Discreteness Noise Floor Signatures of Agyrotropy

Details Discreteness Noise Floor Signatures of Agyrotropy Discreteness Noise Floor Signatures of Agyrotropy

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmsh44a1711l&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #SH44A-1711

Physics

2723 Magnetic Reconnection (7526, 7835), 7526 Magnetic Reconnection (2723, 7835), 7835 Magnetic Reconnection (2723, 7526)

Scientific paper

Since agyrotropy is a null test for cylindrical symmetry of the pressure tensor about the local magnetic field, it will always be non-zero when the pressure tensor is determined from a finite number of (i) macro-particles in PIC or (ii) counted particles from an electrostatic analyzer. This paper refers to the error signal for false agyrotropy that accrues from a gyrotropic Vlasov plasma when approximated by N "readings" as a "discreteness floor". Such a discreteness floor is present in the N readings even when they are selected randomly from an ambient plasma that is gyrotropic. We have determined the discreteness floor for PIC simulation plasmas and that for the Polar Hydra DDEIS measurement system. Examples of changes in this floor will be illustrated across geophysical plasma boundaries where N changes, such as the magnetopause. As this varying discreteness floor is not physical, we have developed a technique to deconvolve the apparent agyrotropy with N readings to a best inference (with error estimate) of the ambient mediums Vlasov agyrotropy. This method has been shown to recover with high precision the agyrotropy profiles of the Harris sheet equilibrium with background that may be determined analytically. This technique for deconvolution will be illustrated for Hydra data to illustrate the discreteness floor removal, and the persistence of (Vlasov) agyrotropy signals at various current sheet crossings on Polar's orbit.

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