palma, Spain
  • 13College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, UK
  • 14National Institute of Oceanography and Applied Geophysics-OGS, Trieste, Italy
  • 15Abdus Salam International Centre for Theoretical Physics, ICTP, ESP Group, Trieste, Italy
  • 16Met Office, Exeter, UK
  • 17Porter School of the Environment and Earth Sciences, Tel Aviv University, Tel Aviv, Israel
  • 18Fondazione Centro Euro-Mediterraneo sui Cambiamenti Climatici - CMCC, Bologna, Italy
  • 19Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland
  • 20Department of Life and Natural Sciences, The Open University of Israel, Raanana, Israel
  • 21CNRM, Météo-France and CNRS, Toulouse, France

Abstract. Many cyclone detection and tracking methods (CDTMs) have been developed in the past to study the climatology of extratropical cyclones. However, all CDTMs have different approaches in defining and tracking cyclone centers. This naturally leads to cyclone track climatologies of inconsistent physical characteristics. More than that, it is typical for CDTMs to produce a non-negligible amount of bogus tracks which can be perceived as “false positives”, or more generally as CDTM artifacts, i.e. tracks of weak atmospheric features that do not correspond to large or mesoscale vortices. Lack of consensus in CDTM outputs and the inclusion of significant amounts of bogus tracks therein, has long prohibited the production of a commonly accepted reference dataset of extratropical cyclone tracks. Such a dataset could allow comparable results on the analysis of storm track climatologies and could also contribute to the evaluation and improvement of CDTMs.

To cover this gap, we present a new methodological approach that combines overlapping tracks from different CDTMs and produces composite tracks that concentrate the agreement of more than one CDTM. In this study we apply this methodology to the outputs of 10 well-established CDTMs which were originally applied to ERA5 reanalysis in the 42-year period of 1979–2020. We tested the sensitivity of our results to the spatio-temporal criteria that identify overlapping cyclone tracks, and for benchmarking reasons, we produced five reference datasets of subjectively tracked cyclones. Results show that climatological numbers of composite tracks are substantially lower than the ones of individual CDTM, while benchmarking scores remain high (i.e. counting the number of subjectively tracked cyclones captured by the composite tracks). This suggests that our method is able to filter out a large portion of bogus tracks. Indeed, our results show that composite tracks tend to describe more intense and longer-lasting cyclones with more distinguished early, mature and decay stages than the cyclone tracks produced by individual CDTMs. Ranking the composite tracks according to their confidence level (defined by the number of contributing CDTMs), it is shown that the higher the confidence level, the more intense and long-lasting cyclones are produced. Given the advantage of our methodology in producing cyclone tracks with physically meaningful, distinctive life stages and including a minimum number of bogus tracks, we propose composite tracks as reference datasets for climatological research in the Mediterranean. The supplementary material provides the composite Mediterranean tracks for all confidence levels and in the conclusion we discuss their adequate use for scientific research and applications.

Emmanouil Flaounas et al.

Status: open (until 23 Feb 2023)

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  • RC1: 'Comment on wcd-2022-63', Anonymous Referee #1, 19 Jan 2023 reply

Emmanouil Flaounas et al.

Emmanouil Flaounas et al.


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Short summary
Cyclone detection and tracking methods (CDTMs) have different approaches in defining and tracking cyclone centers. This leads to disagreements on extratropical cyclone climatologies. We present a new approach that combines tracks from indiviudal CDTMs to produce new composite tracks. These new tracks are shown to correspond to physically meaningful systems with distinctive life stages.