Preliminary results on the evaluation of 3D correlation functions from ACE and WIND simultaneous data

A detailed understanding of second order correlation functions provides a wealth of information about the statistical properties of turbulence, including spectra, correlation functions, cross-correlations, spectral anisotropy, and so on. The evaluation of these correlations in the solar wind from single spacecraft data has been very useful so far, but has typically been limited by the use of the the frozen-in approximation, namely that the solar wind is "rigidly moving," which is made to translate temporal series into spatial series. On the other hand, multiple spacecraft data give the possibility of measuring two point, second order spatial correlation functions directly, in principle greatly expanding the reliability and information content of the observations. We present here preliminary attempts at computing three dimensional correlation functions from simultaneous ACE and WIND data at L1. Both radially aligned [1] and mean magnetic field-aligned coordinate systems will be considered. [1] J. R. Richardson and K. I. Paularena, JGR, 106, 239 (2001)