Magnetic field modelling from scalar-only data: Resolving the Backus effect with the equatorial electrojet

It is well known that models of the global geomagnetic field constructed from only measurements of the field intensity suffer from large errors arising from the Backus or perpendicular error effect. Knowledge of the location of the magnetic dip equator is in principal sufficient to eliminate this error. We investigate constraining the location of the dip equator using observations of the equatorial electrojet in intensity measurements made from the CHAMP satellite. While the models generated are inferior compared with models obtained from oriented three-component vector data, they may be of sufficient quality to allow construction of future global geomagnetic reference models in the absence of vector data.