Abstract
AbstractFor decades, geomagnetic indices have been used extensively to parameterize space weather events, as input to various models and as space weather specifications. The auroral electrojet (AE) index and disturbance storm time index (DST) are two such indices that span multiple solar cycles and have been widely studied. The production of improved spatial coverage analogs to AE and DST is now possible using the SuperMAG collaboration of ground‐based magnetometers. SME is an electrojet index that shares methodology with AE. SMR is a ring current index that shares methodology with DST. As the number of magnetometer stations in the SuperMAG network increases over time, so does the spatial resolution of SME and SMR. Our statistical comparison between the established indices and their new SuperMAG counterparts finds that, for large excursions in geomagnetic activity, AE systematically underestimates SME for later cycles. The difference between distributions of recorded AE and SME values for a single solar maximum can be of the same order as changes in activity seen from one solar cycle to the next. We demonstrate that DST and SMR track each other but are subject to an approximate linear shift as a result of the procedure used to map stations to the magnetic equator. We explain the observed differences between AE and SME with the assistance of a simple model, based on the construction methodology of the electrojet indices. We show that in the case of AE and SME, it is not possible to simply translate between the two indices.
Highlights
Long-term geomagnetic indices have proven to be key parameters for the space weather community
We have found that there is no simple relationship between auroral electrojet (AE) and SME; our results suggest that the driving factors in how they differ depend on the epoch of interest
For space climatological studies over multiple solar cycles, there will be a trade-off between the consistency of station number in AE compared to the improved spatial sensitivity of SME, which increases from one solar cycle to the as the number of SME stations increases
Summary
Long-term geomagnetic indices have proven to be key parameters for the space weather community. Extreme value theory and risk analysis have been applied to DST in order to predict the likelihood of extreme geomagnetic activity (Acero et al, 2018; Riley, 2012; Silrergleit, 1996; Tsubouchi & Omura, 2007) Both AE and DST are regularly considered as benchmarks for the specification of the overall magnetosphere-ionosphere system as they capture overall activity (Chapman et al, 2018; Lockwood, 2013). SME and SMR have been introduced as high spatial resolution counterparts to AE and DST, respectively They share methodology, but, for recent solar cycles, the number of magnetometer stations used is typically 10 times larger than those used in the original indices.
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