Geomagnetic Virtual Observatories

Geomagnetic Virtual Observatories

Earth's magnetic field is primarily generated by motions taking place in our planet's liquid metal core.  Moreover the core field is gradually changing due to poorly understood magnetohydrodynamic processes taking place in this inaccessible region.  Since it is a planetary-scale process, characterizing and monitoring the core dynamo requires global observations. Such observations are provided by the Swarm satellites, however, since the satellites are rapidly moving they are not immediately useful for monitoring core field changes at fixed locations on time scales of months and longer.


In this project, Geomagnetic Virtual Observatories (GVO) data series are derived from Swarm data collected around target locations.  The GVO data product consists of time series of vector magnetic field values at fixed locations, on a uniform grid at satellite altitude.  Such data, regularly distributed in space and time are suitable for modelling the main geomagnetic field, for core flow inversion studies, and for data assimilation studies of the core dynamo process. GVOs are designed to make Swarm 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. The GVOs data product also provide valuable information to those interested in investigating magnetospheric and ionospheric magnetic signals on timescales of months and longer.  GVO time series including all field contributions, and those processed to isolate the core field, are available along with estimated errors.


To illustrate the Swarm DISC GVO data products the first figure below presents a global map of annual differences of the radial field component of the one-monthly Observed Field GVO time series (blue dots) and of the one-monthly Core field GVO time series (red dots). The second figure below presents the annual differences for the four-monthly GVO products.

Geomagnetic Virtual Observatories  





Regularly updated Swarm GVO products are now available from the ESA's Swarm data repository

Hammer, M.D., Cox, G.A., Brown, W.J., Beggan, C. and Finlay C.C., Geomagnetic Virtual Observatories: monitoring geomagnetic secular variation with the Swarm satellites. Earth Planets Space 73, 54 (2021).


Collaboration partners at The British Geological Survey (BGS):

Ciaran Beggan
Senior Scientist, Geomagnetism Department


Will Brown

Global Geomagnetic Field Modeler, Geomagnetism Department


Grace Cox

Geomagnetic Scientist, Geomagnetism Department