Plasma and magnetic field correlations in the solar wind

Abstract

Data from multiple spacecraft are used to determine solar wind plasma and interplanetary magnetic field (IMF) correlation coefficients. These correlation coefficients provide information on solar wind scale lengths and the predictive capability of upstream monitors for space weather purposes. Previous work has looked at plasma and IMF correlation coefficients independently and used much smaller databases than those used in this study. We use data sets from 1977–1984 and 1994–1998 and calculate plasma and IMF correlation coefficients. The IMF correlation coefficients are, on average, slightly higher than those for plasma. Dependence of the correlation coefficients on the spatial separation of the spacecraft is important for placement of upstream monitors; we find a small dependence on the radial separation of the spacecraft but a very strong dependence on spacecraft separation in the YZ (GSE) plane. Scale lengths perpendicular to the flow are about 45 Earth radii (RE) for the IMF components, 70 RE for the speed and IMF magnitude, and over 100 RE for the density. Radial scale lengths are of the order of 400 RE. The plasma and IMF correlation coefficients are larger when values of the density standard deviation are high and when the IMF direction is perpendicular to X (GSE). Front orientations are similar for both plasma and IMF features and are more perpendicular than the average field direction.