How Does the Definition of a Geomagnetic Storm Affect the Contents of the Resulting Storm List?

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Abstract
A geomagnetic storm is a significant and prolonged disturbance of the Earth's magnetic field caused by an enhancement of the ring current. Storms are typically identified using magnetic field measurements from multiple ground‐based magnetometers, and the corresponding dates and times of multiple storms can be collated to form a storm list. There is currently no quantitative definition of a geomagnetic storm, so the contents of a particular storm list are highly dependent on the identification criteria that were used to generate it. The different definitions and identification methods can cause the physical properties of storms in different lists to vary, and these variations may be significant. We take several storm lists with different identification methods, and we compare the probability distributions of a range of solar wind variables and geomagnetic indices between those lists. We also compare the temporal behavior of the storm lists, and discuss how the differences may affect the way geomagnetic storms are defined and studied. We find that changing the definition of the quiet time has a direct impact on the start and end times of the storms, and this can result in a storm being significantly shorter when defined using a more negative quiet time definition. We also find that changes to the threshold value of minimum magnetic disturbance have a greater impact on the properties of the identified storms than changes to the quiet time definition. We provide recommendations on which storm lists to use for different scenarios.
Funding Information
  • Science and Technology Facilities Council (ST/V004883/1)
  • Science and Technology Facilities Council (ST/X001008/1)
  • Natural Environment Research Council (NE/W003198/1)
  • Canadian Space Agency (23SUSTDYNA)

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