Multiple Magnetic Correlation Scales in the Solar Wind

ACE, Cluster, Geotail, IMP-8, Interball, THEMIS, and Wind data from many different intervals in the solar wind are employed to determine the correlation coefficient versus spatial separation function. This function has been used to derive the magnetic correlation scale for solar wind magnetic field turbulence. For this study we define the correlation scale as the exponential decay constant of the correlation coefficient as a function of spacecraft separation and it is one of the fundamental scale lengths in turbulence. We find that the correlation coefficient data is best fit by the sum of two exponentials when we examine the correlation coefficient function versus spacecraft separation at a range of angles with respect to the mean magnetic field direction. We believe the largest decay length associated with one of the exponential function is the magnetic correlation scale for the solar wind and is on the order of several million kilometers. The second exponential function has a decay length on the order of tens of thousands of kilometers and we believe this second decay length is the result of foreshock turbulence. We investigate this hypothesis.