Correlation properties of magnetosheath magnetic field fluctuations

The magnetosheath is characterized by a variety of low-frequency fluctuations, but their features and sources are different. Taking advantage of multipoint magnetic field measurements of the Cluster spacecraft, we present a statistical study to reveal properties of waves. We compute cross-correlation coefficients of magnetic field strengths as measured by pairs of the Cluster spacecraft and determine the correlation length of magnetosheath waves. We discuss the relationship between the correlation length and upstream parameters as well as its connection with the wave mode and frequency power spectrum. In the frequency interval of 0.001-0.125 Hz, we found that the correlation length of fluctuations increases (1) through intervals of high solar wind speeds, (2) with increasing interplanetary magnetic field (IMF) strength, (3) if the cross-correlation between the IMF and magnetosheath magnetic field is higher, and (4) if the amplitude of fluctuations is larger.