Physics – Plasma Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsm51b1814h&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #SM51B-1814
Physics
Plasma Physics
[2744] Magnetospheric Physics / Magnetotail, [2794] Magnetospheric Physics / Instruments And Techniques, [2799] Magnetospheric Physics / General Or Miscellaneous, [7807] Space Plasma Physics / Charged Particle Motion And Acceleration
Scientific paper
Many studies have found that during quiet times the magnetotail current sheet magnetic field may be modeled using the modified Harris magnetic field, B =B0[tanh(z/δ)ex +bz ez] where B0 is the magnetic field strength far from the sheet, δ is the scale length of the current sheet thickness and bz is the ratio of the magnitude of the field at the midplane to the asymptotic field. Using a single spacecraft, precise measurement of the parameters δ and bz are very difficult. The current sheet scale length is problematic since relative motion of the spacecraft and the current sheet cannot be decoupled. This difficulty may be overcome using multiple satellites such as the Cluster mission. Even with multiple spacecrafts, however, the value of the field ratio bz is still difficult to ascertain since it is a small quantity and even a small tilt to the current sheet can result in significant percentage errors. Theory and simulations of nonlinear charged particle dynamics in the modified Harris field have found a signature of the dynamics that manifests itself a series of peaks in the ion distribution function. The separation of the peaks has been shown to scale as a combination of the fourth root of the ion energy and parameters bz and δ. Since we have an independent measure of the current sheet thickness, we may use the distribution function signature to determine the field ratio. In this paper we present the first observations of the ion distribution function signature in Cluster HIA data and use the signature along with the four spacecraft magnetic field data to determine the parameters describing the current sheet topology. We show that the measurements are in good agreement with those using other techniques, but with a significantly lower uncertainty.
Holland Daniel L.
Martin Richard F.
Matsuoka Hiroshi
Presley M. E.
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