Predator-Prey Behaviour of Storm Tracks
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Date
2021
Publication Type
Master Thesis
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Abstract
Extratropical cyclones are the dominant drivers of weather variability in the mid-latitude winter. Patterns of variability of the North Atlantic storm track, such as the serial clus- tering of wind storms, can have large socioeconomic impacts and cause substantial losses. A two-dimensional predator-prey model, which heuristically describes the interaction of local baroclinicity and heat flux in storm tracks, is extended in order to account for com- plex patterns of variability of the North Atlantic storm track. To do so, the constant diabatic forcing of baroclinicity is modified in three ways to include additional sources of potential energy. Each approach is motivated using the ERA-5 reanalysis data and a cyclone tracking algorithm.
Firstly, periodic forcing of the baroclinicity leads to resonant excitation of the oscillator model, which yields quasiperiodicity and low-frequency variability in cyclone activity. This model highlights the importance of the interaction between planetary waves and high-frequency eddy activity for storm track variability. Secondly, the inclusion of a third dimension for a reservoir of potential energy in the high latitudes, which allows for a positive feedback from cyclones on the baroclinicity, yields a globally attracting limit cycle in the model phase space. Such a predator-prey relationship between high-latitude cold air mass and cyclone activity is recovered from reanalysis data. The limit cycle behaviour contradicts the marginal stability implied by the original model and suggests a substantial influence of high-latitude cold air mass on storm track activity. Lastly, a nonlinearity in the tendency of baroclinicity, which allows medium intensity cyclones to restore baroclinicity, yields three distinct regimes of cyclone activity, one of which is akin to periods of cyclone clustering. This model demonstrates that the interaction of successive cyclones can lead to cyclone clustering in a two-dimensional predator-prey system.
The findings confirm that a simple nonlinear oscillator can reproduce complex patterns of variability and reproduce quasiperiodicity, reminiscent of the North Atlantic storm track. However, the modelled interactions are highly simplified and further research is required to gain more physical insights.
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Examiner: Schemm, Sebastian
Examiner: Papritz, Lukas
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ETH Zurich
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Subject
Atmospheric dynamics
Organisational unit
03854 - Wernli, Johann Heinrich / Wernli, Johann Heinrich
02717 - Institut für Atmosphäre und Klima / Inst. Atmospheric and Climate Science