DETERMINATION OF DISPERSION-RELATIONS IN QUASI-STATIONARY PLASMA TURBULENCE USING DUAL SATELLITE DATA

The joint frequency-wavenumber spectrum is one of the basic quantities for analyzing plasma turbulence. It is shown how the full spectrum ca n be recovered from wavefields measured by two or more satellites via spectral methods based on wavelet transforms. Compared to standard cro ss-correlation techniques, different branches in the dispersion relati on can be resolved and quasi-stationary wavefields can be accessed. Us ing this new approach, low frequency magnetic field data from the AMPT E-UKS and AMPTE-IRM spacecraft are investigated and the impact of nonl inear processes on wave propagation at the Earth's foreshock is reveal ed.