Local Vector Activity Proxy Indices: using INTERMAGNET observatories to estimate local magnetic field conditions

The INTERMAGNET network of geomagnetic observatories provides high-quality oneminute data from over 100 observatories around the globe. This distribution of ground observatories is potentially a useful resource to determine new activity proxy indices for different scientific and other purposes. As an example we describe how a global proxy index based on AE can be determined for any geomagnetic field component using data from this network of observatories. We also examine whether there is merit in using a local estimate of the external field activity, as opposed to the large-scale indices. Currently standard global indices are used in data selection procedures (to reject geomagnetically active satellite data) when modelling the internal magnetic field. Active periods are regarded as noise for this purpose, as the external field can mask the signal from the internal field. The technique described here may help in such data selection or in weighting datasets. It may also have other applications, for example to help determine the magnetic field variation in areas poorly covered by geomagnetic observatories or where an observatory 3-hour K measure of local variations does not give enough time resolution.