CALCULATING THE PLASMA DEFORMATION TENSOR AND KINETIC VORTICITY FROM MAGNETIC-FIELD TIME-SERIES - APPLICATIONS TO THE SOLAR-WIND

It is shown that the magnetic induction equation reduces to an autoreg ressive model equation. Assuming weakly ergodic field variations in st eady mean plasma flow, this model permits the estimation of the mean f low deformation tensor, velocity divergence and kinetic vorticity from magnetic field time series. Applications, made to hourly-averaged, in -ecliptic interplanetary magnetic field (IMF) measurements from Ulysse s spacecraft, showed that the direction of maximum deformation rate wa s, for mast of the time, aligned to the mean field, while the vorticit y tended to become perpendicular to the mean radial direction at large heliodistances.