Challenging the Use of Ring Current Indices During Geomagnetic Storms

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Abstract
Abstract The ring current experiences dramatic enhancements during geomagnetic storms, however understanding the global distribution of ring current energy content is restricted by spacecraft coverage. Many studies use ring current indices as a proxy for energy content, but these indices average over spatial variations and include additional contributions. We have conducted an analysis of Van Allen Probes’ data, identifying the spatial distribution and storm-time variations of energy content. Ion observations from the HOPE and RBSPICE instruments were used to estimate energy content in L-MLT bins. The results show large enhancements particularly in the premidnight sector during the main phase, alongside reductions in local time asymmetry and intensity during the recovery phase. A comparison with estimated energy content using the Sym-H index was conducted. In agreement with previous results, the Sym-H index significantly overestimates (by up to ∼ 4 times) the energy content, and we attribute the difference to contributions from additional current systems. A new finding is an observed temporal discrepancy, where energy content estimates from the Sym-H index maximise 3 to 9 hours earlier than in situ observations. Case studies reveal a complex relationship, where variable degrees of agreement between the Sym-H index and in situ measurements are observed. The results highlight the drawbacks of ring current indices and emphasise the variability of the storm time ring current.
Notes
Year of Publication
2021
Journal
Journal of Geophysical Research: Space Physics
Volume
n/a
Number
Number of Pages
e2020JA028423
Date Published
01/2021
URL
https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020JA028423
DOI
https://doi.org/10.1029/2020JA028423