Two Point Measurements of statistical properties of solar wind turbulence

MATTHAEUS W.H.; DASSO S.; WEYGAND J.M.; SMITH C.W.; KIVELSON M.G.

San Francisco, USA

Conferencia; American Geophysical Union, Fall Meeting 2006; 2006

AGU

Multipoint measurements are of central importance in establishing the three dimensional statistical and correlation properties of low frequency interplanetary turbulence, while also serving to corroborate the wealth of information gleaned from single point measurements based on the "frozen-in flow" approximation. Multipoint measurements with widely ranging spatial separations and well controlled time calibration are required to unravel the space-time structure of MHD scale turbulence, which presents complexity in both domains. To address these problems we have been developing methods for statistical and correlation analyses of multiple streams of spacecraft data, and have developed a well documented object oriented (Python based) software framework that is designed for ease of adaptation, flexibility and effective collaboration between groups. Progress on our three target problems will be reviewed here: (1) Determination of the two-point spatial correlation properties of solar wind turbulence. Our main results here are based on simultaneous solar wind magnetic field data from the ACE, Cluster, Geotail, IMP 8, and Wind spacecraft. We have determined [1] the direction averaged spatial correlation function, the correlation (outer) scale, and the inner (Taylor) microscale near 1 AU. The correlation scale is determined to be 1.2 × 106 km, the Taylor scale is 2500 km, and the effective magnetic Reynolds number is calculated to be 230,000. Similar analyses have been carried out plasma sheet data [2]. Taylor scale computations require careful treatment of the Cluster data [3]. (2) Evaluation of accuracy of the frozen in approximation. This ongoing work will focus on comparison of correlation scale, Taylor scale and correlation function data from single and multiple spacecraft. (3) Evaluation of the Eulerian (plasma frame single point multiple time) correlation function. Progress in developing a methodology for this problem will be reviewed. This research supported by the RSSW1AU and Cluster programs.