Correlation Dependences Determined by Simultaneous Multispacecraft Observations of Solar Wind and Imf Structures

Solar wind measurements on board several spacecraft were used to study the two-points correlations of the solar wind plasma structures. The factors having the most influence on the correlation level are the density variability and IMF cone angle. The characteristic length of large solar wind structures is estimated at 500–1000 RE . 1. Available Data and Method We compared simultaneous ion flux data (1 min. resolution) measured by widelyseparated spacecraft (INTERBALL-1, IMP 8 and WIND) in 1995–98. Many cases show similar features at each spacecraft, but in some cases plasma parameters behave very disparately. The global (averaged by the large statistics) value of the correlation coefficient is about 0.73. Multifactoral analysis was used to obtain the dependencies of the correlations on the spacecraft separation and the different plasma and magnetic field parameters. The parameters available for our study are the solar wind speed, number density (or ion flux) and magnetic field components obtained with 1 or 1.5 min. time resolution. All measurements were divided into 6-hour segments. For each segment the WIND and IMP 8 data were time-shifted to the INTERBALL-1 times, compensating for the solar wind propagation time. 2. Results The plasma parameters influence on the correlation level was studied. The influence of density (or ion flux) variability (as estimated by the relative standard deviation rsd) is more than one of absolute values of the density, or the solar wind speed. We conclude that the structures with small variations (rsd < 20%) have small spatial scales and these small scale structures are poorly correlated. On the other hand, plasma structures with large variations (rsd > 20%) have a large Astrophysics and Space Science 277: 323–324, 2001. © 2001 Kluwer Academic Publishers. Printed in the Netherlands. 324 P.A. DALIN ET AL. 1 0 30 60 90 120 0.60 0.65 0.70 0.75 0.80