Physics – Plasma Physics
Scientific paper
Oct 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002jgra..107.1294s&link_type=abstract
Journal of Geophysical Research (Space Physics), Volume 107, Issue A10, pp. SMP 13-1, CiteID 1294, DOI 10.1029/2001JA000126
Physics
Plasma Physics
30
Space Plasma Physics: Magnetic Reconnection, Magnetospheric Physics: Magnetopause, Cusp, And Boundary Layers, Space Plasma Physics: Electrostatic Structures, Magnetospheric Physics: Electric Fields (2411)
Scientific paper
Plasma, electric, and magnetic field data on the Polar spacecraft have been analyzed for the 29 May 1996 magnetopause traversal searching for evidence of in situ reconnection and traversal of the separator. In this paper we confine our analysis to model-free observations and intrasensor coherence of detection of the environs of the separator. (1) We illustrate the first documented penetration of the separator of collisionless magnetic reconnection in temporal proximity to successful Walén tests with opposite slopes. (2) We present the first direct measurements of E∥ at the magnetopause. (3) We make the first empirical argument that E∥ derives from the electron pressure gradient force. (4) We document the first detection of the electron pressure ridge astride the magnetic depression that extends from the separator. (5) We provide the first empirical detection of the reconnection rate at the magnetopause with the locally sub-Alfvénic ion inflow, MAi ~= 0.1, and trans-Alfvénic exhaust at high electron pressure of MiA ~= 1.1-5. (6) We exhibit the first empirical detection of supra-Alfvénic electron flows parallel to B in excess of 5 in narrow sheets. (7) We illustrate the detection of heat flux sheets indicative of separatrices near, but not always in superposition, with the supra-Alfvénic parallel electron bulk flows. (8) We present the first evidence that pressure gradient scales are short enough to explain the electron fluid's measured cross-field drifts not explained by E × B drift but predicted by the measured size of E∥. (9) We illustrate that the size of the observed E∥ is well organized with the limit implied by Vasyliunas's analysis of the generalized Ohm's law of scale length ρs = β1/2(c/ωpi), indicative of the intermediate scale of the diffusion region. (10) We document the first detection of departure from electron gyrotropy not only at the separator crossing but also in its vicinity, an effect presaged by Vasyliunas [1975]. (11) We make the first reports of very large values of electron βe ~= 680 localized at the separator, which imply that the electron thermal gyroradius exceeds the electron inertial length by more than an order of magnitude there. This clearly delineates that the environs of the reversed field region in this data contain non-MHD scales. The ambipolar association and the measured E∥ data imply the presence of the nonideal ρs scale in these layers surrounding the null point. The high βe signals the possible demagnetization of the thermal electrons in any structures with spatial scales of the electron skin depth, which is theoretically anticipated to surround the magnetic null line of the separator proper. This possibility is supported by the large number of temporally unaliased spectra at high βe that are inconsistent with gyrotropy.
Maynard Nelson C.
Mozer Forrest S.
Russell Christopher T.
Scudder Jack D.
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