SuperMAG geomagnetic indices: Do more stations provide better monitoring of the M-I current system?

Abstract:

Over the last few years a wave of new indices have been proposed and released through the SuperMAG initiative. The basic assumption behind these indices is that the more stations used to derive the indices the better the current systems are monitored. This supposedly includes improved timing, intensity and location. Examples are the ring current indices (IAGA SYM-H use six station vs. SuperMAG SMR using ~100 stations) and auroral electrojet indices (IAGA AE use 12 stations vs. SuperMAG SME using ~110 stations).

The purpose of the various magnetic indices is to provide information of the currents in question. The pitfalls, however, are many: 1) do the indices have appropriate temporal resolution?, 2) are they derived from a network of stations with sufficient spatial coverage?, 3) is it reasonable to assume that a given level of an index implies a certain 2D current distribution?, 4) to what extend do the indices actually monitor the current system in mind?. To address some of these problems SuperMAG indices with local time information has been published (e.g. SME 24 local time indices and SMR 4 local time indices).

The basic purpose of the various indices is to monitor the M-I current system. We discuss to what extend the IAGA and SuperMAG indices actually fulfill this objective.