Geomagnetic Virtual Observatories: Global monitoring of geomagnetic secular variation with Swarm data

The ESA Swarm DISC Geomagnetic Virtual Observatories (GVO) project aims to apply the virtual observatory concept to Swarm magnetic field measurements. The Virtual Observatory concept is a data processing method which mimics the behavior of magnetic monthly-mean time-series measured at ground observatories but at fixed locations on a uniform global grid at satellite altitude instead. Here we present several new GVO data products consisting of the average time-series of vector magnetic field values, regularly distributed in space and time which are suitable for monitoring the geomagnetic field. The GVO products consist of an equal-area grid with separation spacing of 300 km and cadence of either 1 month or 4 months. Various levels of processing are applied to remove the effects of altitude change and satellite local-time differences to produce a consistent time series. It is known that monthly time-series can have strong local-time artifacts which are removed with four-monthly averages, though with a loss of temporal resolution. The GVO products are designed to make Swarm magnetic data more accessible to researchers studying the physics of the core dynamo process, and related phenomenon such are secular variation, geomagnetic jerks and rapid core dynamics. In addition, the GVO data products also provide valuable information for investigating magnetospheric and ionospheric magnetic signals on timescales of months and longer.