Normalized correlation coefficients determined for each of the Io-C (panel a)), Io-D (panel b)) and non-Io DAM event (panel c)) as a function of ϕ – an angular separation between two STEREO/WAVES spacecraft. The dashed vertical lines define the ranges of the angular spacecraft separations when C_n changes its sign and where the cross-correlation coefficient is statistically significant (C_n> 0) and not significant (C_n< 0). C_n = −1 means anticorrelation.