Physics
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmsh23a1154v&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #SH23A-1154
Physics
2109 Discontinuities (7811), 2134 Interplanetary Magnetic Fields, 2149 Mhd Waves And Turbulence (2752, 6050, 7836), 7811 Discontinuities (2109), 7863 Turbulence (4490)
Scientific paper
Magnetohydrodynamic (MHD) simulations of Alfvénic turbulence show that a cross-field cascade predominates and generates small scale current sheets across the magnetic field. In these current sheets turbulent energy significantly dissipates. In collisionless plasmas, the width of these sheets should approach the proton inertial length or proton gyroradius and dissipation within the sheets may also occur in association with wave-particle interactions. The nearly collisionless solar wind has long been known to contain discontinuities of these widths, but the identity of these discontinuities and the originating source became unclear after Cluster spacecraft measurements established that discontinuity normals were nearly perpendicular to the background magnetic field. In addition to static tangential discontinuities, the possibility that the discontinuities arise in association with turbulence needs to be considered. We have identified over 6000 discontinuities from a 27-day period using magnetic field data at 1/3 per second resolution with the ACE spacecraft. We conclude that turbulence can account for the origin of the discontinuities, their small or zero normal field components, their small intensity change, and their correlated velocity and magnetic field fluctuations. Using cross-product normals and plasma data, we have found that discontinuity width averages about 4 proton inertial lengths at small proton β(= ratio of gas to magnetic pressure) and 4 proton gyroradii at large proton β. The distribution of separations between successive discontinuities is lognormal which can arise in association with a multiplicative random cascade. In contrast, synthetic phase-random magnetic fields are found to contain less coherent discontinuities confined mostly to small field rotations and a Poisson distribution of successive separations. Solar-wind discontinuities are then substantially coherent which is consistent with sheets generated by turbulence. This work is performed in association with the Living With A Star focus team on Heliospheric Magnetic Fields.
Abramenko Valentina I.
Haggerty Dennis K.
Smith Walter C.
Vasquez Bernard J.
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