Meeting abstract

Solar Wind 9, Nantucket, 5-9 October 1998

Abstract:
We present a novel wavelet method for analysing field-aligned anisotropy in MHD turbulence using in-situ spacecraft data. Using this technique it is possible to measure power levels, spectral indices and intermittency for fluctuations parallel and perpendicular to the field direction, for arbitrary angles of the field to the flow. We show how these relate to the arbitrary solenoidal axisymmetric second order fluctuation tensor for the fluctuations and hence how experimental results can place limits on theoretical models of fluctuations within turbulent MHD flows.

We apply the technique to Ulysses magnetic field measurements taken within high speed solar wind streams emanating from the Sun's polar coronal holes, a data set uniquely suited to this technique, and present our results and their consequences for MHD turbulence models.

An additional benefit of the wavelet technique is the ability to remove certain variations form the data set before analysis. In particular, one can remove discontinuities. We demonstrate that discontinuities contribute significant power to fluctuations {\em along} the field direction and that when they are removed the spectral index of such fluctuations is reduced from near 2 to a value similar to that in other directions.