The basic idea is that the ground magnetic measurements give the curl of the true current system, while the FAC give its divergence. This information is combined to the wanted true current system by using spherical elementary current systems that represent "point sources" (Green's functions) of the curl and divergence operator on the sphere.

If additionally the ionospheric electric field is measured on the analysis area by a coherent scatter radar (like STARE), also the Hall and Pedersen conductance distributions can be calculated.

For more details: see
Literature
(below)

To obtain 2D FAC distributions from the satellites, it is of advantage if the ionospheric situation to be studied can be assumed stationary for the time that either:

- the ionospheric feature moves over the satellites' footpoints, or
- the satellites' footpoints move over the analysis region selected, or
- a combination of the above.

- Amm, O., The elementary current method for calculating
ionospheric current systems from multi-satellite and ground
magnetometer
data,
*J. Geophys. Res., 106*, 24843, 2001. - Amm, O., K. Kauristie, T.I. Pulkkinen, M.J. Engebretson, R.A. Greenwald, H. Lühr, and T. Moretto, Combining multi-point spacecraft and two-dimensional ground-based observations: Theory and example of an IMF BY-related cusp current system, Proc. Cluster II workshop, ESA SP-449, 327, 1999.
- Amm, O., Ionospheric elementary current systems in spherical coordinates and their application, J. Geomagn. Geoelectr., 49, 947, 1997.

- Example plots for a modeled case of a dark plasma vortex:

This is the input data: FAC distribution that CLUSTER II would observe during the 2 minutes when the vortex passes eastward over the MIRACLE array. The FAC data of the different timesteps is reduced to a central reference timestep with respect to the vortex's velocity (upper panel). The footpoints and conjugate magnetic field lines of the CLUSTER II satellites at the reference timestep are shown in the lower panel, for a typical pass over the central MIRACLE field of view.

Ground magnetic field signature (rotated clockwise by 90 degrees) that the IMAGE network would observe at the reference timestep (numbers: vertical downward component):

Output:__True__
(not equivalent) ionospheric currents obtained by the Elementary
Current
Method (ECM):

- Optional, additional input:
Electric field distribution measured by the STARE coherent scatter
radar:

-> Additional output: Hall conductance distribution

and Pedersen conductance
distribution:

For further questions and
proposals
of events to be analysed, contact Olaf
Amm.

Maintained by: Olaf Amm

Latest update: 18.03.2004