11 th EISCAT Workshop, Menlo Park, August 2003 Session: M-I Coupling Magnetospheric plasma drift as simultaneously observed by Cluster (EDI) and ground-based radars (SuperDARN) in magnetically conjugate positions by M. Förster 1, P. Puhl-Quinn 1, H. Vaith 1, G. Paschmann 1, J. Baker 2, R. Greenwald 2, J.M. Quinn 3, and R.B.Torbert Max-Planck-Institut für extraterrestrische Physik, Garching, Germany 2 - JohnsHopkins University, Laurel, Maryland, USA 3 - University of New Hampshire, Durham, NH, USA Abstract The Electron Drift Instrument (EDI) instrument measures the drift velocity of artificially injected electron beams transverse to the magnetic field from which the electric field vector can be deduced. The comparison with ground-based coherent radars of the Super Dual Auroral Radar Network (SuperDARN) is of high scientific interest for the study of magnetospheric convection and its connection with dynamical coupling processes. The comparison must rely on correct mapping procedures by use of relevant geomagnetic field models and on the assumption of equipotentiality along a given magnetic field line. The comparisons show a remarkable good agreement of the electric drift vectors measured by EDI onboard the Cluster satellites and the ground-based observations by SuperDARN while the deviations in magnitude and/or direction are of interest in their own right.

SuperDARN and Cluster-3  - Cluster-3’s footpoint SD drift vector (magenta) Mapped EDI drift (green)

Suppositions Accurate magnetic field line mapping by use of relevant geomagnetic field models (e.g., the Tsyganenko Model T01_01) Assumption of equipotentiality along a given magnetic field line Quasi-static conditions, temporal variations negligible    11 th EISCAT Workshop, Menlo Park, August 2003 Session: M-I Coupling

Faraday’s Law  0 d r i  V i d r m  V m B m, E m B i, E i  11 th EISCAT Workshop, Menlo Park, August 2003 Session: M-I Coupling

12 Mar 2001 SuperDARN and Cluster-3

Auroral currents … cusp

557 nm MSP keogramm  Fort Smith magnetometer  and the riometer voltage  CANOPUS ground-based magnetometer measurements (B x components)

SuperDARN and Cluster-3  - Cluster’s footpoints S-DARN drift vector (magenta) Mapped EDI drift (C1,C2,C3)

Conclusions The Electron Drift Instrument (EDI) allows reliable measurements of the electric drift vector in most parts of the magnetosphere, i. e., also in regions of very low plasma density and small (~ 0.1 mV/m) electric field magnitudes. The comparison must rely on correct mapping procedures by use of relevant geomagnetic field models (e.g., the Tsyganenko model T01_01) and on the assumption of equipotentiality along a given magnetic field line. The comparisions made so far show a remarkable good agreement of the electric drift vectors measured by EDI onboard the Cluster satellites and the ground-based observations by SuperDARN during undisturbed conditions, while deviations in magnitude and/or direction are of interest in their own right. Such deviations occur obviously in regions of field-aligned currents (FACs), as above the auroral zones, where the mapping might fail and the presence of field-aligned potential differences prevents the straightforward comparison. An other type of deviations occurs during magnetospheric reconfigurations due to rapidly changing solar wind conditions and are due to induction electric fields.  Acknowledgements to the ACE ( SWEPAM, MAG ), WIND ( MFI, Plasma ), and Cluster FGM teams. 11 th EISCAT Workshop, Menlo Park, August 2003 Session: M-I Coupling

Auroral currents04:55 UT … cusp

SuperDARN and Cluster-3  - Cluster-3’s footpoint SD drift vector (magenta) Mapped EDI drift (green)